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Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI3 Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials
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Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI3 Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials
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  • Hamid Pashaei Adl
    Hamid Pashaei Adl
    Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
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  • Setatira Gorji
    Setatira Gorji
    Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
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  • Mojtaba Karimi Habil
    Mojtaba Karimi Habil
    Faculty of Physics, University of Tabriz, 51664, Tabriz, Iran
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  • Isaac Suárez
    Isaac Suárez
    Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
    Departamento de Ingenierı́a Electrónica, Escuela Técnica Superior de Ingenierı́a, Universidad de Valencia, Avenida de la Universidad s/n, 46100 Burjassot, Spain
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    Orcidhttp://orcid.org/0000-0002-2773-8801
  • Vladimir S. Chirvony
    Vladimir S. Chirvony
    Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
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    Orcidhttp://orcid.org/0000-0003-4121-9773
  • Andrés F. Gualdrón-Reyes
    Andrés F. Gualdrón-Reyes
    Institute of Advanced Materials (INAM), Universitat Jaume I (UJI), Avenida de Vicent Sos Baynat s/n, 12071 Castelló de la Plana, Spain
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    Orcidhttp://orcid.org/0000-0002-0208-9235
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    Iván Mora-Seró
    Institute of Advanced Materials (INAM), Universitat Jaume I (UJI), Avenida de Vicent Sos Baynat s/n, 12071 Castelló de la Plana, Spain
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    Orcidhttp://orcid.org/0000-0003-2508-0994
  • Luisa M. Valencia
    Luisa M. Valencia
    Departamento de Ciencia de los Materiales e IM y QI. F. Ciencias, IMEYMAT, Campus Rı́o San Pedro, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain
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  • María de la Mata
    María de la Mata
    Departamento de Ciencia de los Materiales e IM y QI. F. Ciencias, IMEYMAT, Campus Rı́o San Pedro, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain
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    Orcidhttp://orcid.org/0000-0002-1581-4838
  • Jesús Hernández-Saz
    Jesús Hernández-Saz
    Departamento de Ingenierı́a y Ciencia de los Materiales y del Transporte, Escuela Técnica Superior de Ingenierı́a, Universidad de Sevilla, Camino Descubrimientos, s/n.- Isla Cartuja, 41092 Sevilla, Spain
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    Orcidhttp://orcid.org/0000-0002-6630-7203
  • Sergio I. Molina
    Sergio I. Molina
    Departamento de Ciencia de los Materiales e IM y QI. F. Ciencias, IMEYMAT, Campus Rı́o San Pedro, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain
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  • Carlos J. Zapata-Rodríguez*
    Carlos J. Zapata-Rodríguez
    Departament d’Òptica i Optometria i Ciències de la Visió, Facultad de Fı́sica, Universitat de València, C/Dr Moliner 50, 46100 Burjassot, Spain
    *(C.J.Z.-R.) E-mail: [email protected]
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  • Juan P. Martínez-Pastor*
    Juan P. Martínez-Pastor
    Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
    *(J.P.M.P.) E-mail: [email protected]
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    Orcidhttp://orcid.org/0000-0003-3683-0578
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ACS Photonics

Cite this: ACS Photonics 2020, 7, 11, 3152–3160
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https://doi.org/10.1021/acsphotonics.0c01219
Published October 26, 2020

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Abstract

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Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled. These results can be of interest for quantum information applications of single emitters on the basis of perovskite nanocrystals with high photon emission rates.

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The manipulation of the spontaneous emission rate is indispensable for a wide variety of technological photonic applications ranging from light emitting diodes to single photon sources. From one side, nanofabrication techniques have enabled the development of different optical metamaterials, which are designed to achieve and exploit light–matter interaction unattainable with natural materials. (1−4) Among the varieties of metamaterials proposed and fabricated so far, hyperbolic metamaterials (HMMs) (5−8) have rapidly gained a key role in nanophotonics due to their peculiar ability to manipulate the near field of a quantum emitter (QE). (9−11) The most intriguing feature of these anisotropic HMM structures is the increase of the photon density of states, which can be used to engineer the light–matter interaction, particularly with emitters, by increasing their emission rates when they are placed close to the HMM surface. Moreover, the position of the emitter in the plane (parallel to the HMM surface) is not critical, only its distance to the HMM surface, to obtain a certain Purcell factor, contrary to the case of resonators, where the Purcell factor decreases enormously when the single emitter does not overlap the maximum of the electric field defined in the cavity. Of course, HMMs can be also further engineered and improved by nanostructuration for obtaining greater Purcell factors. (12) On the other hand, the optical and electrical properties of lead halide perovskites (LHPs) have allowed consideration of these promising materials for developing high quality optoelectronic devices under cheap, straightforward, and low temperature technologies. (13−19) Recently, fully inorganic perovskite nanocrystals (PNCs) of cesium lead halides (CsPbX3, X = Cl, Br, I) were synthesized with precise size and compositional control, tunable, narrow-band emission, and high photoluminescence quantum yield (PLQY) over the whole visible wavelength range. (20−25) At the level of single nanocrystals, LHPs can be also potential candidates for single photon sources. (26−31) For quantum information applications, it is important to increase the photon emission rate (or radiative rate) of a QE, which is commonly achieved by embedding single photon nanomaterials into optical microcavities. (32−36) The photon emission rate enhancement has been experimentally investigated using periodical metal-dielectric structures for different types of single emitters (dye molecules, metal–organic complexes, and quantum dots), (37−40) as also confirmed theoretically. (41,42) It is worth noting the study of recombination rate enhancement using a film of CsPbBr3 PNCs deposited by spin coating on top of single and double metal–insulator–metal cavities. (43) The advantage of using HMMs along with simple deposition techniques of PNCs does not require any deterministic positioning of the QE, as in the case of 2D photonic cavities. (44) The coupling of light emitters to the HMM structure would induce an increase of the exciton radiative recombination rate (and therefore a reduction of the exciton radiative lifetime) by the Purcell effect, (45) which would gain importance by decreasing the average distance between a QE and the HMM structure. Besides, the short distance between PNCs and the HMM also affects the photon emission frequency, like in the case of a QE placed near partially reflecting surfaces, which is a widespread feature of the dipole-surface interaction and, in simple terms, results from the coupling between the dipole and its own image in the metal surface. However, such a shift of the emitted photon frequency is theoretically expected to be very small, (46−51) hindering its experimental determination.
In the present work, we propose the manipulation of photons produced by exciton radiative recombination in CsPbI3 PNCs by means of HMM structures. They consist of several alternating metal (Ag) and dielectric (LiF) layers, whose thickness and period affect the dielectric constant anisotropy and optical modes. The coupling between CsPbI3 PNCs and the HMM modes is controlled by a variable dielectric spacer thickness (investigated in the range of 10–50 nm). Our analysis in terms of the Purcell factor suggests that the confined optical modes are sustained by near field interactions between the emitters and the HMM structure. However, for achieving a successful exciton-HMM coupling, radiative recombination of excitons is a prerequisite, which is undoubtedly achieved in most semiconductors at cryogenic temperatures. The exciton-HMM coupling in our system will lead to the Purcell-enhanced spontaneous emission by a factor greater than three for the thinnest spacer (10 nm), together with a photoluminescence red shift as high as 8 nm (around 20 meV). On the basis of our literature analysis, no precedent is found for such a noticeable emission frequency shift for PNCs on top of HMM structures. Both experimental observations, the Purcell effect and the emitter frequency shift, have been successfully explained theoretically.

Experimental Details and Methods

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Synthesis of CsPbI3 Nanocrystals

CsPbI3 PNCs were synthesized following the hot-injection method described by Kovalenko and co-workers, (20) with some modifications. (52) All the reactants were used as received without an additional purification process. Briefly, a Cs-oleate solution was prepared by mixing 0.41 g of Cs2CO3 (Sigma-Aldrich, 99.9%), 1.25 mL of oleic acid (OA, Sigma-Aldrich, 90%), and 20 mL of 1-octadecene (1-ODE, Sigma-Aldrich, 90%) which were loaded together into a 50 mL three-neck flask at 120 °C under a vacuum for 1 h under constant stirring. Then, the mixture was N2-purged and heated at 150 °C to reach the complete dissolution of Cs2CO3. The solution was stored under N2, keeping the temperature at 100 °C to prevent Cs-oleate oxidation. For the synthesis of CsPbI3 PNCs, 1.0 g of PbI2 (ABCR, 99.999%), and 50 mL of 1-ODE were loaded into a 100 mL three-neck flask. The mixture was simultaneously degassed and heated at 120 °C for 1 h under constant stirring. Then, a mixture of 5 mL each of both pretreated (130 °C) OA and oleylamine (OLA, Sigma-Aldrich, 98%) were separately added to the flask under N2, and the mixture was quickly heated at 170 °C. Simultaneously, 4 mL of Cs-oleate solution was quickly injected to the mixture, and then, the reaction was quenched to immerse the mixture into an ice bath for 5 s. In order to perform the isolation process of PNCs, the colloidal solutions were centrifugated at 4700 rpm for 10 min. Then, PNCs pellets were separated after discarding the supernatant and redispersed in hexane to concentrate the PNCs at 50 mg/mL.

Methodologies

Metal (Ag) and dielectric (LiF) layers were deposited by thermal evaporation under high vacuum (2 × 10–5 mbar) on top of a silicon wafer, which was preliminary cleaned by following the procedure reported in ref (53). The morphology of fabricated HMM structures was characterized by HAADF-STEM using a FEI TALOS F200X at 200 kV, equipped with a field emission gun (FEG) source, that combines high resolution (S)TEM imaging with energy-dispersive X-ray (EDS) signal detection. Cross-section TEM samples were prepared using a Zeiss Auriga FIB, and the samples were placed on a copper grid. The specular reflectance of the same HMM structures was measured at single wavelengths using different lasers by a homemade set up incorporating a goniometer for the HMM-holder and detector (θ–2θ configuration). For low temperature photoluminescence (PL) and time-resolved PL (TRPL) measurements, the samples were held in the coldfinger of a closed-cycle He cryostat (ARS DE-202), which can be cooled down to 15 K, approximately. PL was excited by means of 200 fs pulsed Ti:sapphire passive mode-locked laser (Coherent Mira 900D, 76 MHz repetition rate) operating at a wavelength of 810 nm and doubled to 405 nm by using a BBO crystal. The PL signal was dispersed by a double 0.3 m focal length grating spectrograph (Acton SP-300i from Princeton Instruments) and detected with a cooled Si CCD camera (Newton EMCCD from ANDOR) for PL spectral measurements and with a silicon single photon avalanche photodiode (micro photon device) connected to a time-correlated single-photon counting electronic board (TCC900 from Edinburgh Instruments) for TRPL measurements.

Results and Discussion

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The HMM structure consisted of six periods (eight periods in the case of the structure included in the Supporting Information) of alternating metal (Ag) and dielectric (LiF) layers and finished in the metal (Ag) deposited by thermal evaporation on a silicon wafer, as illustrated in Figure 1a. Two HMM structures were grown with different nominal period and thicknesses of metal and dielectric layers and real thicknesses were estimated at the center of the wafer by HAADF-STEM. Figure 1b shows an HAADF image (Z-contrast) of the HMM evidencing the alternation of Ag (brighter material) and LiF (darker material) layers, whose chemical composition has been further checked by EDS measurements summarized in the right panel of Figure 1b (Ag, F, and Si mapped signals displayed in magenta, cyan and blue, respectively). These analyses allow extracting the thickness of individual layers. Particularly, the average thickness of Ag + LiF layers was around 25 + 35 nm in the HMM structure shown in Figure 1b and 40 + 40 nm in the HMM structure of Figure S1 (see Supporting Information). On the basis of a simple effective medium model for multilayered structures, our fabricated HMMs would exhibit a hyperbolic permittivity dispersion at λ ≥ 370 nm, with ϵx = ϵy = ϵ∥ < 0 and ϵz = ϵ⊥ > 0 (see Figure 1a for axes notations). (54)
(1)
(2)
where f is the fill factor or fraction of metal in the unit cell, i.e., , as determined by metal and dielectric thicknesses dAg and dLiF, and θ is the incident angle of light. The hyperbolic dispersion of the HMM has been confirmed experimentally, where the values of electric permittivity were inferred from the fits of angular reflectance profiles measured at λ = 785 nm (similar angular reflectance profiles were also measured in the HMM with Ag + LiF layers 40 + 40 nm thick by using other wavelengths, as shown in Figure S2 of the Supporting Information) in s and p polarizations (data symbols in Figure 1c) to the numerically calculated curves by MATLAB using eqs 1 and 2 (55) (red and blue continuous lines in Figure 1c). These layered metal-dielectric structures support a large number of electromagnetic states, (56) which is the key point to understand the potential applications of HMMs in future quantum technologies. To confirm these optical modes in our fabricated HMMs is interesting to calculate the local density of states ρ(r0, ω) at a frequency ω0 by means of the well-known dyadic Green’s functions: (54)
(3)
where c is the speed of light. The local density of states (LDOS) of the HMM was calculated using eq 3 and shown in Figure 1d and Figure S1b (Supporting Information) for the different modes of the two fabricated HMM structures, respectively, as a function of k∥.

Figure 1

Figure 1. (a) Schematic representation of thermally evaporated HMM structures, (b) HAADF-STEM image and the corresponding EDX map (Ag, F, and Si are displayed in magenta, cyan, and blue, respectively) of a fabricated HMM structure. (c) Angular reflectance spectra of fabricated HMM structures measured at λ = 785 nm and fitted with ϵ∥ = −4.19 + 1.34i, ϵ⊥ = +1.56 + 0.01i. Blue diamonds and red circles refer to the s and p polarizations, and solid lines correspond to the simulation. (d) Local density of states (LDOS) computed in the near field of the HMM structure with 10 nm spacer.

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For these HMMs, we expect a Purcell enhancement of the radiative emission rate of CsPbI3 nanocrystals due to their exciton coupling to plasmonic HMM modes. For observation of this effect, similarly to the case of only metal surfaces, we need to introduce a spacer layer of variable thickness d between the HMM structure and the PNCs (Figure 2a). The spacer is made of poly(methyl methacrylate) (PMMA) spin coated on the HMM structure at 3000 rpm. Finally, on top of the PMMA spacer layer, CsPbI3 PNCs were deposited by dip coating the substrate into the colloidal solution (1 mg/mL of PNCs in hexane) during 1 min.

Figure 2

Figure 2. (a) Schematic representation of a HMM structure with a monolayer of PNCs on top of the spacer with thickness d. (b) Schematic illustration of experimental setup for measuring PL and TRPL spectra of PNCs at low temperatures. (c) PL spectra of CsPbI3 PNCs deposited on top of HMM substrates for different spacer thicknesses. (d) PL decay kinetics of CsPbI3 PNCs corresponding to (c).

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It is worth mentioning that the above concentration and dipping time were optimized to obtain a partially covered monolayer of CsPbI3 nanocubes (with 14 nm of average cube edge), (57) as illustrated in Figure 2a. This single monolayer of PNCs (meaning a layer made of single nanocrystals dispersed throughout the sample surface without agglomeration, nominally) would ensure an efficient coupling of the emitters to the HMM for a given spacer, because the average PNC-HMM coupling strength would decrease significantly for too thick PNC films, as it would occur if increasing the spacer thickness. Four samples were fabricated with nominal spacer thicknesses d = 10, 20, 50, and 250 nm. The thickest one is considered here as a reference because the exciton-HMM coupling is expected to be negligible in this case.
Figure 2b illustrates the experimental setup for PL and TRPL measurements in backscattering geometry from 15 to 300 K. First of all, it is worth noting that we observe a very weak or meaningless effect of the HMM structure (d = 20 nm) on the PL decay kinetics of CsPbI3 PNCs at room temperature, as shown in Figure S3a of the Supporting Information, whereas at 15 K the same sample demonstrated a clear reduction of the PL decay time (Figure S3b of the Supporting Information). Besides, at room temperature, the PL decay kinetics turn out to be much longer than at 15 K. The origin of the different behavior at room and low temperatures is in the mechanism responsible for the PL decay formation in PNCs. Following the recently proposed concept of delayed luminescence, (58,59) the experimentally observed PL decay kinetics in PNCs are formed with a participation of shallow nonquenching traps, which result in lengthening of the kinetics due to the multiple trapping-detrapping process (a three-level model should be applied in this case (58,59)). In fact, this model could account of the complex PL decay and important changes in PLQY observed at room temperature for CsPbBr3 PNCs in ref (43). This is the reason why one should take with due precaution these previous results using PNCs interacting with metal-dielectric cavities. (43) Since at low temperatures the trapped excitons cannot be longer detrapped to free exciton state, participation of shallow traps in formation of the PL decay kinetics is eliminated, and the PL decay is mainly due to the competition of radiative and nonradiative deactivation channels (the two-level model is applicable). Taking into account that nonradiative exciton recombination is negligible for our PNCs at 15 K, the PL decay kinetics is completely described by the exciton radiative recombination rate. A more detailed description of the delayed luminescence model can be found in section 2 of the Supporting Information.
Therefore, we have developed the experiments at cryogenic temperatures with the goal to reduce the influence of carrier trapping/detrapping and exciton nonradiative recombination channels on the Purcell enhancement by the HMM structure (see the observed increase of the Purcell factor by decreasing temperature in Figure S4e,f of the Supporting Information). That is, the radiative recombination of excitons in CsPbI3 PNCs is the main mechanism responsible of the PL decay kinetics measured at 15 K (Figure 2c). In Figure 2c, we have shown normalized PL spectra to highlight the outstanding PL redshift by reducing the spacer thickness, but absolute PL spectra are presented in Figure S5 of the Supporting Information. As shown in this figure, the PL intensity typically decreases when reducing the spacer thickness, which was observed experimentally by other authors and attributed to the preferential emission of light into the high-k metamaterial modes, (60,61) as first explained for the case of a metal surface (62) (surface plasmon modes in this case). In turn, the preferential emission into the high-k modes of the HMM is the origin of the exciton-HMM coupling that gives rise to these remarkable effects (Purcell effect, PL redshift, and decrease of the PL intensity by reducing d).
The PL peak wavelength for the reference sample is observed at around 705 nm, in good agreement with what is reported by other authors for films of CsPbI3 PNCs at cryogenic temperatures. (57,63) We also tested CsPbBr3 PNCs deposited on top of the same HMM, whose spontaneous emission is peaked at around 520 nm. For these emitters, we did not observed any decay time reduction from 300 down to 15 K. This effect is ascribed to the wavelength dependence of the Purcell factor as a function of the metal fill factor in the HMM, which is equal/smaller than 0.5 in our case and consequently exhibiting a negligible Purcell factor enhancement at around 500 nm (see refs (39) and (64) for example, and section 4 of the Supporting Information). In fact, metal fill factors in the HMM close to the unit would give rise to large Purcell factor values as compared to medium-low metal fill factors, but extended in a broader wavelength/energy region in the latter case. On the contrary, the behavior of the HMM in the first case is more similar to that observed for a metal surface. More interestingly, in the samples with a spacer thinner than 50 nm, a clear redshift is observed with a spacer thickness decrease, being up to 8 nm (20 meV) for the case of the sample with the thinnest spacer layer, d = 10 nm. Although this is not an intuitive effect and cannot be easily explained, we unambiguously attribute it to the coupling of perovskite emitters to the HMM modes, as will be discussed below. Simultaneously, we observe a shortening of the measured PL transients by reducing the HMM-spacer thickness (green, yellow and red dotted transients in Figure 2d), as compared to the one measured for the reference sample (blue dotted transient in Figure 2d). As a consequence, the exciton lifetime deduced from PL transients decreases with reducing the spacer, which is ascribed to a change in the electromagnetic radiation distribution in vacuum, (65) i.e., a Purcell factor enhancement, that arises from the optical coupling of the CsPbI3 PNC emitters to the modes of the HMMs. Indeed, a similar Purcell effect was observed in the second HMM structure fabricated with slightly different parameters (40 + 40 nm period), as observed in Figure S3b of the Supporting Information. Therefore, our results are consistent and reproducible, and they are not sample dependent (i.e., not dependent on the quality of the film made of PNCs). Furthermore, the accuracy of the experiments is guaranteed by preparing all samples under similar conditions and measured using the same protocols, the same day after preparation. TRPL spectra recorded at 15 K for all samples were fitted by using a biexponential decay function where the shortest component (of the order of 1 ns) is attributed to the exciton radiative lifetime, whereas the slower component (several ns) demonstrating much lower relative amplitude (at cryogenic temperatures) can be explained by the exciton recombination dynamics involving shallow traps, as briefly introduced above and presented in more detail within section 2 of the Supporting Information. From these TRPL measurements and fittings, we observe a significant reduction of the average exciton radiative lifetime from ∼1.5 ns down to ∼0.5 ns when reducing the PMMA spacer thickness from 250 to 10 nm. The radiative exciton lifetime of 1.5 ns extracted from the reference sample is very close to the values measured in freshly prepared samples on glass substrates and values reported by us and other authors elsewhere. (59,66) As aforementioned, a clear shortening of the exciton radiative recombination time from 1.5 to 0.5 ns was obtained in average, meaning a clear Purcell enhancement around 3 for the thinnest spacer in the HMM-spacer-PNC structure. This value is similar to other cases reported in the literature using similar HMM structures: Sun et al. (67) reported theoretically 3.21 for vertical component of the Purcell factor at d = 50 nm (for random orientation of the radiant dipole this value would be only 1.42); Shalaginov et al. (68) reported experimentally 2.57 for the Purcell factor of nitrogen-vacancy centers at d = 30 nm; Tumkur et al. (69) reported 1.5–1.4 for a Purcell factor of dye molecules at d = 45 nm, and Jacob et al. (70) reported 1.7 and 1.8 first value comes from calculations and second from measurements when the thickness of the spacer was d = 21 nm.
For the sake of reproducibility and statistics significance of the results, we recorded around 10 PL and TRPL spectra (see Figure S6 of Supporting Information) in the four fabricated HMM-spacer-PNC structures at different excitation points throughout the sample surface. Of course, we observe some dispersion in these curves from point to point, as one would expect statistically. The most striking and surprising finding when analyzing these collections of PL and TRPL data taken at different excitation points for every sample is the observed clear experimental correlation between the PL peak redshift (with respect to the average PL peak measured in the reference sample) and the Purcell factor (ratio τx(ref)/τx(d), where τx(ref) is the average exciton lifetime measured for PNCs on top of the reference HMM sample with d = 250 nm, and τx(d) is the lifetime measured in the other three PNCs-HMM samples with nominal spacers d = 10, 20, and 50 nm) measured at different points of the samples, as observed in Figure 3a. These data evidence two important facts: (i) the data dispersion is more important in samples with thinner spacers (10 and 20 nm) and (ii) even at these data dispersion conditions, we observe a clear correlation between both parameters, the PL peak redshift and Purcell factor. The above mentioned data dispersion is mainly indicative of a certain degree of inhomogeneity in the spacer film thickness. Eventually, even if we optimized the dipping time to cover the HMM + spacer substrate with a single monolayer of PNCs, a certain probability of nanocrystal agglomeration (as also differences in the spin-coated PMMA thickness) is not excluded that would increase the effective value of d. In any case, we can say that a Purcell factor and associated PL peak redshift as high as 3.8 and 8 nm (near 20 meV), respectively, can be measured in some points of the sample with nominal spacer d = 10 nm. In the sample with d = 250 nm (reference), we clearly do not observe changes in the PL peak position, and we only obtain a reasonable dispersion of the exciton lifetime within the range of a 10–15% variation. Both the observed increase in the Purcell factor and the PL peak redshift of PNCs by reducing the spacer thickness should be attributed to the exciton coupling to the HMM modes. In order to explain the experimental results, we propose to consider the model schematically represented in Figure 3b, assuming a monolayer of CsPbI3 PNCs on top of the spacer. In the numerical calculations, the thickness of the CsPbI3 layer and its refractive index are extracted from ref (57) (we are using the same PNCs) and ref (71) respectively. The permittivity of Lithium fluoride (LiF) is taken to be ϵLiF = 1.95, whereas those of silver (Ag) and silicon (Si) are taken out from refs (72) and (73) respectively.

Figure 3

Figure 3. (a) Correlation of the spectral shift and Purcell factor of emitters for the different samples, (b) illustration of a simple model considering a perovskite monolayer on top of PMMA spacer, (c, d) dependence of the Purcell factor and spectral shift as a function of the distance from dipole inside the CsPbI3 and topmost metal surface of the HMM, respectively. Symbols and continuous lines (dashed and dotted-dashed for points A and B, and dotted and solid line for D, E, respectively) correspond to experimental data and simulation, respectively, as described in the text.

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Once we have obtained the LDOS as explained above (Figure 1d), we can undertake the more complex calculation of the normalized rate of power emission of a radiating dipole which is located at different positions above the spacer layer, as explained below. From here on, we follow the theoretical treatment given in (74) which allows us to write the current density as
(4)
Equation 4 originates from its time derivative, j⃗(r⃗,t) = , where j⃗(r⃗,t) = and the dipole moment is μ⃗(t) = ; thus, the current density can be thought as an oscillating dipole with origin at the center of the charge distribution. On the other hand, the electric field of an arbitrarily oriented electric dipole located at r⃗ = r⃗0 can be determined by the Green’s function G⃗(r⃗,r⃗0):
(5)
Finally, after computing the electric field, the normalized rate of power emission reads as (74)
(6)
where and are the primary dipole and scattered electric fields, respectively. Radiant dipoles would be randomly oriented in nature in the case of cubic nanocrystals used in the present work; thus, a more appropriate estimation for the energy dissipation rate is an average over horizontal and vertical dipoles:
(7)
The classical enhancement in the radiative emission rate (P = 1/τx(d)) with respect to reference (P0 = 1/τx(ref)) will be defined as . Furthermore, as described above, one of the most important experimental results in the HMM-emitter system is the spectral red shift of the PL peak of emitters. For analytical calculations of this frequency shift of the emitters, again Dyadic Green’s function has been used: (74)
(8)
where γ0 ≡ 1/τx(ref), τx(ref) = 1.5 ns. Numerically computed Purcell factor and spectral shift of the emitters with above given equations have been presented respectively in Figure 3c,d as a function of the spacer thickness (continuous lines). Given that the PNC film consists of isolated nanocrystals instead of a continuous perovskite layer, but spatially separated PNCs in the plane (several to hundreds of nm) of slightly different size due to size dispersion introduced by the chemical synthesis (11–16 nm57), we have calculated the Purcell factor and PL peak shift of the PNCs by changing the location of the point dipole source inside the continuous perovskite monolayer: curves labeled as A, B, C, D, and E in Figure 3c,d, in correspondence to locations A, B, C, D, and E in Figure 3b, in which points E and D are symmetrical to points A and B with respect to the center, respectively.
The experimental average values for these two magnitudes, from data in Figure 3a, are given by symbols with error bars in Figures 3c,d. As clearly demonstrated by calculated curves in Figure 3d, the PL peak redshift is very sensitive to the location of the point dipole source inside the PNC monolayer. This sensitivity above the center of the CsPbI3 layer (points A–B) is different from below (points D–E) due to the different contrast of the refractive index between the PNC-monolayer and its upper and lower dielectric media. As one can see from Figure 3d, when the point dipole source is exactly at the center the spectral shift is practically zero. However, by moving the location of the point emitter toward the top or down surface of the perovskite layer the frequency shift increases, in such a way that our experimental results would be consistent with the point dipole source located between points different from the center of the perovskite layer (Figure 3b), as shown in Figure 3d. On the contrary, the Purcell factor is not as sensitive as the spectral shift when changing the location of the point dipole source, as observed in Figure 3c. Even like that, the experimental values of Purcell factors for samples with spacers 10, 20, and 50 nm can be accounted for by calculated curves with the dipole located out of center, as occurred for the PL peak redshift. Additionally, in Figures S7 and S8 of the Supporting Information, we have included the spectral and spacer dependences of the Purcell factor, for HMM structures with Ag + LiF layers of 40 + 40 nm (Figure S7) and 25 + 35 nm (Figure S8). In the first case (Ag + LiF layers of 40 + 40 nm or filling factor 50%), we obtain a maximum Purcell factor of 3.5 at around 600 nm (see Figure S7), but around 2.2 at 700 nm, whereas in the second case (Ag + LiF layers of 25 + 35 nm or filling factor 42%) we have achieved a shift of the spectral dependence of the Purcell factor toward the red (see Figure S8), being now its peak value closer to the emission wavelength of the CsPbI3 PNCs. From our calculations, a maximum value of Purcell factor in the range 4.5–5 (depending on the dipole position) is theoretically expected for a spacer layer around 2–3 nm (in agreement with ref (75)); experimentally, we are able to deposit a minimum of 10 nm thick layer of PMMA (the spacer) in a controlled way, and hence we would expect values in the range 2.8–3.8 (depending on the dipole position), very close to experimental values (see Figure 3a). Of course, the dispersion in the Purcell factor can be also due to inhomogeneities in the spacer thickness and, to a smaller extent (because of less sensitive), inhomogeneities in the Ag/LiF layers; however, the position (or distance between the dipole and the interface with the HMM surface or air) of the radiant dipole will define the PL redshift.
Figure 4 shows the fabricated structure that has been modeled in 3D COMSOL Multiphysics, frequency domain, RF module, which is a software based on finite element method (FEM). The oscillating electric point dipole, which emits light at the wavelength of 705 nm, is located on the top surface of the spacer in this simulation. To eliminate the reflection from the outer boundaries, the model is truncated by a perfectly matched layer (PML). This figure illustrates the normalized spatial distribution of the absolute value of the electric field of a point source dipole, with the polarization parallel (Figure 4a–c) and perpendicular (Figure 4b–d) to the multilayer stacks, when it is located at the top surface of the thinnest (Figure 4a–b corresponding to d = 10 nm) and thickest (Figure 4c–d corresponding to d = 250 nm) spacers of the same HMM structure (25 + 35 nm). To show the propagation of the energy flux, we plotted the Poynting vectors in logarithmic scale within the plane where the dipole oscillates. Additionally, the electric field is spatially expanded into the Ag-LiF metal-dielectric multilayer for both dipole polarizations when the dipole gets close to the HMM structure (by using sufficiently thin spacers). The power dissipated down to the HMM structure is the key physics to understand the observed increase of the spontaneous emission rate of our emitters. On the contrary, for a very thick spacer (the case of our reference device), the point dipole is very far from the multilayer, and its interaction with the metal-dielectric multilayer is substantially reduced, and hence a great amount of the dipole power emits to the top side of the HMM structure.

Figure 4

Figure 4. (a, b) Distribution of the normalized electric field |E| of a horizontal and vertical dipole (arrows) located on top of HMM substrate when d = 10 nm (c, d) are respectively, correspond to (a, b) when d = 250 nm. The point source emits at λ = 705 nm, and the cones show the direction of the energy flows in logarithmic scale.

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Conclusion

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To summarize, we investigated an enhancement of the rate of spontaneous emission of CsPbI3 PNCs by means of HMM substrates. These substrates have been fabricated by the alternative deposition of thin metal (Ag) and dielectric (LiF) layers by means of thermal evaporation. The coupling of excitons photogenerated in CsPbI3 PNCs to the optical modes of these HMM substrates induces a reduction by more than a factor 3 of the exciton radiative lifetime due to the Purcell effect, as measured in the sample with a nominal spacer thickness (distance between HMM and QEs) of 10 nm. Along with that, varying the spacer (and therefore the exciton-HMM coupling) affects also the PL peak wavelength, which is shifted to the longer wavelengths by up to 8 nm for the thinnest spacer. These experimental results are in agreement with theoretical calculations. These results are important for the future development of single photon sources and other quantum photonic applications based on the combination and integration of perovskite nanocrystals (for which different emission wavelengths are possible) and HMM structures, and eventually nanostructure for further Purcell enhancing.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsphotonics.0c01219.

  • (1) Details of another HMM structure with 50% filling factor of metal. (2) The delayed luminescence in perovskite nanocrystals and effect on Purcell factor. (3) Additional experimental results in the HMM structure with 42% filling factor of metal. (4) Purcell factor of the HMM structures as a function of wavelength and spacer thickness (PDF)

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Author Information

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  • Corresponding Authors
    • Carlos J. Zapata-Rodríguez - Departament d’Òptica i Optometria i Ciències de la Visió, Facultad de Fı́sica, Universitat de València, C/Dr Moliner 50, 46100 Burjassot, Spain;  Email: [email protected]
    • Juan P. Martínez-Pastor - Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain;  Orcidhttp://orcid.org/0000-0003-3683-0578;  Email: [email protected]
  • Authors
    • Hamid Pashaei Adl - Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
    • Setatira Gorji - Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain
    • Mojtaba Karimi Habil - Faculty of Physics, University of Tabriz, 51664, Tabriz, Iran
    • Isaac Suárez - Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain;  Departamento de Ingenierı́a Electrónica, Escuela Técnica Superior de Ingenierı́a, Universidad de Valencia, Avenida de la Universidad s/n, 46100 Burjassot, Spain;  Orcidhttp://orcid.org/0000-0002-2773-8801
    • Vladimir S. Chirvony - Instituto de Ciencia de Materiales (ICMUV), Universidad de Valencia, C/Catedrático José Beltrán 2, 46980 Paterna, Spain;  Orcidhttp://orcid.org/0000-0003-4121-9773
    • Andrés F. Gualdrón-Reyes - Institute of Advanced Materials (INAM), Universitat Jaume I (UJI), Avenida de Vicent Sos Baynat s/n, 12071 Castelló de la Plana, Spain;  Orcidhttp://orcid.org/0000-0002-0208-9235
    • Iván Mora-Seró - Institute of Advanced Materials (INAM), Universitat Jaume I (UJI), Avenida de Vicent Sos Baynat s/n, 12071 Castelló de la Plana, Spain;  Orcidhttp://orcid.org/0000-0003-2508-0994
    • Luisa M. Valencia - Departamento de Ciencia de los Materiales e IM y QI. F. Ciencias, IMEYMAT, Campus Rı́o San Pedro, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain
    • María de la Mata - Departamento de Ciencia de los Materiales e IM y QI. F. Ciencias, IMEYMAT, Campus Rı́o San Pedro, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain;  Orcidhttp://orcid.org/0000-0002-1581-4838
    • Jesús Hernández-Saz - Departamento de Ingenierı́a y Ciencia de los Materiales y del Transporte, Escuela Técnica Superior de Ingenierı́a, Universidad de Sevilla, Camino Descubrimientos, s/n.- Isla Cartuja, 41092 Sevilla, Spain;  Orcidhttp://orcid.org/0000-0002-6630-7203
    • Sergio I. Molina - Departamento de Ciencia de los Materiales e IM y QI. F. Ciencias, IMEYMAT, Campus Rı́o San Pedro, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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Financial support from Spanish MINECO through Projects No. TEC2017-86102-C2-1-R and TEC2017-86102-C2-2-R, the European Research Council (ERC) via Consolidator Grant (724424-No-LIMIT), the Generalitat Valenciana via Prometeo Grant Q-Devices (Prometeo/2018/098), the 2014-2020 ERDF Operational Programme, and the Junta de Andalucı́a (FEDER-UCA18-106586 and TEP946 INNANOMAT research group) are gratefully acknowledged. S.G. acknowledges her “Grisolia” grant from Generalitat Valenciana. M.dlM. acknowledges financial support from MICINN (IJCI-2017-31507).

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    Luo, Q.; Ma, H.; Hou, Q.; Li, Y.; Ren, J.; Dai, X.; Yao, Z.; Zhou, Y.; Xiang, L.; Du, H. All-carbon-electrode-based endurable flexible perovskite solar cells. Adv. Funct. Mater. 2018, 28, 1706777,  DOI: 10.1002/adfm.201706777
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    Shin, S. S.; Suk, J. H.; Kang, B. J.; Yin, W.; Lee, S. J.; Noh, J. H.; Ahn, T. K.; Rotermund, F.; Cho, I. S.; Seok, S. I. Energy-level engineering of the electron transporting layer for improving open-circuit voltage in dye and perovskite-based solar cells. Energy Environ. Sci. 2019, 12, 958– 964,  DOI: 10.1039/C8EE03672A
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    19
    Energy-level engineering of the electron transporting layer for improving open-circuit voltage in dye and perovskite-based solar cells
    Shin, Seong Sik; Suk, Jae Ho; Kang, Bong Joo; Yin, Wenping; Lee, Seon Joo; Noh, Jun Hong; Ahn, Tae Kyu; Rotermund, Fabian; Cho, In Sun; Seok, Sang Il
    Energy & Environmental Science (2019), 12 (3), 958-964CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    Next-generation solar cells, such as dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs), are fabricated in a configuration where light absorbers are located between the electron transporting layer (ETL) and the hole transporting layer (HTM). Although the most efficient DSSCs and PSCs have been fabricated using TiO2 as the ETL, TiO2 exhibits inherently low electron mobility with difficulty controlling the energy levels (i.e., conduction and valence bands) as it possesses a single phase of two components. Here, we report the synthesis of Sr-substituted BaSnO3 (BSSO) by a low-temp. soln. process as a new alternative to TiO2 for both PSCs and DSSCs. The energy-level tailoring by Sr incorporation into BaSnO3 minimizes the open-circuit voltage (VOC) loss at the interfaces of ETL/perovskite and ETL/electrolyte in the PSCs and DSSCs, thereby leading to an improved VOC from 0.65 to 0.72 V in DSSC and 1.07 to 1.13 V in PSCs. Addnl., the BSSO ETL-based PSC shows improved photostability compared to the TiO2 analog. Our results show that energy-level tuned BSSO can be applied as a universal ETL for improving efficiency in both PSCs and DSSCs.
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  20. 20
    Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of cesium lead halide perovskites (CsPbX3, X= Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut. Nano Lett. 2015, 15, 3692– 3696,  DOI: 10.1021/nl5048779
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    20
    Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut
    Protesescu, Loredana; Yakunin, Sergii; Bodnarchuk, Maryna I.; Krieg, Franziska; Caputo, Riccarda; Hendon, Christopher H.; Yang, Ruo Xi; Walsh, Aron; Kovalenko, Maksym V.
    Nano Letters (2015), 15 (6), 3692-3696CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Metal halides perovskites, such as hybrid org.-inorg. MeNH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as soln.-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. A new avenue for halide perovskites was demonstrated by designing highly luminescent perovskite-based colloidal quantum dot materials. Monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorg. perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) were synthesized using inexpensive com. precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The luminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color std., high quantum yields of ≤90%, and radiative lifetimes at 1-29 ns. The compelling combination of enhanced optical properties and chem. robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410-530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegrdn.
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  21. 21
    Zhang, F.; Zhong, H.; Chen, C.; Wu, X.-g.; Hu, X.; Huang, H.; Han, J.; Zou, B.; Dong, Y. Brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X= Br, I, Cl) quantum dots: potential alternatives for display technology. ACS Nano 2015, 9, 4533– 4542,  DOI: 10.1021/acsnano.5b01154
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    21
    Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology
    Zhang, Feng; Zhong, Haizheng; Chen, Cheng; Wu, Xian-gang; Hu, Xiangmin; Huang, Hailong; Han, Junbo; Zou, Bingsuo; Dong, Yuping
    ACS Nano (2015), 9 (4), 4533-4542CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    A ligand-assisted repptn. strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with abs. quantum yield up to 70% at room temp. and low excitation fluencies is reported. To illustrate the photoluminescence enhancements in these quantum dots, comprehensive compn. and surface characterizations and time- and temp.-dependent photoluminescence spectra were studied. Comparisons between small-sized CH3NH3PbBr3 quantum dots (av. diam. 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 μm) suggested that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size redn. as well as proper chem. passivations of the Br-rich surface. Wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn4+ as color converters were fabricated, providing enhanced color quality for display technol. The colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.
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    Kovalenko, M. V.; Protesescu, L.; Bodnarchuk, M. I. Properties and potential optoelectronic applications of lead halide perovskite nanocrystals. Science 2017, 358, 745– 750,  DOI: 10.1126/science.aam7093
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    Properties and potential optoelectronic applications of lead halide perovskite nanocrystals
    Kovalenko, Maksym V.; Protesescu, Loredana; Bodnarchuk, Maryna I.
    Science (Washington, DC, United States) (2017), 358 (6364), 745-750CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    A review. Semiconducting lead halide perovskites (LHPs) have not only become prominent thin-film absorber materials in photovoltaics but have also proven to be disruptive in the field of colloidal semiconductor nanocrystals (NCs). The most important feature of LHP NCs is their so-called defect-tolerance-the apparently benign nature of structural defects, highly abundant in these compds., with respect to optical and electronic properties. Here, we review the important differences that exist in the chem. and physics of LHP NCs as compared with more conventional, tetrahedrally bonded, elemental, and binary semiconductor NCs (such as silicon, germanium, cadmium selenide, gallium arsenide, and indium phosphide). We survey the prospects of LHP NCs for optoelectronic applications such as in television displays, light-emitting devices, and solar cells, emphasizing the practical hurdles that remain to be overcome.
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    Li, X.; Cao, F.; Yu, D.; Chen, J.; Sun, Z.; Shen, Y.; Zhu, Y.; Wang, L.; Wei, Y.; Wu, Y. All inorganic halide perovskites nanosystem: synthesis, structural features, optical properties and optoelectronic applications. Small 2017, 13, 1603996,  DOI: 10.1002/smll.201603996
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    Hassanabadi, E.; Latifi, M.; Gualdron-Reyes, A. F.; Masi, S.; Yoon, S. J.; Poyatos, M.; Julian-Lopez, B.; Mora-Sero, I. Ligand & Band Gap Engineering: Tailoring the Protocol Synthesis for Achieving High-Quality CsPbI3 Quantum Dots. Nanoscale 2020, 12, 14194,  DOI: 10.1039/D0NR03180A
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    24
    Ligand & band gap engineering: tailoring the protocol synthesis for achieving high-quality CsPbI3 quantum dots
    Hassanabadi, Ehsan; Latifi, Masoud; Gualdron-Reyes, Andres. F.; Masi, Sofia; Yoon, Seog Joon; Poyatos, Macarena; Julian-Lopez, Beatriz; Mora-Sero, Ivan
    Nanoscale (2020), 12 (26), 14194-14203CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Hot-injection has become the most widespread method used for the synthesis of perovskite quantum dots (QDs) with enormous interest for application in optoelectronic devices. However, there are some aspects of the chem. involved in this synthesis that have not been completely investigated. In this work, we synthesized ultra-high stable CsPbI3 QDs for more than 15 mo by controlling two main parameters: synthesis temp. and the concn. of capping ligands. By increasing the capping ligand concn. during the QD synthesis, we were able to grow CsPbI3 in a broad range of temps., improving the photophys. properties of QDs by increasing the synthesis temp. We achieved the max. photoluminescence quantum yield (PLQY) of 93% for a synthesis conducted at 185°C, establishing an efficient surface passivation to decrease the d. of non-radiative recombination sites. Under these optimized synthesis conditions, deep red LEDs with an External Quantum Efficiency (EQE) higher than 6% were achieved. The performance of these LEDs is higher than that of the reported CsPbI3 QD-LEDs contg. std. capping agents, without addnl. elements or further element exchange. We show that it is possible to produce stable CsPbI3 QDs with high PLQY and red emission beyond the requirement of the Rec. 2020 stds. for red color.
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    Navarro Arenas, J.; Soosaimanickam, A.; Pashaei Adl, H.; Abargues, R.; Boix, P. P.; Rodrı́guez-Cantó, P. J.; Martı́nez-Pastor, J. P. Ligand-Length Modification in CsPbBr3 Perovskite Nanocrystals and Bilayers with PbS Quantum Dots for Improved Photodetection Performance. Nanomaterials 2020, 10, 1297,  DOI: 10.3390/nano10071297
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    Hu, F.; Zhang, H.; Sun, C.; Yin, C.; Lv, B.; Zhang, C.; Yu, W. W.; Wang, X.; Zhang, Y.; Xiao, M. Single Photon Emission from Single Perovskite Nanocrystals of Cesium Lead Bromide. ACS Nano 2015, 9, 12410,  DOI: 10.1021/acsnano.5b05769
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    Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters
    Hu, Fengrui; Zhang, Huichao; Sun, Chun; Yin, Chunyang; Lv, Bihu; Zhang, Chunfeng; Yu, William W.; Wang, Xiaoyong; Zhang, Yu; Xiao, Min
    ACS Nano (2015), 9 (12), 12410-12416CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Single photon emission was obsd. from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly 2 orders of magnitude increase in their absorption cross sections at similar emission colors. The radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temps. to favor an extremely fast output of single photons. The above superior optical properties have paved the way toward quantum-light applications of perovskite NCs in various quantum information processing schemes.
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  27. 27
    Utzat, H.; Sun, W.; Kaplan, A. E.; Krieg, F.; Ginterseder, M.; Spokoyny, B.; Klein, N. D.; Shulenberger, K. E.; Perkinson, C. F.; Kovalenko, M. V. Coherent single-photon emission from colloidal lead halide perovskite quantum dots. Science 2019, 363, 1068– 1072,  DOI: 10.1126/science.aau7392
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    Coherent single-photon emission from colloidal lead halide perovskite quantum dots
    Utzat, Hendrik; Sun, Weiwei; Kaplan, Alexander E. K.; Krieg, Franziska; Ginterseder, Matthias; Spokoyny, Boris; Klein, Nathan D.; Shulenberger, Katherine E.; Perkinson, Collin F.; Kovalenko, Maksym V.; Bawendi, Moungi G.
    Science (Washington, DC, United States) (2019), 363 (6431), 1068-1072CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Chem. made colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. The authors now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 ps, an appreciable fraction of their 210-ps radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Their results present a starting point for the rational design of lead halide perovskite-based quantum emitters that have fast emission, wide spectral tunability, and scalable prodn. and that benefit from the hybrid integration with nanophotonic components that has been demonstrated for colloidal materials.
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    Li, C.; Xu, Z.-Q.; Mendelson, N.; Kianinia, M.; Toth, M.; Aharonovich, I. Purification of single-photon emission from hBN using post-processing treatments. Nanophotonics 2019, 8, 2049– 2055,  DOI: 10.1515/nanoph-2019-0099
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    Purification of single-photon emission from hBN using post-processing treatments
    Li, Chi; Xu, Zai-Quan; Mendelson, Noah; Kianinia, Mehran; Toth, Milos; Aharonovich, Igor
    Nanophotonics (2019), 8 (11), 2049-2055CODEN: NANOLP; ISSN:2192-8614. (Walter de Gruyter GmbH)
    Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising components for on-chip quantum information processing. Recently, large-area hBN films prepd. by chem. vapor deposition (CVD) were found to host uniform, high densities of SPEs. However, the purity of these emitters has, to date, been low, hindering their applications in practical devices. In this work, we present two methods for post-growth processing of hBN, which significantly improve SPEs in hBN films that had been transferred from substrates used for CVD. The emitters exhibit high photon purities in excess of 90% and narrow linewidths of ∼3 nm at room temp. Our work lays a foundation for producing high-quality emitters in an ultra-compact two-dimensional material system and paves the way for deployment of hBN SPEs in scalable on-chip photonic and quantum devices.
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    Turiansky, M.; Alkauskas, A.; Bassett, L.; Van de Walle, C. Boron Dangling Bonds as Single Photon Emitters in Hexagonal Boron Nitride. Phys. Rev. Lett. 2019,  DOI: 10.1103/PhysRevLett.123.127401
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    Sun, Y.; Yaroshenko, V.; Chebykin, A.; Ageev, E.; Makarov, S.; Zuev, D. Metal-dielectric nanoantenna for radiation control of a single-photon emitter. Opt. Mater. Express 2020, 10, 29– 35,  DOI: 10.1364/OME.10.000029
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    Metal-dielectric nanoantenna for radiation control of a single-photon emitter
    Sun, Yali; Yaroshenko, Vitaly; Chebykin, Alexander; Ageev, Eduard; Makarov, Sergey; Zuev, Dmitry
    Optical Materials Express (2020), 10 (1), 29-35CODEN: OMEPAX; ISSN:2159-3930. (Optical Society of America)
    The control of fluorescent properties of single-photon sources in solid-state host systems via optically resonant nanostructures is a key issue in quantum nanophotonics. Here we propose a design of a resonant metal-dielec. nanoantenna for the Purcell factor and radiation pattern control of a quantum emitter placed in the gap between metal and dielec. components of the nanostructure. We demonstrate that large Purcell factor, considerable field enhancement in the gap as well as high directivity can be achieved. The developed nanosystem can be utilized for different solid-state host systems from nanocrystals to 2D materials.
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    Shalaginov, M. Y.; Vorobyov, V. V.; Liu, J.; Ferrera, M.; Akimov, A. V.; Lagutchev, A.; Smolyaninov, A. N.; Klimov, V. V.; Irudayaraj, J.; Kildishev, A. V. Enhancement of single-photon emission from nitrogen-vacancy centers with TiN/(Al, Sc) N hyperbolic metamaterial. Laser & Photonics Reviews 2015, 9, 120– 127,  DOI: 10.1002/lpor.201400185
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    Enhancement of single-photon emission from nitrogen-vacancy centers with TiN/(Al,Sc)N hyperbolic metamaterial
    Shalaginov, Mikhail Y.; Vorobyov, Vadim V.; Liu, Jing; Ferrera, Marcello; Akimov, Alexey V.; Lagutchev, Alexei; Smolyaninov, Andrey N.; Klimov, Vasily V.; Irudayaraj, Joseph; Kildishev, Alexander V.; Boltasseva, Alexandra; Shalaev, Vladimir M.
    Laser & Photonics Reviews (2015), 9 (1), 120-127CODEN: LPRAB8; ISSN:1863-8880. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The broadband enhancement of single-photon emission from nitrogen-vacancy centers in nanodiamonds coupled to a planar multilayer metamaterial with hyperbolic dispersion is studied exptl. The metamaterial is fabricated as an epitaxial metal/dielec. superlattice consisting of CMOS-compatible ceramics: titanium nitride (TiN) and aluminum scandium nitride (AlxSc1-xN). It is demonstrated that employing the metamaterial results in significant enhancement of collected single-photon emission and redn. of the excited-state lifetime. Our results could have an impact on future CMOS-compatible integrated quantum sources.
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    Optical microcavities
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    Nature (London, United Kingdom) (2003), 424 (6950), 839-846CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    A review. Optical microcavities confine light to small vols. by resonant recirculation. Devices based on optical microcavities are already indispensable for a wide range of applications and studies. For example, microcavities made of active III-V semiconductor materials control laser emission spectra to enable long-distance transmission of data over optical fibers; they also ensure narrow spot-size laser read/write beams in CD and DVD players. In quantum optical devices, microcavities can coax atoms or quantum dots to emit spontaneous photons in a desired direction or can provide an environment where dissipative mechanisms such as spontaneous emission are overcome so that quantum entanglement of radiation and matter is possible. Applications of these remarkable devices are as diverse as their geometrical and resonant properties.
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    Shen, S.; Li, J.; Wu, Y. Magnetically controllable photon blockade under a weak quantum-dot–cavity coupling condition. Phys. Rev. A: At., Mol., Opt. Phys. 2020, 101, 023805,  DOI: 10.1103/PhysRevA.101.023805
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    Gérard, J.; Sermage, B.; Gayral, B.; Legrand, B.; Costard, E.; Thierry-Mieg, V. Enhanced spontaneous emission by quantum boxes in a monolithic optical microcavity. Phys. Rev. Lett. 1998, 81, 1110,  DOI: 10.1103/PhysRevLett.81.1110
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    Enhanced spontaneous emission by quantum boxes in a monolithic optical microcavity
    Gerard, J. M.; Sermage, B.; Gayral, B.; Legrand, B.; Costard, E.; Thierry-Mieg, V.
    Physical Review Letters (1998), 81 (5), 1110-1113CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Semiconductor quantum boxes (QB's) are well suited to cavity quantum electrodynamic expts. in the solid state because of their sharp emission. We study by time-resolved photoluminescence InAs QB's placed in the core of small-vol. and high-finesse GaAs/AlAs pillar microresonators. A spontaneous emission rate enhancement by a factor of up to 5 is selectively obsd. for the QB's which are on resonance with 1-cavity mode. We explain its magnitude by considering the Purcell figure of merit of the micropillars and the effect of the random spatial and spectral distributions of the QB's.
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    Takahashi, H.; Kassa, E.; Christoforou, C.; Keller, M. Strong coupling of a single ion to an optical cavity. Phys. Rev. Lett. 2020, 124, 013602,  DOI: 10.1103/PhysRevLett.124.013602
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    Strong Coupling of a Single Ion to an Optical Cavity
    Takahashi, Hiroki; Kassa, Ezra; Christoforou, Costas; Keller, Matthias
    Physical Review Letters (2020), 124 (1), 013602CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
    Strong coupling between an atom and an electromagnetic resonator is an important condition in cavity quantum electrodynamics. While strong coupling in various phys. systems has been achieved so far, it remained elusive for single at. ions. Here, we achieve a coupling strength of 2πx(12.3±0.1) MHz between a single Ca40+ ion and an optical cavity, exceeding both at. and cavity decay rates which are 2πx11.5 and 2πx(4.1±0.1) MHz, resp. We use cavity assisted Raman spectroscopy to precisely characterize the ion-cavity coupling strength and observe a spectrum featuring the normal mode splitting in the cavity transmission due to the ion-cavity interaction. Our work paves the way towards new applications of cavity quantum electrodynamics utilizing single trapped ions in the strong coupling regime for quantum optics and quantum technologies.
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    Reithmaier, J. P.; Sek, G.; Loffler, A.; Hofmann, C.; Kuhn, S.; Reitzenstein, S.; Keldysh, L. V.; Kulakovskii, V. D.; Reinecke, T. L.; Forchel, A. Strong coupling in a single quantum dot–semiconductor microcavity system. Nature 2004, 432, 197– 200,  DOI: 10.1038/nature02969
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    Strong coupling in a single quantum dot-semiconductor microcavity system
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    Nature (London, United Kingdom) (2004), 432 (7014), 197-200CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    The authors report the observation of strong coupling of a single 2-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of ∼140 μeV.
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    Li, L.; Wang, W.; Luk, T. S.; Yang, X.; Gao, J. Enhanced quantum dot spontaneous emission with multilayer metamaterial nanostructures. ACS Photonics 2017, 4, 501– 508,  DOI: 10.1021/acsphotonics.6b01039
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    Enhanced Quantum Dot Spontaneous Emission with Multilayer Metamaterial Nanostructures
    Li, Ling; Wang, Wei; Luk, Ting S.; Yang, Xiaodong; Gao, Jie
    ACS Photonics (2017), 4 (3), 501-508CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    The Purcell effect of quantum dot (QD) spontaneous emission with Ag-SiO2 multilayer metamaterial nanostructures was demonstrated in expt. and simulation. A broadband enhanced spontaneous emission rate of QDs is obsd. due to large local d. of states in the epsilon-near-zero and hyperbolic regions of multilayer structures. Multilayer gratings are used to further enhance the QD spontaneous emission as the QDs located inside the grating grooves strongly interact with high-k coupled surface plasmon polariton modes. Photoluminescence decay measurements are in good agreement with both anal. treatment with a nonlocal effect and 3-dimensional finite-element simulation. Detailed studies of QD position and polarization effects on emission rate enhancement for multilayer and multilayer grating nanostructures provide important insight for understanding the coupling mechanisms of emitter-multilayer interaction and the engineering of local d. of states in metamaterial nanostructures. These results will advance many applications in light-emitting devices, nanoscale lasers, quantum electrodynamics, and quantum information processing.
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    Wang, L.; Li, S.; Zhang, B.; Qin, Y.; Tian, Z.; Fang, Y.; Li, Y.; Liu, Z.; Mei, Y. Asymmetrically curved hyperbolic metamaterial structure with gradient thicknesses for enhanced directional spontaneous emission. ACS Appl. Mater. Interfaces 2018, 10, 7704– 7708,  DOI: 10.1021/acsami.7b19721
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    Asymmetrically Curved Hyperbolic Metamaterial Structure with Gradient Thicknesses for Enhanced Directional Spontaneous Emission
    Wang, Lu; Li, Shilong; Zhang, Biran; Qin, Yuzhou; Tian, Ziao; Fang, Yangfu; Li, Yonglei; Liu, Zhaowei; Mei, Yongfeng
    ACS Applied Materials & Interfaces (2018), 10 (9), 7704-7708CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Hyperbolic metamaterials (HMMs) on a curved surface are demonstrated for an efficient outcoupling of nonradiative modes, which lead to an enhanced spontaneous emission. Those high-wavevector plasmonic modes can propagate along the curved structure and emit into the far field, realizing a directional light emission with max. fluorescent intensity. Detailed simulations disclose a high Purcell factor and a spatial power distribution in the curved HMM, which agrees with the exptl. result. The work presents remarkable enhancing capability in both the Purcell factor and emission intensity, which could suggest a unique structure design in metamaterials for potential application in, e.g., high-speed optical sensing and communications.
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    Roth, D. J.; Ginzburg, P.; Hirvonen, L. M.; Levitt, J. A.; Nasir, M. E.; Suhling, K.; Richards, D.; Podolskiy, V. A.; Zayats, A. V. Singlet–Triplet Transition Rate Enhancement inside Hyperbolic Metamaterials. Laser Photonics Rev. 2019, 13, 1900101,  DOI: 10.1002/lpor.201900101
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    Singlet-Triplet Transition Rate Enhancement inside Hyperbolic Metamaterials
    Roth, Diane J.; Ginzburg, Pavel; Hirvonen, Liisa M.; Levitt, James A.; Nasir, Mazhar E.; Suhling, Klaus; Richards, David; Podolskiy, Viktor A.; Zayats, Anatoly V.
    Laser & Photonics Reviews (2019), 13 (9), n/a1900101CODEN: LPRAB8; ISSN:1863-8899. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The spontaneous emission process is known to be largely affected by the surrounding electromagnetic environment of emitters, which manifests itself via the Purcell enhancement of decay rates. This phenomenon has been extensively investigated in the case of dipolar transitions in quantum systems, commonly delivering fast decay rates in comparison to forbidden transitions such as high-order multipolar transitions or spin-forbidden, singlet-triplet phosphorescence processes. Here, a decay rate enhancement of almost 2750-fold is demonstrated for a ruthenium-based phosphorescent emitter located inside a plasmonic hyperbolic metamaterial. The std. electromagnetic local d. of states description, typically employed for the Purcell factor anal. of dipolar transitions, is unable to account for a photoluminescence enhancement of this magnitude, which is attributed to the interplay between the local d. of states and strongly inhomogeneous electromagnetic fields inside the metamaterial. The large available range of spontaneous emission lifetimes reported here enables application of phosphorescent emitters in novel, fast, and efficient light-emitting sources, beneficial for optical communications, quantum information processing, spectroscopy, or bio-imaging.
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    Lee, K. J.; Lee, Y. U.; Kim, S. J.; André, P. Hyperbolic dispersion dominant regime identified through spontaneous emission variations near metamaterial interfaces. Adv. Mater. Interfaces 2018, 5, 1701629,  DOI: 10.1002/admi.201701629
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    Lu, D.; Ferrari, L.; Kan, J. J.; Fullerton, E. E.; Liu, Z. Optimization of nanopatterned multilayer hyperbolic metamaterials for spontaneous light emission enhancement. Phys. Status Solidi A 2018, 215, 1800263,  DOI: 10.1002/pssa.201800263
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    Morozov, K. M.; Ivanov, K. A.; de Sa Pereira, D.; Menelaou, C.; Monkman, A. P.; Pozina, G.; Kaliteevski, M. A. Revising of the Purcell effect in periodic metal-dielectric structures: the role of absorption. Sci. Rep. 2019, 9, 1– 9,  DOI: 10.1038/s41598-019-46071-5
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    Modelling optimal behavioural strategies in structured populations using a novel theoretical framework
    Morozov, Andrew; Kuzenkov, Oleg A.; Arashkevich, Elena G.
    Scientific Reports (2019), 9 (1), 1-15CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
    Understanding complex behavioral patterns of organisms obsd. in nature can be facilitated using math. modeling. The conventional paradigm in animal behavior modeling consists of maximisation of some evolutionary fitness function. However, the definition of fitness of an organism or population is generally subjective, and using different criteria can lead us to contradictory model predictions regarding optimal behavior. Moreover, structuring of natural populations in terms of individual size or developmental stage creates an extra challenge for theor. modeling. Here we revisit and formalise the definition of evolutionary fitness to describe long-term selection of strategies in deterministic self-replicating systems for generic modeling settings which involve an arbitrary function space of inherited strategies. Then we show how optimal behavioral strategies can be obtained for different developmental stages in a generic von-Foerster stage-structured population model with an arbitrary mortality term. We implement our theor. framework to explore patterns of optimal diel vertical migration (DVM) of two dominant zooplankton species in the north-eastern Black Sea. We parameterise the model using 7 years of empirical data from 2007-2014 and show that the obsd. DVM can be explained as the result of a trade-off between depth-dependent metabolic costs for grazers, anoxia zones, available food, and visual predation.
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    Caligiuri, V.; Palei, M.; Imran, M.; Manna, L.; Krahne, R. Planar double-epsilon-near-zero cavities for spontaneous emission and Purcell effect enhancement. ACS Photonics 2018, 5, 2287– 2294,  DOI: 10.1021/acsphotonics.8b00121
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    Planar Double-Epsilon-Near-Zero Cavities for Spontaneous Emission and Purcell Effect Enhancement
    Caligiuri, Vincenzo; Palei, Milan; Imran, Muhammad; Manna, Liberato; Krahne, Roman
    ACS Photonics (2018), 5 (6), 2287-2294CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    The enhancement of the photophys. response of fluorophores is a crucial factor for photonic and optoelectronic technols. that involve fluorophores as gain media. Recent advances in the development of an extreme light propagation regime, called epsilon-near-zero (ENZ), provide a promising approach in this respect. The authors design metal/dielec. nanocavities to be resonant with the absorption and emission bands of the employed fluorophores. Using CsPbBr3 perovskite nanocrystal films as light emitters, the authors study the spontaneous emission and decay rate enhancement induced by a specifically tailored double-epsilon-near-zero (double ENZ) structure. The authors exptl. demonstrate the existence of 2 ENZ wavelengths, by directly measuring their dielec. permittivity via ellipsometric anal. The double ENZ nature of this plasmonic nanocavity was exploited to achieve both surface plasmon enhanced absorption (SPEA) and surface plasmon coupled emission (SPCE), inducing a significant enhancement of both the spontaneous emission and the decay rate of the perovskite nanocrystal film that is placed on top of the nanocavity. Finally, the possibility of tailoring the 2 ENZ wavelengths of this structure within the visible spectrum simply by finely designing the thickness of the 2 dielec. layers, which enables resonance matching with a broad variety of dyes are discussed. The device design is appealing for many practical applications, ranging from sensing to low threshold amplified spontaneous emission, since the authors achieve a strong PL enhancement with structures that allow for straightforward fluorophore deposition on a planar surface that keeps the fluorophores exposed and accessible.
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    Hennessy, K.; Badolato, A.; Winger, M.; Gerace, D.; Atatüre, M.; Gulde, S.; Fält, S.; Hu, E. L.; Imamoğlu, A. Quantum nature of a strongly coupled single quantum dot–cavity system. Nature 2007, 445, 896– 899,  DOI: 10.1038/nature05586
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    Quantum nature of a strongly coupled single quantum dot-cavity system
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    Nature (London, United Kingdom) (2007), 445 (7130), 896-899CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Cavity quantum electrodynamics (QED) studies the interaction between a quantum emitter and a single radiation-field mode. When an atom is strongly coupled to a cavity mode, it is possible to realize important quantum information processing tasks, such as controlled coherent coupling and entanglement of distinguishable quantum systems. Realizing these tasks in the solid state is clearly desirable, and coupling semiconductor self-assembled quantum dots to monolithic optical cavities is a promising route to this end. However, validating the efficacy of quantum dots in quantum information applications requires confirmation of the quantum nature of the quantum-dot-cavity system in the strong-coupling regime. Here we find such confirmation by observing quantum correlations in photoluminescence from a photonic crystal nanocavity interacting with one, and only one, quantum dot located precisely at the cavity elec. field max. When off-resonance, photon emission from the cavity mode and quantum-dot excitons is anticorrelated at the level of single quanta, proving that the mode is driven solely by the quantum dot despite an energy mismatch between cavity and excitons. When tuned to resonance, the exciton and cavity enter the strong-coupling regime of cavity QED and the quantum-dot exciton lifetime reduces by a factor of 145. The generated photon stream becomes antibunched, proving that the strongly coupled exciton/photon system is in the quantum regime. Our observations unequivocally show that quantum information tasks are achievable in solid-state cavity QED.
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    Purcell, E. M.; Torrey, H. C.; Pound, R. V. Resonance absorption by nuclear magnetic moments in a solid. Phys. Rev. 1946, 69, 37,  DOI: 10.1103/PhysRev.69.37
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    Resonance absorption by nuclear magnetic moments in a solid
    Purcell, E. M.; Torrey, H. C.; Pound, R. V.
    Physical Review (1946), 69 (), 37-8CODEN: PHRVAO; ISSN:0031-899X.
    In the method for the detn. of nuclear magnetic moments by mol. beams (Rabi, et al, C.A. 32, 3257.6), transitions are induced between energy levels which correspond to different orientations of the nuclear spin in a strong, const., applied magnetic field. The absorption of radio-frequency energy, due to such transitions, was observed in a solid material (paraffin) which contains protons. Exptl. procedure and results are given.
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    Classical aspects of energy transfer in molecular systesm
    Kuhn, Hans
    Journal of Chemical Physics (1970), 53 (1), 101-8CODEN: JCPSA6; ISSN:0021-9606.
    The decay time of the luminescence of a mol. S in front of a metal mirror depends markedly on its distance from the mirror. This phenomenon is quant. explained by considering the radiation field of this dipole, given by the Hertz classical equation. This field arrives at the mol., after being reflected at the mirror, with a retardation of the order of 10-15 sec. The decay time of the luminescence depends on the phase shift produced by this retardation, and thus on the ratio of the distance of the oscillator from the mirror, and the wavelength of the emitted light. By measuring the distance dependence of the decay time of the luminescence this retardation effect can be studied. In quantum-mech. terms the phenomenon can be described as being due to a stimulation or inhibition of the emission of the light quantum. In contrast to the known cases of stimulated emission, the stimulating field is the radiation field of the emitter quantum itself. The energy transfer from an excited mol. S to an acceptor A can be treated in a similar manner by considering the phenomenon as a retardation effect. In classical terms the field of S induces A to oscillate, and the induced field of A arriving at S slows down this oscillator. Simple equations are given for the energy transfer from an excited dipole or quadrupole, and for a row of many dipoles, oscillating in phase, to a weakly absorbing acceptor layer. The latter case is considered as a model for a J-aggregating dye and by comparison with exptl. data conclusions concerning the size of a J aggregate are drawn.
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    Hider, M. H.; Leung, P. Frequency shifts of molecules at rough metal surfaces. Phys. Rev. B: Condens. Matter Mater. Phys. 1991, 44, 3262,  DOI: 10.1103/PhysRevB.44.3262
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    Frequency shifts of molecules at rough metal surfaces
    Hider, M. H.; Leung, P. T.
    Physical Review B: Condensed Matter and Materials Physics (1991), 44 (7), 3262-5CODEN: PRBMDO; ISSN:0163-1829.
    The frequency shifts for dipolar transitions of mols. at rough metallic surfaces were studied in a phenomenol. model following the approach of previous work with the surface roughness modeled by a shallow grating profile in most cases. Such surface-induced shifts are indeed observable for mol. frequencies away from the surface-plasmon resonance frequency of the metal; the presence of surface roughness can either enhance or suppress the flat-surface-induced shifts, leading to extra morphol.-dependent resonances originated from the radiative coupling between the mol. emission and the substrate surface plasmon; and the effects in the perfectly reflecting limit can be worked out anal. with numerical results showing interesting features that are unique for this case. Correlations were made with respect to previous expts. on vibrational shifts as well as to recent calcns. from a microscopic approach.
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    Borensztein, Y.; Abeles, F.; Lopez-Rios, T. Frequency shifts of an ensemble of electric dipole resonances near a conducting surface. Phys. Rev. Lett. 1984, 53, 854,  DOI: 10.1103/PhysRevLett.53.854
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    Physical Review Letters (1984), 53 (8), 854CODEN: PRLTAO; ISSN:0031-9007.
    The variation of the resonance frequency obtained from an exact calcn. of the reflectance for the Ag-island film system investigated exptl. by W. R. Holland and P. G. Hall (1984) is presented; the Ag-island film is treated within the Maxwell Garnett (MG) effective medium theory. The results are compared with the exptl. and calcd. values of Holland and Hall; the 2 theor. treatments give similar results for thicknesses >20 nm, while the MG one is in better agreement with the exptl. data below 20 nm, because the effective medium theory takes into account the long-range interaction between the particles.
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    Frequency shifts of an electric-dipole resonance near a conducting surface
    Holland, W. R.; Hall, D. G.
    Physical Review Letters (1984), 52 (12), 1041-4CODEN: PRLTAO; ISSN:0031-9007.
    The resonance frequency of an elec. dipole placed near a conducting surface is shifted by the dipole-surface interaction. The observation and measurement are reported of these shifts at optical frequencies for an exptl. system that consists of a metal island film spaced a distance d from a continuous Ag film. The dependence of the shift in the frequency of the island resonance on d shows good agreement with that predicted by a classical theory of the dipole-surface interaction.
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    Chance, R.; Prock, A.; Silbey, R. Frequency shifts of an electric-dipole transition near a partially reflecting surface. Phys. Rev. A: At., Mol., Opt. Phys. 1975, 12, 1448,  DOI: 10.1103/PhysRevA.12.1448
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    Frequency shifts of an electric-dipole transition near a partially reflecting surface
    Chance, R. R.; Prock, A.; Silbey, R.
    Physical Review A: Atomic, Molecular, and Optical Physics (1975), 12 (4), 1448-52CODEN: PLRAAN; ISSN:1050-2947.
    The classical theory of dipole radiation was used to calc. the change in frequency of an elec.-dipole-allowed transition due to the presence of a nearby reflecting surface. The result is compared to that for a perfect reflector.
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    Gualdron-Reyes, A. F.; Yoon, S. J.; Barea, E. M.; Agouram, S.; Munoz-Sanjose, V.; Melendez, A. M.; Nino-Gomez, M. E.; Mora-Sero, I. Controlling the phase segregation in mixed halide perovskites through nanocrystal size. ACS Energy Letters 2019, 4, 54– 62,  DOI: 10.1021/acsenergylett.8b02207
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    Controlling the Phase Segregation in Mixed Halide Perovskites through Nanocrystal Size
    Gualdron-Reyes, Andres. F.; Yoon, Seog Joon; Barea, Eva M.; Agouram, Said; Munoz-Sanjose, Vicente; Melendez, Angel M.; Nino-Gomez, Martha E.; Mora-Sero, Ivan
    ACS Energy Letters (2019), 4 (1), 54-62CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    Mixed halide perovskites are 1 of the promising candidates in developing solar cells and light-emitting diodes (LEDs), among other applications, because of their tunable optical properties. Photoinduced phase segregation, by formation of segregated Br-rich and I-rich domains, limits the overall applicability. The phase segregation was tracked with increasing cryst. size of CsPbBr3-xIx and their luminescence under continuous-wave laser irradn. (405 nm, 10 mW cm-2) and obsd. the occurrence of the phase segregation from the threshold size of 46 ± 7 nm. These results have an outstanding agreement with the diffusion length (45.8 nm) calcd. also exptl. from the emission lifetime and segregation rates. Through Kelvin probe force microscopy, the correlation between the phase segregation and the reversible halide ion migration among grain centers and boundaries was confirmed. These results open a way to achieve segregation-free mixed halide perovskites and improve their performances in optoelectronic devices.
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    Saliba, M.; Correa-Baena, J.-P.; Wolff, C. M.; Stolterfoht, M.; Phung, N.; Albrecht, S.; Neher, D.; Abate, A. How to Make over 20% Efficient Perovskite Solar Cells in Regular (n–i–p) and Inverted (p–i–n) Architectures. Chem. Mater. 2018, 30, 4193– 4201,  DOI: 10.1021/acs.chemmater.8b00136
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    How to Make over 20% Efficient Perovskite Solar Cells in Regular (n-i-p) and Inverted (p-i-n) Architectures
    Saliba, Michael; Correa-Baena, Juan-Pablo; Wolff, Christian M.; Stolterfoht, Martin; Phung, Nga; Albrecht, Steve; Neher, Dieter; Abate, Antonio
    Chemistry of Materials (2018), 30 (13), 4193-4201CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Perovskite solar cells (PSCs) are currently one of the most promising photovoltaic technologies for highly efficient and cost-effective solar energy prodn. In only a few years, an unprecedented progression of prepn. procedures and material compns. delivered lab.-scale devices that have now reached record power conversion efficiencies (PCEs) >20%, competing with most established solar cell materials such as Si, CIGS, and CdTe. However, despite a large no. of researchers currently involved in this topic, only a few groups in the world can reproduce >20% efficiencies on a regular n-i-p architecture. Here, we present detailed protocols for prepg. PSCs in regular (n-i-p) and inverted (p-i-n) architectures with ≥20% PCE. We aim to provide a comprehensive, reproducible description of our device fabrication protocols. We encourage the practice of reporting detailed and transparent protocols that can be more easily reproduced by other labs. A better reporting std. may, in turn, accelerate the development of perovskite solar cells and related research fields.
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    Cortes, C.; Newman, W.; Molesky, S.; Jacob, Z. Quantum nanophotonics using hyperbolic metamaterials. J. Opt. 2012, 14, 063001,  DOI: 10.1088/2040-8978/14/6/063001
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    Quantum nanophotonics using hyperbolic metamaterials
    Cortes, C. L.; Newman, W.; Molesky, S.; Jacob, Z.
    Journal of Optics (Bristol, United Kingdom) (2012), 14 (6), 063001/1-063001/15CODEN: JOOPCA; ISSN:2040-8978. (Institute of Physics Publishing)
    A review. Engineering optical properties using artificial nanostructured media known as metamaterials has led to breakthrough devices with capabilities from super-resoln. imaging to invisibility. In this paper, we review metamaterials for quantum nanophotonic applications, a recent development in the field. This seeks to address many challenges in the field of quantum optics using advances in nanophotonics and nanofabrication. We focus on the class of nanostructured media with hyperbolic dispersion that have emerged as one of the most promising metamaterials with a multitude of practical applications from subwavelength imaging, nanoscale waveguiding, biosensing to nonlinear switching. We present the various design and characterization principles of hyperbolic metamaterials and explain the most important property of such media: a broadband enhancement in the electromagnetic d. of states. We review several recent expts. that have explored this phenomenon using spontaneous emission from dye mols. and quantum dots. We finally point to future applications of hyperbolic metamaterials, using the broadband enhancement in the spontaneous emission to construct single-photon sources.
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    Noginov, M.; Barnakov, Y. A.; Zhu, G.; Tumkur, T.; Li, H.; Narimanov, E. Bulk photonic metamaterial with hyperbolic dispersion. Appl. Phys. Lett. 2009, 94, 151105,  DOI: 10.1063/1.3115145
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    Bulk photonic metamaterial with hyperbolic dispersion
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    Applied Physics Letters (2009), 94 (15), 151105/1-151105/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    The authors demonstrated the thickest bulk photonic metamaterial reported in the literature based on an Ag-filled alumina membrane. The material is highly anisotropic with hyperbolic dispersion at λ > 0.84 μm. The refraction of light in the direction expected of isotropic media with n < 1 was exptl. demonstrated at λ = 632.8 nm. This makes the material potentially suitable for a variety of applications ranging from subdiffraction imaging to optical cloaking. (c) 2009 American Institute of Physics.
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    Mahmoodi, M.; Tavassoli, S. H.; Takayama, O.; Sukham, J.; Malureanu, R.; Lavrinenko, A. V. Existence Conditions of High-k Modes in Finite Hyperbolic Metamaterials. Laser & Photonics Reviews 2019, 13, 1800253,  DOI: 10.1002/lpor.201800253
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    Navarro-Arenas, J.; Suárez, I.; Chirvony, V. S.; Gualdrón-Reyes, A. F.; Mora-Seró, I.; Martı́nez-Pastor, J. Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X= Br, I) Perovskite Nanocrystals. J. Phys. Chem. Lett. 2019, 10, 6389– 6398,  DOI: 10.1021/acs.jpclett.9b02369
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    Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X = Br, I) Perovskite Nanocrystals
    Navarro-Arenas, Juan; Suarez, Isaac; Chirvony, Vladimir S.; Gualdron-Reyes, Andres F.; Mora-Sero, Ivan; Martinez-Pastor, Juan
    Journal of Physical Chemistry Letters (2019), 10 (20), 6389-6398CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    CsPbX3 perovskite nanocrystals (PNCs) have emerged as an excellent material for stimulated emission purposes, with even more prospective applications than conventional colloidal quantum dots. A better understanding of the phys. mechanisms responsible for amplified spontaneous emission (ASE) is required to achieve more ambitious targets (lasing under continuous wave optical or elec. excitation). Establish the intrinsic mechanisms underlying ASE in PNCs of 3 different band gaps (CsPbBr3, CsPbBr1.5I1.5, and CsPbI3). The characterization at cryogenic temps. does not reveal any evidence of the biexciton mechanism in the formation of ASE. The measured shift toward long wavelengths of the ASE band is easily explained by the reabsorption in the PNC layer, which becomes stronger for thicker layers. In this way, the threshold of ASE is detd. only by optical losses at a given geometry, which is the single-exciton mechanism responsible for ASE. Exptl. results are properly reproduced by a phys. model.
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    Trap-Limited Dynamics of Excited Carriers and Interpretation of the Photoluminescence Decay Kinetics in Metal Halide Perovskites
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    A review. Interpretation of the photoluminescence (PL) decay kinetics in metal halide perovskites (MHPs) is extremely important for understanding the mechanisms and control of charge recombination in these promising photovoltaic and optoelectronic materials. In this work, we give a review of current models describing the PL decay kinetics in MHP layers and nanocrystals with particular attention to the interpretation of long-lived PL decay components (hundreds of nanoseconds to microseconds). First, we analyze phenomenol. photophys. models based on the rate equations, which describe the charge carrier recombination in MHP layers as an exclusively intrinsic bulk process. An important role of the carrier diffusion and nonradiative recombination on the layer surfaces is then discussed. A recently published approach is then analyzed, in the framework of which the obsd. long-lived components of PL decay kinetics in MHP nanocrystals are described in terms of the delayed luminescence mechanism arising due to the processes of multiple trapping and detrapping of carriers by shallow nonquenching traps. The possible origin of the shallow traps and perspectives to include the carrier trapping and detrapping processes in a model describing PL kinetics in MHP layers are discussed.
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    Chirvony, V. S.; Sekerbayev, K. S.; Adl, H. P.; Suárez, I.; Taurbayev, Y. T.; Gualdrón-Reyes, A. F.; Mora-Seró, I.; Martı́nez-Pastor, J. P. Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films. J. Lumin. 2020, 221, 117092,  DOI: 10.1016/j.jlumin.2020.117092
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    Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films
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    Journal of Luminescence (2020), 221 (), 117092CODEN: JLUMA8; ISSN:0022-2313. (Elsevier B.V.)
    In this paper we present crit. anal. of different points of view on interpretation of the photoluminescence (PL) decay kinetics in lead halide perovskites prepd. in the form of well passivated nanocrystals (PNCs) or thin polycryst. layers. In addn. to the literature data, our own measurements are also considered. For PNCs, a strong dependence of the PL lifetimes on the type of passivating ligand was obsd. with a consistently high PL quantum yield. It is shown that such ligand effects, as well as a decrease in the PL lifetime with decreasing temp., are well qual. explained by the phenomenol. model of thermally activated delayed luminescence, in which the extension of the PL decay time with temp. occurs due to the participation of shallow non-quenching traps. In the case of thin perovskite layers, we conclude that the PL kinetics under sufficiently low excitation intensity is detd. by the excitation quenching on the layer surfaces. We demonstrate that a large variety of possible PL decay kinetics for thin polycryst. perovskite films can be modelled by means of one-dimensional diffusion equation with use of the diffusion coeff. D and surface recombination velocity S as parameters and conclude that long-lived PL kinetics are formed in case of low D and/or S values.
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    Light-matter interactions can be controlled by manipulating the photonic environment. An optical topol. transition in strongly anisotropic metamaterials results in a dramatic increase in the photon d. of states, an effect that can be used to engineer this interaction. A transition in the topol. of the iso-frequency surface from a closed ellipsoid to an open hyperboloid using artificially nanostructured metamaterials is described. This topol. transition manifests itself in increased rates of spontaneous emission of emitters positioned near the metamaterial. Altering the topol. of the iso-frequency surface by using metamaterials provides a fundamentally new route to manipulating light-matter interactions.
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    A review. The large sp. surface area of perovskite nanocrystals (NCs) increases the likelihood of surface defects compared to that of bulk single crystals and polycryst. thin films. It is crucial to comprehend and control their defect population to exploit the potential of perovskite NCs. This Perspective describes and classifies recent advances in understanding defect chem. and avenues toward defect d. redn. in perovskite NCs, and it does so in the context of the promise perceived in light-emitting devices. Several pathways for decreasing the defect d. are explored, including advanced NC syntheses, new surface-capping strategies, doping with metal ions and rare earths, engineering elemental compensation, and the translation of core-shell heterostructures into the perovskite materials family. The authors close with challenges that remain in perovskite NC defect research.
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    Hyperbolic metamaterials can enhance spontaneous emission, but the radiation-matter coupling is not optimized if the light source is placed outside such media. We demonstrate a 3-fold improvement of the Purcell factor over its outer value and a significant enlargement in bandwidth by including the emitter within a Si/Ag periodic multilayer metamaterial. To ext. the plasmonic modes of the structure into the far field we implement two types of 1D grating with triangular and rectangular profile, obtaining a 10-fold radiative enhancement at visible frequencies.
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    A review with 138 refs. The methods described are essentially those of classical electromagnetic theory, the idea being that the mol. and the surface are sepd. so that their only interaction is via the electromagnetic fields. Reflection of electromagnetic waves at an interface, mol. fluorescence near a metal, shift and broadening of mol. vibration modes, and Raman scattering at metal surfaces are discussed.
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    Sun Lu; Jiang Chun
    Optics express (2016), 24 (7), 7719-27 ISSN:.
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    A broadband enhancement of emission from N-vacancy centers in nanodiamonds was exptl. demonstrated. The enhancement is achieved by using a multilayer metamaterial with hyperbolic dispersion. The metamaterial is fabricated as a stack of alternating Au and alumina layers. The approach paves the way towards the construction of efficient single-photon sources as planar on-chip devices. (c) 2013 American Institute of Physics.
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    The authors have developed a simple method to fabricate lamellar metal-dielec. hyperbolic metamaterials on flat, flexible, and curvilinear substrates, which allows for functionalization of dielec. layers by dye mols. The control of spontaneous emission of dye mols. with hyperbolic metamaterials was studied in 2 different sample configurations, and the effect is much stronger when emitters are placed inside the metamaterial rather than on its surface. (c) 2011 American Institute of Physics.
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    Integration of Nanoscale Light Emitters and Hyperbolic Metamaterials: An Efficient Platform for the Enhancement of Random Laser Action
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    ACS Photonics (2018), 5 (3), 718-727CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    The 1st attempt to integrate hyperbolic metamaterials with light emitting nanostructures enables strong enhancement of random laser action with reduced lasing threshold. The differential quantum efficiency can be enhanced by >4 times. The underlying mechanism can be interpreted well based on the fact that the high-k modes excited by hyperbolic metamaterials can greatly increase the possibility of forming close loops decreasing the energy consumption for the propagation of scattered photons in the matrix. Out-coupled propagation of the high-k modes reaches to the far-field without being trapped inside the metamaterials due to the coupling with the random distribution of light emitting nanoparticles also plays an important role. Electromagnetic simulations derived from the finite-difference time-domain (FDTD) method are executed to support the interpretation. Realizing strong enhancement of laser action assisted by hyperbolic metamaterials provides an attractive, simple, and efficient scheme for the development of high performance optoelectronic devices, including phototransistors, and many other solid state lighting systems. Besides, because of increasing light absorption assisted by hyperbolic metamaterials structure, the approach shown is also useful for the application of highly efficient solar cells.
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  • Abstract

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    Figure 1

    Figure 1. (a) Schematic representation of thermally evaporated HMM structures, (b) HAADF-STEM image and the corresponding EDX map (Ag, F, and Si are displayed in magenta, cyan, and blue, respectively) of a fabricated HMM structure. (c) Angular reflectance spectra of fabricated HMM structures measured at λ = 785 nm and fitted with ϵ∥ = −4.19 + 1.34i, ϵ⊥ = +1.56 + 0.01i. Blue diamonds and red circles refer to the s and p polarizations, and solid lines correspond to the simulation. (d) Local density of states (LDOS) computed in the near field of the HMM structure with 10 nm spacer.

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    Figure 2

    Figure 2. (a) Schematic representation of a HMM structure with a monolayer of PNCs on top of the spacer with thickness d. (b) Schematic illustration of experimental setup for measuring PL and TRPL spectra of PNCs at low temperatures. (c) PL spectra of CsPbI3 PNCs deposited on top of HMM substrates for different spacer thicknesses. (d) PL decay kinetics of CsPbI3 PNCs corresponding to (c).

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    Figure 3

    Figure 3. (a) Correlation of the spectral shift and Purcell factor of emitters for the different samples, (b) illustration of a simple model considering a perovskite monolayer on top of PMMA spacer, (c, d) dependence of the Purcell factor and spectral shift as a function of the distance from dipole inside the CsPbI3 and topmost metal surface of the HMM, respectively. Symbols and continuous lines (dashed and dotted-dashed for points A and B, and dotted and solid line for D, E, respectively) correspond to experimental data and simulation, respectively, as described in the text.

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    Figure 4

    Figure 4. (a, b) Distribution of the normalized electric field |E| of a horizontal and vertical dipole (arrows) located on top of HMM substrate when d = 10 nm (c, d) are respectively, correspond to (a, b) when d = 250 nm. The point source emits at λ = 705 nm, and the cones show the direction of the energy flows in logarithmic scale.

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      Jeon, Nam Joong; Noh, Jun Hong; Yang, Woon Seok; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il
      Nature (London, United Kingdom) (2015), 517 (7535), 476-480CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Here we combine the promising, owing to its comparatively narrow bandgap, but relatively unstable formamidinium lead iodide (FAPbI3) with methylammonium lead bromide (MAPbBr3) as the light-harvesting unit in a bilayer solar cell architecture. We investigated phase stability, morphol. of the perovskite layer, hysteresis in current-voltage characteristics, and overall performance as a function of chem. compn. Our results show that incorporation of MAPbBr3 into FAPbI3 stabilizes the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to >18% under a std. illumination of 100 mW/cm2. These findings further emphasize the versatility and performance potential of inorg.-org. lead halide perovskite materials for photovoltaic applications.
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    17. 17
      Correa-Baena, J.-P.; Abate, A.; Saliba, M.; Tress, W.; Jacobsson, T. J.; Grätzel, M.; Hagfeldt, A. The rapid evolution of highly efficient perovskite solar cells. Energy Environ. Sci. 2017, 10, 710– 727,  DOI: 10.1039/C6EE03397K
      17
      The rapid evolution of highly efficient perovskite solar cells
      Correa-Baena, Juan-Pablo; Abate, Antonio; Saliba, Michael; Tress, Wolfgang; Jesper Jacobsson, T.; Gratzel, Michael; Hagfeldt, Anders
      Energy & Environmental Science (2017), 10 (3), 710-727CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      A review. Perovskite solar cells (PSCs) have attracted much attention because of their rapid rise to 22% efficiencies. Here, we review the rapid evolution of PSCs as they enter a new phase that could revolutionize the photovoltaic industry. In particular, we describe the properties that make perovskites so remarkable, and the current understanding of the PSC device physics, including the operation of state-of-the-art solar cells with efficiencies above 20%. The extraordinary progress of long-term stability is discussed and we provide an outlook on what the future of PSCs might soon bring the photovoltaic community. Some challenges remain in terms of reducing non-radiative recombination and increasing cond. of the different device layers, and these will be discussed in depth in this review.
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    18. 18
      Luo, Q.; Ma, H.; Hou, Q.; Li, Y.; Ren, J.; Dai, X.; Yao, Z.; Zhou, Y.; Xiang, L.; Du, H. All-carbon-electrode-based endurable flexible perovskite solar cells. Adv. Funct. Mater. 2018, 28, 1706777,  DOI: 10.1002/adfm.201706777
      There is no corresponding record for this reference.
    19. 19
      Shin, S. S.; Suk, J. H.; Kang, B. J.; Yin, W.; Lee, S. J.; Noh, J. H.; Ahn, T. K.; Rotermund, F.; Cho, I. S.; Seok, S. I. Energy-level engineering of the electron transporting layer for improving open-circuit voltage in dye and perovskite-based solar cells. Energy Environ. Sci. 2019, 12, 958– 964,  DOI: 10.1039/C8EE03672A
      19
      Energy-level engineering of the electron transporting layer for improving open-circuit voltage in dye and perovskite-based solar cells
      Shin, Seong Sik; Suk, Jae Ho; Kang, Bong Joo; Yin, Wenping; Lee, Seon Joo; Noh, Jun Hong; Ahn, Tae Kyu; Rotermund, Fabian; Cho, In Sun; Seok, Sang Il
      Energy & Environmental Science (2019), 12 (3), 958-964CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      Next-generation solar cells, such as dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs), are fabricated in a configuration where light absorbers are located between the electron transporting layer (ETL) and the hole transporting layer (HTM). Although the most efficient DSSCs and PSCs have been fabricated using TiO2 as the ETL, TiO2 exhibits inherently low electron mobility with difficulty controlling the energy levels (i.e., conduction and valence bands) as it possesses a single phase of two components. Here, we report the synthesis of Sr-substituted BaSnO3 (BSSO) by a low-temp. soln. process as a new alternative to TiO2 for both PSCs and DSSCs. The energy-level tailoring by Sr incorporation into BaSnO3 minimizes the open-circuit voltage (VOC) loss at the interfaces of ETL/perovskite and ETL/electrolyte in the PSCs and DSSCs, thereby leading to an improved VOC from 0.65 to 0.72 V in DSSC and 1.07 to 1.13 V in PSCs. Addnl., the BSSO ETL-based PSC shows improved photostability compared to the TiO2 analog. Our results show that energy-level tuned BSSO can be applied as a universal ETL for improving efficiency in both PSCs and DSSCs.
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    20. 20
      Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of cesium lead halide perovskites (CsPbX3, X= Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut. Nano Lett. 2015, 15, 3692– 3696,  DOI: 10.1021/nl5048779
      20
      Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut
      Protesescu, Loredana; Yakunin, Sergii; Bodnarchuk, Maryna I.; Krieg, Franziska; Caputo, Riccarda; Hendon, Christopher H.; Yang, Ruo Xi; Walsh, Aron; Kovalenko, Maksym V.
      Nano Letters (2015), 15 (6), 3692-3696CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Metal halides perovskites, such as hybrid org.-inorg. MeNH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as soln.-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. A new avenue for halide perovskites was demonstrated by designing highly luminescent perovskite-based colloidal quantum dot materials. Monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorg. perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) were synthesized using inexpensive com. precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The luminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color std., high quantum yields of ≤90%, and radiative lifetimes at 1-29 ns. The compelling combination of enhanced optical properties and chem. robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410-530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegrdn.
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    21. 21
      Zhang, F.; Zhong, H.; Chen, C.; Wu, X.-g.; Hu, X.; Huang, H.; Han, J.; Zou, B.; Dong, Y. Brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X= Br, I, Cl) quantum dots: potential alternatives for display technology. ACS Nano 2015, 9, 4533– 4542,  DOI: 10.1021/acsnano.5b01154
      21
      Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology
      Zhang, Feng; Zhong, Haizheng; Chen, Cheng; Wu, Xian-gang; Hu, Xiangmin; Huang, Hailong; Han, Junbo; Zou, Bingsuo; Dong, Yuping
      ACS Nano (2015), 9 (4), 4533-4542CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A ligand-assisted repptn. strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with abs. quantum yield up to 70% at room temp. and low excitation fluencies is reported. To illustrate the photoluminescence enhancements in these quantum dots, comprehensive compn. and surface characterizations and time- and temp.-dependent photoluminescence spectra were studied. Comparisons between small-sized CH3NH3PbBr3 quantum dots (av. diam. 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 μm) suggested that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size redn. as well as proper chem. passivations of the Br-rich surface. Wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn4+ as color converters were fabricated, providing enhanced color quality for display technol. The colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.
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    22. 22
      Kovalenko, M. V.; Protesescu, L.; Bodnarchuk, M. I. Properties and potential optoelectronic applications of lead halide perovskite nanocrystals. Science 2017, 358, 745– 750,  DOI: 10.1126/science.aam7093
      22
      Properties and potential optoelectronic applications of lead halide perovskite nanocrystals
      Kovalenko, Maksym V.; Protesescu, Loredana; Bodnarchuk, Maryna I.
      Science (Washington, DC, United States) (2017), 358 (6364), 745-750CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A review. Semiconducting lead halide perovskites (LHPs) have not only become prominent thin-film absorber materials in photovoltaics but have also proven to be disruptive in the field of colloidal semiconductor nanocrystals (NCs). The most important feature of LHP NCs is their so-called defect-tolerance-the apparently benign nature of structural defects, highly abundant in these compds., with respect to optical and electronic properties. Here, we review the important differences that exist in the chem. and physics of LHP NCs as compared with more conventional, tetrahedrally bonded, elemental, and binary semiconductor NCs (such as silicon, germanium, cadmium selenide, gallium arsenide, and indium phosphide). We survey the prospects of LHP NCs for optoelectronic applications such as in television displays, light-emitting devices, and solar cells, emphasizing the practical hurdles that remain to be overcome.
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    23. 23
      Li, X.; Cao, F.; Yu, D.; Chen, J.; Sun, Z.; Shen, Y.; Zhu, Y.; Wang, L.; Wei, Y.; Wu, Y. All inorganic halide perovskites nanosystem: synthesis, structural features, optical properties and optoelectronic applications. Small 2017, 13, 1603996,  DOI: 10.1002/smll.201603996
      There is no corresponding record for this reference.
    24. 24
      Hassanabadi, E.; Latifi, M.; Gualdron-Reyes, A. F.; Masi, S.; Yoon, S. J.; Poyatos, M.; Julian-Lopez, B.; Mora-Sero, I. Ligand & Band Gap Engineering: Tailoring the Protocol Synthesis for Achieving High-Quality CsPbI3 Quantum Dots. Nanoscale 2020, 12, 14194,  DOI: 10.1039/D0NR03180A
      24
      Ligand & band gap engineering: tailoring the protocol synthesis for achieving high-quality CsPbI3 quantum dots
      Hassanabadi, Ehsan; Latifi, Masoud; Gualdron-Reyes, Andres. F.; Masi, Sofia; Yoon, Seog Joon; Poyatos, Macarena; Julian-Lopez, Beatriz; Mora-Sero, Ivan
      Nanoscale (2020), 12 (26), 14194-14203CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Hot-injection has become the most widespread method used for the synthesis of perovskite quantum dots (QDs) with enormous interest for application in optoelectronic devices. However, there are some aspects of the chem. involved in this synthesis that have not been completely investigated. In this work, we synthesized ultra-high stable CsPbI3 QDs for more than 15 mo by controlling two main parameters: synthesis temp. and the concn. of capping ligands. By increasing the capping ligand concn. during the QD synthesis, we were able to grow CsPbI3 in a broad range of temps., improving the photophys. properties of QDs by increasing the synthesis temp. We achieved the max. photoluminescence quantum yield (PLQY) of 93% for a synthesis conducted at 185°C, establishing an efficient surface passivation to decrease the d. of non-radiative recombination sites. Under these optimized synthesis conditions, deep red LEDs with an External Quantum Efficiency (EQE) higher than 6% were achieved. The performance of these LEDs is higher than that of the reported CsPbI3 QD-LEDs contg. std. capping agents, without addnl. elements or further element exchange. We show that it is possible to produce stable CsPbI3 QDs with high PLQY and red emission beyond the requirement of the Rec. 2020 stds. for red color.
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    25. 25
      Navarro Arenas, J.; Soosaimanickam, A.; Pashaei Adl, H.; Abargues, R.; Boix, P. P.; Rodrı́guez-Cantó, P. J.; Martı́nez-Pastor, J. P. Ligand-Length Modification in CsPbBr3 Perovskite Nanocrystals and Bilayers with PbS Quantum Dots for Improved Photodetection Performance. Nanomaterials 2020, 10, 1297,  DOI: 10.3390/nano10071297
      There is no corresponding record for this reference.
    26. 26
      Hu, F.; Zhang, H.; Sun, C.; Yin, C.; Lv, B.; Zhang, C.; Yu, W. W.; Wang, X.; Zhang, Y.; Xiao, M. Single Photon Emission from Single Perovskite Nanocrystals of Cesium Lead Bromide. ACS Nano 2015, 9, 12410,  DOI: 10.1021/acsnano.5b05769
      26
      Superior Optical Properties of Perovskite Nanocrystals as Single Photon Emitters
      Hu, Fengrui; Zhang, Huichao; Sun, Chun; Yin, Chunyang; Lv, Bihu; Zhang, Chunfeng; Yu, William W.; Wang, Xiaoyong; Zhang, Yu; Xiao, Min
      ACS Nano (2015), 9 (12), 12410-12416CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Single photon emission was obsd. from single CsPbBr3 perovskite nanocrystals (NCs) synthesized from a facile colloidal approach. Compared with traditional metal-chalcogenide NCs, these CsPbBr3 NCs exhibit nearly 2 orders of magnitude increase in their absorption cross sections at similar emission colors. The radiative lifetime of CsPbBr3 NCs is greatly shortened at both room and cryogenic temps. to favor an extremely fast output of single photons. The above superior optical properties have paved the way toward quantum-light applications of perovskite NCs in various quantum information processing schemes.
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    27. 27
      Utzat, H.; Sun, W.; Kaplan, A. E.; Krieg, F.; Ginterseder, M.; Spokoyny, B.; Klein, N. D.; Shulenberger, K. E.; Perkinson, C. F.; Kovalenko, M. V. Coherent single-photon emission from colloidal lead halide perovskite quantum dots. Science 2019, 363, 1068– 1072,  DOI: 10.1126/science.aau7392
      27
      Coherent single-photon emission from colloidal lead halide perovskite quantum dots
      Utzat, Hendrik; Sun, Weiwei; Kaplan, Alexander E. K.; Krieg, Franziska; Ginterseder, Matthias; Spokoyny, Boris; Klein, Nathan D.; Shulenberger, Katherine E.; Perkinson, Collin F.; Kovalenko, Maksym V.; Bawendi, Moungi G.
      Science (Washington, DC, United States) (2019), 363 (6431), 1068-1072CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Chem. made colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. The authors now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 ps, an appreciable fraction of their 210-ps radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Their results present a starting point for the rational design of lead halide perovskite-based quantum emitters that have fast emission, wide spectral tunability, and scalable prodn. and that benefit from the hybrid integration with nanophotonic components that has been demonstrated for colloidal materials.
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    28. 28
      Li, C.; Xu, Z.-Q.; Mendelson, N.; Kianinia, M.; Toth, M.; Aharonovich, I. Purification of single-photon emission from hBN using post-processing treatments. Nanophotonics 2019, 8, 2049– 2055,  DOI: 10.1515/nanoph-2019-0099
      28
      Purification of single-photon emission from hBN using post-processing treatments
      Li, Chi; Xu, Zai-Quan; Mendelson, Noah; Kianinia, Mehran; Toth, Milos; Aharonovich, Igor
      Nanophotonics (2019), 8 (11), 2049-2055CODEN: NANOLP; ISSN:2192-8614. (Walter de Gruyter GmbH)
      Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising components for on-chip quantum information processing. Recently, large-area hBN films prepd. by chem. vapor deposition (CVD) were found to host uniform, high densities of SPEs. However, the purity of these emitters has, to date, been low, hindering their applications in practical devices. In this work, we present two methods for post-growth processing of hBN, which significantly improve SPEs in hBN films that had been transferred from substrates used for CVD. The emitters exhibit high photon purities in excess of 90% and narrow linewidths of ∼3 nm at room temp. Our work lays a foundation for producing high-quality emitters in an ultra-compact two-dimensional material system and paves the way for deployment of hBN SPEs in scalable on-chip photonic and quantum devices.
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    29. 29
      Turiansky, M.; Alkauskas, A.; Bassett, L.; Van de Walle, C. Boron Dangling Bonds as Single Photon Emitters in Hexagonal Boron Nitride. Phys. Rev. Lett. 2019,  DOI: 10.1103/PhysRevLett.123.127401
      There is no corresponding record for this reference.
    30. 30
      Sun, Y.; Yaroshenko, V.; Chebykin, A.; Ageev, E.; Makarov, S.; Zuev, D. Metal-dielectric nanoantenna for radiation control of a single-photon emitter. Opt. Mater. Express 2020, 10, 29– 35,  DOI: 10.1364/OME.10.000029
      30
      Metal-dielectric nanoantenna for radiation control of a single-photon emitter
      Sun, Yali; Yaroshenko, Vitaly; Chebykin, Alexander; Ageev, Eduard; Makarov, Sergey; Zuev, Dmitry
      Optical Materials Express (2020), 10 (1), 29-35CODEN: OMEPAX; ISSN:2159-3930. (Optical Society of America)
      The control of fluorescent properties of single-photon sources in solid-state host systems via optically resonant nanostructures is a key issue in quantum nanophotonics. Here we propose a design of a resonant metal-dielec. nanoantenna for the Purcell factor and radiation pattern control of a quantum emitter placed in the gap between metal and dielec. components of the nanostructure. We demonstrate that large Purcell factor, considerable field enhancement in the gap as well as high directivity can be achieved. The developed nanosystem can be utilized for different solid-state host systems from nanocrystals to 2D materials.
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    31. 31
      Shalaginov, M. Y.; Vorobyov, V. V.; Liu, J.; Ferrera, M.; Akimov, A. V.; Lagutchev, A.; Smolyaninov, A. N.; Klimov, V. V.; Irudayaraj, J.; Kildishev, A. V. Enhancement of single-photon emission from nitrogen-vacancy centers with TiN/(Al, Sc) N hyperbolic metamaterial. Laser & Photonics Reviews 2015, 9, 120– 127,  DOI: 10.1002/lpor.201400185
      31
      Enhancement of single-photon emission from nitrogen-vacancy centers with TiN/(Al,Sc)N hyperbolic metamaterial
      Shalaginov, Mikhail Y.; Vorobyov, Vadim V.; Liu, Jing; Ferrera, Marcello; Akimov, Alexey V.; Lagutchev, Alexei; Smolyaninov, Andrey N.; Klimov, Vasily V.; Irudayaraj, Joseph; Kildishev, Alexander V.; Boltasseva, Alexandra; Shalaev, Vladimir M.
      Laser & Photonics Reviews (2015), 9 (1), 120-127CODEN: LPRAB8; ISSN:1863-8880. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The broadband enhancement of single-photon emission from nitrogen-vacancy centers in nanodiamonds coupled to a planar multilayer metamaterial with hyperbolic dispersion is studied exptl. The metamaterial is fabricated as an epitaxial metal/dielec. superlattice consisting of CMOS-compatible ceramics: titanium nitride (TiN) and aluminum scandium nitride (AlxSc1-xN). It is demonstrated that employing the metamaterial results in significant enhancement of collected single-photon emission and redn. of the excited-state lifetime. Our results could have an impact on future CMOS-compatible integrated quantum sources.
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    32. 32
      Vahala, K. J. Optical microcavities. Nature 2003, 424, 839– 846,  DOI: 10.1038/nature01939
      32
      Optical microcavities
      Vahala, Kerry J.
      Nature (London, United Kingdom) (2003), 424 (6950), 839-846CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      A review. Optical microcavities confine light to small vols. by resonant recirculation. Devices based on optical microcavities are already indispensable for a wide range of applications and studies. For example, microcavities made of active III-V semiconductor materials control laser emission spectra to enable long-distance transmission of data over optical fibers; they also ensure narrow spot-size laser read/write beams in CD and DVD players. In quantum optical devices, microcavities can coax atoms or quantum dots to emit spontaneous photons in a desired direction or can provide an environment where dissipative mechanisms such as spontaneous emission are overcome so that quantum entanglement of radiation and matter is possible. Applications of these remarkable devices are as diverse as their geometrical and resonant properties.
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    33. 33
      Shen, S.; Li, J.; Wu, Y. Magnetically controllable photon blockade under a weak quantum-dot–cavity coupling condition. Phys. Rev. A: At., Mol., Opt. Phys. 2020, 101, 023805,  DOI: 10.1103/PhysRevA.101.023805
      There is no corresponding record for this reference.
    34. 34
      Gérard, J.; Sermage, B.; Gayral, B.; Legrand, B.; Costard, E.; Thierry-Mieg, V. Enhanced spontaneous emission by quantum boxes in a monolithic optical microcavity. Phys. Rev. Lett. 1998, 81, 1110,  DOI: 10.1103/PhysRevLett.81.1110
      34
      Enhanced spontaneous emission by quantum boxes in a monolithic optical microcavity
      Gerard, J. M.; Sermage, B.; Gayral, B.; Legrand, B.; Costard, E.; Thierry-Mieg, V.
      Physical Review Letters (1998), 81 (5), 1110-1113CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Semiconductor quantum boxes (QB's) are well suited to cavity quantum electrodynamic expts. in the solid state because of their sharp emission. We study by time-resolved photoluminescence InAs QB's placed in the core of small-vol. and high-finesse GaAs/AlAs pillar microresonators. A spontaneous emission rate enhancement by a factor of up to 5 is selectively obsd. for the QB's which are on resonance with 1-cavity mode. We explain its magnitude by considering the Purcell figure of merit of the micropillars and the effect of the random spatial and spectral distributions of the QB's.
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    35. 35
      Takahashi, H.; Kassa, E.; Christoforou, C.; Keller, M. Strong coupling of a single ion to an optical cavity. Phys. Rev. Lett. 2020, 124, 013602,  DOI: 10.1103/PhysRevLett.124.013602
      35
      Strong Coupling of a Single Ion to an Optical Cavity
      Takahashi, Hiroki; Kassa, Ezra; Christoforou, Costas; Keller, Matthias
      Physical Review Letters (2020), 124 (1), 013602CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
      Strong coupling between an atom and an electromagnetic resonator is an important condition in cavity quantum electrodynamics. While strong coupling in various phys. systems has been achieved so far, it remained elusive for single at. ions. Here, we achieve a coupling strength of 2πx(12.3±0.1) MHz between a single Ca40+ ion and an optical cavity, exceeding both at. and cavity decay rates which are 2πx11.5 and 2πx(4.1±0.1) MHz, resp. We use cavity assisted Raman spectroscopy to precisely characterize the ion-cavity coupling strength and observe a spectrum featuring the normal mode splitting in the cavity transmission due to the ion-cavity interaction. Our work paves the way towards new applications of cavity quantum electrodynamics utilizing single trapped ions in the strong coupling regime for quantum optics and quantum technologies.
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    36. 36
      Reithmaier, J. P.; Sek, G.; Loffler, A.; Hofmann, C.; Kuhn, S.; Reitzenstein, S.; Keldysh, L. V.; Kulakovskii, V. D.; Reinecke, T. L.; Forchel, A. Strong coupling in a single quantum dot–semiconductor microcavity system. Nature 2004, 432, 197– 200,  DOI: 10.1038/nature02969
      36
      Strong coupling in a single quantum dot-semiconductor microcavity system
      Reithmaier, J. P.; Sek, G.; Loeffler, A.; Hofmann, C.; Kuhn, S.; Reitzenstein, S.; Keldysh, L. V.; Kulakovskii, V. D.; Reinecke, T. L.; Forchel, A.
      Nature (London, United Kingdom) (2004), 432 (7014), 197-200CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      The authors report the observation of strong coupling of a single 2-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of ∼140 μeV.
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    37. 37
      Li, L.; Wang, W.; Luk, T. S.; Yang, X.; Gao, J. Enhanced quantum dot spontaneous emission with multilayer metamaterial nanostructures. ACS Photonics 2017, 4, 501– 508,  DOI: 10.1021/acsphotonics.6b01039
      37
      Enhanced Quantum Dot Spontaneous Emission with Multilayer Metamaterial Nanostructures
      Li, Ling; Wang, Wei; Luk, Ting S.; Yang, Xiaodong; Gao, Jie
      ACS Photonics (2017), 4 (3), 501-508CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      The Purcell effect of quantum dot (QD) spontaneous emission with Ag-SiO2 multilayer metamaterial nanostructures was demonstrated in expt. and simulation. A broadband enhanced spontaneous emission rate of QDs is obsd. due to large local d. of states in the epsilon-near-zero and hyperbolic regions of multilayer structures. Multilayer gratings are used to further enhance the QD spontaneous emission as the QDs located inside the grating grooves strongly interact with high-k coupled surface plasmon polariton modes. Photoluminescence decay measurements are in good agreement with both anal. treatment with a nonlocal effect and 3-dimensional finite-element simulation. Detailed studies of QD position and polarization effects on emission rate enhancement for multilayer and multilayer grating nanostructures provide important insight for understanding the coupling mechanisms of emitter-multilayer interaction and the engineering of local d. of states in metamaterial nanostructures. These results will advance many applications in light-emitting devices, nanoscale lasers, quantum electrodynamics, and quantum information processing.
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    38. 38
      Wang, L.; Li, S.; Zhang, B.; Qin, Y.; Tian, Z.; Fang, Y.; Li, Y.; Liu, Z.; Mei, Y. Asymmetrically curved hyperbolic metamaterial structure with gradient thicknesses for enhanced directional spontaneous emission. ACS Appl. Mater. Interfaces 2018, 10, 7704– 7708,  DOI: 10.1021/acsami.7b19721
      38
      Asymmetrically Curved Hyperbolic Metamaterial Structure with Gradient Thicknesses for Enhanced Directional Spontaneous Emission
      Wang, Lu; Li, Shilong; Zhang, Biran; Qin, Yuzhou; Tian, Ziao; Fang, Yangfu; Li, Yonglei; Liu, Zhaowei; Mei, Yongfeng
      ACS Applied Materials & Interfaces (2018), 10 (9), 7704-7708CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Hyperbolic metamaterials (HMMs) on a curved surface are demonstrated for an efficient outcoupling of nonradiative modes, which lead to an enhanced spontaneous emission. Those high-wavevector plasmonic modes can propagate along the curved structure and emit into the far field, realizing a directional light emission with max. fluorescent intensity. Detailed simulations disclose a high Purcell factor and a spatial power distribution in the curved HMM, which agrees with the exptl. result. The work presents remarkable enhancing capability in both the Purcell factor and emission intensity, which could suggest a unique structure design in metamaterials for potential application in, e.g., high-speed optical sensing and communications.
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    39. 39
      Roth, D. J.; Ginzburg, P.; Hirvonen, L. M.; Levitt, J. A.; Nasir, M. E.; Suhling, K.; Richards, D.; Podolskiy, V. A.; Zayats, A. V. Singlet–Triplet Transition Rate Enhancement inside Hyperbolic Metamaterials. Laser Photonics Rev. 2019, 13, 1900101,  DOI: 10.1002/lpor.201900101
      39
      Singlet-Triplet Transition Rate Enhancement inside Hyperbolic Metamaterials
      Roth, Diane J.; Ginzburg, Pavel; Hirvonen, Liisa M.; Levitt, James A.; Nasir, Mazhar E.; Suhling, Klaus; Richards, David; Podolskiy, Viktor A.; Zayats, Anatoly V.
      Laser & Photonics Reviews (2019), 13 (9), n/a1900101CODEN: LPRAB8; ISSN:1863-8899. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The spontaneous emission process is known to be largely affected by the surrounding electromagnetic environment of emitters, which manifests itself via the Purcell enhancement of decay rates. This phenomenon has been extensively investigated in the case of dipolar transitions in quantum systems, commonly delivering fast decay rates in comparison to forbidden transitions such as high-order multipolar transitions or spin-forbidden, singlet-triplet phosphorescence processes. Here, a decay rate enhancement of almost 2750-fold is demonstrated for a ruthenium-based phosphorescent emitter located inside a plasmonic hyperbolic metamaterial. The std. electromagnetic local d. of states description, typically employed for the Purcell factor anal. of dipolar transitions, is unable to account for a photoluminescence enhancement of this magnitude, which is attributed to the interplay between the local d. of states and strongly inhomogeneous electromagnetic fields inside the metamaterial. The large available range of spontaneous emission lifetimes reported here enables application of phosphorescent emitters in novel, fast, and efficient light-emitting sources, beneficial for optical communications, quantum information processing, spectroscopy, or bio-imaging.
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    40. 40
      Lee, K. J.; Lee, Y. U.; Kim, S. J.; André, P. Hyperbolic dispersion dominant regime identified through spontaneous emission variations near metamaterial interfaces. Adv. Mater. Interfaces 2018, 5, 1701629,  DOI: 10.1002/admi.201701629
      There is no corresponding record for this reference.
    41. 41
      Lu, D.; Ferrari, L.; Kan, J. J.; Fullerton, E. E.; Liu, Z. Optimization of nanopatterned multilayer hyperbolic metamaterials for spontaneous light emission enhancement. Phys. Status Solidi A 2018, 215, 1800263,  DOI: 10.1002/pssa.201800263
      There is no corresponding record for this reference.
    42. 42
      Morozov, K. M.; Ivanov, K. A.; de Sa Pereira, D.; Menelaou, C.; Monkman, A. P.; Pozina, G.; Kaliteevski, M. A. Revising of the Purcell effect in periodic metal-dielectric structures: the role of absorption. Sci. Rep. 2019, 9, 1– 9,  DOI: 10.1038/s41598-019-46071-5
      42
      Modelling optimal behavioural strategies in structured populations using a novel theoretical framework
      Morozov, Andrew; Kuzenkov, Oleg A.; Arashkevich, Elena G.
      Scientific Reports (2019), 9 (1), 1-15CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
      Understanding complex behavioral patterns of organisms obsd. in nature can be facilitated using math. modeling. The conventional paradigm in animal behavior modeling consists of maximisation of some evolutionary fitness function. However, the definition of fitness of an organism or population is generally subjective, and using different criteria can lead us to contradictory model predictions regarding optimal behavior. Moreover, structuring of natural populations in terms of individual size or developmental stage creates an extra challenge for theor. modeling. Here we revisit and formalise the definition of evolutionary fitness to describe long-term selection of strategies in deterministic self-replicating systems for generic modeling settings which involve an arbitrary function space of inherited strategies. Then we show how optimal behavioral strategies can be obtained for different developmental stages in a generic von-Foerster stage-structured population model with an arbitrary mortality term. We implement our theor. framework to explore patterns of optimal diel vertical migration (DVM) of two dominant zooplankton species in the north-eastern Black Sea. We parameterise the model using 7 years of empirical data from 2007-2014 and show that the obsd. DVM can be explained as the result of a trade-off between depth-dependent metabolic costs for grazers, anoxia zones, available food, and visual predation.
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    43. 43
      Caligiuri, V.; Palei, M.; Imran, M.; Manna, L.; Krahne, R. Planar double-epsilon-near-zero cavities for spontaneous emission and Purcell effect enhancement. ACS Photonics 2018, 5, 2287– 2294,  DOI: 10.1021/acsphotonics.8b00121
      43
      Planar Double-Epsilon-Near-Zero Cavities for Spontaneous Emission and Purcell Effect Enhancement
      Caligiuri, Vincenzo; Palei, Milan; Imran, Muhammad; Manna, Liberato; Krahne, Roman
      ACS Photonics (2018), 5 (6), 2287-2294CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      The enhancement of the photophys. response of fluorophores is a crucial factor for photonic and optoelectronic technols. that involve fluorophores as gain media. Recent advances in the development of an extreme light propagation regime, called epsilon-near-zero (ENZ), provide a promising approach in this respect. The authors design metal/dielec. nanocavities to be resonant with the absorption and emission bands of the employed fluorophores. Using CsPbBr3 perovskite nanocrystal films as light emitters, the authors study the spontaneous emission and decay rate enhancement induced by a specifically tailored double-epsilon-near-zero (double ENZ) structure. The authors exptl. demonstrate the existence of 2 ENZ wavelengths, by directly measuring their dielec. permittivity via ellipsometric anal. The double ENZ nature of this plasmonic nanocavity was exploited to achieve both surface plasmon enhanced absorption (SPEA) and surface plasmon coupled emission (SPCE), inducing a significant enhancement of both the spontaneous emission and the decay rate of the perovskite nanocrystal film that is placed on top of the nanocavity. Finally, the possibility of tailoring the 2 ENZ wavelengths of this structure within the visible spectrum simply by finely designing the thickness of the 2 dielec. layers, which enables resonance matching with a broad variety of dyes are discussed. The device design is appealing for many practical applications, ranging from sensing to low threshold amplified spontaneous emission, since the authors achieve a strong PL enhancement with structures that allow for straightforward fluorophore deposition on a planar surface that keeps the fluorophores exposed and accessible.
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    44. 44
      Hennessy, K.; Badolato, A.; Winger, M.; Gerace, D.; Atatüre, M.; Gulde, S.; Fält, S.; Hu, E. L.; Imamoğlu, A. Quantum nature of a strongly coupled single quantum dot–cavity system. Nature 2007, 445, 896– 899,  DOI: 10.1038/nature05586
      44
      Quantum nature of a strongly coupled single quantum dot-cavity system
      Hennessy, K.; Badolato, A.; Winger, M.; Gerace, D.; Atatuere, M.; Gulde, S.; Faelt, S.; Hu, E. L.; Imamoglu, A.
      Nature (London, United Kingdom) (2007), 445 (7130), 896-899CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Cavity quantum electrodynamics (QED) studies the interaction between a quantum emitter and a single radiation-field mode. When an atom is strongly coupled to a cavity mode, it is possible to realize important quantum information processing tasks, such as controlled coherent coupling and entanglement of distinguishable quantum systems. Realizing these tasks in the solid state is clearly desirable, and coupling semiconductor self-assembled quantum dots to monolithic optical cavities is a promising route to this end. However, validating the efficacy of quantum dots in quantum information applications requires confirmation of the quantum nature of the quantum-dot-cavity system in the strong-coupling regime. Here we find such confirmation by observing quantum correlations in photoluminescence from a photonic crystal nanocavity interacting with one, and only one, quantum dot located precisely at the cavity elec. field max. When off-resonance, photon emission from the cavity mode and quantum-dot excitons is anticorrelated at the level of single quanta, proving that the mode is driven solely by the quantum dot despite an energy mismatch between cavity and excitons. When tuned to resonance, the exciton and cavity enter the strong-coupling regime of cavity QED and the quantum-dot exciton lifetime reduces by a factor of 145. The generated photon stream becomes antibunched, proving that the strongly coupled exciton/photon system is in the quantum regime. Our observations unequivocally show that quantum information tasks are achievable in solid-state cavity QED.
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    45. 45
      Purcell, E. M.; Torrey, H. C.; Pound, R. V. Resonance absorption by nuclear magnetic moments in a solid. Phys. Rev. 1946, 69, 37,  DOI: 10.1103/PhysRev.69.37
      45
      Resonance absorption by nuclear magnetic moments in a solid
      Purcell, E. M.; Torrey, H. C.; Pound, R. V.
      Physical Review (1946), 69 (), 37-8CODEN: PHRVAO; ISSN:0031-899X.
      In the method for the detn. of nuclear magnetic moments by mol. beams (Rabi, et al, C.A. 32, 3257.6), transitions are induced between energy levels which correspond to different orientations of the nuclear spin in a strong, const., applied magnetic field. The absorption of radio-frequency energy, due to such transitions, was observed in a solid material (paraffin) which contains protons. Exptl. procedure and results are given.
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    46. 46
      Kuhn, H. Classical aspects of energy transfer in molecular systems. J. Chem. Phys. 1970, 53, 101– 108,  DOI: 10.1063/1.1673749
      46
      Classical aspects of energy transfer in molecular systesm
      Kuhn, Hans
      Journal of Chemical Physics (1970), 53 (1), 101-8CODEN: JCPSA6; ISSN:0021-9606.
      The decay time of the luminescence of a mol. S in front of a metal mirror depends markedly on its distance from the mirror. This phenomenon is quant. explained by considering the radiation field of this dipole, given by the Hertz classical equation. This field arrives at the mol., after being reflected at the mirror, with a retardation of the order of 10-15 sec. The decay time of the luminescence depends on the phase shift produced by this retardation, and thus on the ratio of the distance of the oscillator from the mirror, and the wavelength of the emitted light. By measuring the distance dependence of the decay time of the luminescence this retardation effect can be studied. In quantum-mech. terms the phenomenon can be described as being due to a stimulation or inhibition of the emission of the light quantum. In contrast to the known cases of stimulated emission, the stimulating field is the radiation field of the emitter quantum itself. The energy transfer from an excited mol. S to an acceptor A can be treated in a similar manner by considering the phenomenon as a retardation effect. In classical terms the field of S induces A to oscillate, and the induced field of A arriving at S slows down this oscillator. Simple equations are given for the energy transfer from an excited dipole or quadrupole, and for a row of many dipoles, oscillating in phase, to a weakly absorbing acceptor layer. The latter case is considered as a model for a J-aggregating dye and by comparison with exptl. data conclusions concerning the size of a J aggregate are drawn.
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    47. 47
      Hider, M. H.; Leung, P. Frequency shifts of molecules at rough metal surfaces. Phys. Rev. B: Condens. Matter Mater. Phys. 1991, 44, 3262,  DOI: 10.1103/PhysRevB.44.3262
      47
      Frequency shifts of molecules at rough metal surfaces
      Hider, M. H.; Leung, P. T.
      Physical Review B: Condensed Matter and Materials Physics (1991), 44 (7), 3262-5CODEN: PRBMDO; ISSN:0163-1829.
      The frequency shifts for dipolar transitions of mols. at rough metallic surfaces were studied in a phenomenol. model following the approach of previous work with the surface roughness modeled by a shallow grating profile in most cases. Such surface-induced shifts are indeed observable for mol. frequencies away from the surface-plasmon resonance frequency of the metal; the presence of surface roughness can either enhance or suppress the flat-surface-induced shifts, leading to extra morphol.-dependent resonances originated from the radiative coupling between the mol. emission and the substrate surface plasmon; and the effects in the perfectly reflecting limit can be worked out anal. with numerical results showing interesting features that are unique for this case. Correlations were made with respect to previous expts. on vibrational shifts as well as to recent calcns. from a microscopic approach.
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    48. 48
      Morawitz, H. Self-coupling of a two-level system by a mirror. Phys. Rev. 1969, 187, 1792,  DOI: 10.1103/PhysRev.187.1792
      There is no corresponding record for this reference.
    49. 49
      Borensztein, Y.; Abeles, F.; Lopez-Rios, T. Frequency shifts of an ensemble of electric dipole resonances near a conducting surface. Phys. Rev. Lett. 1984, 53, 854,  DOI: 10.1103/PhysRevLett.53.854
      49
      Frequency shifts of an ensemble of electric dipole resonances near a conducting surface
      Borensztein, Y.; Abeles, F.; Lopez-Rios, T.
      Physical Review Letters (1984), 53 (8), 854CODEN: PRLTAO; ISSN:0031-9007.
      The variation of the resonance frequency obtained from an exact calcn. of the reflectance for the Ag-island film system investigated exptl. by W. R. Holland and P. G. Hall (1984) is presented; the Ag-island film is treated within the Maxwell Garnett (MG) effective medium theory. The results are compared with the exptl. and calcd. values of Holland and Hall; the 2 theor. treatments give similar results for thicknesses >20 nm, while the MG one is in better agreement with the exptl. data below 20 nm, because the effective medium theory takes into account the long-range interaction between the particles.
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    50. 50
      Holland, W.; Hall, D. Frequency shifts of an electric-dipole resonance near a conducting surface. Phys. Rev. Lett. 1984, 52, 1041,  DOI: 10.1103/PhysRevLett.52.1041
      50
      Frequency shifts of an electric-dipole resonance near a conducting surface
      Holland, W. R.; Hall, D. G.
      Physical Review Letters (1984), 52 (12), 1041-4CODEN: PRLTAO; ISSN:0031-9007.
      The resonance frequency of an elec. dipole placed near a conducting surface is shifted by the dipole-surface interaction. The observation and measurement are reported of these shifts at optical frequencies for an exptl. system that consists of a metal island film spaced a distance d from a continuous Ag film. The dependence of the shift in the frequency of the island resonance on d shows good agreement with that predicted by a classical theory of the dipole-surface interaction.
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    51. 51
      Chance, R.; Prock, A.; Silbey, R. Frequency shifts of an electric-dipole transition near a partially reflecting surface. Phys. Rev. A: At., Mol., Opt. Phys. 1975, 12, 1448,  DOI: 10.1103/PhysRevA.12.1448
      51
      Frequency shifts of an electric-dipole transition near a partially reflecting surface
      Chance, R. R.; Prock, A.; Silbey, R.
      Physical Review A: Atomic, Molecular, and Optical Physics (1975), 12 (4), 1448-52CODEN: PLRAAN; ISSN:1050-2947.
      The classical theory of dipole radiation was used to calc. the change in frequency of an elec.-dipole-allowed transition due to the presence of a nearby reflecting surface. The result is compared to that for a perfect reflector.
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    52. 52
      Gualdron-Reyes, A. F.; Yoon, S. J.; Barea, E. M.; Agouram, S.; Munoz-Sanjose, V.; Melendez, A. M.; Nino-Gomez, M. E.; Mora-Sero, I. Controlling the phase segregation in mixed halide perovskites through nanocrystal size. ACS Energy Letters 2019, 4, 54– 62,  DOI: 10.1021/acsenergylett.8b02207
      52
      Controlling the Phase Segregation in Mixed Halide Perovskites through Nanocrystal Size
      Gualdron-Reyes, Andres. F.; Yoon, Seog Joon; Barea, Eva M.; Agouram, Said; Munoz-Sanjose, Vicente; Melendez, Angel M.; Nino-Gomez, Martha E.; Mora-Sero, Ivan
      ACS Energy Letters (2019), 4 (1), 54-62CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Mixed halide perovskites are 1 of the promising candidates in developing solar cells and light-emitting diodes (LEDs), among other applications, because of their tunable optical properties. Photoinduced phase segregation, by formation of segregated Br-rich and I-rich domains, limits the overall applicability. The phase segregation was tracked with increasing cryst. size of CsPbBr3-xIx and their luminescence under continuous-wave laser irradn. (405 nm, 10 mW cm-2) and obsd. the occurrence of the phase segregation from the threshold size of 46 ± 7 nm. These results have an outstanding agreement with the diffusion length (45.8 nm) calcd. also exptl. from the emission lifetime and segregation rates. Through Kelvin probe force microscopy, the correlation between the phase segregation and the reversible halide ion migration among grain centers and boundaries was confirmed. These results open a way to achieve segregation-free mixed halide perovskites and improve their performances in optoelectronic devices.
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    53. 53
      Saliba, M.; Correa-Baena, J.-P.; Wolff, C. M.; Stolterfoht, M.; Phung, N.; Albrecht, S.; Neher, D.; Abate, A. How to Make over 20% Efficient Perovskite Solar Cells in Regular (n–i–p) and Inverted (p–i–n) Architectures. Chem. Mater. 2018, 30, 4193– 4201,  DOI: 10.1021/acs.chemmater.8b00136
      53
      How to Make over 20% Efficient Perovskite Solar Cells in Regular (n-i-p) and Inverted (p-i-n) Architectures
      Saliba, Michael; Correa-Baena, Juan-Pablo; Wolff, Christian M.; Stolterfoht, Martin; Phung, Nga; Albrecht, Steve; Neher, Dieter; Abate, Antonio
      Chemistry of Materials (2018), 30 (13), 4193-4201CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Perovskite solar cells (PSCs) are currently one of the most promising photovoltaic technologies for highly efficient and cost-effective solar energy prodn. In only a few years, an unprecedented progression of prepn. procedures and material compns. delivered lab.-scale devices that have now reached record power conversion efficiencies (PCEs) >20%, competing with most established solar cell materials such as Si, CIGS, and CdTe. However, despite a large no. of researchers currently involved in this topic, only a few groups in the world can reproduce >20% efficiencies on a regular n-i-p architecture. Here, we present detailed protocols for prepg. PSCs in regular (n-i-p) and inverted (p-i-n) architectures with ≥20% PCE. We aim to provide a comprehensive, reproducible description of our device fabrication protocols. We encourage the practice of reporting detailed and transparent protocols that can be more easily reproduced by other labs. A better reporting std. may, in turn, accelerate the development of perovskite solar cells and related research fields.
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    54. 54
      Cortes, C.; Newman, W.; Molesky, S.; Jacob, Z. Quantum nanophotonics using hyperbolic metamaterials. J. Opt. 2012, 14, 063001,  DOI: 10.1088/2040-8978/14/6/063001
      54
      Quantum nanophotonics using hyperbolic metamaterials
      Cortes, C. L.; Newman, W.; Molesky, S.; Jacob, Z.
      Journal of Optics (Bristol, United Kingdom) (2012), 14 (6), 063001/1-063001/15CODEN: JOOPCA; ISSN:2040-8978. (Institute of Physics Publishing)
      A review. Engineering optical properties using artificial nanostructured media known as metamaterials has led to breakthrough devices with capabilities from super-resoln. imaging to invisibility. In this paper, we review metamaterials for quantum nanophotonic applications, a recent development in the field. This seeks to address many challenges in the field of quantum optics using advances in nanophotonics and nanofabrication. We focus on the class of nanostructured media with hyperbolic dispersion that have emerged as one of the most promising metamaterials with a multitude of practical applications from subwavelength imaging, nanoscale waveguiding, biosensing to nonlinear switching. We present the various design and characterization principles of hyperbolic metamaterials and explain the most important property of such media: a broadband enhancement in the electromagnetic d. of states. We review several recent expts. that have explored this phenomenon using spontaneous emission from dye mols. and quantum dots. We finally point to future applications of hyperbolic metamaterials, using the broadband enhancement in the spontaneous emission to construct single-photon sources.
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    55. 55
      Noginov, M.; Barnakov, Y. A.; Zhu, G.; Tumkur, T.; Li, H.; Narimanov, E. Bulk photonic metamaterial with hyperbolic dispersion. Appl. Phys. Lett. 2009, 94, 151105,  DOI: 10.1063/1.3115145
      55
      Bulk photonic metamaterial with hyperbolic dispersion
      Noginov, M. A.; Barnakov, Yu. A.; Zhu, G.; Tumkur, T.; Li, H.; Narimanov, E. E.
      Applied Physics Letters (2009), 94 (15), 151105/1-151105/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      The authors demonstrated the thickest bulk photonic metamaterial reported in the literature based on an Ag-filled alumina membrane. The material is highly anisotropic with hyperbolic dispersion at λ > 0.84 μm. The refraction of light in the direction expected of isotropic media with n < 1 was exptl. demonstrated at λ = 632.8 nm. This makes the material potentially suitable for a variety of applications ranging from subdiffraction imaging to optical cloaking. (c) 2009 American Institute of Physics.
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    56. 56
      Mahmoodi, M.; Tavassoli, S. H.; Takayama, O.; Sukham, J.; Malureanu, R.; Lavrinenko, A. V. Existence Conditions of High-k Modes in Finite Hyperbolic Metamaterials. Laser & Photonics Reviews 2019, 13, 1800253,  DOI: 10.1002/lpor.201800253
      There is no corresponding record for this reference.
    57. 57
      Navarro-Arenas, J.; Suárez, I.; Chirvony, V. S.; Gualdrón-Reyes, A. F.; Mora-Seró, I.; Martı́nez-Pastor, J. Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X= Br, I) Perovskite Nanocrystals. J. Phys. Chem. Lett. 2019, 10, 6389– 6398,  DOI: 10.1021/acs.jpclett.9b02369
      57
      Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X = Br, I) Perovskite Nanocrystals
      Navarro-Arenas, Juan; Suarez, Isaac; Chirvony, Vladimir S.; Gualdron-Reyes, Andres F.; Mora-Sero, Ivan; Martinez-Pastor, Juan
      Journal of Physical Chemistry Letters (2019), 10 (20), 6389-6398CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      CsPbX3 perovskite nanocrystals (PNCs) have emerged as an excellent material for stimulated emission purposes, with even more prospective applications than conventional colloidal quantum dots. A better understanding of the phys. mechanisms responsible for amplified spontaneous emission (ASE) is required to achieve more ambitious targets (lasing under continuous wave optical or elec. excitation). Establish the intrinsic mechanisms underlying ASE in PNCs of 3 different band gaps (CsPbBr3, CsPbBr1.5I1.5, and CsPbI3). The characterization at cryogenic temps. does not reveal any evidence of the biexciton mechanism in the formation of ASE. The measured shift toward long wavelengths of the ASE band is easily explained by the reabsorption in the PNC layer, which becomes stronger for thicker layers. In this way, the threshold of ASE is detd. only by optical losses at a given geometry, which is the single-exciton mechanism responsible for ASE. Exptl. results are properly reproduced by a phys. model.
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    58. 58
      Chirvony, V. S.; Martı́nez-Pastor, J. P. Trap-Limited Dynamics of Excited Carriers and Interpretation of the Photoluminescence Decay Kinetics in Metal Halide Perovskites. J. Phys. Chem. Lett. 2018, 9, 4955– 4962,  DOI: 10.1021/acs.jpclett.8b01241
      58
      Trap-Limited Dynamics of Excited Carriers and Interpretation of the Photoluminescence Decay Kinetics in Metal Halide Perovskites
      Chirvony, Vladimir S.; Martinez-Pastor, Juan P.
      Journal of Physical Chemistry Letters (2018), 9 (17), 4955-4962CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      A review. Interpretation of the photoluminescence (PL) decay kinetics in metal halide perovskites (MHPs) is extremely important for understanding the mechanisms and control of charge recombination in these promising photovoltaic and optoelectronic materials. In this work, we give a review of current models describing the PL decay kinetics in MHP layers and nanocrystals with particular attention to the interpretation of long-lived PL decay components (hundreds of nanoseconds to microseconds). First, we analyze phenomenol. photophys. models based on the rate equations, which describe the charge carrier recombination in MHP layers as an exclusively intrinsic bulk process. An important role of the carrier diffusion and nonradiative recombination on the layer surfaces is then discussed. A recently published approach is then analyzed, in the framework of which the obsd. long-lived components of PL decay kinetics in MHP nanocrystals are described in terms of the delayed luminescence mechanism arising due to the processes of multiple trapping and detrapping of carriers by shallow nonquenching traps. The possible origin of the shallow traps and perspectives to include the carrier trapping and detrapping processes in a model describing PL kinetics in MHP layers are discussed.
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    59. 59
      Chirvony, V. S.; Sekerbayev, K. S.; Adl, H. P.; Suárez, I.; Taurbayev, Y. T.; Gualdrón-Reyes, A. F.; Mora-Seró, I.; Martı́nez-Pastor, J. P. Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films. J. Lumin. 2020, 221, 117092,  DOI: 10.1016/j.jlumin.2020.117092
      59
      Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films
      Chirvony, Vladimir S.; Sekerbayev, Kairolla S.; Pashaei Adl, Hamid; Suarez, Isaac; Taurbayev, Yerzhan T.; Gualdron-Reyes, Andres F.; Mora-Sero, Ivan; Martinez-Pastor, Juan P.
      Journal of Luminescence (2020), 221 (), 117092CODEN: JLUMA8; ISSN:0022-2313. (Elsevier B.V.)
      In this paper we present crit. anal. of different points of view on interpretation of the photoluminescence (PL) decay kinetics in lead halide perovskites prepd. in the form of well passivated nanocrystals (PNCs) or thin polycryst. layers. In addn. to the literature data, our own measurements are also considered. For PNCs, a strong dependence of the PL lifetimes on the type of passivating ligand was obsd. with a consistently high PL quantum yield. It is shown that such ligand effects, as well as a decrease in the PL lifetime with decreasing temp., are well qual. explained by the phenomenol. model of thermally activated delayed luminescence, in which the extension of the PL decay time with temp. occurs due to the participation of shallow non-quenching traps. In the case of thin perovskite layers, we conclude that the PL kinetics under sufficiently low excitation intensity is detd. by the excitation quenching on the layer surfaces. We demonstrate that a large variety of possible PL decay kinetics for thin polycryst. perovskite films can be modelled by means of one-dimensional diffusion equation with use of the diffusion coeff. D and surface recombination velocity S as parameters and conclude that long-lived PL kinetics are formed in case of low D and/or S values.
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    60. 60
      Krishnamoorthy, H. N.; Jacob, Z.; Narimanov, E.; Kretzschmar, I.; Menon, V. M. Topological transitions in metamaterials. Science 2012, 336, 205– 209,  DOI: 10.1126/science.1219171
      60
      Topological Transitions in Metamaterials
      Krishnamoorthy, Harish N. S.; Jacob, Zubin; Narimanov, Evgenii; Kretzschmar, Ilona; Menon, Vinod M.
      Science (Washington, DC, United States) (2012), 336 (6078), 205-209CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Light-matter interactions can be controlled by manipulating the photonic environment. An optical topol. transition in strongly anisotropic metamaterials results in a dramatic increase in the photon d. of states, an effect that can be used to engineer this interaction. A transition in the topol. of the iso-frequency surface from a closed ellipsoid to an open hyperboloid using artificially nanostructured metamaterials is described. This topol. transition manifests itself in increased rates of spontaneous emission of emitters positioned near the metamaterial. Altering the topol. of the iso-frequency surface by using metamaterials provides a fundamentally new route to manipulating light-matter interactions.
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    61. 61
      Krishna, K. H.; Sreekanth, K.; Strangi, G. Dye-embedded and nanopatterned hyperbolic metamaterials for spontaneous emission rate enhancement. J. Opt. Soc. Am. B 2016, 33, 1038– 1043,  DOI: 10.1364/JOSAB.33.001038
      61
      Dye-embedded and nanopatterned hyperbolic metamaterials for spontaneous emission rate enhancement
      Krishna, K. H.; Sreekanth, K. V.; Strangi, G.
      Journal of the Optical Society of America B: Optical Physics (2016), 33 (6), 1038-1043CODEN: JOBPDE; ISSN:0740-3224. (Optical Society of America)
      Enhancement of spontaneous emission is a dynamic and challenging fundamental quantum phenomenon in optics and in a nutshell it opens new avenues for a spectrum of futuristic applications. Here, we exptl. demonstrate a large improvement in spontaneous emission rate enhancement of fluorescent mols. using dye-embedded and grating-coupled (nanopatterned) multilayered metal-dielec. hyperbolic metamaterials (HMMs). About a 35-fold spontaneous emission decay rate enhancement of dye mols. is obtained using a two-dimensional (2D) silver diffraction grating coupled with dye-embedded hyperbolic metamaterial. Further, we numerically and exptl. demonstrate a comparative study on the modification of spontaneous emission of fluorescent dye mols. placed in the vicinity of a HMM structure and a dye mols. embedded HMM structure. The obtained results pave the way for finding fruitful applications, including single photon sources.
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    62. 62
      Gontijo, I.; Boroditsky, M.; Yablonovitch, E.; Keller, S.; Mishra, U.; DenBaars, S. Coupling of InGaN quantum-well photoluminescence to silver surface plasmons. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 60, 11564,  DOI: 10.1103/PhysRevB.60.11564
      62
      Coupling of InGaN quantum-well photoluminescence to silver surface plasmons
      Gontijo, I.; Boroditsky, M.; Yablonovitch, E.; Keller, S.; Mishra, U. K.; DenBaars, S. P.
      Physical Review B: Condensed Matter and Materials Physics (1999), 60 (16), 11564-11567CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      The coincidence in excitation energy between surface plasmons on Ag and the GaN band gap is exploited to couple the semiconductor spontaneous emission into the metal surface plasmons. A 3-nm InGaN/GaN quantum well (QW) is positioned 12 nm from an 8-nm Ag layer, well within the surface plasmon fringing field depth. A spectrally sharp photoluminescence dip, by a factor ≈55, indicates that electron-hole energy is being rapidly transferred to plasmon excitation, due to the spatial overlap between the semiconductor QW and the surface plasmon elec. field. Thus, spontaneous emission into surface plasmons is ≈55 times faster than normal spontaneous emission from InGaN quantum wells. If efficient antenna structures can be incorporated into the metal film, there could be a corresponding increase in external light emission efficiency.
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    63. 63
      Zheng, X.; Hou, Y.; Sun, H.-T.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M. Reducing Defects in Halide Perovskite Nanocrystals for Light-Emitting Applications. J. Phys. Chem. Lett. 2019, 10, 2629– 2640,  DOI: 10.1021/acs.jpclett.9b00689
      63
      Reducing Defects in Halide Perovskite Nanocrystals for Light-Emitting Applications
      Zheng, Xiaopeng; Hou, Yi; Sun, Hong-Tao; Mohammed, Omar F.; Sargent, Edward H.; Bakr, Osman M.
      Journal of Physical Chemistry Letters (2019), 10 (10), 2629-2640CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      A review. The large sp. surface area of perovskite nanocrystals (NCs) increases the likelihood of surface defects compared to that of bulk single crystals and polycryst. thin films. It is crucial to comprehend and control their defect population to exploit the potential of perovskite NCs. This Perspective describes and classifies recent advances in understanding defect chem. and avenues toward defect d. redn. in perovskite NCs, and it does so in the context of the promise perceived in light-emitting devices. Several pathways for decreasing the defect d. are explored, including advanced NC syntheses, new surface-capping strategies, doping with metal ions and rare earths, engineering elemental compensation, and the translation of core-shell heterostructures into the perovskite materials family. The authors close with challenges that remain in perovskite NC defect research.
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    64. 64
      Ferrari, L.; Lu, D.; Lepage, D.; Liu, Z. Enhanced spontaneous emission inside hyperbolic metamaterials. Opt. Express 2014, 22, 4301– 4306,  DOI: 10.1364/OE.22.004301
      64
      Enhanced spontaneous emission inside hyperbolic metamaterials
      Ferrari, Lorenzo; Lu, Dylan; Lepage, Dominic; Liu, Zhaowei
      Optics Express (2014), 22 (4), 4301-4306CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)
      Hyperbolic metamaterials can enhance spontaneous emission, but the radiation-matter coupling is not optimized if the light source is placed outside such media. We demonstrate a 3-fold improvement of the Purcell factor over its outer value and a significant enlargement in bandwidth by including the emitter within a Si/Ag periodic multilayer metamaterial. To ext. the plasmonic modes of the structure into the far field we implement two types of 1D grating with triangular and rectangular profile, obtaining a 10-fold radiative enhancement at visible frequencies.
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    65. 65
      Ford, G. W.; Weber, W. H. Electromagnetic interactions of molecules with metal surfaces. Phys. Rep. 1984, 113, 195– 287,  DOI: 10.1016/0370-1573(84)90098-X
      65
      Electromagnetic interactions of molecules with metal surfaces
      Ford, G. W.; Weber, W. H.
      Physics Reports (1984), 113 (4), 195-287CODEN: PRPLCM; ISSN:0370-1573.
      A review with 138 refs. The methods described are essentially those of classical electromagnetic theory, the idea being that the mol. and the surface are sepd. so that their only interaction is via the electromagnetic fields. Reflection of electromagnetic waves at an interface, mol. fluorescence near a metal, shift and broadening of mol. vibration modes, and Raman scattering at metal surfaces are discussed.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXmvFCjtQ%253D%253D&md5=54fa95b496752182e0f85d163ede71de
    66. 66
      Diroll, B. T.; Zhou, H.; Schaller, R. D. Low-temperature absorption, photoluminescence, and lifetime of CsPbX3 (X= Cl, Br, I) nanocrystals. Adv. Funct. Mater. 2018, 28, 1800945,  DOI: 10.1002/adfm.201800945
      There is no corresponding record for this reference.
    67. 67
      Sun, L.; Jiang, C. Quantum interference in a single anisotropic quantum dot near hyperbolic metamaterials. Opt. Express 2016, 24, 7719– 7727,  DOI: 10.1364/OE.24.007719
      67
      Quantum interference in a single anisotropic quantum dot near hyperbolic metamaterials
      Sun Lu; Jiang Chun
      Optics express (2016), 24 (7), 7719-27 ISSN:.
      We theoretically demonstrate an anisotropic quantum vacuum created by a judiciously designed hyperbolic metamaterial. An electric dipole located nearby shows strong orientation dependence in the decay rate. With a proper arrangement of the ellipsoid-shaped CdSe/ZnSe quantum dot relative to the Ag/TiO<sub>2</sub> metamaterial, the anisotropies of quantum vacuum and quantum dot are harnessed to achieve an extraordinary quantum interference between radiative decay channels of orthogonal transitions. The ratio between cross damping term and spontaneous decay rate, Γ<sub>ij</sub>/Γ<sub>ii</sub>, which never exceeds unity in previously reported works reaches 1.04 in our numerical results. The corresponding evolution of excited state population in quantum dot is also dramatically modified.
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    68. 68
      Shalaginov, M. Y.; Ishii, S.; Liu, J.; Liu, J.; Irudayaraj, J.; Lagutchev, A.; Kildishev, A.; Shalaev, V. Broadband enhancement of spontaneous emission from nitrogen-vacancy centers in nanodiamonds by hyperbolic metamaterials. Appl. Phys. Lett. 2013, 102, 173114,  DOI: 10.1063/1.4804262
      68
      Broadband enhancement of spontaneous emission from nitrogen-vacancy centers in nanodiamonds by hyperbolic metamaterials
      Shalaginov, M. Y.; Ishii, S.; Liu, J.; Liu, J.; Irudayaraj, J.; Lagutchev, A.; Kildishev, A. V.; Shalaev, V. M.
      Applied Physics Letters (2013), 102 (17), 173114/1-173114/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      A broadband enhancement of emission from N-vacancy centers in nanodiamonds was exptl. demonstrated. The enhancement is achieved by using a multilayer metamaterial with hyperbolic dispersion. The metamaterial is fabricated as a stack of alternating Au and alumina layers. The approach paves the way towards the construction of efficient single-photon sources as planar on-chip devices. (c) 2013 American Institute of Physics.
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    69. 69
      Tumkur, T.; Zhu, G.; Black, P.; Barnakov, Y. A.; Bonner, C.; Noginov, M. Control of spontaneous emission in a volume of functionalized hyperbolic metamaterial. Appl. Phys. Lett. 2011, 99, 151115,  DOI: 10.1063/1.3631723
      69
      Control of spontaneous emission in a volume of functionalized hyperbolic metamaterial
      Tumkur, T.; Zhu, G.; Black, P.; Barnakov, Yu. A.; Bonner, C. E.; Noginov, M. A.
      Applied Physics Letters (2011), 99 (15), 151115/1-151115/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      The authors have developed a simple method to fabricate lamellar metal-dielec. hyperbolic metamaterials on flat, flexible, and curvilinear substrates, which allows for functionalization of dielec. layers by dye mols. The control of spontaneous emission of dye mols. with hyperbolic metamaterials was studied in 2 different sample configurations, and the effect is much stronger when emitters are placed inside the metamaterial rather than on its surface. (c) 2011 American Institute of Physics.
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    70. 70
      Jacob, Z.; Kim, J.-Y.; Naik, G. V.; Boltasseva, A.; Narimanov, E. E.; Shalaev, V. M. Engineering photonic density of states using metamaterials. Appl. Phys. B: Lasers Opt. 2010, 100, 215– 218,  DOI: 10.1007/s00340-010-4096-5
      70
      Engineering photonic density of states using metamaterials
      Jacob, Z.; Kim, J.-Y.; Naik, G. V.; Boltasseva, A.; Narimanov, E. E.; Shalaev, V. M.
      Applied Physics B: Lasers and Optics (2010), 100 (1), 215-218CODEN: APBOEM; ISSN:0946-2171. (Springer)
      The photonic d. of states (PDOS), like its electronic counterpart, is one of the key phys. quantities governing a variety of phenomena and hence PDOS manipulation is the route to new photonic devices. The PDOS is conventionally altered by exploiting the resonance within a device such as a microcavity or a bandgap structure like a photonic crystal. Here we show that nanostructured metamaterials with hyperbolic dispersion can dramatically enhance the photonic d. of states paving the way for metamaterial-based PDOS engineering.
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    71. 71
      Werner, J.; Nogay, G.; Sahli, F.; Yang, T. C.-J.; Brauninger, M.; Christmann, G.; Walter, A.; Kamino, B. A.; Fiala, P.; Loper, P. Complex refractive indices of cesium–formamidinium-based mixed-halide perovskites with optical band gaps from 1.5 to 1.8 eV. ACS Energy Letters 2018, 3, 742– 747,  DOI: 10.1021/acsenergylett.8b00089
      71
      Complex Refractive Indices of Cesium-Formamidinium-Based Mixed-Halide Perovskites with Optical Band Gaps from 1.5 to 1.8 eV
      Werner, Jeremie; Nogay, Gizem; Sahli, Florent; Yang, Terry Chien-Jen; Brauninger, Matthias; Christmann, Gabriel; Walter, Arnaud; Kamino, Brett A.; Fiala, Peter; Loper, Philipp; Nicolay, Sylvain; Jeangros, Quentin; Niesen, Bjoern; Ballif, Christophe
      ACS Energy Letters (2018), 3 (3), 742-747CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Cs-formamidinium-based mixed-halide perovskite materials with optical band gaps 1.5-1.8 eV are studied by variable-angle spectroscopic ellipsometry. The detd. complex refractive indexes are shown to depend on the fabrication procedure and environmental conditions during processing. This data is complemented by addnl. optical and structural characterization, as well as the demonstration of efficient perovskite solar cells. The data is used in optical simulations to provide guidelines for the optimization of perovskite/Si tandem solar cells.
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    72. 72
      Rakić, A. D.; Djurišić, A. B.; Elazar, J. M.; Majewski, M. L. Optical properties of metallic films for vertical-cavity optoelectronic devices. Appl. Opt. 1998, 37, 5271– 5283,  DOI: 10.1364/AO.37.005271
      72
      Optical properties of metallic films for vertical-cavity optoelectronic devices
      Rakic, Aleksandar D.; Djurisic, Aleksandra B.; Elazar, Jovan M.; Majewski, Marian L.
      Applied Optics (1998), 37 (22), 5271-5283CODEN: APOPAI; ISSN:0003-6935. (Optical Society of America)
      The authors present models for the optical functions of 11 metals used as mirrors and contacts in optoelectronic and optical devices: noble metals (Ag, Au, Cu), Al, Be, and transition metals (Cr, Ni, Pd, Pt, Ti, W). The authors used two simple phenomenol. models, the Lorentz-Drude (D) and the Brendel-Bormann (BB), to interpret both the free-electron and the interband parts of the dielec. response of metals in a wide spectral range from 0.1 to 6 eV. The authors' results show that the BB model was needed to describe appropriately the interband absorption in noble metals, while for Al, Be, and the transition metals both models exhibit good agreement with the exptl. data. A comparison with measurements on surface normal structures confirmed that the reflectance and the phase change on reflection from semiconductor-metal interfaces (including the case of metallic multilayers) can be accurately described using the proposed models for the optical functions of metallic films and the matrix method for multilayer calcns.
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    73. 73
      Aspnes, D. E.; Studna, A. Dielectric functions and optical parameters of si, ge, gap, gaas, gasb, inp, inas, and insb from 1.5 to 6.0 ev. Phys. Rev. B: Condens. Matter Mater. Phys. 1983, 27, 985,  DOI: 10.1103/PhysRevB.27.985
      73
      Dielectric functions and optical parameters of silicon, germanium, gallium phosphide, gallium arsenide, gallium antimonide, indium phosphide, indium arsenide, and indium antimonide from 1.5 to 6.0 eV
      Aspnes, D. E.; Studna, A. A.
      Physical Review B: Condensed Matter and Materials Physics (1983), 27 (2), 985-1009CODEN: PRBMDO; ISSN:0163-1829.
      Pseudodielec. functions <ε> = <ε1> + i<ε2> measured by spectroscopic ellipsometry and refractive indices ~n + ik, reflectivities R, and absorption coeffs. α calcd. from these data are reported. Rather than correct ellipsometric results for the presence of overlayers, the authors have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. The results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atm. regardless of the technique used to obtain the data. Differences among the data and previous results can generally be understood in terms of inadequate sample prepn., although results obtained by Kramers-Kronig anal. of reflectance measurements often show effects due to improper extrapolations. These results illustrate the importance of proper sample prepn. and of the capability of sep. detg. both ε1 and ε2 in optical measurements.
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    74. 74
      Novotny, L.; Hecht, B. Principles of Nano-Optics; Cambridge University Press, 2012.
      There is no corresponding record for this reference.
    75. 75
      Lin, H.-I.; Shen, K.-C.; Liao, Y.-M.; Li, Y.-H.; Perumal, P.; Haider, G.; Cheng, B. H.; Liao, W.-C.; Lin, S.-Y.; Lin, W.-J. Integration of nanoscale light emitters and hyperbolic metamaterials: an efficient platform for the enhancement of random laser action. ACS Photonics 2018, 5, 718– 727,  DOI: 10.1021/acsphotonics.7b01266
      75
      Integration of Nanoscale Light Emitters and Hyperbolic Metamaterials: An Efficient Platform for the Enhancement of Random Laser Action
      Lin, Hung-I.; Shen, Kun-Ching; Liao, Yu-Ming; Li, Yao-Hsuan; Perumal, Packiyaraj; Haider, Golam; Cheng, Bo Han; Liao, Wei-Cheng; Lin, Shih-Yao; Lin, Wei-Ju; Lin, Tai-Yuan; Chen, Yang-Fang
      ACS Photonics (2018), 5 (3), 718-727CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      The 1st attempt to integrate hyperbolic metamaterials with light emitting nanostructures enables strong enhancement of random laser action with reduced lasing threshold. The differential quantum efficiency can be enhanced by >4 times. The underlying mechanism can be interpreted well based on the fact that the high-k modes excited by hyperbolic metamaterials can greatly increase the possibility of forming close loops decreasing the energy consumption for the propagation of scattered photons in the matrix. Out-coupled propagation of the high-k modes reaches to the far-field without being trapped inside the metamaterials due to the coupling with the random distribution of light emitting nanoparticles also plays an important role. Electromagnetic simulations derived from the finite-difference time-domain (FDTD) method are executed to support the interpretation. Realizing strong enhancement of laser action assisted by hyperbolic metamaterials provides an attractive, simple, and efficient scheme for the development of high performance optoelectronic devices, including phototransistors, and many other solid state lighting systems. Besides, because of increasing light absorption assisted by hyperbolic metamaterials structure, the approach shown is also useful for the application of highly efficient solar cells.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsphotonics.0c01219.

    • (1) Details of another HMM structure with 50% filling factor of metal. (2) The delayed luminescence in perovskite nanocrystals and effect on Purcell factor. (3) Additional experimental results in the HMM structure with 42% filling factor of metal. (4) Purcell factor of the HMM structures as a function of wavelength and spacer thickness (PDF)


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