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

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.