Switching Fluorescent–Phosphorescent Radioluminescence in Organic X‐Ray Scintillators via a Host–Guest Strategy

ABSTRACT Organic scintillators have attracted increasing attention for applications in medical diagnostics, nondestructive inspection and high‐energy physics. Regulating the radioluminescence (RL) lifetime and emission wavelength is crucial for developing organic scintillators that meet diverse application requirements, yet remains challenging. Achieving switchable fluorescent‐phosphorescent RL through a simple and effective approach is therefore highly desirable for x‐ray imaging applications. Here, we report an efficient host–guest strategy to realize switching between fluorescence and phosphorescence in RL from a single guest emitter. Accordingly, the fluorescence and phosphorescence exhibit decay lifetimes of 4.28 ns (emission at 450 nm) and 1140.41 ms (emission at 529 nm), respectively. Moreover, the phosphorescent scintillator demonstrated pronounced scintillation performance at elevated temperatures. Notably, 2‐TBASF@DMAP exhibits a long afterglow exceeding 0.8 s over a wide temperature range from 78 to 375 K, highlighting its strong potential for high‐temperature x‐ray detection and advanced imaging technologies. This work opens new possibilities for organic scintillators in multimodal detection, as the switchable emission modes enable enhanced signal discrimination and environmental responsiveness.