UV­B Persistent Luminescence of CaF₂:Gd³⁺ for Radiation Labeling and Tracing

Abstract Persistent luminescence (PersL) has attracted considerable attention in the last two decades for its potential applications in the fields of emergency indicators, energy‐saving lighting, biomedical imaging, and dynamic anti‐counterfeiting. However, the wavelengths of PersL reported so far usually fall into the visible and near‐infrared range. The preparation of advanced optical materials bearing UV PersL remains elusive. Here the PersL characteristic of CaF₂:Gd³⁺ is systematically studied. After exposure to X‐ray radiation, CaF₂:Gd³⁺ continues to emit UV­‐B (UVB) PersL peaking at 313 nm, corresponding to the ⁶P_7/2 → ⁸S_7/2 transition of Gd³⁺. By virtue of X‐ray photoelectron spectroscopy measurements, the valence variation model is excluded to explain the UVB PersL of CaF₂:Gd³⁺. Finally, it is demonstrated that such UVB PersL of CaF₂:Gd³⁺ can be used for static labeling and dynamic tracing.