Guanidinium-Based Hybrid Antimony Halide Scintillators for High-Resolution X-ray Imaging and 3D Reconstruction

Regulating excited-state dynamics is essential for developing high-performance scintillators. Herein, we systematically investigate how the coordination environments of Sb3+ influences self-trapped exciton (STE)-mediated scintillation in a series of zero-dimensional guanidinium-based hybrid antimony halides. Four compounds, (DPG)3SbCl6, (DPG)3SbBr6, (TPG)2SbCl5, and (TPG)2SbBr5, featuring either symmetric octahedral [SbX6]3- or distorted square-pyramidal [SbX5]2- units, are investigated. Through combined structural analyses, spectroscopic studies, and theoretical calculations, we reveal that octahedral coordination effectively suppresses the stereochemical activity of the Sb3+ 5s2 lone pair, reduces lattice relaxation, and minimizes nonradiative losses. In contrast, the distorted square-pyramidal geometry induces enhanced structural relaxation and electron-phonon coupling, resulting in pronounced thermal quenching. Notably, (DPG)3SbBr6 achieves an optimal balance among exciton localization, structural rigidity, and scintillation performance, delivering a high light yield of 15412 photons MeV-1 and low-dose X-ray detection with high-resolution (10.1 lp mm-1) radiography and three-dimensional X-ray imaging. This work elucidates the critical role of Sb3+ coordination environments in regulating STE dynamics and scintillation properties, offering valuable guidance for the rational design of efficient hybrid metal halide scintillators.