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Tuning the Ultrafast Response of Fano Resonances in Halide Perovskite Nanoparticles
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  • Paolo Franceschini*
    Paolo Franceschini
    Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
    *Email: [email protected]
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  • Luca Carletti*
    Luca Carletti
    Department of Information Engineering, University of Padova, Padova 35131, Italy
    Department of Information Engineering, University of Brescia, Brescia 25123, Italy
    *Email: [email protected]
    More by Luca Carletti
    Orcidhttp://orcid.org/0000-0001-6268-9817
  • Anatoly P. Pushkarev
    Anatoly P. Pushkarev
    ITMO University, Saint Petersburg 197101, Russia
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    Orcidhttp://orcid.org/0000-0002-1793-6812
  • Fabrizio Preda
    Fabrizio Preda
    Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy
    NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy (www.nireos.com)
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  • Antonio Perri
    Antonio Perri
    Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy
    NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy (www.nireos.com)
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  • Andrea Tognazzi
    Andrea Tognazzi
    Department of Information Engineering, University of Brescia, Brescia 25123, Italy
    National Institute of Optics (INO), Consiglio Nazionale delle Ricerche (CNR), Brescia 25123, Italy
    More by Andrea Tognazzi
  • Andrea Ronchi
    Andrea Ronchi
    Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
    More by Andrea Ronchi
  • Gabriele Ferrini
    Gabriele Ferrini
    Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
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  • Stefania Pagliara
    Stefania Pagliara
    Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
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  • Francesco Banfi
    Francesco Banfi
    FemtoNanoOptics Group, Université de Lyon, CNRS, Université Claude Bernard Lyon 1, Institut Lumière Matière, F-69622 Villeurbanne, France
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    Orcidhttp://orcid.org/0000-0002-7465-8417
  • Dario Polli
    Dario Polli
    Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy
    NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy (www.nireos.com)
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    Orcidhttp://orcid.org/0000-0002-6960-5708
  • Giulio Cerullo
    Giulio Cerullo
    Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy
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    Orcidhttp://orcid.org/0000-0002-9534-2702
  • Costantino De Angelis
    Costantino De Angelis
    Department of Information Engineering, University of Brescia, Brescia 25123, Italy
    National Institute of Optics (INO), Consiglio Nazionale delle Ricerche (CNR), Brescia 25123, Italy
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    Orcidhttp://orcid.org/0000-0001-8029-179X
  • Sergey V. Makarov
    Sergey V. Makarov
    ITMO University, Saint Petersburg 197101, Russia
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    Orcidhttp://orcid.org/0000-0002-9257-6183
  • Claudio Giannetti*
    Claudio Giannetti
    Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    *Email: [email protected]
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    Orcidhttp://orcid.org/0000-0003-2664-9492
Open PDFSupporting Information (1)

ACS Nano

Cite this: ACS Nano 2020, 14, 10, 13602–13610
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https://doi.org/10.1021/acsnano.0c05710
Published October 15, 2020

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Abstract

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The full control of the fundamental photophysics of nanosystems at frequencies as high as few THz is key for tunable and ultrafast nanophotonic devices and metamaterials. Here we combine geometrical and ultrafast control of the optical properties of halide perovskite nanoparticles, which constitute a prominent platform for nanophotonics. The pulsed photoinjection of free carriers across the semiconducting gap leads to a subpicosecond modification of the far-field electromagnetic properties that is fully controlled by the geometry of the system. When the nanoparticle size is tuned so as to achieve the overlap between the narrowband excitons and the geometry-controlled Mie resonances, the ultrafast modulation of the transmittivity is completely reversed with respect to what is usually observed in nanoparticles with different sizes, in bulk systems, and in thin films. The interplay between chemical, geometrical, and ultrafast tuning offers an additional control parameter with impact on nanoantennas and ultrafast optical switches.

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The study of light–matter interactions in halide perovskites (HPs) has revolutionized the photonics community in the past decade. (1,2) The wide interest in this class of materials, which comprises compounds of the form ABX3, where A stands for organic (e.g., CH3NH3═MA) or inorganic (e.g., Cs) cations, B is usually lead (Pb), and X is chosen between the halogens I, Br, or Cl, mainly stems from their outstanding optoelectronic properties, such as strong excitonic resonances at room temperature, (3) tunable band-gaps, and emission wavelengths within the entire visible spectrum, (4−6) and long carrier diffusion lengths. (7,8) These features, combined with low-cost fabrication methods, boosted the development of photovoltaic solar cells with power conversion efficiency exceeding 20%. (9)
Halide perovskites constitute also a promising platform for ultrafast optical switching applications. Subpicosecond visible light pulses can be used to photoinject free carriers across the HP semiconducting gap, thus triggering the kind of multistep dynamics that is at the basis of any ultrafast photonic device operating at frequencies as high as several THz. (10−17) Tuning the density and energy-distribution of the photocarriers thus provides an additional control parameter for achieving the complete tunability of HPs optical properties on the picosecond time scale.
Recent advances in the development of HP-based metamaterials (18−21) and nanoantennas (22,23) brought into play an additional degree of freedom to control HP optical properties on ultrafast time scales. (24−26) In this framework, a geometry-based approach was proposed after the observation of tunable Fano resonances in nanoparticles (NPs), arising from the coupling of the discrete excitonic states to the continuum of the geometry-driven Mie modes of the nanostructures. (27) Tuning the interference by a suitable choice of the nanoparticle size allows one to dramatically modify the excitonic line shape, up to the point of reversing the scattering resonant peak into a dip. (27)
In this work, we combine geometrical and ultrafast manipulation of the optical conductivity of Mie-resonant CsPbBr3 nanoparticles (see Figure 1a). Our time- and energy-resolved pump–probe data show that, when the nanoparticle size is tuned to achieve a dip in the excitonic Fano line shape, the photoinduced band gap renormalization and the subsequent band filling drive a modification of the optical constants, which is opposite as compared to that observed in bulk HP and in NPs exhibiting a peak in the excitonic Fano line shape. The analysis of the photophysics of Fano resonances in HP NPs is complemented by finite element simulations, which offer insights into the interplay between the nonequilibrium charge distribution and the coupling of the optical transitions to the geometry-controlled cavity modes and allow us to extract the intrinsic band-filling dynamics. The combination of optical and geometrical control offers an additional platform for ultrafast optoelectronic nanodevices and metamaterials. CsPbBr3 nanoparticles, exhibiting tunable Fano resonances, represent a prospective building-block for ultrafast all-optical switching in nonlinear nanophotonic designs. (28,29) The observation of an opposite photoinduced response in nanoparticles exhibiting different Fano lineshapes represents an interesting method to control the nonlinear response of dielectric media in nanodevices and metamaterials with subwavelength spatial resolution. (30,31)

Figure 1

Figure 1. Structural and optical properties of hybrid perovskites nanoparticles. (a) Concept of the pump–probe experiment on HP nanoparticles. The right panel displays a scanning electron microscopy image of the 300 nm NPs sample. (b, c) Size distribution of CsPbBr3 nanoparticles with average diameter ϕ̅ = 150 nm (b, green bars) and 300 nm (c, purple bars). The size distribution has been calculated by analysis of the scanning electron microscopy images. The solid line represents the normal fit to the experimental distributions. For both samples, the standard deviation of the normal distribution is 10% of the average size. (d) Experimental measured extinction spectra of the CsPbBr3 nanoparticles with an average diameter of 150 nm (green markers) and 300 nm (pink markers). In the spectral region investigated in the time-resolved experiment, the extinction data have been fitted (solid black lines) with eq 1. For the 150 nm sample, we estimated q=(−18.1 ± 0.2) and Γ = (0.107 ± 0.003) eV, while q = (−0.41 ± 0.01) and Γ = (0.123 ± 0.005) eV for the 300 nm sample. The right panel sketches the energy overlap between the discrete excitonic level (yellow line) and the continuum of states (square), which gives rise to the Fano low-q resonance for 300 nm particles. (e) Schematics of the electron dynamics triggered by the pulsed photoexcitation (blue arrow): the initial creation of the nonthermal electron–hole distributions within the valence (VB) and conduction bands (CB) leads to the renormalization of the equilibrium gap, Eg0, which reduces to Eg = Eg0 – δEgBGR. At later times, the interactions drive the formation of a long-lived quasi-thermal distribution at the gap edges and a consequent increase of the effective optical band gap, Eg = Eg0 + δEgBF.

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Results

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Isolated CsPbBr3 nanoparticles with different average sizes (see distributions in Figure 1b,c) were deposited on a quartz transparent substrate with an average coverage density σcov = 3 NP/μm2. (27) The samples were optically characterized by measuring the extinction, X = – log 10T, where T is the sample transmission. In Figure 1d, we report the extinction, which includes both the scattering and absorption contributions, of samples with 150 and 300 nm average NP diameter (ϕ̅). In both cases, the extinction can be reproduced by the following expression:
(1)
where the first term on the right-hand side represents a Fano asymmetric excitonic line width with amplitude a, centered at Eg – Eb, Eb being the exciton binding energy, and with a line shape controlled by the broadening parameter Γ and the profile index q. Xbck(ℏω, Eg) accounts for the absorption across the semiconducting edge at Eg (see section S2 for more details).
For 150 nm NPs, the small overlap between the excitonic line at Eg – Eb ≃ 2.4 eV and the Mie resonances results in a moderate asymmetry of the peak in the extinction spectrum (green markers in Figure 1d), corresponding to q ≃ −18 (high-q resonance). When the NP size is increased (300 nm), the overlap between the Mie modes and the excitonic resonance increases. As a result, the scattering contribution strongly increases, (27) thus turning the extinction line shape into a dip (pink markers in Figure 1d), which corresponds to q ≃ −0.4 (low-q resonance). The separate scattering and absorption contributions to the total extinction of single NPs are discussed in the Supporting Information.
In this work, we use ∼40 fs (fwhm) light pulses at 2.9 eV photon energy to trigger the out-of-equilibrium dynamics in HP NPs. In general, it is known that in bulk semiconductors the sudden photogeneration of high-density nonthermal electrons (holes) within the conduction (valence) band (see Figure 1e) modifies the electron screening, thus shrinking the band gap. This phenomenon, known as band gap renormalization (BGR), manifests itself into a photoinduced absorption increase below the semiconducting band edge, (14) corresponding to a photoinduced dynamical decrease of the effective band gap, Eg = Eg0 – δEgBGR. Within ≈1 ps, the electron–electron and electron–phonon interactions drive the relaxation of the nonthermal population and the creation of a long-lived quasi-thermal distribution, described by an effective temperature and chemical potential, which overfills the electron (hole) states at the band edges (see Figure 1e). The consequent bleaching of the band-edge transitions, known as band filling (BF) or dynamic Burstein–Moss effect, (33,34) leads to the photoinduced dynamical increase of the effective band gap, Eg = Eg0 + δEgBF, until the equilibrium distribution is eventually recovered on the nanosecond time scale via interband recombination. (10) To address the role of the geometry in controlling the modulation of the optical properties consequent to the BGR and BF processes, we performed broadband pump–probe experiments on NPs all the way from Fano high-q to low-q resonance conditions. The pump-induced relative transmittivity variation, δT/T(ℏω, Δt), is measured in the 2.2–2.5 eV energy range by means of a delayed (Δt) supercontinuum white light probe detected through a collinear interferometer (GEMINI by NIREOS), (35,36) as described in the Methods. The energy- and time-dependent δT/T(ℏω, Δt) is reported for 150 and 300 nm NPs (see Figure 2a,b). More experimental data for different NP sizes are shown in Figure S1.

Figure 2

Figure 2. Ultrafast dynamics of the nanoparticle optical properties. Energy- and time-resolved differential transmission maps for 150 nm (a) and 300 nm (b) CsPbBr3 nanoparticles pumped at 2.9 eV, with an incident fluence of 54 μJ/cm2. The top panels display δT/T(ℏω) spectra at fixed probe delays (200 fs, dashed line; 2 ps solid line) for 150 and 300 nm nanoparticles, respectively. For graphical reasons, the data reported in panel b are magnified by a factor of 4.

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In the Fano high-q resonance condition (150 nm, Figure 2a), the δT/T(ℏω, Δt) signal is characterized by a short-lived negative component at ℏω ≃ 2.3 eV and a long-lived signal, which turns from positive to negative at the exciton peak at Eg – Eb ≃ 2.4 eV. The presence of two different spectral components can be appreciated by plotting δT/T spectra at different delays (Δt = 0.2 and 2 ps, top panel of Figure 2a). The negative transmittivity variation at short delays reflects a photoinduced increase of below-gap absorption, which is the signature of the BGR effect, as already observed in thin films. (14) On the picosecond time scale, this effect decays as a result of hot carrier cooling through electron–phonon interactions. (14) As a consequence, after ∼2 ps the positive (negative) transmittivity variation at ℏω < (>)2.4 eV can be reproduced, over the entire frequency range, by a rigid blue-shift, by δEg = (5.1 ± 0.4) meV, of the excitonic line in eq 1. Such a shift is the typical manifestation of the conventional band filling effect, which has been already reported in HP thin-films. (10) We remark that the transmittivity variation measured in our pump–probe experiment refers to the effective response of the sample, which can be modeled as an inhomogeneous film with CsPbBr3 NPs, with volume filling fraction fvol. Therefore, in order to quantitatively compare our results to previous data on thin films, we extracted the pump-induced shift of the band gap of the individual nanoparticles (δEgNP) by calculating the scaling factor (C̃), which relates δEgNP to the measured effective δEg. As described in section S2, we adopted the Modified Maxwell–Garnett Mie (MMGM) theory (37) for the effective medium, which accounts for size-dispersed spherical particles embedded in a host matrix, to calculate the scaling factor as the ratio between the intrinsic absorption variation of an individual NP and the effective absorption variation of the film. From our analysis, we estimated C̃ = 60 ± 40. Considering that, for small shifts, the transmittivity variation in the proximity of a peak is directly proportional to the shift amplitude, we can thus assume that δEgNP ≃ C̃·δEg = (300 ± 200) meV, which is in quantitative agreement with data reported in ref (10).
The nonequilibrium optical response of CsPbBr3 nanoparticles progressively changes when the NP size is increased and the overlap between the exciton resonance at ∼2.4 eV and the geometry-controlled continuum of the Mie modes is enhanced. In the Fano low-q resonance condition, obtained for 300 nm NP size, the δT/T(ℏω, Δt) signals associated with both the band gap renormalization and band filling effects are reversed, as shown in Figure 2b. In this condition, the subpicosecond below-gap transmittivity change is positive, thus suggesting a photoinduced decrease of below-gap absorption in opposition to the conventional band gap renormalization effect measured in films and nanoparticles far from the Fano low-q resonance condition.
Our results demonstrate that the nonequilibrium optical properties of CsPbBr3 NPs following ultrafast excitation are crucially controlled by the NP size. The photogenerated electron/hole population in the conduction and valence bands gives rise to a photoinduced variation of the far-field optical properties, which qualitatively and quantitatively depend on the interference between the excitonic resonance and the geometrically controlled Mie modes. To gain further insights into the interplay between nonequilibrium photoinjected free carriers and the geometry-controlled Fano interference, we performed full-vectorial numerical electromagnetic simulations implemented with the finite element method in COMSOL. In these numerical calculations, we considered isolated HP nanospheres deposited on a quartz substrate with refractive index 1.45. The numerical simulations of the full electromagnetic problem go beyond the Mie theory for isolated NPs, which is presented in section S6, and allow us to account for the NP–substrate interaction that affects spectral position, amplitude, and phase of the resonances in the NP. (38)
The frequency dependent transmittivity variation of the single NP is calculated as δT/T(NP)(ℏω) = 10–(XoutNP(ℏω)–XeqNP(ℏω)) – 1 (for details, see Methods). The equilibrium extinction, XeqNP(ℏω), is obtained by solving the NP scattering problem and assuming the complex refractive index of bulk CsPbBr3 (extracted from ref (27)). The out-of-equilibrium extinction, XoutNP(ℏω), is obtained by properly modifying the equilibrium optical properties to account for the effect of photogenerated nonequilibrium carriers. More specifically, we assume that the photoexcitation process initially injects an excess density of electrons (ne) and holes (nh) approximately equal to the density of absorbed photons, i.e., ne ≃ nh ≃ nph. On the subpicosecond time scale, the photoinjected free carrier density, nfc = ne + nh ≃ 2nph ≃ 1.2 × 1020 cm–3 (see the Methods for the calculation of nph), overcomes the screening critical concentration, ncr ≈ 3.4 × 1018 cm–3 (see section S5 of the Supporting Information), (32) thus leading to a photoinduced bandgap renormalization and a related change of the absorption coefficient expressed as (32)
(2)
Within ≈1 ps, the carrier–carrier and carrier–phonon interactions lead to the relaxation of the photoinjected free carriers and to the onset of a quasi-thermal effective carriers distribution which completely fills the states at the bottom (top) of the conduction (valence) band. The bleaching of the gap-edge transitions (band filling) manifests itself as (32)
(3)
where the effective Fermi–Dirac populations in the valence and conduction bands, fv and fc, respectively, are controlled by the effective Fermi levels EFv* and EFc* and by the effective temperature T*. The photoinduced absorption change related to transition of free carriers within the conduction (valence) band is accounted for by a Drude model, as described in section S5 of the Supporting Information. We calculated δT/T(NP)(ℏω) for different NP sizes, namely, 150 and 300 nm (Figure 3a,b, respectively), corresponding to the Fano high-q resonance and low-q resonance conditions. While the Drude contribution is always negligible (see Figure 3), the BGR and BF dominate the transmittivity change, as can be evidenced by calculating separately the two contributions to the δT/T(NP)(ℏω) signal. For both NP sizes, the BGR effect has been estimated by assuming nfc/ncr ≃ 2nph/ncr = 35 in eq 2. The BF effect has been reproduced by assuming that the effective thermal energy of the free carriers is given by the excess energy injected by the pump photons and equally shared between electrons and holes, i.e., 3/2kT* = (ℏωp – Eg0)/2. Considering ℏωp = 2.9 eV and Eg0 ≃ 2.4 eV, we obtain T* ≃3000 K. EFv* and EFc* are then self-consistently calculated (see eqs S21 and S22) assuming nfc = 2nph. The results reported in Figure 3 show that, for 150 nm NP size, the BGR results in an additional below edge absorption (negative δT/T), which is opposite to the signal related to the BF process. In contrast, when the NP size matches the Fano low-q resonance condition (300 nm, Figure 3b), both the BGR and BF contributions to the differential transmittivity variation are of opposite sign as compared to the high-q resonant case. Moreover, the results obtained from the simulations are consistent with the experimental data obtained for a wider set of CsPbBr3 NP samples. Indeed, in the case of nanoparticles with average sizes of ∼100 nm and ∼220 nm, whose extinction spectrum is characterized by a peak (high-q) near the exciton line (see Figure S1a), their out-of-equilibrium optical properties (reported in Figure S1b,d) exhibit spectral features similar to those reported for 150 nm NP sample. These numerical results support our experimental findings and demonstrate that the photoinduced modulation of the NP optical properties is controlled by the geometry of the system.

Figure 3

Figure 3. Numerical simulations. Differential transmittivity spectrum, δT/T(NP)(ℏω), calculated for individual (a) 150 nm and (b) 300 nm nanoparticles. The separate contributions of the bandgap renormalization (BGR), band filling (BF), and Drude effects to the total signal are calculated by assuming the photoinjected free carrier density nfc ≃ 1.2 × 1020 cm–3, for both nanoparticle sizes.

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The numerical results reported in Figure 3 offer important insights into the photophysics of HP NPs and provide a guide for disentangling the BGR and BF dynamics, which experimentally overlap on the picosecond time scale. The results reported in Figure 3a,b indicate that, for both NP sizes, the δT/T(NP) at ℏω ≃2.2 eV is dominated by the BF effect, whereas the BGR signal is negligible. As a consequence, time traces at this photon energy, although smaller in amplitude with respect to data at higher photon energy, directly reproduce the dynamics of the BF alone. In Figure 4a,b, we report δT/T(ℏω = 2.23 eV, Δt) time traces (black dots), which can be fitted by a single exponential function (black lines) with similar time constant τBF = 480 ± 20 fs. The BGR dynamics can then be retrieved by analyzing the time-traces taken at different photon energies for which the BGR contribution is not negligible. In Figure 4a,b, we report δT/T(ℏω = 2.3 eV, Δt) time traces (red dots), which exhibit a multiexponential behavior. In Figure 4c, we report the components of the multiexponential fit which directly represent the time evolution of the actual BGR process; the curves are obtained by subtracting the properly scaled BF contribution from the full δT/T dynamics at ℏω = 2.3 eV (see section S4 for more details). For both NP sizes, the build-up time of the BGR signal is ≈200 fs, whereas the relaxation of the nonthermal carriers responsible for the BGR takes place within 400 ± 10 fs, a time scale compatible with the carrier cooling mediated by the coupling to optical phonons. (39) We underline that, in the time-resolved traces, the dynamics of the δT/T signal is proportional to the nonequilibrium population within the valence and conduction bands. This population, which is bottlenecked by the presence of the gap, decays on a time scale much longer than the inverse of the exciton line width (∼ℏ/Γ = 6 fs) that accounts for the whole of quasi-elastic scattering processes which reduce the exciton lifetime. The procedure here introduced and based on time- and frequency-resolved optical measurements constitutes a way to disentangle the BGR and BF processes. Our results show that, microscopically, the two processes are almost independent of the NP size, as expected since the exciton Bohr’s radius (∼7 nm) (5) is much smaller than the NP size. The observed inversion of the δT/T(ℏω, Δt) signals in the Fano low-q resonance condition is thus a genuine effect of the geometry of the system, which controls the subpicosecond modulation of the optical properties.

Figure 4

Figure 4. Disentangling band filling and bandgap renormalization. Differential time traces at specific photon energies are reported for NP sizes matching the Fano high-q resonance (150 nm, panel a) and low-q resonance conditions (300 nm, panel b). The black solid lines represent the single exponential fitting to the time traces taken at ℏω = 2.23 eV (black dots). The red solid lines represent the multiexponential fitting to the time traces taken at ℏω = 2.3 eV (red dots). Panel c displays the BGR signal obtained by subtracting the BF dynamics from the time traces taken at ℏω = 2.3 eV and shown in panels a and b. The solid lines represent the exponential fitting to the BGR dynamics.

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The numerical simulations also reproduce the local electric field enhancement FE, defined as the ratio between the modulus of the electric field (E⃗(x,y,z)) and the amplitude of the incident plane wave (E0): FE = ∥E⃗(x,y,z)∥/E0. Figure 5 shows equilibrium and out-of-equilibrium FE at 2.38 eV for a single nanoparticle with 150 and 300 nm diameter sizes. The black arrows represent the electric field vector for the same excitation parameters used to obtain the plots reported in Figure 3. For 150 nm NPs, the equilibrium resonance (panel a) is dominated by the electric dipole (ED) mode. The ED spatial pattern is maintained also in out-of-equilibrium conditions (panel b). On the other hand, the nature of the resonance dramatically changes for 300 nm NPs. The electric field distribution in Figure 5c suggests that both ED and MD (magnetic dipole) resonances contribute to the electromagnetic response at equilibrium, the latter exhibiting a typical field leakage toward the substrate. The MD contribution in 300 nm NPs, for the probe spectral region considered (2.20–2.45 eV), is consistent with the observation (40) that the MD mode takes place when the relation λ0/n ≈ ϕ̅ is fulfilled, with λ0/n being the light wavelength inside the particle. Indeed, from ref (27), n = 2.1 at ℏω = 2.2 eV, which gives λ0/n = 270 ≈ 300 nm (see multipole modes decomposition for NPs of different sizes in section S6). In the Fano low-q resonance condition, the photoexcitation strongly alters the mode spatial distribution (panel d) by shifting up the MD center of mass and increasing the ED mode contribution at the NP–substrate interface.

Figure 5

Figure 5. Electric field enhancement. Electric field enhancement on the plane of the vertical cross-section of the nanoparticle. The panels show the equilibrium (a, c) and out-of-equilibrium (b, d) FE for a single CsPbBr3 NP with diameters of 150 (a, b) and 300 nm (c, d). The incident monochromatic wave centered at 2.38 eV propagates from the top to the bottom along the Z axis. The black arrows represent the electric field vector E⃗ in the NP volume. The red arrows represent the Poynting vector S⃗ outside the NP surface. The dashed white line represents the substrate surface. The scale bar is 100 nm.

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In order to connect the near field solutions to the total scattering, it is instructive to plot the Poynting vector at the NP interface (red arrows). In the Fano high-q resonance condition (150 nm NPs in panels a and b), photoexcitation leads to a quenching of the total scattered energy, corresponding to the positive transmittivity variation measured in the experiments. In contrast, the out-of-equilibrium Poynting vector in Fano low-q resonance NPs (300 nm NPs in panels c and d) indicates an overall transient scattering enhancement associated with the ED and MD photoinduced change and corresponding to the negative measured transmittivity variation.

Conclusions

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In conclusion, we have studied the photoinduced subpicosecond optical modulation of the Fano resonance formed by the coupling of an excitonic state with Mie modes in halide perovskite NPs. In particular, we have demonstrated that the ultrafast modification of the optical properties induced by the band gap renormalization and band filling mechanisms dramatically depends on the geometry of the NPs. In the low-q resonance Fano condition, the contribution of the two effects to the relative transmittivity variation is completely reversed with respect to the high-q resonant case and to what was previously observed in thin films and bulk materials. (16) Importantly, this is the demonstration of the ultrafast control of the optical response in nanoparticles where Mie resonances are coupled with excitons. In previous studies, the ultrafast all-optical switching in Mie-resonant nanoparticles was carried out with standard semiconductors like amorphous silicon (28,41−43) and gallium arsenide, (44) for which excitonic effects are negligible at room temperature. Beside the physical effects arising from the coupling between the exciton and Mie modes, there is an important advantage of high absorption and sharp band-edge in CsPbBr3 perovskites, allowing us to greatly reduce the fluence required to observe ultrafast tuning. CsPbBr3 nanoparticles exhibit an amplitude of the transmittivity modulation that is 2 orders of magnitude larger as compared to that measured in silicon-based Mie resonators under similar photoexcitation conditions. (42) Although in this work we focused on CsPbBr3 nanoparticles, the results and modeling discussed simply rely on the geometry-driven overlap between the exciton line and the continuum of Mie resonances. As a consequence, the present results can be promptly extended to a wider class of perovskite-based nanonstructures. The present results offer insights into the photophysics of halide perovskite nanoparticles and provide an additional parameter to control their optical properties at frequencies as high as few terahertz, with impact on perovskite-based optoelectronic devices, metamaterials, and switchable nanoantennas.

Methods

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Samples

Perovskite NPs are deposited on the ITO and glass substrates according to the following protocol. A solution 1 consists of lead(II) bromide (PbBr2, 36.7 mg, 0.1 mmol) and cesium(I) bromide (CsBr, 21.2 mg, 0.1 mmol) dissolved in 1 mL of anhydrous dimethyl sulfoxide (DMSO). A solution 2 consists of poly(ethylene oxide) (PEO, average Mw 70 000, 10 mg) stirred at 300 rpm in 1 mL of DMSO at 70° for 10 h. 1 and 2 are mixed in a 1:3 mass ratio and stirred at 100° for 10 min to give a perovskite-polymer ink. The latter is deposited on precleaned glass and ITO substrates by spin-casting at 1500 rpm for 1 min. The deposited films are annealed at 130° for 3 min to produce NPs with an average size of 150 nm and at 80° for 10 min to obtain NPs with an average size of 300 nm. All the procedures are conducted inside a N2-filled glovebox with both O2 and H2O levels not exceeding 1 ppm. Extinction spectra are measured in a UV–vis-NIR spectrophotometer (Shimadzu UV-2600).

Time-Resolved Pump–Probe Spectroscopy

The optical pump–probe setup is based on a Yb-laser system (Pharos, Light Conversion), which delivers 37.5 μJ, 270 fs pulses at 1030 nm central wavelength, and 400 kHz repetition rate. A portion of the laser with 30 μJ energy is used to pump an optical parametric amplifier (Orpheus-F, Light Conversion). The output signal at 850 nm is frequency doubled to obtain a pump pulse at 425 nm (2.9 eV), bandwidth (45) Δλ ∼ 7 nm, with 52 nJ energy per pulse that is focused within 350 μm spot size (fwhm). The 54 μJ/cm2 incident pump fluence is such that the average absorbed photon density is nph ≃ 6 × 1019 cm–3 (see section S3 for more details). The other portion of the laser is focused on a sapphire crystal to generate a white-light continuum probe ranging from 500 to 1000 nm, which is then reduced to the region 500–600 nm (2.1–2.5 eV) by a colored bandpass glass filter (∼1 mW). The pump is modulated by a mechanical chopper working at 2.5 kHz. The pump pulse is delayed in time with respect to the probe pulse by using a linear motorized stage (Physik Instrumente M403.2DG). The pump and the probe beams are orthogonally polarized: the pump is linearly horizontally polarized, whereas the probe is vertically polarized. The two beams are noncollinearly focused onto the sample: the pump impinges on the sample at normal incidence, while the incident angle of the probe is less than 10°. After the interaction with the sample, the linear and differential transmission spectra (at fixed pump–probe delay) are detected by means of a common-path birefringent interferometer, GEMINI (from NIREOS), which generates two collinear replicas of the incoming light. When the relative delay between the two probe replicas is varied, the light interferogram is obtained on a single-pixel photodiode. The linear transmission spectrum is obtained by computing the Fourier transform of the interferogram, while the differential transmission spectrum is retrieved by computing the Fourier transform of the interferogram demodulated by a lock-in amplifier at the chopping frequency. The pump-induced relative transmittivity variation is defined as δT/T(ℏω, Δt) = [Tout(ℏω, Δt) – Teq(ℏω)]/Teq(ℏω), where Tout and Teq are the out-of- and equilibrium transmittivities.

Simulations

We performed full-vectorial numerical simulations implemented with the finite element method in COMSOL. In our simulations, we consider the linear scattering problem of an electric field impinging on isolated CsPbBr3 nanospheres deposited on a quartz substrate. From the simulations, we calculated the absorption and scattering cross-section of the single nanoparticle, Cabs and Csca, respectively, to obtain the extinction cross-section Cext of the single nanoparticle as Cext = Cabs + Csca. (46) The absorption (scattering) cross-section is calculated as Cabs = wabs/Ii (Csca = wsca/Ii), where wabs (wsca) is the rate at which the energy is absorbed (scattered) by the particle and Ii is the incident light intensity. (46) The incident field is a linearly polarized plane wave since the focal spot size in the experiment is much larger than the sphere diameter. To obtain the transmittivity of the layer from Cext, we assumed that the nanoparticles are weakly coupled and that they are uniformly distributed on the substrate surface with a coverage distribution density σcov = 3 NP/μm2. The transmittivity is given by T = 10–X, where the extinction X is related to Cext through X = σcov·Cext · log 10 e. (46) The equilibrium transmittivity of the nanoparticle is obtained by solving the linear scattering problem for a single CsPbBr3 sphere, where the equilibrium complex refractive index equals the experimental refractive index of CsPbBr3 thin films, reported in ref (27). The out-of-equilibrium transmittivity is obtained by solving the linear scattering problem for a single CsPbBr3 sphere, where the equilibrium complex refractive index is modified according to eqs 2 and 3. This procedure is applied to nanoparticles with diameters of 150 and 300 nm.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.0c05710.

  • Equilibrium extinction spectra for additional samples, time- and energy-resolved differential transmission maps for additional samples, details on the effective medium optical properties analysis, calculation of the pump photon density, details on the analysis of the time-resolved traces, models of the dynamics of the single nanoparticle optical properties, efficiency factors, and mode decompositions of the single particle

Terms & Conditions

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Author Information

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  • Corresponding Authors
    • Paolo Franceschini - Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium;  Email: [email protected]
    • Luca Carletti - Department of Information Engineering, University of Padova, Padova 35131, Italy;  Department of Information Engineering, University of Brescia, Brescia 25123, Italy;  Orcidhttp://orcid.org/0000-0001-6268-9817;  Email: [email protected]
    • Claudio Giannetti - Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  Orcidhttp://orcid.org/0000-0003-2664-9492;  Email: [email protected]
  • Authors
    • Anatoly P. Pushkarev - ITMO University, Saint Petersburg 197101, Russia;  Orcidhttp://orcid.org/0000-0002-1793-6812
    • Fabrizio Preda - Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy;  NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy (www.nireos.com)
    • Antonio Perri - Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy;  NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy (www.nireos.com)
    • Andrea Tognazzi - Department of Information Engineering, University of Brescia, Brescia 25123, Italy;  National Institute of Optics (INO), Consiglio Nazionale delle Ricerche (CNR), Brescia 25123, Italy
    • Andrea Ronchi - Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
    • Gabriele Ferrini - Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    • Stefania Pagliara - Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy;  ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
    • Francesco Banfi - FemtoNanoOptics Group, Université de Lyon, CNRS, Université Claude Bernard Lyon 1, Institut Lumière Matière, F-69622 Villeurbanne, France;  Orcidhttp://orcid.org/0000-0002-7465-8417
    • Dario Polli - Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy;  NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy (www.nireos.com);  Orcidhttp://orcid.org/0000-0002-6960-5708
    • Giulio Cerullo - Dipartimento di Fisica, Politecnico di Milano, Milano 20133, Italy;  Orcidhttp://orcid.org/0000-0002-9534-2702
    • Costantino De Angelis - Department of Information Engineering, University of Brescia, Brescia 25123, Italy;  National Institute of Optics (INO), Consiglio Nazionale delle Ricerche (CNR), Brescia 25123, Italy;  Orcidhttp://orcid.org/0000-0001-8029-179X
    • Sergey V. Makarov - ITMO University, Saint Petersburg 197101, Russia;  Orcidhttp://orcid.org/0000-0002-9257-6183
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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P.F. and C.G acknowledge financial support from MIUR through PRIN 2015 (Prot. 2015C5SEJJ001) and PRIN 2017 (Prot. 20172H2SC4) Programs. G.F., S.P., and C.G. acknowledge support from Università Cattolica del Sacro Cuore through Grants D.1, D.2.2, and D.3.1. L.C. acknowledges STARS StG project PULSAR. S.M and A.P. acknowledge the Russian Science Foundation (project 20-73-10183). F.B. acknowledges financial support from the IDEXLYON Project-Programme Investissements d’Avenir (Grant ANR-16 -IDEX-0005), France. NIREOS acknowledges financial support from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 814492 (SimDOME).

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    We studied the ultrafast transient response of photoexcitations in two hybrid org.-inorg. perovskite films used for high efficiency photovoltaic cells, namely, CH3NH3PbI3 and CH3NH3PbI1.1Br1.9 using polarized broadband pump-probe spectroscopy in the spectral range of 0.3-2.7 eV with 300 fs time resoln. For CH3NH3PbI3 with above-gap excitation we found both photogenerated carriers and excitons, but only carriers are photogenerated with below-gap excitation. In contrast, mainly excitons are photogenerated in CH3NH3PbI1.1Br1.9. Surprisingly, we also discovered in CH3NH3PbI3, but not in CH3NH3PbI1.1Br1.9, transient photoinduced polarization memory for both excitons and photocarriers, which is also reflected in the steady state photoluminescence. From the polarization memory dynamics we obtained the excitons diffusion const. in CH3NH3PbI3, D ≈ 0.01 cm2 s-1.
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  12. 12
    Milot, R. L.; Eperon, G. E.; Snaith, H. J.; Johnston, M. B.; Herz, L. M. Temperature-Dependent Charge-Carrier Dynamics in CH3NH3PbI3 Perovskite Thin Films. Adv. Funct. Mater. 2015, 25, 6218– 6227,  DOI: 10.1002/adfm.201502340
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    12
    Temperature-Dependent Charge-Carrier Dynamics in CH3NH3PbI3 Perovskite Thin Films
    Milot, Rebecca L.; Eperon, Giles E.; Snaith, Henry J.; Johnston, Michael B.; Herz, Laura M.
    Advanced Functional Materials (2015), 25 (39), 6218-6227CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The photoluminescence, transmittance, charge-carrier recombination dynamics, mobility, and diffusion length of CH3NH3PbI3 are investigated in the temp. range from 8 to 370 K. Profound changes in the optoelectronic properties of this prototypical photovoltaic material are obsd. across the two structural phase transitions occurring at 160 and 310 K. Drude-like terahertz photocond. spectra at all temps. above 80 K suggest that charge localization effects are absent in this range. The monomol. charge-carrier recombination rate generally increases with rising temp., indicating a mechanism dominated by ionized impurity mediated recombination. Deduced activation energies Ea assocd. with ionization are found to increase markedly from the room-temp. tetragonal (Ea ≈ 20 meV) to the higher-temp. cubic (Ea ≈ 200 meV) phase adopted above 310 K. Conversely, the bimol. rate const. decreases with rising temp. as charge-carrier mobility declines, while the Auger rate const. is highly phase specific, suggesting a strong dependence on electronic band structure. The charge-carrier diffusion length gradually decreases with rising temp. from about 3 μm at -93 °C to 1.2 μm at 67 °C but remains well above the optical absorption depth in the visible spectrum. These results demonstrate that there are no fundamental obstacles to the operation of cells based on CH3NH3PbI3 under typical field conditions.
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  13. 13
    Yang, Y.; Ostrowski, D. P.; France, R. M.; Zhu, K.; van de Lagemaat, J.; Luther, J. M.; Beard, M. C. Observation of a Hot-Phonon Bottleneck in Lead-Iodide Perovskites. Nat. Photonics 2016, 10, 53– 59,  DOI: 10.1038/nphoton.2015.213
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    13
    Observation of a hot-phonon bottleneck in lead-iodide perovskites
    Yang, Ye; Ostrowski, David P.; France, Ryan M.; Zhu, Kai; van de Lagemaat, Jao; Luther, Joseph M.; Beard, Matthew C.
    Nature Photonics (2016), 10 (1), 53-59CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)
    We study the carrier dynamics in planar Me ammonium lead iodide perovskite films using broadband transient absorption spectroscopy. We show that the sharp optical absorption onset is due to an exciton transition that is inhomogeneously broadened with a binding energy of 9 meV. We fully characterize the transient absorption spectrum by free-carrier-induced bleaching of the exciton transition, quasi-Fermi energy, carrier temp. and bandgap renormalization const. The photo-induced carrier temp. is extd. from the transient absorption spectra and monitored as a function of delay time for different excitation wavelengths and photon fluences. We find an efficient hot-phonon bottleneck that slows down cooling of hot carriers by three to four orders of magnitude in time above a crit. injection carrier d. of ∼5 × 1017 cm-3. Compared with mol. beam epitaxially grown GaAs, the crit. d. is an order of magnitude lower and the relaxation time is approx. three orders of magnitude longer.
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  14. 14
    Price, M. B.; Butkus, J.; Jellicoe, T. C.; Sadhanala, A.; Briane, A.; Halpert, J. E.; Broch, K.; Hodgkiss, J. M.; Friend, R. H.; Deschler, F. Hot-Carrier Cooling and Photoinduced Refractive Index Changes in Organic-Inorganic Lead Halide. Nat. Commun. 2015, 6, 8420,  DOI: 10.1038/ncomms9420
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    14
    Hot-carrier cooling and photoinduced refractive index changes in organic-inorganic lead halide perovskites
    Price, Michael B.; Butkus, Justinas; Jellicoe, Tom C.; Sadhanala, Aditya; Briane, Anouk; Halpert, Jonathan E.; Broch, Katharina; Hodgkiss, Justin M.; Friend, Richard H.; Deschler, Felix
    Nature Communications (2015), 6 (), 8420CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Metal-halide perovskites are at the frontier of optoelectronic research due to soln. processability and excellent semiconductor properties. Here we use transient absorption spectroscopy to study hot-carrier distributions in CH3NH3PbI3 and quantify key semiconductor parameters. Above bandgap, non-resonant excitation creates quasi-thermalized carrier distributions within 100 fs. During carrier cooling, a sub-bandgap transient absorption signal arises at ∼1.6 eV, which is explained by the interplay of bandgap renormalization and hot-carrier distributions. At higher excitation densities, a 'phonon bottleneck' substantially slows carrier cooling. This effect indicates a low contribution from inelastic carrier-impurity or phonon-impurity scattering in these polycryst. materials, which supports high charge-carrier mobilities. Photoinduced reflectivity changes distort the shape of transient absorption spectra and must be included to ext. phys. consts. Using a simple band-filling model that accounts for these changes, we det. a small effective mass of mr=0.14 mo, which agrees with band structure calcns. and high photovoltaic performance.
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  15. 15
    Herz, L. M. Charge-Carrier Dynamics in Organic - Inorganic Metal Halide Perovskites. Annu. Rev. Phys. Chem. 2016, 67, 65– 89,  DOI: 10.1146/annurev-physchem-040215-112222
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    15
    Charge-Carrier Dynamics in Organic-Inorganic Metal Halide Perovskites
    Herz, Laura M.
    Annual Review of Physical Chemistry (2016), 67 (), 65-89CODEN: ARPLAP; ISSN:0066-426X. (Annual Reviews)
    Hybrid org.-inorg. metal halide perovskites have recently emerged as exciting new light-harvesting and charge-transporting materials for efficient photovoltaic devices. Yet knowledge of the nature of the photogenerated excitations and their subsequent dynamics is only just emerging. This article reviews the current state of the field, focusing first on a description of the crystal and electronic band structure that give rise to the strong optical transitions that enable light harvesting. An overview is presented of the numerous exptl. approaches toward detg. values for exciton binding energies, which appear to be small (a few milli-eV to a few tens of milli-eV) and depend significantly on temp. because of assocd. changes in the dielec. function. Exptl. evidence for charge-carrier relaxation dynamics within the first few picoseconds after excitation is discussed in terms of thermalization, cooling, and many-body effects. Charge-carrier recombination mechanisms are reviewed, encompassing trap-assisted nonradiative recombination that is highly specific to processing conditions, radiative bimol. (electron-hole) recombination, and nonradiative many-body (Auger) mechanisms.
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  16. 16
    Tamming, R. R.; Butkus, J.; Price, M. B.; Vashishtha, P.; Prasad, S. K. K.; Halpert, J. E.; Chen, K.; Hodgkiss, J. M. Ultrafast Spectrally Resolved Photoinduced Complex Refractive Index Changes in CsPbX3 Perovskites. ACS Photonics 2019, 6, 345– 350,  DOI: 10.1021/acsphotonics.9b00091
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    16
    Ultrafast Spectrally Resolved Photoinduced Complex Refractive Index Changes in CsPbBr3 Perovskites
    Tamming, Ronnie R.; Butkus, Justinas; Price, Michael B.; Vashishtha, Parth; Prasad, Shyamal K. K.; Halpert, Jonathan E.; Chen, Kai; Hodgkiss, Justin M.
    ACS Photonics (2019), 6 (2), 345-350CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    The exceptional optoelectronic properties of metal halide perovskites have been illuminated by extensive spectroscopic studies. Recent measurements suggest strong photoinduced refractive index changes in these materials, which influence their functionality and obscure access to photoinduced extinction spectra from transient absorption spectroscopy, but such photorefractive effects are difficult to measure and model. Here, we use white light pulse interferometry-an exptl. straightforward adaptation of transient absorption spectroscopy-to directly probe photoinduced refractive index changes in CsPbBr3 films and nanocrystals on ultrafast time scales. Strong photoinduced refractive index changes are spectrally resolved and used to access extinction spectra, and these intrinsic optical parameters are then used to directly resolve more accurate photoexcited carrier temps. and bandgap renormalization, resolving ambiguities in the present literature. As well as understanding the intrinsic photoresponse of semiconductors, quantifying photoinduced refractive effects will be valuable for designing photonic devices including switches, lasers, and concg. photovoltaics.
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  17. 17
    Palmieri, T.; Baldini, E.; Steinhoff, A.; Akrap, A.; Kollár, M.; Horváth, E.; Forró, L.; Jahnke, F.; Chergui, M. Mahan Excitons in Room-Temperature Methylammonium Lead Bromide Perovskites. Nat. Commun. 2020, 11, 850,  DOI: 10.1038/s41467-020-14683-5
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    17
    Mahan excitons in room-temperature methylammonium lead bromide perovskites
    Palmieri, Tania; Baldini, Edoardo; Steinhoff, Alexander; Akrap, Ana; Kollar, Marton; Horvath, Endre; Forro, Laszlo; Jahnke, Frank; Chergui, Majed
    Nature Communications (2020), 11 (1), 850CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Abstr.: In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temp. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calcns. to reveal that org.-inorg. lead-bromide perovskites host Mahan excitons at room temp. Persistence of the Wannier exciton peak and the enhancement of the above-bandgap absorption are obsd. at all achievable photoexcitation densities, well above the Mott d. This is supported by the soln. of the semiconductor Bloch equations, which confirms that no sharp transition between the insulating and conductive phase occurs. Our results demonstrate the robustness of the bound states in a regime where exciton dissocn. is otherwise expected, and offer promising perspectives in fundamental physics and in room-temp. applications involving high densities of charge carriers.
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  18. 18
    Gholipour, B.; Adamo, G.; Cortecchia, D.; Krishnamoorthy, H. N. S.; Birowosuto, M. D.; Zheludev, N. I.; Soci, C. Organometallic Perovskite Metasurfaces. Adv. Mater. 2017, 29, 1604268,  DOI: 10.1002/adma.201604268
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    Makarov, S. V.; Milichko, V.; Ushakova, E. V.; Omelyanovich, M.; Cerdan Pasaran, A.; Haroldson, R.; Balachandran, B.; Wang, H.; Hu, W.; Kivshar, Y. S.; Zakhidov, A. A. Multifold Emission Enhancement in Nanoimprinted Hybrid Perovskite Metasurfaces. ACS Photonics 2017, 4, 728– 735,  DOI: 10.1021/acsphotonics.6b00940
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    19
    Multifold Emission Enhancement in Nanoimprinted Hybrid Perovskite Metasurfaces
    Makarov, Sergey V.; Milichko, Valentin; Ushakova, Elena V.; Omelyanovich, Mikhail; Cerdan Pasaran, Andrea; Haroldson, Ross; Balachandran, Balasubramaniam; Wang, Honglei; Hu, Walter; Kivshar, Yuri S.; Zakhidov, Anvar A.
    ACS Photonics (2017), 4 (4), 728-735CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    Recent developments in the physics of high-index resonant dielec. nanostructures suggest alternative mechanisms for subwavelength light control driven by Mie resonances with a strong magnetic response that can be employed for the design of novel optical metasurfaces. Here the authors demonstrate metasurfaces based on nanoimprinted perovskite films optimized by alloying the org. cation part of perovskites. Such metasurfaces can exhibit a significant enhancement of both linear and nonlinear luminescence (≤70 times) combined with advanced stability. The results suggest a cost-effective approach based on nanoimprint lithog. and combined with simple chem. reactions for creating a new generation of functional metasurfaces that may pave the way toward highly efficient planar optoelectronic metadevices.
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  20. 20
    Gao, Y.; Huang, C.; Hao, C.; Sun, S.; Zhang, L.; Zhang, C.; Duan, Z.; Wang, K.; Jin, Z.; Zhang, N.; Kildishev, A. V.; Qiu, C.-W.; Song, Q.; Xiao, S. Lead Halide Perovskite Nanostructures for Dynamic Color Display. ACS Nano 2018, 12, 8847– 8854,  DOI: 10.1021/acsnano.8b02425
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    20
    Lead Halide Perovskite Nanostructures for Dynamic Color Display
    Gao, Yisheng; Huang, Can; Hao, Chenglong; Sun, Shang; Zhang, Lei; Zhang, Chen; Duan, Zonghui; Wang, Kaiyang; Jin, Zhongwei; Zhang, Nan; Kildishev, Alexander V.; Qiu, Cheng-Wei; Song, Qinghai; Xiao, Shumin
    ACS Nano (2018), 12 (9), 8847-8854CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Nanoprint-based color display using either extrinsic structural colors or intrinsic emission colors is a rapidly emerging research field for high-d. information storage. Nevertheless, advanced applications, e.g., dynamic full-color display and secure information encryption, call for demanding requirements on in situ color change, nonvacuum operation, prompt response, and favorable reusability. By transplanting the concept of elec./chem. doping in the semiconductor industry, we demonstrate an in situ reversible color nanoprinting paradigm via photon doping, triggered by the interplay of structural colors and photon emission of lead halide perovskite gratings. It solves the aforementioned challenges at one go. By controlling the pumping light, the synergy between interlaced mechanisms enables color tuning over a large range with a transition time on the nanosecond scale(coating process) in a nonvacuum environment. Our design presents a promising realization of in situ dynamic color nanoprinting and will empower the advances in structural color and classified nanoprinting.
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  21. 21
    Berestennikov, A. S.; Voroshilov, P. M.; Makarov, S. V.; Kivshar, Y. S. Active Meta-Optics and Nanophotonics with Halide Perovskites. Appl. Phys. Rev. 2019, 6, 031307,  DOI: 10.1063/1.5107449
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    21
    Active meta-optics and nanophotonics with halide perovskites
    Berestennikov, Alexander S.; Voroshilov, Pavel M.; Makarov, Sergey V.; Kivshar, Yuri S.
    Applied Physics Reviews (2019), 6 (3), 031307/1-031307/20CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)
    A review. Meta-optics based on optically resonant all-dielec. structures is a rapidly developing research area driven by its potential applications for low-loss efficient metadevices. Active, light-emitting subwavelengh nanostructures and metasurfaces are of particular interest for meta-optics, as they offer unique opportunities for novel types of compact light sources and nanolasers. Recently, the study of "halide perovskites" has attracted enormous attention due to their exceptional optical and elec. properties. As a result, this family of materials can provide a prospective platform for modern nanophotonics and meta-optics, allowing us to overcome many obstacles assocd. with the use of conventional semiconductor materials. Here, we review the recent progress in the field of halide-perovskite meta-optics with the central focus on light-emitting nanoantennas and metasurfaces for the emerging field of "active metadevices. (c) 2019 American Institute of Physics.
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  22. 22
    Tiguntseva, E. Y.; Zograf, G. P.; Komissarenko, F. E.; Zuev, D. A.; Zakhidov, A. A.; Makarov, S. V.; Kivshar, Y. S. Light-Emitting Halide Perovskite Nanoantennas. Nano Lett. 2018, 18, 1185– 1190,  DOI: 10.1021/acs.nanolett.7b04727
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    Light-Emitting Halide Perovskite Nanoantennas
    Tiguntseva, E. Y.; Zograf, G. P.; Komissarenko, F. E.; Zuev, D. A.; Zakhidov, A. A.; Makarov, S. V.; Kivshar, Yuri. S.
    Nano Letters (2018), 18 (2), 1185-1190CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Nanoantennas made of high-index dielecs. with low losses in visible and IR frequency ranges have emerged as a novel platform for advanced nanophotonic devices. On the other hand, halide perovskites are known to possess high refractive index, and they support excitons at room temp. with high binding energies and quantum yield of luminescence that makes them very attractive for all-dielec. resonant nanophotonics. Here we employ halide perovskites to create light-emitting nanoantennas with enhanced photoluminescence due to the coupling of their excitons to dipolar and multipolar Mie resonances. We demonstrate that the halide perovskite nanoantennas can emit light in the range of 530-770 nm depending on their compn. We employ a simple technique based on laser ablation of thin films prepd. by wet-chem. methods as a novel cost-effective approach for the fabrication of resonant perovskite nanostructures.
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  23. 23
    Makarov, S.; Furasova, A.; Tiguntseva, E.; Hemmetter, A.; Berestennikov, A.; Pushkarev, A.; Zakhidov, A.; Kivshar, Y. Halide-Perovskite Resonant Nanophotonics. Adv. Opt. Mater. 2019, 7, 1800784,  DOI: 10.1002/adom.201800784
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    There is no corresponding record for this reference.
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    Manjappa, M.; Srivastava, Y. K.; Solanki, A.; Kumar, A.; Sum, T. C.; Singh, R. Hybrid Lead Halide Perovskites for Ultrasensitive Photoactive Switching in Terahertz Metamaterial Devices. Adv. Mater. 2017, 29, 1605881,  DOI: 10.1002/adma.201605881
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    Chanana, A.; Liu, X.; Zhang, C.; Vardeny, Z. V.; Nahata, A. Ultrafast Frequency-Agile Terahertz Devices Using Methylammonium Lead Halide Perovskites. Sci. Adv. 2018, 4, eaar7353,  DOI: 10.1126/sciadv.aar7353
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    There is no corresponding record for this reference.
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    Huang, C.; Zhang, C.; Xiao, S.; Wang, Y.; Fan, Y.; Liu, Y.; Zhang, N.; Qu, G.; Ji, H.; Han, J.; Ge, L.; Kivshar, Y.; Song, Q. Ultrafast Control of Vortex Microlasers. Science 2020, 367, 1018– 1021,  DOI: 10.1126/science.aba4597
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    26
    Ultrafast control of vortex microlasers
    Huang, Can; Zhang, Chen; Xiao, Shumin; Wang, Yuhan; Fan, Yubin; Liu, Yilin; Zhang, Nan; Qu, Geyang; Ji, Hongjun; Han, Jiecai; Ge, Li; Kivshar, Yuri; Song, Qinghai
    Science (Washington, DC, United States) (2020), 367 (6481), 1018-1021CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
    The development of classical and quantum information-processing technol. calls for on-chip integrated sources of structured light. Although integrated vortex microlasers have been previously demonstrated, they remain static and possess relatively high lasing thresholds, making them unsuitable for high-speed optical communication and computing. We introduce perovskite-based vortex microlasers and demonstrate their application to ultrafast all-optical switching at room temp. By exploiting both mode symmetry and far-field properties, we reveal that the vortex beam lasing can be switched to linearly polarized beam lasing, or vice versa, with switching times of 1 to 1.5 ps and energy consumption that is orders of magnitude lower than in previously demonstrated all-optical switching. Our results provide an approach that breaks the long-standing trade-off between low energy consumption and high-speed nanophotonics, introducing vortex microlasers that are switchable at terahertz frequencies.
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  27. 27
    Tiguntseva, E. Y.; Baranov, D. G.; Pushkarev, A. P.; Munkhbat, B.; Komissarenko, F.; Franckevicius, M.; Zakhidov, A. A.; Shegai, T.; Kivshar, Y. S.; Makarov, S. V. Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles. Nano Lett. 2018, 18, 5522– 5529,  DOI: 10.1021/acs.nanolett.8b01912
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    27
    Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles
    Tiguntseva, Ekaterina Y.; Baranov, Denis G.; Pushkarev, Anatoly P.; Munkhbat, Battulga; Komissarenko, Filipp; Franckevicius, Marius; Zakhidov, Anvar A.; Shegai, Timur; Kivshar, Yuri S.; Makarov, Sergey V.
    Nano Letters (2018), 18 (9), 5522-5529CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Halide perovskites are known to support excitons at room temps. with high quantum yield of luminescence that make them attractive for all-dielec. resonant nanophotonics and meta-optics. Here we report the observation of broadly tunable Fano resonances in halide perovskite nanoparticles originating from the coupling of excitons to the Mie resonances excited in the nanoparticles. Signatures of the photon-exciton ("hybrid") Fano resonances are obsd. in dark-field spectra of isolated nanoparticles, and also in the extinction spectra of aperiodic lattices of such nanoparticles. In the latter case, chem. tunability of the exciton resonance allows reversible tuning of the Fano resonance across the 100 nm bandwidth in the visible frequency range, providing a novel approach to control optical properties of perovskite nanostructures. The proposed method of chem. tuning paves the way to an efficient control of emission properties of on-chip-integrated light-emitting nanoantennas.
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  28. 28
    Shcherbakov, M. R.; Vabishchevich, P. P.; Shorokhov, A. S.; Chong, K. E.; Choi, D.-Y.; Staude, I.; Miroshnichenko, A. E.; Neshev, D. N.; Fedyanin, A. A.; Kivshar, Y. S. Ultrafast All-Optical Switching with Magnetic Resonances in Nonlinear Dielectric Nanostructures. Nano Lett. 2015, 15, 6985– 6990,  DOI: 10.1021/acs.nanolett.5b02989
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    Ultrafast All-Optical Switching with Magnetic Resonances in Nonlinear Dielectric Nanostructures
    Shcherbakov Maxim R; Vabishchevich Polina P; Shorokhov Alexander S; Fedyanin Andrey A; Chong Katie E; Choi Duk-Yong; Staude Isabelle; Miroshnichenko Andrey E; Neshev Dragomir N; Kivshar Yuri S
    Nano letters (2015), 15 (10), 6985-90 ISSN:.
    We demonstrate experimentally ultrafast all-optical switching in subwavelength nonlinear dielectric nanostructures exhibiting localized magnetic Mie resonances. We employ amorphous silicon nanodisks to achieve strong self-modulation of femtosecond pulses with a depth of 60% at picojoule-per-disk pump energies. In the pump-probe measurements, we reveal that switching in the nanodisks can be governed by pulse-limited 65 fs-long two-photon absorption being enhanced by a factor of 80 with respect to the unstructured silicon film. We also show that undesirable free-carrier effects can be suppressed by a proper spectral positioning of the magnetic resonance, making such a structure the fastest all-optical switch operating at the nanoscale.
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    Maragkou, M. Ultrafast Responses. Nat. Mater. 2015, 14, 1086,  DOI: 10.1038/nmat4467
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    Dielectric nanostructures Ultrafast responses
    Maragkou, Maria
    Nature Materials (2015), 14 (11), 1086CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    There is no expanded citation for this reference.
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    Soukoulis, C. M.; Wegener, M. Past Achievements and Future Challenges in the Development of Three-Dimensional Photonic Metamaterials. Nat. Photonics 2011, 5, 523– 530,  DOI: 10.1038/nphoton.2011.154
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    Past achievements and future challenges in the development of three-dimensional photonic metamaterials
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    Nature Photonics (2011), 5 (9), 523-530CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)
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    In band-like semiconductors, charge carriers form a thermal energy distribution rapidly after optical excitation. In hybrid perovskites, the cooling of such thermal carrier distributions occurs on timescales of about 300 fs via carrier-phonon scattering. However, the initial build-up of the thermal distribution proved difficult to resolve with pump-probe techniques due to the requirement of high resolution, both in time and pump energy. Here, we use two-dimensional electronic spectroscopy with sub-10 fs resolution to directly observe the carrier interactions that lead to a thermal carrier distribution. We find that thermalization occurs dominantly via carrier-carrier scattering under the investigated fluences and report the dependence of carrier scattering rates on excess energy and carrier density. We extract characteristic carrier thermalization times from below 10 to 85 fs. These values allow for mobilities of 500 cm(2) V(-1) s(-1) at carrier densities lower than 2 × 10(19) cm(-3) and limit the time for carrier extraction in hot carrier solar cells.Carrier-carrier scattering rates determine the fundamental limits of carrier transport and electronic coherence. Using two-dimensional electronic spectroscopy with sub-10 fs resolution, Richter and Branchi et al. extract carrier thermalization times of 10 to 85 fs in hybrid perovskites.
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    Science (Washington, DC, United States) (2019), 365 (6451), 374-377CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    The capability of on-chip wavefront modulation has the potential to revolutionize many optical device technologies. However, the realization of power-efficient phase-gradient metasurfaces that offer full-phase modulation (0 to 2π) and high operation speeds remains elusive. We present an approach to continuously steer light that is based on creating a virtual frequency-gradient metasurface by combining a passive metasurface with an advanced frequency-comb source. Spatiotemporal redirection of light naturally occurs as optical phase-fronts reorient at a speed controlled by the frequency gradient across the virtual metasurface. An exptl. realization of laser beam steering with a continuously changing steering angle is demonstrated with a single metasurface over an angle of 25° in just 8 ps. This work can support integrated-on-chip solns. for spatiotemporal optical control, directly affecting emerging applications such as solid-state light detection and ranging (LIDAR), three-dimensional imaging, and augmented or virtual systems.
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    Optical metasurfaces are regular quasi-planar nanopatterns that can apply diverse spatial and spectral transformations to light waves. However, metasurfaces are no longer adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. We experimentally realise an ultrafast tunable metasurface consisting of subwavelength gallium arsenide nanoparticles supporting Mie-type resonances in the near infrared. Using transient reflectance spectroscopy, we demonstrate a picosecond-scale absolute reflectance modulation of up to 0.35 at the magnetic dipole resonance of the metasurfaces and a spectral shift of the resonance by 30 nm, both achieved at unprecedentedly low pump fluences of less than 400 μJ cm(-2). Our findings thereby enable a versatile tool for ultrafast and efficient control of light using light.Metasurfaces are not adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. Here, Shcherbakov et al. realise an ultrafast tunable metasurface with picosecond-scale large absolute reflectance modulation at low pump fluences.
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  • Abstract

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    Figure 1

    Figure 1. Structural and optical properties of hybrid perovskites nanoparticles. (a) Concept of the pump–probe experiment on HP nanoparticles. The right panel displays a scanning electron microscopy image of the 300 nm NPs sample. (b, c) Size distribution of CsPbBr3 nanoparticles with average diameter ϕ̅ = 150 nm (b, green bars) and 300 nm (c, purple bars). The size distribution has been calculated by analysis of the scanning electron microscopy images. The solid line represents the normal fit to the experimental distributions. For both samples, the standard deviation of the normal distribution is 10% of the average size. (d) Experimental measured extinction spectra of the CsPbBr3 nanoparticles with an average diameter of 150 nm (green markers) and 300 nm (pink markers). In the spectral region investigated in the time-resolved experiment, the extinction data have been fitted (solid black lines) with eq 1. For the 150 nm sample, we estimated q=(−18.1 ± 0.2) and Γ = (0.107 ± 0.003) eV, while q = (−0.41 ± 0.01) and Γ = (0.123 ± 0.005) eV for the 300 nm sample. The right panel sketches the energy overlap between the discrete excitonic level (yellow line) and the continuum of states (square), which gives rise to the Fano low-q resonance for 300 nm particles. (e) Schematics of the electron dynamics triggered by the pulsed photoexcitation (blue arrow): the initial creation of the nonthermal electron–hole distributions within the valence (VB) and conduction bands (CB) leads to the renormalization of the equilibrium gap, Eg0, which reduces to Eg = Eg0 – δEgBGR. At later times, the interactions drive the formation of a long-lived quasi-thermal distribution at the gap edges and a consequent increase of the effective optical band gap, Eg = Eg0 + δEgBF.

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    Figure 2

    Figure 2. Ultrafast dynamics of the nanoparticle optical properties. Energy- and time-resolved differential transmission maps for 150 nm (a) and 300 nm (b) CsPbBr3 nanoparticles pumped at 2.9 eV, with an incident fluence of 54 μJ/cm2. The top panels display δT/T(ℏω) spectra at fixed probe delays (200 fs, dashed line; 2 ps solid line) for 150 and 300 nm nanoparticles, respectively. For graphical reasons, the data reported in panel b are magnified by a factor of 4.

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    Figure 3

    Figure 3. Numerical simulations. Differential transmittivity spectrum, δT/T(NP)(ℏω), calculated for individual (a) 150 nm and (b) 300 nm nanoparticles. The separate contributions of the bandgap renormalization (BGR), band filling (BF), and Drude effects to the total signal are calculated by assuming the photoinjected free carrier density nfc ≃ 1.2 × 1020 cm–3, for both nanoparticle sizes.

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    Figure 4

    Figure 4. Disentangling band filling and bandgap renormalization. Differential time traces at specific photon energies are reported for NP sizes matching the Fano high-q resonance (150 nm, panel a) and low-q resonance conditions (300 nm, panel b). The black solid lines represent the single exponential fitting to the time traces taken at ℏω = 2.23 eV (black dots). The red solid lines represent the multiexponential fitting to the time traces taken at ℏω = 2.3 eV (red dots). Panel c displays the BGR signal obtained by subtracting the BF dynamics from the time traces taken at ℏω = 2.3 eV and shown in panels a and b. The solid lines represent the exponential fitting to the BGR dynamics.

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    Figure 5

    Figure 5. Electric field enhancement. Electric field enhancement on the plane of the vertical cross-section of the nanoparticle. The panels show the equilibrium (a, c) and out-of-equilibrium (b, d) FE for a single CsPbBr3 NP with diameters of 150 (a, b) and 300 nm (c, d). The incident monochromatic wave centered at 2.38 eV propagates from the top to the bottom along the Z axis. The black arrows represent the electric field vector E⃗ in the NP volume. The red arrows represent the Poynting vector S⃗ outside the NP surface. The dashed white line represents the substrate surface. The scale bar is 100 nm.

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  • References

    This article references 46 other publications.

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      Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut
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      The optical and structural studies of mixed halide perovskite (MAPbBr3-xIx) single crystals are reported. Mixed halide perovskite single crystals showed strong light soaking phenomena with light illumination conditions that were correlated to the trapping and detrapping events from defect sites. By systematic study with optical anal., the pseudocubic phase of mixed halide perovskites generates light soaking phenomena. Photoinduced changes are related to the existence of multiple phases or halide migrations.
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      The authors find that methylammonium lead trihalide perovskites are particularly well-suited as light absorbers and charge transporters in photovoltaic cells because they allow for an unexpected combination of both low charge recombination rates and high charge-carrier mobilities. The authors establish lower bounds of-10 cm2 V-1 s'1 for the high-frequency charge mobility, which is remarkably high for a soln.-processed material. The planar heterojunction photovoltaic cells may only be achieved because the ratio of bimol. charge recombination rate to charge mobility is over four orders of magnitude lower than that predicted from Langevin theory. Such effects are likely to arise from spatial sepn. of opposite charge carriers within the metal-halide structure or across a cryst. domain. Modeling and tuning recombination channels, e.g. through halide and metal substitutions, or crystallite size, will hold the clue to raising material performance.
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      8
      Electron-hole diffusion lengths > 175 μm in solution-grown CH3NH3PbI3 single crystals
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      Long, balanced electron and hole diffusion lengths greater than 100 nm in the polycryst. organolead trihalide compd. CH3NH3PbI3 are crit. for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a soln.-growth method can exceed 175 μm under 1 sun (100 mW cm-2) illumination and exceed 3 mm under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-mm-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycryst. thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.
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      Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. High-Performance Photovoltaic Perovskite Layers Fabricated through Intramolecular Exchange. Science 2015, 348, 1234– 1237,  DOI: 10.1126/science.aaa9272
      9
      High-performance photovoltaic perovskite layers fabricated through intramolecular exchange
      Yang, Woon Seok; Noh, Jun Hong; Jeon, Nam Joong; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il
      Science (Washington, DC, United States) (2015), 348 (6240), 1234-1237CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). An approach is reported for depositing high-quality FAPbI3 films, involving FAPbI3 crystn. by the direct intramol. exchange of dimethylsulfoxide (DMSO) mols. intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallog. orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepd. by this technique, the FAPbI3-based PSCs are fabricated with max. power conversion efficiency greater than 20%.
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      Manser, J. S.; Kamat, P. V. Band Filling with Free Charge Carriers in Organometal Halide Perovskites. Nat. Photonics 2014, 8, 737,  DOI: 10.1038/nphoton.2014.171
      10
      Band filling with free charge carriers in organometal halide perovskites
      Manser, Joseph S.; Kamat, Prashant V.
      Nature Photonics (2014), 8 (9), 737-743CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)
      The unique and promising properties of semiconducting organometal halide perovskites have brought these materials to the forefront of solar energy research. Here, we present new insights into the excited-state properties of CH3NH3PbI3 thin films through femtosecond transient absorption spectroscopy measurements. The photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via recombination of free electrons and holes. Addnl., charge accumulation in the perovskite films leads to an increase in the intrinsic bandgap that follows the Burstein-Moss band filling model. Both the recombination mechanism and the band-edge shift are studied as a function of the photogenerated carrier d. and serve to elucidate the behavior of charge carriers in hybrid perovskites. These results offer insights into the intrinsic photophysics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications.
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    11. 11
      Sheng, C.; Zhang, C.; Zhai, Y.; Mielczarek, K.; Wang, W.; Ma, W.; Zakhidov, A.; Vardeny, Z. V. Exciton versus Free Carrier Photogeneration in Organometal Trihalide Perovskites Probed by Broadband Ultrafast Polarization Memory Dynamics. Phys. Rev. Lett. 2015, 114, 116601,  DOI: 10.1103/PhysRevLett.114.116601
      11
      Exciton versus free carrier photogeneration in organometal trihalide perovskites probed by broadband ultrafast polarization memory dynamics
      Sheng, ChuanXiang; Zhang, Chuang; Zhai, Yaxin; Mielczarek, Kamil; Wang, Weiwei; Ma, Wanli; Zakhidov, Anvar; Vardeny, Z. Valy
      Physical Review Letters (2015), 114 (11), 116601/1-116601/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      We studied the ultrafast transient response of photoexcitations in two hybrid org.-inorg. perovskite films used for high efficiency photovoltaic cells, namely, CH3NH3PbI3 and CH3NH3PbI1.1Br1.9 using polarized broadband pump-probe spectroscopy in the spectral range of 0.3-2.7 eV with 300 fs time resoln. For CH3NH3PbI3 with above-gap excitation we found both photogenerated carriers and excitons, but only carriers are photogenerated with below-gap excitation. In contrast, mainly excitons are photogenerated in CH3NH3PbI1.1Br1.9. Surprisingly, we also discovered in CH3NH3PbI3, but not in CH3NH3PbI1.1Br1.9, transient photoinduced polarization memory for both excitons and photocarriers, which is also reflected in the steady state photoluminescence. From the polarization memory dynamics we obtained the excitons diffusion const. in CH3NH3PbI3, D ≈ 0.01 cm2 s-1.
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    12. 12
      Milot, R. L.; Eperon, G. E.; Snaith, H. J.; Johnston, M. B.; Herz, L. M. Temperature-Dependent Charge-Carrier Dynamics in CH3NH3PbI3 Perovskite Thin Films. Adv. Funct. Mater. 2015, 25, 6218– 6227,  DOI: 10.1002/adfm.201502340
      12
      Temperature-Dependent Charge-Carrier Dynamics in CH3NH3PbI3 Perovskite Thin Films
      Milot, Rebecca L.; Eperon, Giles E.; Snaith, Henry J.; Johnston, Michael B.; Herz, Laura M.
      Advanced Functional Materials (2015), 25 (39), 6218-6227CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The photoluminescence, transmittance, charge-carrier recombination dynamics, mobility, and diffusion length of CH3NH3PbI3 are investigated in the temp. range from 8 to 370 K. Profound changes in the optoelectronic properties of this prototypical photovoltaic material are obsd. across the two structural phase transitions occurring at 160 and 310 K. Drude-like terahertz photocond. spectra at all temps. above 80 K suggest that charge localization effects are absent in this range. The monomol. charge-carrier recombination rate generally increases with rising temp., indicating a mechanism dominated by ionized impurity mediated recombination. Deduced activation energies Ea assocd. with ionization are found to increase markedly from the room-temp. tetragonal (Ea ≈ 20 meV) to the higher-temp. cubic (Ea ≈ 200 meV) phase adopted above 310 K. Conversely, the bimol. rate const. decreases with rising temp. as charge-carrier mobility declines, while the Auger rate const. is highly phase specific, suggesting a strong dependence on electronic band structure. The charge-carrier diffusion length gradually decreases with rising temp. from about 3 μm at -93 °C to 1.2 μm at 67 °C but remains well above the optical absorption depth in the visible spectrum. These results demonstrate that there are no fundamental obstacles to the operation of cells based on CH3NH3PbI3 under typical field conditions.
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    13. 13
      Yang, Y.; Ostrowski, D. P.; France, R. M.; Zhu, K.; van de Lagemaat, J.; Luther, J. M.; Beard, M. C. Observation of a Hot-Phonon Bottleneck in Lead-Iodide Perovskites. Nat. Photonics 2016, 10, 53– 59,  DOI: 10.1038/nphoton.2015.213
      13
      Observation of a hot-phonon bottleneck in lead-iodide perovskites
      Yang, Ye; Ostrowski, David P.; France, Ryan M.; Zhu, Kai; van de Lagemaat, Jao; Luther, Joseph M.; Beard, Matthew C.
      Nature Photonics (2016), 10 (1), 53-59CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)
      We study the carrier dynamics in planar Me ammonium lead iodide perovskite films using broadband transient absorption spectroscopy. We show that the sharp optical absorption onset is due to an exciton transition that is inhomogeneously broadened with a binding energy of 9 meV. We fully characterize the transient absorption spectrum by free-carrier-induced bleaching of the exciton transition, quasi-Fermi energy, carrier temp. and bandgap renormalization const. The photo-induced carrier temp. is extd. from the transient absorption spectra and monitored as a function of delay time for different excitation wavelengths and photon fluences. We find an efficient hot-phonon bottleneck that slows down cooling of hot carriers by three to four orders of magnitude in time above a crit. injection carrier d. of ∼5 × 1017 cm-3. Compared with mol. beam epitaxially grown GaAs, the crit. d. is an order of magnitude lower and the relaxation time is approx. three orders of magnitude longer.
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    14. 14
      Price, M. B.; Butkus, J.; Jellicoe, T. C.; Sadhanala, A.; Briane, A.; Halpert, J. E.; Broch, K.; Hodgkiss, J. M.; Friend, R. H.; Deschler, F. Hot-Carrier Cooling and Photoinduced Refractive Index Changes in Organic-Inorganic Lead Halide. Nat. Commun. 2015, 6, 8420,  DOI: 10.1038/ncomms9420
      14
      Hot-carrier cooling and photoinduced refractive index changes in organic-inorganic lead halide perovskites
      Price, Michael B.; Butkus, Justinas; Jellicoe, Tom C.; Sadhanala, Aditya; Briane, Anouk; Halpert, Jonathan E.; Broch, Katharina; Hodgkiss, Justin M.; Friend, Richard H.; Deschler, Felix
      Nature Communications (2015), 6 (), 8420CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Metal-halide perovskites are at the frontier of optoelectronic research due to soln. processability and excellent semiconductor properties. Here we use transient absorption spectroscopy to study hot-carrier distributions in CH3NH3PbI3 and quantify key semiconductor parameters. Above bandgap, non-resonant excitation creates quasi-thermalized carrier distributions within 100 fs. During carrier cooling, a sub-bandgap transient absorption signal arises at ∼1.6 eV, which is explained by the interplay of bandgap renormalization and hot-carrier distributions. At higher excitation densities, a 'phonon bottleneck' substantially slows carrier cooling. This effect indicates a low contribution from inelastic carrier-impurity or phonon-impurity scattering in these polycryst. materials, which supports high charge-carrier mobilities. Photoinduced reflectivity changes distort the shape of transient absorption spectra and must be included to ext. phys. consts. Using a simple band-filling model that accounts for these changes, we det. a small effective mass of mr=0.14 mo, which agrees with band structure calcns. and high photovoltaic performance.
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    15. 15
      Herz, L. M. Charge-Carrier Dynamics in Organic - Inorganic Metal Halide Perovskites. Annu. Rev. Phys. Chem. 2016, 67, 65– 89,  DOI: 10.1146/annurev-physchem-040215-112222
      15
      Charge-Carrier Dynamics in Organic-Inorganic Metal Halide Perovskites
      Herz, Laura M.
      Annual Review of Physical Chemistry (2016), 67 (), 65-89CODEN: ARPLAP; ISSN:0066-426X. (Annual Reviews)
      Hybrid org.-inorg. metal halide perovskites have recently emerged as exciting new light-harvesting and charge-transporting materials for efficient photovoltaic devices. Yet knowledge of the nature of the photogenerated excitations and their subsequent dynamics is only just emerging. This article reviews the current state of the field, focusing first on a description of the crystal and electronic band structure that give rise to the strong optical transitions that enable light harvesting. An overview is presented of the numerous exptl. approaches toward detg. values for exciton binding energies, which appear to be small (a few milli-eV to a few tens of milli-eV) and depend significantly on temp. because of assocd. changes in the dielec. function. Exptl. evidence for charge-carrier relaxation dynamics within the first few picoseconds after excitation is discussed in terms of thermalization, cooling, and many-body effects. Charge-carrier recombination mechanisms are reviewed, encompassing trap-assisted nonradiative recombination that is highly specific to processing conditions, radiative bimol. (electron-hole) recombination, and nonradiative many-body (Auger) mechanisms.
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    16. 16
      Tamming, R. R.; Butkus, J.; Price, M. B.; Vashishtha, P.; Prasad, S. K. K.; Halpert, J. E.; Chen, K.; Hodgkiss, J. M. Ultrafast Spectrally Resolved Photoinduced Complex Refractive Index Changes in CsPbX3 Perovskites. ACS Photonics 2019, 6, 345– 350,  DOI: 10.1021/acsphotonics.9b00091
      16
      Ultrafast Spectrally Resolved Photoinduced Complex Refractive Index Changes in CsPbBr3 Perovskites
      Tamming, Ronnie R.; Butkus, Justinas; Price, Michael B.; Vashishtha, Parth; Prasad, Shyamal K. K.; Halpert, Jonathan E.; Chen, Kai; Hodgkiss, Justin M.
      ACS Photonics (2019), 6 (2), 345-350CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      The exceptional optoelectronic properties of metal halide perovskites have been illuminated by extensive spectroscopic studies. Recent measurements suggest strong photoinduced refractive index changes in these materials, which influence their functionality and obscure access to photoinduced extinction spectra from transient absorption spectroscopy, but such photorefractive effects are difficult to measure and model. Here, we use white light pulse interferometry-an exptl. straightforward adaptation of transient absorption spectroscopy-to directly probe photoinduced refractive index changes in CsPbBr3 films and nanocrystals on ultrafast time scales. Strong photoinduced refractive index changes are spectrally resolved and used to access extinction spectra, and these intrinsic optical parameters are then used to directly resolve more accurate photoexcited carrier temps. and bandgap renormalization, resolving ambiguities in the present literature. As well as understanding the intrinsic photoresponse of semiconductors, quantifying photoinduced refractive effects will be valuable for designing photonic devices including switches, lasers, and concg. photovoltaics.
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    17. 17
      Palmieri, T.; Baldini, E.; Steinhoff, A.; Akrap, A.; Kollár, M.; Horváth, E.; Forró, L.; Jahnke, F.; Chergui, M. Mahan Excitons in Room-Temperature Methylammonium Lead Bromide Perovskites. Nat. Commun. 2020, 11, 850,  DOI: 10.1038/s41467-020-14683-5
      17
      Mahan excitons in room-temperature methylammonium lead bromide perovskites
      Palmieri, Tania; Baldini, Edoardo; Steinhoff, Alexander; Akrap, Ana; Kollar, Marton; Horvath, Endre; Forro, Laszlo; Jahnke, Frank; Chergui, Majed
      Nature Communications (2020), 11 (1), 850CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Abstr.: In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temp. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calcns. to reveal that org.-inorg. lead-bromide perovskites host Mahan excitons at room temp. Persistence of the Wannier exciton peak and the enhancement of the above-bandgap absorption are obsd. at all achievable photoexcitation densities, well above the Mott d. This is supported by the soln. of the semiconductor Bloch equations, which confirms that no sharp transition between the insulating and conductive phase occurs. Our results demonstrate the robustness of the bound states in a regime where exciton dissocn. is otherwise expected, and offer promising perspectives in fundamental physics and in room-temp. applications involving high densities of charge carriers.
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    18. 18
      Gholipour, B.; Adamo, G.; Cortecchia, D.; Krishnamoorthy, H. N. S.; Birowosuto, M. D.; Zheludev, N. I.; Soci, C. Organometallic Perovskite Metasurfaces. Adv. Mater. 2017, 29, 1604268,  DOI: 10.1002/adma.201604268
      There is no corresponding record for this reference.
    19. 19
      Makarov, S. V.; Milichko, V.; Ushakova, E. V.; Omelyanovich, M.; Cerdan Pasaran, A.; Haroldson, R.; Balachandran, B.; Wang, H.; Hu, W.; Kivshar, Y. S.; Zakhidov, A. A. Multifold Emission Enhancement in Nanoimprinted Hybrid Perovskite Metasurfaces. ACS Photonics 2017, 4, 728– 735,  DOI: 10.1021/acsphotonics.6b00940
      19
      Multifold Emission Enhancement in Nanoimprinted Hybrid Perovskite Metasurfaces
      Makarov, Sergey V.; Milichko, Valentin; Ushakova, Elena V.; Omelyanovich, Mikhail; Cerdan Pasaran, Andrea; Haroldson, Ross; Balachandran, Balasubramaniam; Wang, Honglei; Hu, Walter; Kivshar, Yuri S.; Zakhidov, Anvar A.
      ACS Photonics (2017), 4 (4), 728-735CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      Recent developments in the physics of high-index resonant dielec. nanostructures suggest alternative mechanisms for subwavelength light control driven by Mie resonances with a strong magnetic response that can be employed for the design of novel optical metasurfaces. Here the authors demonstrate metasurfaces based on nanoimprinted perovskite films optimized by alloying the org. cation part of perovskites. Such metasurfaces can exhibit a significant enhancement of both linear and nonlinear luminescence (≤70 times) combined with advanced stability. The results suggest a cost-effective approach based on nanoimprint lithog. and combined with simple chem. reactions for creating a new generation of functional metasurfaces that may pave the way toward highly efficient planar optoelectronic metadevices.
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    20. 20
      Gao, Y.; Huang, C.; Hao, C.; Sun, S.; Zhang, L.; Zhang, C.; Duan, Z.; Wang, K.; Jin, Z.; Zhang, N.; Kildishev, A. V.; Qiu, C.-W.; Song, Q.; Xiao, S. Lead Halide Perovskite Nanostructures for Dynamic Color Display. ACS Nano 2018, 12, 8847– 8854,  DOI: 10.1021/acsnano.8b02425
      20
      Lead Halide Perovskite Nanostructures for Dynamic Color Display
      Gao, Yisheng; Huang, Can; Hao, Chenglong; Sun, Shang; Zhang, Lei; Zhang, Chen; Duan, Zonghui; Wang, Kaiyang; Jin, Zhongwei; Zhang, Nan; Kildishev, Alexander V.; Qiu, Cheng-Wei; Song, Qinghai; Xiao, Shumin
      ACS Nano (2018), 12 (9), 8847-8854CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Nanoprint-based color display using either extrinsic structural colors or intrinsic emission colors is a rapidly emerging research field for high-d. information storage. Nevertheless, advanced applications, e.g., dynamic full-color display and secure information encryption, call for demanding requirements on in situ color change, nonvacuum operation, prompt response, and favorable reusability. By transplanting the concept of elec./chem. doping in the semiconductor industry, we demonstrate an in situ reversible color nanoprinting paradigm via photon doping, triggered by the interplay of structural colors and photon emission of lead halide perovskite gratings. It solves the aforementioned challenges at one go. By controlling the pumping light, the synergy between interlaced mechanisms enables color tuning over a large range with a transition time on the nanosecond scale(coating process) in a nonvacuum environment. Our design presents a promising realization of in situ dynamic color nanoprinting and will empower the advances in structural color and classified nanoprinting.
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    21. 21
      Berestennikov, A. S.; Voroshilov, P. M.; Makarov, S. V.; Kivshar, Y. S. Active Meta-Optics and Nanophotonics with Halide Perovskites. Appl. Phys. Rev. 2019, 6, 031307,  DOI: 10.1063/1.5107449
      21
      Active meta-optics and nanophotonics with halide perovskites
      Berestennikov, Alexander S.; Voroshilov, Pavel M.; Makarov, Sergey V.; Kivshar, Yuri S.
      Applied Physics Reviews (2019), 6 (3), 031307/1-031307/20CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)
      A review. Meta-optics based on optically resonant all-dielec. structures is a rapidly developing research area driven by its potential applications for low-loss efficient metadevices. Active, light-emitting subwavelengh nanostructures and metasurfaces are of particular interest for meta-optics, as they offer unique opportunities for novel types of compact light sources and nanolasers. Recently, the study of "halide perovskites" has attracted enormous attention due to their exceptional optical and elec. properties. As a result, this family of materials can provide a prospective platform for modern nanophotonics and meta-optics, allowing us to overcome many obstacles assocd. with the use of conventional semiconductor materials. Here, we review the recent progress in the field of halide-perovskite meta-optics with the central focus on light-emitting nanoantennas and metasurfaces for the emerging field of "active metadevices. (c) 2019 American Institute of Physics.
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    22. 22
      Tiguntseva, E. Y.; Zograf, G. P.; Komissarenko, F. E.; Zuev, D. A.; Zakhidov, A. A.; Makarov, S. V.; Kivshar, Y. S. Light-Emitting Halide Perovskite Nanoantennas. Nano Lett. 2018, 18, 1185– 1190,  DOI: 10.1021/acs.nanolett.7b04727
      22
      Light-Emitting Halide Perovskite Nanoantennas
      Tiguntseva, E. Y.; Zograf, G. P.; Komissarenko, F. E.; Zuev, D. A.; Zakhidov, A. A.; Makarov, S. V.; Kivshar, Yuri. S.
      Nano Letters (2018), 18 (2), 1185-1190CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Nanoantennas made of high-index dielecs. with low losses in visible and IR frequency ranges have emerged as a novel platform for advanced nanophotonic devices. On the other hand, halide perovskites are known to possess high refractive index, and they support excitons at room temp. with high binding energies and quantum yield of luminescence that makes them very attractive for all-dielec. resonant nanophotonics. Here we employ halide perovskites to create light-emitting nanoantennas with enhanced photoluminescence due to the coupling of their excitons to dipolar and multipolar Mie resonances. We demonstrate that the halide perovskite nanoantennas can emit light in the range of 530-770 nm depending on their compn. We employ a simple technique based on laser ablation of thin films prepd. by wet-chem. methods as a novel cost-effective approach for the fabrication of resonant perovskite nanostructures.
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    23. 23
      Makarov, S.; Furasova, A.; Tiguntseva, E.; Hemmetter, A.; Berestennikov, A.; Pushkarev, A.; Zakhidov, A.; Kivshar, Y. Halide-Perovskite Resonant Nanophotonics. Adv. Opt. Mater. 2019, 7, 1800784,  DOI: 10.1002/adom.201800784
      There is no corresponding record for this reference.
    24. 24
      Manjappa, M.; Srivastava, Y. K.; Solanki, A.; Kumar, A.; Sum, T. C.; Singh, R. Hybrid Lead Halide Perovskites for Ultrasensitive Photoactive Switching in Terahertz Metamaterial Devices. Adv. Mater. 2017, 29, 1605881,  DOI: 10.1002/adma.201605881
      There is no corresponding record for this reference.
    25. 25
      Chanana, A.; Liu, X.; Zhang, C.; Vardeny, Z. V.; Nahata, A. Ultrafast Frequency-Agile Terahertz Devices Using Methylammonium Lead Halide Perovskites. Sci. Adv. 2018, 4, eaar7353,  DOI: 10.1126/sciadv.aar7353
      There is no corresponding record for this reference.
    26. 26
      Huang, C.; Zhang, C.; Xiao, S.; Wang, Y.; Fan, Y.; Liu, Y.; Zhang, N.; Qu, G.; Ji, H.; Han, J.; Ge, L.; Kivshar, Y.; Song, Q. Ultrafast Control of Vortex Microlasers. Science 2020, 367, 1018– 1021,  DOI: 10.1126/science.aba4597
      26
      Ultrafast control of vortex microlasers
      Huang, Can; Zhang, Chen; Xiao, Shumin; Wang, Yuhan; Fan, Yubin; Liu, Yilin; Zhang, Nan; Qu, Geyang; Ji, Hongjun; Han, Jiecai; Ge, Li; Kivshar, Yuri; Song, Qinghai
      Science (Washington, DC, United States) (2020), 367 (6481), 1018-1021CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)
      The development of classical and quantum information-processing technol. calls for on-chip integrated sources of structured light. Although integrated vortex microlasers have been previously demonstrated, they remain static and possess relatively high lasing thresholds, making them unsuitable for high-speed optical communication and computing. We introduce perovskite-based vortex microlasers and demonstrate their application to ultrafast all-optical switching at room temp. By exploiting both mode symmetry and far-field properties, we reveal that the vortex beam lasing can be switched to linearly polarized beam lasing, or vice versa, with switching times of 1 to 1.5 ps and energy consumption that is orders of magnitude lower than in previously demonstrated all-optical switching. Our results provide an approach that breaks the long-standing trade-off between low energy consumption and high-speed nanophotonics, introducing vortex microlasers that are switchable at terahertz frequencies.
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    27. 27
      Tiguntseva, E. Y.; Baranov, D. G.; Pushkarev, A. P.; Munkhbat, B.; Komissarenko, F.; Franckevicius, M.; Zakhidov, A. A.; Shegai, T.; Kivshar, Y. S.; Makarov, S. V. Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles. Nano Lett. 2018, 18, 5522– 5529,  DOI: 10.1021/acs.nanolett.8b01912
      27
      Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles
      Tiguntseva, Ekaterina Y.; Baranov, Denis G.; Pushkarev, Anatoly P.; Munkhbat, Battulga; Komissarenko, Filipp; Franckevicius, Marius; Zakhidov, Anvar A.; Shegai, Timur; Kivshar, Yuri S.; Makarov, Sergey V.
      Nano Letters (2018), 18 (9), 5522-5529CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Halide perovskites are known to support excitons at room temps. with high quantum yield of luminescence that make them attractive for all-dielec. resonant nanophotonics and meta-optics. Here we report the observation of broadly tunable Fano resonances in halide perovskite nanoparticles originating from the coupling of excitons to the Mie resonances excited in the nanoparticles. Signatures of the photon-exciton ("hybrid") Fano resonances are obsd. in dark-field spectra of isolated nanoparticles, and also in the extinction spectra of aperiodic lattices of such nanoparticles. In the latter case, chem. tunability of the exciton resonance allows reversible tuning of the Fano resonance across the 100 nm bandwidth in the visible frequency range, providing a novel approach to control optical properties of perovskite nanostructures. The proposed method of chem. tuning paves the way to an efficient control of emission properties of on-chip-integrated light-emitting nanoantennas.
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    28. 28
      Shcherbakov, M. R.; Vabishchevich, P. P.; Shorokhov, A. S.; Chong, K. E.; Choi, D.-Y.; Staude, I.; Miroshnichenko, A. E.; Neshev, D. N.; Fedyanin, A. A.; Kivshar, Y. S. Ultrafast All-Optical Switching with Magnetic Resonances in Nonlinear Dielectric Nanostructures. Nano Lett. 2015, 15, 6985– 6990,  DOI: 10.1021/acs.nanolett.5b02989
      28
      Ultrafast All-Optical Switching with Magnetic Resonances in Nonlinear Dielectric Nanostructures
      Shcherbakov Maxim R; Vabishchevich Polina P; Shorokhov Alexander S; Fedyanin Andrey A; Chong Katie E; Choi Duk-Yong; Staude Isabelle; Miroshnichenko Andrey E; Neshev Dragomir N; Kivshar Yuri S
      Nano letters (2015), 15 (10), 6985-90 ISSN:.
      We demonstrate experimentally ultrafast all-optical switching in subwavelength nonlinear dielectric nanostructures exhibiting localized magnetic Mie resonances. We employ amorphous silicon nanodisks to achieve strong self-modulation of femtosecond pulses with a depth of 60% at picojoule-per-disk pump energies. In the pump-probe measurements, we reveal that switching in the nanodisks can be governed by pulse-limited 65 fs-long two-photon absorption being enhanced by a factor of 80 with respect to the unstructured silicon film. We also show that undesirable free-carrier effects can be suppressed by a proper spectral positioning of the magnetic resonance, making such a structure the fastest all-optical switch operating at the nanoscale.
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    29. 29
      Maragkou, M. Ultrafast Responses. Nat. Mater. 2015, 14, 1086,  DOI: 10.1038/nmat4467
      29
      Dielectric nanostructures Ultrafast responses
      Maragkou, Maria
      Nature Materials (2015), 14 (11), 1086CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      There is no expanded citation for this reference.
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    30. 30
      Soukoulis, C. M.; Wegener, M. Past Achievements and Future Challenges in the Development of Three-Dimensional Photonic Metamaterials. Nat. Photonics 2011, 5, 523– 530,  DOI: 10.1038/nphoton.2011.154
      30
      Past achievements and future challenges in the development of three-dimensional photonic metamaterials
      Soukoulis, Costas M.; Wegener, Martin
      Nature Photonics (2011), 5 (9), 523-530CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)
      A review. Photonic metamaterials are man-made structures composed of tailored micro- or nanostructured metallodielec. subwavelength building blocks. This deceptively simple yet powerful concept allows the realization of many new and unusual optical properties, such as magnetism at optical frequencies, neg. refractive index, large pos. refractive index, zero reflection through impedance matching, perfect absorption, giant CD and enhanced nonlinear optical properties. Possible applications of metamaterials include ultrahigh-resoln. imaging systems, compact polarization optics and cloaking devices. This Review describes recent progress in the fabrication of three-dimensional metamaterial structures and discusses some of the remaining challenges.
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    31. 31
      Peruch, S.; Neira, A.; Wurtz, G. A.; Wells, B.; Podolskiy, V. A.; Zayats, A. V. Geometry Defines Ultrafast Hot-Carrier Dynamics and Kerr Nonlinearity in Plasmonic Metamaterial Waveguides and Cavities. Adv. Opt. Mater. 2017, 5, 1700299,  DOI: 10.1002/adom.201700299
      There is no corresponding record for this reference.
    32. 32
      Bennett, B. R.; Soref, R. A.; Del Alamo, J. A. Carrier-Induced Change in Refractive Index of InP, GaAs and InGaAsP. IEEE J. Quantum Electron. 1990, 26, 113– 122,  DOI: 10.1109/3.44924
      32
      Carrier-induced change in refractive index of indium phosphide, gallium arsenide, and indium gallium arsenide phosphide (InGaAsP)
      Bennett, Brian R.; Soref, Richard A.; Del Alamo, Jesus A.
      IEEE Journal of Quantum Electronics (1990), 26 (1), 113-22CODEN: IEJQA7; ISSN:0018-9197.
      The change in refractive index Δn was theor. estd. produced by injection of free carriers in InP, GaAs, and InGaAsP. Bandfilling (Burstein-Moss effect), band-gap shrinkage, and free-carrier absorption (plasma effect) were included. Carrier concns. of 1016-01019 cm-3 and photon energies of 0.8-2.0 eV were considered. Predictions of Δn are in agreement with the limited exptl. data available. Refractive index changes ≤10-12 are predicted for carrier concns. of 1018 cm-3, suggesting that low-loss optical phase modulators and switches using carrier injection are feasible in these materials.
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    33. 33
      Burstein, E. Anomalous Optical Absorption Limit in InSb. Phys. Rev. 1954, 93, 632– 633,  DOI: 10.1103/PhysRev.93.632
      33
      Anomalous optical absorption limit in InSb
      Burstein, Elias
      Physical Review (1954), 93 (), 632-3CODEN: PHRVAO; ISSN:0031-899X.
      Tanenbaum and Briggs (C.A. 48, 448d) report that the room-temp. optical absorption limit of InSb is 7.0 μ; of a rather impure sample, 3.2 μ. This anomalous effect is confirmed. It is shown to be due to the small effective mass of the electrons in InSb rather than to a specific impurity effect.
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    34. 34
      Moss, T. The Interpretation of the Properties of Indium Antimonide. Proc. Phys. Soc., London, Sect. B 1954, 67, 775– 782,  DOI: 10.1088/0370-1301/67/10/306
      34
      The interpretation of the properties of indium antimonide
      Moss, T. S.
      Proceedings of the Physical Society, London (1954), 67B (), 775-82CODEN: PPSOAU; ISSN:0370-1328.
      The extremely high mobility of electrons in InSb and the marked dependence of the absorption edge on purity for n-type samples are both attributed to an abnormally small effective electron mass. This mass has been estd. in 3 ways. The 3 estimates so obtained show agreement. It is concluded that the effective mass of the conduction electrons in InSb is near 0.03 of the free electron mass. The magnitude of the photocond. observed in intrinsic InSb at room temp. can be explained by simple photoconductive theory with a quantum efficiency of approx. unity.
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    35. 35
      Preda, F.; Kumar, V.; Crisafi, F.; Figueroa del Valle, D. G.; Cerullo, G.; Polli, D. Broadband Pump-Probe Spectroscopy at 20-MHz Modulation Frequency. Opt. Lett. 2016, 41, 2970– 2973,  DOI: 10.1364/OL.41.002970
      35
      Broadband pump-probe spectroscopy at 20-MHz modulation frequency
      Preda Fabrizio; Kumar Vikas; Crisafi Francesco; Figueroa Del Valle Diana Gisell; Cerullo Giulio; Polli Dario
      Optics letters (2016), 41 (13), 2970-3 ISSN:.
      We introduce an innovative high-sensitivity broadband pump-probe spectroscopy system, based on Fourier-transform detection, operating at 20-MHz modulation frequency. A common-mode interferometer employing birefringent wedges creates two phase-locked delayed replicas of the broadband probe pulse, interfering at a single photodetector. A single-channel lock-in amplifier demodulates the interferogram, whose Fourier transform provides the differential transmission spectrum. Our approach combines broad spectral coverage with high sensitivity, due to high-frequency modulation and detection. We demonstrate its performances by measuring two-dimensional differential transmission maps of a carbon nanotubes sample, simultaneously acquiring the signal over the entire 950-1350 nm range with 2.7·10<sup>-6</sup> rms noise over 1.5 s integration time.
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    36. 36
      Preda, F.; Oriana, A.; Rehault, J.; Lombardi, L.; Ferrari, A. C.; Cerullo, G.; Polli, D. Linear and Nonlinear Spectroscopy by a Common-Path Birefringent Interferometer. IEEE J. Sel. Top. Quantum Electron. 2017, 23, 88– 96,  DOI: 10.1109/JSTQE.2016.2630840
      There is no corresponding record for this reference.
    37. 37
      Battie, Y.; Resano-Garcia, A.; Chaoui, N.; Zhang, Y.; En Naciri, A. Extended Maxwell-Garnett-Mie Formulation Applied to Size Dispersion of Metallic Nanoparticles Embedded in Host Liquid Matrix. J. Chem. Phys. 2014, 140, 044705,  DOI: 10.1063/1.4862995
      37
      Extended Maxwell-Garnett-Mie formulation applied to size dispersion of metallic nanoparticles embedded in host liquid matrix
      Battie, Y.; Resano-Garcia, A.; Chaoui, N.; Zhang, Y.; En Naciri, A.
      Journal of Chemical Physics (2014), 140 (4), 044705/1-044705/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The optical properties of metallic spherical nanoparticles embedded in host liq. matrix are studied. Extended Maxwell-Garnett-Mie formulation which accounts for size dispersion, the intrinsic confinement, and extrinsic size effect, is proposed for the calcn. of the effective dielec. function and absorption coeff. of size dispersion of colloidal soln. of Au and Ag nanoparticles in water. The size distribution induces an inhomogeneous broadening and an increase of the amplitude of the plasmon band. A large red shift of the plasmon band is also obsd. for Ag nanoparticles. Compared to the conventional Maxwell Garnett theory, we demonstrated that this model gives better description of the measured absorption spectra of colloidal Au solns. (c) 2014 American Institute of Physics.
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    38. 38
      Markovich, D. L.; Ginzburg, P.; Samusev, A.; Belov, P. A.; Zayats, A. V. Magnetic Dipole Radiation Tailored by Bubstrates: Numerical Investigation. Opt. Express 2014, 22, 10693– 10702,  DOI: 10.1364/OE.22.010693
      38
      Magnetic dipole radiation tailored by substrates: numerical investigation
      Markovich, D. L.; Ginzburg, P.; Samusev, A. K.; Belov, P. A.; Zayats, A. V.
      Optics Express (2014), 22 (9), 10693-10702, 10 pp.CODEN: OPEXFF; ISSN:1094-4087. (Optical Society of America)
      Nanoparticles of high refractive index materials can possess strong magnetic polarizabilities and give rise to artificial magnetism in the optical spectral range. While the response of individual dielec. or metal spherical particles can be described anal. via multipole decompn. in the Mie series, the influence of substrates, in many cases present in exptl. observations, requires different approaches. Here, the comprehensive numerical studies of the influence of a substrate on the spectral response of high-index dielec. nanoparticles were performed. In particular, glass, perfect elec. conductor, gold, and hyperbolic metamaterial substrates were investigated. Optical properties of nanoparticles were characterized via scattering cross-section spectra, elec. field profiles, and induced elec. and magnetic moments. The presence of substrates was shown to have significant impact on particle's magnetic resonances and resonant scattering cross-sections. Variation of substrate material provides an addnl. degree of freedom in tailoring optical properties of magnetic multipoles, important in many applications.
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    39. 39
      Richter, J. M.; Branchi, F.; Valduga de Almeida Camargo, F.; Zhao, B.; Friend, R. H.; Cerullo, G.; Deschler, F. Ultrafast Carrier Thermalization in Lead Iodide Perovskite Probed with Two-Dimensional Electronic Spectroscopy. Nat. Commun. 2017, 8, 376,  DOI: 10.1038/s41467-017-00546-z
      39
      Ultrafast carrier thermalization in lead iodide perovskite probed with two-dimensional electronic spectroscopy
      Richter Johannes M; Zhao Baodan; Friend Richard H; Deschler Felix; Branchi Federico; Valduga de Almeida Camargo Franco; Cerullo Giulio
      Nature communications (2017), 8 (1), 376 ISSN:.
      In band-like semiconductors, charge carriers form a thermal energy distribution rapidly after optical excitation. In hybrid perovskites, the cooling of such thermal carrier distributions occurs on timescales of about 300 fs via carrier-phonon scattering. However, the initial build-up of the thermal distribution proved difficult to resolve with pump-probe techniques due to the requirement of high resolution, both in time and pump energy. Here, we use two-dimensional electronic spectroscopy with sub-10 fs resolution to directly observe the carrier interactions that lead to a thermal carrier distribution. We find that thermalization occurs dominantly via carrier-carrier scattering under the investigated fluences and report the dependence of carrier scattering rates on excess energy and carrier density. We extract characteristic carrier thermalization times from below 10 to 85 fs. These values allow for mobilities of 500 cm(2) V(-1) s(-1) at carrier densities lower than 2 × 10(19) cm(-3) and limit the time for carrier extraction in hot carrier solar cells.Carrier-carrier scattering rates determine the fundamental limits of carrier transport and electronic coherence. Using two-dimensional electronic spectroscopy with sub-10 fs resolution, Richter and Branchi et al. extract carrier thermalization times of 10 to 85 fs in hybrid perovskites.
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    40. 40
      Makarov, S. V.; Zalogina, A. S.; Tajik, M.; Zuev, D. A.; Rybin, M. V.; Kuchmizhak, A. A.; Juodkazis, S.; Kivshar, Y. Light-Induced Tuning and Reconfiguration of Nanophotonic Structures. Laser Photonics Rev. 2017, 11, 1700108,  DOI: 10.1002/lpor.201700108
      There is no corresponding record for this reference.
    41. 41
      Makarov, S.; Kudryashov, S.; Mukhin, I.; Mozharov, A.; Milichko, V.; Krasnok, A.; Belov, P. Tuning of Magnetic Optical Response in a Dielectric Nanoparticle by Ultrafast Photoexcitation of Dense Electron-Hole Plasma. Nano Lett. 2015, 15, 6187– 6192,  DOI: 10.1021/acs.nanolett.5b02534
      41
      Tuning of magnetic optical response in a dielectric nanoparticle by ultrafast photoexcitation of dense electron-hole plasma
      Makarov, Sergey; Kudryashov, Sergey; Mukhin, Ivan; Mozharov, Alexey; Milichko, Valentin; Krasnok, Alexander; Belov, Pavel
      Nano Letters (2015), 15 (9), 6187-6192CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      We propose a novel approach for efficient tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser irradn. This concept is based on ultrafast photoinjection of dense (>1020 cm-3) electron-hole plasma within such nanoparticle, drastically changing its transient dielec. permittivity. This allows manipulation by both elec. and magnetic nanoparticle responses, resulting in dramatic changes of its scattering diagram and scattering cross section. We exptl. demonstrate 20% tuning of reflectance of a single silicon nanoparticle by femtosecond laser pulses with wavelength in the vicinity of the magnetic dipole resonance. Such a single-particle nanodevice enables designing of fast and ultracompact optical switchers and modulators.
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    42. 42
      Baranov, D. G.; Makarov, S. V.; Milichko, V. A.; Kudryashov, S. I.; Krasnok, A. E.; Belov, P. A. Nonlinear Transient Dynamics of Photoexcited Resonant Silicon Nanostructures. ACS Photonics 2016, 3, 1546– 1551,  DOI: 10.1021/acsphotonics.6b00358
      42
      Nonlinear Transient Dynamics of Photoexcited Resonant Silicon Nanostructures
      Baranov, Denis G.; Makarov, Sergey V.; Milichko, Valentin A.; Kudryashov, Sergey I.; Krasnok, Alexander E.; Belov, Pavel A.
      ACS Photonics (2016), 3 (9), 1546-1551CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      Optically generated electron-hole plasma in high-index dielec. nanostructures was demonstrated as a means of tuning their optical properties. Until now an ultrafast operation regime of such plasma-driven nanostructures was not attained. Pump-probe expts. with resonant Si nanoparticles were performed, and dense optical plasma generation near the magnetic dipole resonance with an ultrafast (∼2.5 ps) relaxation rate is reported. From exptl. results, an anal. model describing the transient response of a nanocryst. Si nanoparticle to an intense laser pulse was developed, and theor. plasma-induced optical nonlinearity leads to ultrafast reconfiguration of the scattering power pattern. The 100 fs switching to a unidirectional scattering regime upon irradn. of the nanoparticle by an intense femtosecond pulse was demonstrated. The work lays the foundation for developing ultracompact and ultrafast all-optical signal processing devices.
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    43. 43
      Shaltout, A. M.; Lagoudakis, K. G.; van de Groep, J.; Kim, S. J.; Vučković, J.; Shalaev, V. M.; Brongersma, M. L. Spatiotemporal Light Control with Frequency-Gradient Metasurfaces. Science 2019, 365, 374– 377,  DOI: 10.1126/science.aax2357
      43
      Spatiotemporal light control with frequency-gradient metasurfaces
      Shaltout, Amr M.; Lagoudakis, Konstantinos G.; van de Groep, Jorik; Kim, Soo Jin; Vuckovic, Jelena; Shalaev, Vladimir M.; Brongersma, Mark L.
      Science (Washington, DC, United States) (2019), 365 (6451), 374-377CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      The capability of on-chip wavefront modulation has the potential to revolutionize many optical device technologies. However, the realization of power-efficient phase-gradient metasurfaces that offer full-phase modulation (0 to 2π) and high operation speeds remains elusive. We present an approach to continuously steer light that is based on creating a virtual frequency-gradient metasurface by combining a passive metasurface with an advanced frequency-comb source. Spatiotemporal redirection of light naturally occurs as optical phase-fronts reorient at a speed controlled by the frequency gradient across the virtual metasurface. An exptl. realization of laser beam steering with a continuously changing steering angle is demonstrated with a single metasurface over an angle of 25° in just 8 ps. This work can support integrated-on-chip solns. for spatiotemporal optical control, directly affecting emerging applications such as solid-state light detection and ranging (LIDAR), three-dimensional imaging, and augmented or virtual systems.
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    44. 44
      Shcherbakov, M. R.; Liu, S.; Zubyuk, V. V.; Vaskin, A.; Vabishchevich, P. P.; Keeler, G.; Pertsch, T.; Dolgova, T. V.; Staude, I.; Brener, I.; Fedyanin, A. A. Ultrafast All-Optical Tuning of Direct-Gap Semiconductor Metasurfaces. Nat. Commun. 2017, 8, 17,  DOI: 10.1038/s41467-017-00019-3
      44
      Ultrafast all-optical tuning of direct-gap semiconductor metasurfaces
      Shcherbakov Maxim R; Zubyuk Varvara V; Vabishchevich Polina P; Dolgova Tatyana V; Fedyanin Andrey A; Liu Sheng; Keeler Gordon; Brener Igal; Vaskin Aleksandr; Pertsch Thomas; Staude Isabelle
      Nature communications (2017), 8 (1), 17 ISSN:.
      Optical metasurfaces are regular quasi-planar nanopatterns that can apply diverse spatial and spectral transformations to light waves. However, metasurfaces are no longer adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. We experimentally realise an ultrafast tunable metasurface consisting of subwavelength gallium arsenide nanoparticles supporting Mie-type resonances in the near infrared. Using transient reflectance spectroscopy, we demonstrate a picosecond-scale absolute reflectance modulation of up to 0.35 at the magnetic dipole resonance of the metasurfaces and a spectral shift of the resonance by 30 nm, both achieved at unprecedentedly low pump fluences of less than 400 μJ cm(-2). Our findings thereby enable a versatile tool for ultrafast and efficient control of light using light.Metasurfaces are not adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. Here, Shcherbakov et al. realise an ultrafast tunable metasurface with picosecond-scale large absolute reflectance modulation at low pump fluences.
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    45. 45
      Polli, D.; Brida, D.; Mukamel, S.; Lanzani, G.; Cerullo, G. Effective Temporal Resolution in Pump-Probe Spectroscopy with Strongly Chirped Pulses. Phys. Rev. A: At., Mol., Opt. Phys. 2010, 82, 053809,  DOI: 10.1103/PhysRevA.82.053809
      45
      Effective temporal resolution in pump-probe spectroscopy with strongly chirped pulses
      Polli, D.; Brida, D.; Mukamel, S.; Lanzani, G.; Cerullo, G.
      Physical Review A: Atomic, Molecular, and Optical Physics (2010), 82 (5, Pt. B), 053809/1-053809/8CODEN: PLRAAN; ISSN:1050-2947. (American Physical Society)
      This paper introduces a general theor. description of femtosecond pump-probe spectroscopy with chirped pulses whose joint spectral and temporal profile is expressed by Wigner spectrograms. The actual exptl. time resoln. intimately depends on the pulse-sample interaction and the commonly used instrumental response function needs to be replaced by a sample-dependent effective response function. Also using the proper configurations in excitation and/or detection, it is possible to overcome the temporal smearing of the measured dynamics due to chirp-induced pulse broadening and recover the temporal resoln. that would be afforded by the transform-limited pulses. The authors verify these predictions with expts. using broadband chirped pump and probe pulses. Results allow optimization of the temporal resoln. in the common case when the chirp of the pump and/or probe pulse is not cor. and may be extended to a broad range of time-resolved expts.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFWjtLrE&md5=1b13d95180bed1c80fb2037928bbcd8a
    46. 46
      Bohren, C. F.; Huffman, D. R. Absorption and Scattering of Light by Small Particles, 1st ed.; John Wiley & Sons: New York, 1983.
      There is no corresponding record for this reference.

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.0c05710.

    • Equilibrium extinction spectra for additional samples, time- and energy-resolved differential transmission maps for additional samples, details on the effective medium optical properties analysis, calculation of the pump photon density, details on the analysis of the time-resolved traces, models of the dynamics of the single nanoparticle optical properties, efficiency factors, and mode decompositions of the single particle


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