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.
Ma et al. (Tue,) studied this question.