Organic Ionic Host–Guest Phosphor with Dual-Confined Nonradiation for Constructing Ultrahigh-Temperature X-ray Scintillator

Scintillators with X-ray-excitable luminescence have attracted great attention in the fields of medical radiography, nondestructive inspection, and high-energy physics. However, thermal quenching significantly reduces radioluminescence efficiency, particularly for those phosphorescent scintillators with promising radiation-induced triplet exciton utilization, ultimately limiting their applications in high-temperature scenarios. Herein, we develop ultrahigh-temperature scintillators based on organic ionic host–guest phosphorescence systems with unprecedented thermal-stable emissions up to 673 K. The guest phosphor features spin-vibronic coupling-assisted intersystem crossing, effectively transforming phosphorescence to thermally activated delayed fluorescence for overcoming thermal inactivation of triplet excitons. Meanwhile, the rigid ionic host and guest with robust electrostatic interactions minimize both the intrinsic and extrinsic nonradiations of excitons, the so-called dual-confined nonradiation. These two mechanisms work synergistically, contributing to the highly efficient triplet exciton-based luminescence with a room-temperature phosphorescence efficiency of 38.7% and ultrahigh-temperature-resistant dual emissions. Such an innovative ionic host–guest scintillator achieves an impressively low X-ray detection limit of 71.5 nGy s–1 and remarkably bright photoluminescence (efficiency of 80.4% at 483 K), enabling ultrahigh-temperature X-ray imaging.