Microstructural stiffness engineering of low dimensional metal halide perovskites for efficient X-ray imaging

Low dimensional metal halide perovskites (MHPs) have a soft lattice, leading to strong exciton phonon coupling and exciton localization. Microstructural stiffness engineering is an effective tool for modulating the mechanical and electrical properties of materials, but its complex effects on the luminescence of low dimensional MHPs remain lacking. Here, we report microstructural stiffness engineering of low dimensional MHPs by halogen replacement in Ag-X bonds and [AgX₄]^3- (X = Br, Cl) units to increase the Young's modulus from 15.6 to 18.3 GPa, resulting in a 10-fold enhancement of X-ray excited luminescence (XEL) intensity and a 16-fold enhancement of photoluminescence quantum yield (PLQY), from 2.8% to 44.3%. Spectroscopic analysis reveals that high stiffness in Rb₂AgCl₃ facilitates the radiative pathway of defect-bound excitons and efficiently decreases the non-radiative transitions. The projected crystal orbital Hamilton population shows that the shorter Ag-Cl bonds impart Rb₂AgCl₃ with superior anti-deformation ability upon photoexcitation, leading to enhanced radiation resistance performance. A scintillation screen based on Rb₂AgCl₃@PDMS achieves zero self-absorption, an ultra-low detection limit of 44.7 nGy_air s^-1, and a high resolution of 20 lp mm^-1, outperforming most reported X-ray detectors. This work sheds light on stiffness engineering for the rational design of efficient emitters.