Coinage Metal Cluster Scintillator for X-ray Imaging

luminescence

X-ray scintillators are a type of optical functional material that can convert high-energy X-rays to low-energy visible photons. 2 The emerging organic−inorganic hybrid scintillators beyond conventional CsI(Tl) and Lu 3 Al 5 O 12 :Ce (LuAG:Ce) single crystals have become a research hot spot in recent years, and breakthroughs have been made in the development of metal halide (perovskite) scintillators (films and ceramics), MOF scintillators, and a small number of organic scintillators. 3−6 However, problems related to environmental pollution, instability, and inflexibility limit their application in the field of X-ray imaging. Therefore, a new generation of scintillators with excellent comprehensive performance is crucially required. The metal cluster family is considered to be a promising alternative platform for X-ray scintillators as they exhibit highly efficient photoluminescence, offering commercialization prospects in solid-state lighting devices with high scintillation performance. In addition, compared with organic dyes, metal clusters with high-Z metals possess higher X-ray absorption efficiencies. 7 In their recent work published in ACS Central Science, 1 the authors synthesized a gold−copper (Au−Cu) cluster using a simple and mild one-pot method (Figure 1a). With the introduction of heavy atoms, the Au−Cu cluster exhibited excellent X-ray absorption and emitted bright radioluminescence under X-ray excitation, with a minimum detection limit of 31.7 nGy s −1 (Figure 1b), lower than that of CsPbBr 3 scintillators (∼50 nGy s −1 ).
The authors conducted a detailed investigation of the luminescence mechanism of the Au−Cu cluster using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). As shown in Figure 1c,d, the distribution of natural transition orbits (NTO) of the Au−Cu cluster shows that the highest occupied natural transition orbits (HONTO) and the lowest unoccupied natural transition orbits (LUNTO) exhibit low overlap and large Published: July 10, 2023 In this issue of ACS Central Science, Kai Li, Shuang-Quan Zang, and co-workers report a coinage metal cluster scintillator with thermally activated delayed fluorescence (TADF) activity for high-performance X-ray imaging.
With the introduction of heavy atoms, the Au−Cu cluster exhibited excellent X-ray absorption and emitted bright radioluminescence under X-ray excitation.

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Coinage metal clusters are reported as a substitute for traditional commercial X-ray imaging scintillators with broad application prospects.

Kai Han and Zhiguo Xia*
Published 2023 by American Chemical Society dipole distance changes, showing typical charge transfer (CT) characteristics, resulting in a small energy gap between the first singlet (S 1 ) and triplet (T 1 ) excited states (ΔE ST = 0.08 eV). In addition, the spin−orbit coupling (SOC) matrices between the low-lying singlet and triplet excited states results indicate that the Au−Cu cluster had a high SOC value due to the heavy atom effect (Figure 1d). Thus, the electronic structure of the excited state and the heavy atom effect of the Au−Cu cluster itself endow it with TADF optical activity. 8 This greatly improves the exciton utilization of the excited state and is the main reason for its excellent radioluminescence performance. Given this and the processability of the Au−Cu cluster, it was successfully prepared as a large flexible scintillator screen. The scintillator screen can reach a high resolution of 12.5 LP mm −1 , achieving high-performance X-ray imaging of the internal structure of real items, for example, a computer mouse (see Figure 1e). This work reported an Au−Cu cluster that not only exhibits excellent radioluminescence properties compared to traditional scintillators but also is environmentally friendly and stable to water and oxygen for long-term and consistent X-ray imaging. More importantly, coinage metal clusters have been demonstrated to be a highly promising radioluminescent material with broad application prospects. This work has very important guiding significance for the development of a new generation of scintillators via TADF activity for further application in security, medical diagnostics, industrial materials inspection, and nuclear power stations.  This work reported an Au−Cu cluster that not only exhibits excellent radioluminescent properties compared to traditional scintillators but also is environmentally friendly and stable to water and oxygen for long-term and consistent X-ray imaging.