Limiting Exciton Diffusion Enhances the Optical Response of CsPbBr₃ Nanocrystal Films at High Excitation Densities

Ultrafast radiation detection requires materials to maintain favorable optical properties under dense excitation. In this work, we investigate lead halide perovskite nanocrystal (NC) films using the $Z$-scan luminescence method and show that their optical response under dense excitation is strongly influenced by the choice of surface ligand. We specifically report that using long organic ligands has a positive effect on the optical performance compared to short inorganic ligands because it limits exciton diffusion between neighboring NCs. These conclusions are based on $Z$-scan luminescence data, a numerical model incorporating inter-NC exciton diffusion, and measurements of a heterostructured detector under ionizing radiation. In addition, encapsulating the NCs in a SiO₂ shell is identified as an effective strategy to reduce inter-NC exciton diffusion while providing improved chemical stability. Together, the experimental results and numerical modeling presented in this work establish predictive tools for the design of nanocomposite materials with optimized ultrafast luminescence properties.