Unveiling the Dynamics of Frenkel Defects in Fluoride Materials for X-Ray-Induced Persistent Luminescence and Advanced Imaging Applications

The persistent luminescence (PersL) induced by X-rays in fluoride materials has garnered widespread application within the field of optoelectronics. However, the complexity of the trap systems in multi-component fluoride materials has impeded further exploration into PersL properties. Here, a compound consisting solely of fluoride and lanthanide ions is focused on, which simplifies the revelation of the PersL mechanism under X-ray excitation. Experimental and theoretical results reveal that the PersL phenomenon is primarily attributed to the migration and recovery processes of interstitial fluoride ions within the lattice. Depending on the localization of the interstitial fluoride ions, the corresponding Frenkel defects can be classified into two distinct types: those that are readily self-recoverable near the matrix lanthanide ions and those that are less likely to self-recover near the dopant ions. The anomalous PersL phenomena observed at temperatures that do not correspond to the thermoluminescence spectra further substantiate the existence of these dynamic traps. Furthermore, leveraging the material's superior PersL properties, a scintillator film is prepared and utilized for X-ray PersL imaging in static displays. These findings provide a refined understanding of the PersL mechanism related to Frenkel defects, laying a solid foundation for the continued application and development of PersL technology.