Cooling Condition Effect on Spectral Properties and Smartphone-Based Anticounterfeiting Application of...

The influence of cooling history for the Zn₃Ga₂Ge₂O₁₀/Cr³⁺ phosphors prepared by solid state reaction on the spectral properties was discovered, and an anticounterfeiting scheme based on the identification with smartphone was proposed and experimentally demonstrated using the studied phosphors. A combination of color-tunable visible fluorescence emission and near-infrared (NIR) afterglow emission in Zn₃Ga₂Ge₂O₁₀/x mol % Cr³⁺(x = 0, 0.05, 1, 2, 3, and 4) phosphors to achieve multimode anticounterfeiting was reported. It is found that with the increasing Cr³⁺ concentrations, the visible emission can be tuned from green, light pink, and light red to deep red under 254 nm ultraviolet (UV) excitation. This phenomenon is related to the formation of oxygen vacancies in the host during the process of natural cooling and the characteristic emission of Cr³⁺. In addition, the persistent time of the Cr³⁺ emission centered at 700 nm can be also tuned by various Cr³⁺ concentrations. A possible mechanism was deduced to explain the afterglow phenomenon. Lastly, a flower pattern applied in anticounterfeiting was fabricated using the Zn₃Ga₂Ge₂O₁₀/x mol % Cr³⁺ (x = 0, 0.05, 1, 2, 3, and 4) phosphors to present tunable color and NIR afterglow signals at different excitation modes, and the camera of smartphone was chosen as a detection tool to take the NIR images. The results obtained above suggest that the prepared phosphors at natural cooling condition have great potential in affording advanced optical anticounterfeiting.