Solvent‐Mediated Charge Transfer Regulation of Inner Core Clusters in Hybrid Copper(I)‐Based Halides for High‐Efficiency X‐Ray Scintillation

Cu(I)-based metal halides have gained significant interest as scintillators. However, their X-ray luminescence efficiency is mainly determined by the competition between radiative organic ligands and nonradiative metal cluster-centered charge transfer. How to regulate their charge transfer to enhance radiative emission is an intractable challenge. Here, guided by coordination dynamics, we present a solvent mediation strategy to modulate coordination environments and intramolecular charge transfer of organic cuprous halides to achieve vibrant emissions. Mechanistic studies reveal that the coordinated clusters can efficiently absorb radiation ionization to generate electron-hole pairs and transfer them to ligands for enhanced luminescence. Conversely, ligand-free structures exhibit an absence of organic-ligand-related excited states upon excitation, leading to luminescence quenching. Due to optimized metal-to-ligand charge transfer (MLCT) dynamics, a five times enhancement of emission efficiency was achieved with a peak photoluminescence quantum yield (PLQY) of 82.14%. Correspondingly, radioluminescence (RL) was significantly improved to 2.22 and 10 times greater than that of (Lu,Y)₂SiO₅:Ce (LYSO) and C₆H₁₈N₂Cu₂Br₄ with a high light yield of 73881 photons/MeV (C₁₂H₂₈N₄Cu₂I₂) and excellent photochemical stability. A high X-ray imaging resolution of 9.7 lp mm^-1 was also demonstrated by the soft C₁₂H₂₈N₄Cu₂I₂ screen even with the thickness of 30 µm. Our study provides a solvent-mediated ligand engineering of copper halide cluster scintillators.