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

ABSTRACT 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 Sn 4+ ‐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()‐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 Sn 4+ ‐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 Sn 4+ ‐based metal halides as high‐performance scintillators for next‐generation X‐ray imaging technologies.