of crystals to deliquescence, the failure of scintillation performance to meet development needs, and the high cost have forced us to continue our research to find the next generation of highly efficient scintillators with high light output, fast scintillation decay, and low cost. [2] The recently developed low-dimensional all-inorganic Cu(I)-based perovskite crystals are very attractive as they have stability in the air, a high PLQY, and are self-absorptionfree due to large Stokes shift, such as Rb 2 CuBr 3 , Rb 2 CuCl 3 , and Cs 3 Cu 2 I 5 . [3] In contrast, Cs 3 Cu 2 I 5 was regarded as the most promising halide perovskite scintillator because its inherent nonradioactive nature renders it more suitable for radiation detection. [4] Nevertheless, the long scintillation decay time of Cs 3 Cu 2 I 5 has been reported in previous studies, severely limiting its practical applications. Because almost all scintillation applications require scintillators with fast scintillation decay time, which is an important physical parameter characterizing how fast the scintillator light decays and is directly related to the timing resolution of the radiation detector. [5] To date, bulk Cs 3 Cu 2 I 5 single crystals have been grown mainly by the melting method, but the resulting single crystals exhibit slightly different scintillation decay times due to different growth techniques. Because large-size crystals are required for both commercialization and practical applications of scintillator materials, Dongsheng Yuan [6] successfully grew bulk Cs 3 Cu 2 I 5 single crystal by the vertical Bridgman method and achieved ion doping. The grown crystals exhibit excellent optical yield and energy resolution but slow scintillation decay kinetics. Their scintillation decay times contain both fast and slow components, 157 ns (12%) and 996 ns (87%). Even the successful introduction of Tl + did not have a suppressive effect on its slow decay. Luis Stand and colleagues [7] from the University of Tennessee also used the Bridgman method to grow a more transparent, high-quality Cs 3 Cu 2 I 5 single crystal, which exhibited higher light yields, but with an unimproved decay time of 280 ns (7%) and 1020 ns (93%). Recently, Yuntao Wu's group [8] obtained large-sized Cs 3 Cu 2 I 5 and Cs 3 Cu 2 I 5 :Tl single crystals with high optical yield and excellent energy resolution by optimizing the crystal growth process. Particularly, the Cs 3 Cu 2 I 5 :Tl possesses a remarkable energy resolution of 3.4% at 662 keV, and an ultrahigh light yield of 87 000 photons/ MeV under 137Cs γ-ray radiation demonstrates the great Copper(I) halide perovskite Cs 3 Cu 2 I 5 has recently attracted tremendous interest and has been considered an exceptionally promising scintillator due to its high quantum yield. However, its slow scintillation decay time, previously considered an intrinsic property, is a significant drawback preventing its practical application and commercialization. But in this work, it is found that the high-quality Cs 3 Cu 2 I 5 single-crystal grown by the...
