Achieving Ultrahigh Photoluminescence Quantum Yield in Highly Stable Cs₃Cu₂I₅ Perovskite Single Crystals Through Melt Growth

Low-dimensional halide perovskites Cs₃Cu₂I₅ have garnered increasing attention for their exceptional luminescent properties, attributed to their stability, high photoluminescence quantum yield (PLQY), and scintillation efficiency. Here, we report the growth of transparent Cs₃Cu₂I₅ crystals via the Bridgman method, emphasizing precise control of melt stoichiometry for optimal performance. Through melt composition optimization, significant improvements in crystal clarity and structural integrity were achieved, enhancing transmittance from 30% to over 80% and achieving nearly 100% PLQY. Notably, it exhibited self-absorption-free behavior due to a large Stokes shift of 1.15 eV, indicative of a substantial exciton binding energy (383 meV) associated with exciton self-trapping. Lastly, under ²⁴¹Am γ-ray irradiation at 59.5 keV, the energy resolution improved to 14.9% with the transparent Cs₃Cu₂I₅ crystals, demonstrating its potential for high-performance scintillation applications.