Heterostructure CaF2@CsPbX3 Nanoscintillators with Enhanced Stability and Brightness for High-Resolution X-ray Imaging.

X-ray imaging plays a critical role in medicine, security, and nondestructive testing, whereas existing detectors have limitations of costly fabrication, afterglow, and incompatibility for flexible devices. Metal halide perovskite nanocrystals (NCs) have recently emerged as promising alternatives owing to their facile synthesis, emission tunability, ultrafast response, and solution processability. However, their inherently poor environmental stability and film-quality degradation at high precursor concentrations hinder practical deployment. Here, we present a fluoride-engineering strategy by incorporating CaF2 NCs into CsPbX3 (X = Cl, Br, or I) lattices to form a heterostructure. This strategy simultaneously passivates intrinsic defects and suppresses aggregation, enabling the fabrication of uniform, high-quality films. Surface-anchored CaF2 NCs serve as effective barriers in concentrated solutions, suppressing self-absorption and aggregation by preventing the close packing of adjacent perovskite NCs. As a result, the heterostructure CsPbX3/CaF2 film exhibits significantly improved X-ray-excited optical luminescence, environmental stability, and suppressed self-absorption, along with superior high-resolution imaging. This work establishes fluoride incorporation as a general strategy to unlock the full potential of perovskite scintillators for next-generation optoelectronics and imaging.