Heterovalent Co‐Doped LiLuF₄ Composite Flexible Films as Persistent Luminescence Scintillator for X‐Ray High‐Resolution Extension Imaging

Abstract Scintillators with high light yield, spatial resolution, and detection sensitivity are desirable for X‐ray imaging. Howerer, it remains challenging to improve the light yield and radiation detection capability of alkali metal rare‐earth fluoride (ALnF₄). Herein, a type of Cu²⁺ ion heterovalent co‐doped LiLuF₄:Tb,Cu microcrystalline scintillation material with high light yield, persistent, and thermostimulated luminescence is obtained by defect engineering. The heterovalent codoping strategy not only increases the radioluminescence (RL) intensity, but also introduces more carrier traps in the material to enhance the long‐afterglow and thermoluminescence intensity of LiLuF₄:Tb microcrystals. After doping of 3 mol% Cu²⁺ ions, the RL efficiency is increased by 88.61%, and the X‐ray detection limit of LiLuF₄:Tb,Cu reaches 2.7928 nGy·s^‒1. This detectivity is considerably lower than the medical imaging requirements (5.5 µGy·s^‒1). Furthermore, a large‐area flexible scintillation film of dimensions 30 × 30 cm² is prepared to achieve high spatial resolution X‐ray imaging of 22 LP mm⁻¹@MTF(modulation transfer function) = 0.2. Besides, this flexible film enables X‐ray imaging of curved objects and stores optical information for >48 h. This work provides a paradigm for improving the RL intensity and X‐ray detection sensitivity of alkali rare‐earth fluorides by crystal defect engineering, and enriches X‐ray high resolution extended imaging applications.