Defect‐Engineered Zero‐Dimensional Perovskite Cs ₃ LuCl ₆ : Tb ³⁺ Scintillator with Exceptional Thermal Stability for Flexible High‐Temperature X‐Ray Imaging

ABSTRACT Traditional scintillators face severe deployment limitations in harsh‐environment owing to insufficient thermal stability, which triggers light yield attenuation and imaging fidelity degradation under high temperatures. To overcome this critical challenge, we present a defect‐engineered zero‐dimensional (0D) halide perovskite scintillator Cs 3 LuCl 6 : Tb 3+ with exceptional thermal stability and superior scintillation performance. This material achieves complete suppression of photoluminescence (PL) thermal quenching up to 200°C, and more impressively retains 110% of its room‐temperature radioluminescence (RL) intensity at 650 K. The distinctive thermally enhanced luminescence is attributed to the strong quantum confinement of the 0D architecture, highly localized 4f electrons of Tb 3+ , and Frenkel defects generated by Cl − displacement in lattice upon X‐ray irradiation, all of which are validated by first‐principles calculations. In terms of core scintillation metrics, scintillator Cs 3 LuCl 6 : 50%Tb 3+ delivers a 49 200 photons/MeV light yield and a low detection limit of 117 nGy/s. Flexible scintillator films fabricated by incorporating Cs 3 LuCl 6 : 50%Tb 3+ into polydimethylsiloxane (PDMS) achieve a spatial resolution of 16.7 lp/mm and exhibit enhanced imaging performance at elevated temperature relative to room temperature. This work establishes a theory‐driven structure‐defect‐luminescence design strategy for developing high‐performance flexible scintillators tailored to extreme‐temperature X‐ray imaging applications.