X‑ray-Excited Long-Lasting Narrowband Ultraviolet‑B Persistent Luminescence from Gd³⁺-Doped Sr₂P₂O₇ Phosphor

Persistent phosphors emitting in the narrowband ultraviolet-B (NB-UVB) spectral region have aroused significant interest, owing to their special self-illuminating feature in realizing many advanced technological applications under excitation-free conditions, such as dermatological therapy and invisible optical tagging. Here, we focus our discussion on a new Gd³⁺-doped persistent phosphor, Sr₂P₂O₇:Gd³⁺, which exhibits long-lasting NB-UVB persistent luminescence peaking at 312 nm for more than 24 h after charging by an X-ray beam. The NB-UVB light emission from the charged Sr₂P₂O₇:Gd³⁺ phosphor can be clearly detected by a UVB camera in bright indoor environment. More importantly, the enhancement of NB-UVB afterglow intensity and decay time can be observed under continuous photostimulation of polychromic indoor ambient light. Furthermore, applying charged Sr₂P₂O₇:Gd³⁺ phosphors as invisible optical taggants, clear and interference-free recognition of the encrypted message and location of different objects have been realized due to the lack of UVB light in bright indoor environment. The as-prepared Sr₂P₂O₇:Gd³⁺ persistent phosphor is expected to offer new directional solutions for the development and application of ultraviolet luminescence technology.