Coordination Polyhedron‐Selective Luminescence and Efficient X‐Ray Scintillation of Zn ²⁺ ‐Doped Cesium Cadmium Chloride Perovskites

Abstract The identification of lattice sites emission centers in hexagonal CsCdCl 3 perovskite is still challenging. Herein, Zn 2+ dopant having the d 10 outer electron configuration, effectively eliminated interference from typical dopants’ electron transitions. The Zn 2+ ‐doped hexagonal CsCdCl 3 is synthesized via precipitation method, while the cubic phase is prepared through grinding method in contrast. The hexagonal phase exhibits a coordination polyhedron‐selective dual emission: yellow‐green self‐trapped excitons (STEs) emission from [ZnCl 6 ] 4− octahedra soft‐lattice and orange STEs emission from corners‐sharing [CdZnCl 9 ] 5− dimer. The similar yellow‐green STEs emission in cubic phase further confirms the dominant role of [ZnCl 6 ] 4− octahedra to promote strong electron‐phonon coupling. The photoluminescence quantum yields (PLQYs) of Zn 2+ ‐doped hexagonal and cubic CsCdCl 3 reached 83.4% and 67.3%, respectively. Density functional theory calculations suggest that the corners‐sharing [CdZnCl 9 ] 5− dimer mediated exciton transport channel between CBM and CBM+1 band of anti‐thermal quenching (ATQ) process and the ligand‐to‐metal charge transfer (LMCT) transitions occurred from Cl − (p)→Cd 2+ /Zn 2+ (s). Moreover, Zn 2+ ‐doped hexagonal CsCdCl 3 demonstrates encouraging X‐ray scintillation performance, achieving a high light yield of 83 700 photons MeV −1 and an ultra‐low detection limit of 52.3 nGy air s −1 . This work not only demonstrates a potential X‐ray scintillator but also offers a broadened perspective into the excitons’ recombination mechanism in doped perovskite.