Defects in Ligand‐Exchange‐Passivated Mixed‐Halide Double Perovskite Nanocrystals for X‐ray Imaging

Abstract Nanostructured scintillators, renowned for their exceptional miniaturization and portability, are typically designed with homogeneous dopant ion concentration profiles. While these profiles facilitate consistent optical properties, they may pose challenges in terms of compromising light emission intensity and overall scintillation efficiency. A pressing issue in the field of X‐ray flat‐panel minidetectors is the lack of specific and innovative strategies to significantly enhance radioluminescence capabilities, which has hindered further advancements. This research showcases an efficacious strategy for synthesizing ligand‐exchange‐passivated mixed‐halide double perovskite nanocrystals (NCs) tailored for their remarkable scintillation capabilities. The mixed‐halide composition is fine‐tuned via anion exchange between Bi 3+ and Tb 3+ ‐doped Cs 2 AgInCl 6 NCs and potassium bromide (KBr). Additionally, the initial oleic acid ligands are substituted with 1‐dodecanethiol (1‐DT), effectively compensating for inherent halogen vacancies and mitigating halide ion migration. The underlying passivation mechanism is elucidated through a comprehensive approach that combined spectroscopic experiments and theoretical calculations. Consequently, the fabricated transparent scintillator films, incorporating synthesized mixed‐halide double perovskite NCs, exhibit a high light yield of ≈20 952 photons MeV −1 , a sensitive detection limit of 207.5 nGy air s −1 , exceptional spatial resolution of 8.1 lp mm −1 , and unparalleled stability under prolonged X‐ray irradiation.