Regulating Mn2+/Mn4+ Activators in ZnGa2O4 via Mg2+/Ge4+ Doping to Generate Multimode Luminescence for Advanced Anti-Counterfeiting

Traditional fluorescent anti-counterfeiting materials usually display monochromatic luminescence at a fixed excitation mode, which greatly reduces the efficiency of anti-counterfeiting applications. Recently, developing a multilevel anti-counterfeiting material with tunable photoluminescence is a hot topic in the arena of advanced anti-counterfeit research. Here, spinel- structured solid solutions of ZnGa2-x(Mg/Ge)(x)O4:0.001Mn (x = 0-1.2) have been successfully synthesized by a high-temperature solid-state reaction. In this solid solution, Mn2+ and Mn4+ ions were substituted for the tetrahedral site (Zn site) and the octahedral site (Ga site), respectively, which emitted a green light at similar to 505 nm with afterglow and a red light at similar to 668 nm with the absence of afterglow. The Mn2+ and Mn4+ luminescent centers in ZnGa2O4 were effectively regulated by the incorporation of Mg2+/Ge4+, which resulted in more Mg2+ ions occupying the Zn site and thus leading to more Mn4+ ions in the Ga site and less Mn2+ ions in the Zn site. Therefore, doping Mg2+/Ge4+ contributed to a greatly enhanced red emission for Mn4+ ions at similar to 668 nm and a weakened green emission for Mn2+ ions at similar to 505 nm. The luminescent materials prepared in this study show dynamic and multicolor changes and a higher anti-counterfeiting security, indicating that they have potential for use in advanced luminescent anti-counterfeit materials. The research results in this work provide guidance for the development of multimode luminescent materials in anti-counterfeiting applications.