Constructing Organic Phosphorescent Scintillators with Enhanced Triplet Exciton Utilization Through Multi‐Mode Radioluminescence for Efficient X‐Ray Imaging

Abstract The development of organic phosphorescent scintillators with high exciton utilization efficiency has attracted significant attention but remains a difficult challenge because of the inherent spin‐forbidden feature of X‐ray‐induced triplet excitons. Herein, a design strategy is proposed to develop organic phosphorescent scintillators through thermally activated exciton release to convert stabilized spin‐forbidden triplet excitons to spin‐allowed singlet excitons, which enables singlet exciton‐dominated multi‐mode emission simultaneously from the lowest singlet, triplet, and stabilized triplet states. The resultant scintillators demonstrate a maximum photoluminescence efficiency of 65.8% and a minimum X‐ray radiation detection limit of 110 nGy s⁻¹; this allows efficient radiography imaging with a spatial resolution of ≈10.0 lp mm⁻¹. This study advances the fundamental understanding of exciton dynamics under X‐ray excitation, significantly broadening the practical use of phosphorescent materials for safety‐critical industries and medical diagnostics.