Charge separation state carrier storage-triggered thermally activated delayed phosphorescence in an organic scintillator

ABSTRACT Organic scintillators are among the most promising due to their inherent merits in terms of heavy metal–free constituents, synthesis designability, affordability of raw materials, and low usage costs. However, the limited X-ray excited luminescence (XEL) property of organic scintillators affects their application. To date, the main approaches for improving the XEL property of organic scintillators have focused on introducing heavy atoms to increase the absorbance of X-rays and establishing new luminescence pathways, such as thermally activated delayed fluorescence (TADF), to increase the exciton utilization efficiency. Even so, the XEL property of organic scintillators is not ideal compared with that of commercial inorganic scintillators. In this work, a highly stable charge separation (CS) state trap was introduced into the design of an organic scintillator. Combined with a unique thermally activated delayed phosphorescence (TADP) process, highly efficient capture and conversion of high-energy carriers are realized. As a result, the exciton generation efficiency dramatically increases, with an ultrahigh XEL intensity, and X-ray afterglow imaging at room temperature is achieved for the first time. This work provides a brand-new strategy for the design of high-performance organic scintillators.