Unveiling The Role of Cu + Doping in Rb 2 AgBr 3 Scintillators toward Enhanced Photoluminescence Quantum Efficiency and Light Yield

Doping in luminescent metal halides has become an effective strategy for tailoring the optoelectronic properties. Herein, Cu + is introduced into Rb 2 AgBr 3 to design the synthesis of Rb 2 AgBr 3 : x Cu + , which possess cold‐white light emission at room‐temperature without changing the spectral profiles; however, the Cu + incorporation significantly enhances the photoluminescence quantum efficiency to 98.8% in Rb 2 AgBr 3 :0.05Cu + . Additionally, a high scintillation light yield of up to 79 250 photons MeV −1 and a low detection limit of 714.83 nGy s −1 have been achieved via this Cu + doping engineering. X‐ray imaging with a spatial resolution of up to 5.8 lp mm −1 is further realized using a large scintillator film prepared by mixing polydimethylsiloxane with Cu + doped Rb 2 AgBr 3 scintillators. This study provides a Cu + doping design principle for improving both the photoluminescence and scintillation performances of metal halides.