Efficient Organic‐Inorganic Sn 4+ ‐Based Halide Phosphorescent Scintillators Enabled by Enhanced Triplet Exciton Utilization and Excited Energy Level Regulation

Despite remarkable X-ray scintillation performance of inorganic or organic crystal materials, their practical application is often hindered by poor processability, weak X-ray absorption, and/or inefficient exciton utilization. Developing organic-inorganic hybrid metal-halide phosphorescent scintillators is thus of vital importance for X-ray imaging applications, yet remains scarcely explored. Herein, we report a series of organic-inorganic hybrid Sn⁴⁺-based metal halides, designated as 3PP(R)-Sn-Cl (R = H, F1, F2, Cl, Br), which exhibit efficient fluorescence, thermally activated delayed fluorescence (TADF), and room-temperature phosphorescence (RTP) tailored through the substituent "R". Multiple weak intermolecular interactions and strategic variation of the "R" group effectively modulate molecular stacking and excited-state dynamics, thereby boosting X-ray absorption and triplet exciton utilization. As a result, 3PP( H ${\bf H}$ )-Sn-Cl achieves a record RTP efficiency of 79.1% and a long lifetime of 164.4 ms, the highest values reported to date for undoped Sn⁴⁺-based halides. Furthermore, we demonstrate multilevel information encryption applications leveraging the highly sensitive thermochromism properties of 3PP(R)-Sn-Cl. More importantly, benefiting from strong heavy-atom-effect and efficient triplet exciton utilization, 3PP(Br)-Sn-Cl exhibits a high light yield of 31213.3 photons MeV^-1 and a low detection limit of 328.2 nGy/s under X-ray irradiation, enabling efficient radiography with a spatial resolution over 14.0 lp mm^-1. This work for the first time demonstrates Sn⁴⁺-based metal halides as high-performance scintillators for next-generation X-ray imaging technologies.