Coordination-Dependent Exciton Dynamics and Scintillation in 0D Sb3+-Based Organic-Inorganic Hybrid Metal Halides

0D Sb 3+ -based organic-inorganic hybrid metal halide (OIMH) scintillators have gained significant attention due to their efficient self-trapped exciton (STE) emission. However, the interplay between local structural distortion, defect-states, and STE emission remains insufficiently understood. Herein, two structurally distinct 0D Sb 3 + -based OIMHs, [HP(o-tol) 3 ] 2 SbBr 5 and [HP(m-tol) 3 ] 4 SbBr 7 , are investigated to elucidate structure-property relationships governing exciton dynamics. Specifically, [HP(o-tol) 3 ] 2 SbBr 5 features a highly distorted [SbBr 5 ] 2− square pyramid with an active lone pair, whereas [HP(m-tol) 3 ] 4 SbBr 7 contains a symmetric [SbBr 6 ] 3− octahedron with an inactive lone pair. Despite stronger distortion, the former exhibits a low photoluminescence quantum yield (PLQY) of 6%, while the latter achieves a high PLQY of 81%. Through combined photophysical analysis and first-principles calculations, we reveal that the stronger distortion induces defect-states, which compete with STE emission and lead to enhanced non-radiative losses. Consequently, [HP(m-tol) 3 ] 4 SbBr 7 demonstrates promising X-ray scintillation performance, with a light yield (LY) of 12200 ± 200 photons MeV −1 . This performance enabled the fabrication of flexible [HP(m-tol) 3 ] 4 SbBr 7 @SEBS scintillator films, achieving a spatial resolution of 8.0 lp mm −1 and high-quality 2D & 3D X-ray imaging and tomography, offering a promising path for future medical and industrial inspection technologies.