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 interests 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 pathways to enhance radiative emission is 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 transferred 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 dynamics, 5 times enhancement of emission efficiency was achieved with a peak photoluminescence quantum yield (PLQY) of 82.14%. Correspondingly, radioluminescence 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 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.