Highly Effective Hybrid Copper(I) Iodide Cluster Emitter with Negative Thermal Quenched Phosphorescence for X‐Ray Imaging

Abstract The low efficiency triplet emission of hybrid copper(I) iodide clusters is a critical obstacle to their further practical optoelectronic application. Herein, we present an efficient hybrid copper(I) iodide cluster emitter (DBA) 4 Cu 4 I 4 , where the cooperation of excited state structure reorganization and the metallophilicity interaction enables ultra‐bright triplet yellow‐orange emission with a photoluminescence quantum yield over 94.9 %, and the phonon‐assisted de‐trapping process of exciton induces the negative thermal quenching effect at 80–300 K. We also investigate the potential of this emitter for X‐ray imaging. The (DBA) 4 Cu 4 I 4 wafer demonstrates a light yield higher than 10 4 photons MeV −1 and a high spatial resolution of ≈5.0 lp mm −1 , showing great potential in practical X‐ray imaging applications. Our new copper(I) iodide cluster emitter can serve as a model for investigating the thermodynamic mechanism of photoluminescence in hybrid copper(I) halide phosphorescence materials.