High‐Brightness and Fast‐Response in Cerium‐Doped Halide Double Perovskite Scintillators Based on Defect‐Suppressed Strategies for High‐Speed X‐Ray Imaging

ABSTRACT High‐performance scintillators play a core role in the development of advanced medical imaging technologies, particularly in complex detection scenarios requiring both high sensitivity and high temporal resolution. However, developing a scintillator that simultaneously combines outstanding radioluminescence (RL) efficiency with fast decay characteristics remains a formidable challenge. Here, Ce 3+ ‐doped Cs 2 NaGdCl 6 (CNGC) double perovskite is designed to regulate the luminescence efficiency feature of the scintillator by introducing Br − to suppress the formation of Cl vacancy defects. Notably, the doping of Br − significantly reduces the defect density in CNGC:Ce 3+ , decreases non‐radiative recombination, and achieves a high photoluminescence quantum yield (PLQY) of 90.2%. Based on its outstanding scintillation performance, including a high light yield (LY) of 47637 photons MeV −1 , a short RL decay time of 153 ns, and a low detection limit of 74.95 nGy s −1 , the CNGC:15%Ce 3+ ,3%Br − scintillator film can capture clear high‐speed X‐ray imaging of the flowing contrast agents in simulated angiography. This work develops a novel scintillator material that not only holds immense potential as a candidate material for diverse ultrafast radiation detection applications, but also establishes a foundation for designing scintillators that simultaneously exhibit high LY and rapid RL decay characteristics.