Tailor Traps in Bi-Doped NaGdGeO Phosphors by Introducing Eu Ions to Switch Multimodal Phosphorescence Emission.

Featured with a tunable excitation/emission wavelength and excellent physicochemical stability, inorganic fluorescent materials are widely used in the fields of anti-counterfeiting. Here, we design a multi-stimuli-responsive dynamic fluorescence and phosphorescence anti-counterfeiting material by introducing Eu ions in NaGdGeO: Bi to tailor the trap structure. The photoluminescence (PL), long persistent luminescence (LPL), and photo-stimulated luminescence (PSL) colors of NaGdGeO: Bi, Eu can be switched by varying the excitation modes (ultraviolet, near infrared, and X-ray light). Especially, the LPL and PSL colors of NaGdGeO: Bi, Eu vary with increasing decay and stimulation times. In addition, X-ray excitation ensures the specificity of the luminescence of NaGdGeO: Bi, Eu compared with ultraviolet excitation. This rapidly-changing-color fluorescent material offers the possibility of sophisticated anti-counterfeiting applications in the future.