Large-sized organic host–guest crystals with rapid fluorescence for efficient scintillators

Abstract

Organic scintillators have garnered extensive attention due to their advantages of flexibility, low cost, and ease of processing. However, some reported organic scintillators with phosphorescent or thermally activated delayed fluorescent (TADF) characteristics typically exhibit long fluorescence decay lifetimes, leading to ghosting and signal delay in X-ray imaging. It is necessary to reduce the scintillator's fluorescence lifetime. In this study, a series of organic host–guest doped materials was constructed via a rational molecular design approach. p-Terphenyl (PT) was used as the host while 2,5-bis(4-biphenylyl) thiophene (BP1T), 5,5′-Di([1,1′-biphenyl]-4-yl)-2,2′-bithiophene (BP2T), and 2,5-bis[5-(4-phenylphenyl) thiophen-2-yl]thiophene (BP3T) were adopted as the guests. Centimeter-sized organic doped crystals were successfully grown using the Bridgman method. The results indicate that ultrafast fluorescence decay times of 0.30, 0.44, and 0.50 ns were obtained in the BP1T-PT, BP2T-PT, and BP3T-PT crystals, respectively, and all emission wavelengths exhibited a significant red shift. The as-prepared crystals demonstrated good machinability and could be readily machined into crystal plates (15 mm × 15 mm × 2 mm) for direct application in X-ray imaging. The resulting images successfully resolved the internal geometry of the object. This work provides a feasible strategy for developing large-sized organic scintillators with short decay lifetimes.