Rare-Earth Co-doped BaLu₂F₈ Nanocomposite Film with Enhanced Radioluminescence for High-Resolution X-ray Imaging

Rare-earth fluorides have been shown to be promising scintillators for medical radiography applications. However, they are mostly explored in the alkali metal-based category, and it remains challenging to obtain alkaline-earth-based rare-earth fluoride (ALn₂F₈) nanocomposites with high scintillation performance. In this work, rod-shaped BaLu₂F₈ (BLF) nanocrystals (NCs) are synthesized as a scintillation matrix by a facile liquid-liquid-solid hydrothermal method. Through a lanthanide-doped strategy, Tb-doped BLF NCs exhibit efficient green emission with excellent spectral matching of normal photoelectric conversion devices. The emission performance of Tb³⁺-based BLF is enhanced by the effective energy transfer process from Ce³⁺ ⁵D_5/2 and Tb³⁺ ⁵D₃. Subsequently, the scintillation performance of prepared BLF:Ce,Tb NCs is assessed, with high X-ray sensitivity, a low detection limit (142.4 nGy s^-1), and a larger relative light output (21 480 photons/MeV), which is 2.4 times higher than that of the commercial scintillator. Furthermore, large-area (25 cm × 25 cm) flexible composite films are further prepared with optimal BLF:Ce,Tb NCs, which show excellent X-ray imaging with a spatial resolution up to 24.6 line pairs mm^-1. These findings demonstrate co-doped ALn₂F₈-based nanocomposite scintillators with potential applications in high-resolution industrial nondestructive inspection and biological imaging.