CaF 2 :Eu@CaF 2 Core/Shell Nanoscintillators for Reversible Ratiometric X‐Ray Detection and High‐Resolution Imaging via Ordered Microarray Film

ABSTRACT Scintillators, which convert high‐energy X‐ray photons into low‐energy visible photons, are key components in indirect X‐ray detection devices. However, it remains a significant challenge to develop a single scintillator capable of accurate real‐time X‐ray detection based on ratiometric intensity variations. Moreover, most scintillator films consist of disordered luminescent centers, which suffer from severe optical crosstalk and consequently degrade imaging resolution. Here, monodisperse CaF 2 :Eu nanoscintillators (NSs) are synthesized via a modified hot‐injection strategy, enabling controlled nucleation and a narrow size distribution. F‐centers mediated electron transfer within the crystal lattice facilitates the partial reduction of Eu 3+ to Eu 2+ during nanoparticle growth. By further constructing a CaF 2 :Eu@CaF 2 core–shell structure, X‐ray‐induced Frenkel defects regulate the excitation dynamics of Eu 2+ emission, allowing reversible modulation of the Eu 2+ /Eu 3+ emission ratio for ratiometric dose‐rate sensing. Integration of these NSs into anodic aluminum oxide (AAO) templates yields flexible, ordered microarray scintillation films that effectively suppress optical crosstalk, leading to significantly improved spatial resolution in X‐ray imaging. This work provides a promising strategy for the development of advanced NSs for accurate X‐ray detection and high‐resolution imaging.