Electron Cascade‐Triggered Synergy in Organic–Inorganic Composite Film for High‐Performance X‐Ray Imaging

ABSTRACT Organic scintillators offer compelling advantages, including easy production, flexibility, and high quantum yield, yet the low atomic number intrinsically limits X‐ray absorbance, compromising radioluminescence intensity and detection sensitivity. To address this challenge, a composite scintillator is devised by integrating high‐Z LiLuF 4 :Tb nanocrystals with 9,10‐diphenylanthracene (DPA) in a polystyrene matrix. This architecture yields a ninefold enhancement of DPA radioluminescence intensity, and make it retains the original ultrafast decay dynamics, which exceed the performance of current state‐of‐the‐art thermally activated delayed fluorescence (TADF) and hot‐exciton scintillators to a certain extent. The optimized composite film exhibits a remarkable light yield of 40 466 photons/MeV and an ultralow detection limit of 43.7 nGy air /s, outperforming commercial inorganic benchmarks (BGO and LYSO:Ce). Furthermore, it enables high‐resolution X‐ray imaging with a spatial resolution exceeding 26 lp/mm. Mechanistic investigations reveal an electron cascade triggered by escaped fast electrons from the LiLuF 4 :Tb nanocrystals, which synergistically amplifies the excitation of DPA molecules. It is worth noting that this strategy is applicable to diverse organic scintillators, such as anthracene, tetraarylethene, and TPE‐4Br, as evidenced by a significant boost in their radioluminescence intensity. This work thus elucidates nanoscale energy conversion pathways of escaped electrons and establishes a transformative platform for high‐sensitivity, low‐dose radiation detection and imaging.