Trade-Off Between Scintillation Light Yield and Nanosecond Decay in CsCu ₂ I ₃ –CuI Crystals

Lead-free copper halides such as CsCu 2 I 3 are emerging as environmentally stable scintillators with high density and broad emission, yet their relatively slow decay, dominated by self-trapped exciton recombination, limits fast radiation detection. Here, we accelerate scintillation kinetics in CsCu 2 I 3 by forming a CuI nanocrystal (NC) layer on the surface of the CsCu 2 I 3 crystal using an antisolvent crystallization approach. Two types of CsCu 2 I 3 crystals were synthesized: those with CuI NC layer and without NCs. Structural, photoluminescence (PL), time-resolved PL, and γ-ray-induced scintillation measurements reveal that CuI NCs introduce a distinct 420 nm emission band and an ultrafast subnanosecond PL decay component absent in undoped CsCu 2 I 3 . Under 662 keV γ-ray excitation, NC-layered crystals exhibit significantly faster scintillation decay but a ∼40% reduction in light yield (LY) compared to pristine samples of 26 photons per keV. Light alkali doping (Na +, K + ) about 0.2% exerts only minor effects, confirming that CuI NCs dominate the emission dynamics. These findings demonstrate a viable pathway to accelerate emission in copper halides while elucidating the intrinsic trade-off between response speed and LY. Improving CuI NCs quantum efficiency offers a promising route toward fast, high-efficiency, lead-free scintillators for advanced radiation detection.