Cooling Condition Effect on Spectral Properties and Smartphone-Based Anticounterfeiting Application of Zn 3 Ga 2 Ge 2 O 10 /Cr 3+ Phosphors.

The influence of cooling history for the Zn 3 Ga 2 Ge 2 O 10 /Cr 3+ 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 Zn 3 Ga 2 Ge 2 O 10 / x mol % Cr 3+ ( x = 0, 0.05, 1, 2, 3, and 4) phosphors to achieve multimode anticounterfeiting was reported. It is found that with the increasing Cr 3+ 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 Cr 3+ . In addition, the persistent time of the Cr 3+ emission centered at 700 nm can be also tuned by various Cr 3+ concentrations. A possible mechanism was deduced to explain the afterglow phenomenon. Lastly, a flower pattern applied in anticounterfeiting was fabricated using the Zn 3 Ga 2 Ge 2 O 10 / x mol % Cr 3+ ( 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.