X-ray-Excited Long-Lasting Narrowband Ultraviolet-B Persistent Luminescence from Gd 3+ -Doped Sr 2 P 2 O 7 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 Gd 3+ -doped persistent phosphor, Sr 2 P 2 O 7 :Gd 3+ , 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 Sr 2 P 2 O 7 :Gd 3+ 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 Sr 2 P 2 O 7 :Gd 3+ 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 Sr 2 P 2 O 7 :Gd 3+ persistent phosphor is expected to offer new directional solutions for the development and application of ultraviolet luminescence technology.