Coordination‐Dependent Exciton Dynamics and Scintillation in 0D Sb 3+ ‐Based Organic‐Inorganic Hybrid Metal Halides

ABSTRACT 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.