Heterovalent Cd2+-Doped Cs3Cu2I5 Scintillators with Modulated Exciton-Phonon Coupling for High-Resolution X-ray Imaging.

Zero-dimensional (0D) copper-based halides have demonstrated significant potential in the field of high-performance X-ray detection owing to their exceptional optical properties, low toxicity, and structural stability. However, their photoluminescence (PL) efficiency and imaging resolution are limited by intrinsic defects that induce non-radiative recombination and strong exciton-phonon coupling. In this work, millimeter-scale Cd2+-doped Cs3Cu2I5 single crystals were prepared via a room-temperature solvent-assisted evaporation method. Heterovalent Cd2+ doping effectively suppressed non-radiative recombination and facilitated the radiative relaxation of self-trapped excitons (STEs). Temperature-dependent PL analysis revealed a reduction in the Huang-Rhys factor from 44.56 to 37.23, indicating weakened exciton-phonon coupling. As a result, the photoluminescence quantum yield (PLQY) increased from 84.6 to 96.2%. First-principles calculations revealed that Cd2+ doping altered the local electronic environment via a heterovalent charge-compensation mechanism. Furthermore, scintillator films fabricated from the doped single crystals demonstrated a spatial resolution of 26.5 lp/mm at MTF = 0.2, representing competitive imaging performance among reported copper-based halide scintillators. This work provides an effective heterovalent doping strategy for improving the luminescence and imaging performance of copper-based halide scintillators and offers useful insights into the influence of heterovalent doping on STE-mediated radiative processes.