Co-doping Zn2+/Sn4+ in ZnGa2O4:Cr3+ for dynamic near-infrared luminescence and advanced anti-counterfeiting

In the arena of advanced anti-counterfeit research, developing a multi-level, anti-counterfeit material with tunable luminescence is a hot topic. However, current research has mainly focused on the visible light signal, despite the fact that near-infrared is also suitable for optical anti-counterfeit applications. The importance of the near-infrared signal is because it is more difficult to observe than the visible light signal. Here, a new, persistent, luminescent, near-infrared material composed of Zn2+xGa4-2xSnxO8:0.5%Cr3+ (x = 0-0.4) has been synthesized using the sol-gel method. A new anti-site-like defect [Zn ' Ga- Sn.Ga]appeared after incorporating both Zn2+ and Sn4+, along with an intrinsic, anti-site defect [Zn ' Ga- Ga.Zn]. Specifically, the former and latter defects contributed to the deep and shallow traps, respectively. Introducing Zn2+ and Sn4+ resulted in a significant, two-fold enhancement of the NIR emission intensity. This led to an obvious improvement in its persistent luminescence. In the absence of light irradiation, the NIR emitted light lasted for several hours. If heated, the disappeared NIR signal reappeared and lasted for 10 min. Primarily due to both the shallow and deep traps, the prepared samples exhibited dynamic NIR luminescence behavior. This behavior then contributed to the dynamic display information. Collectively, these results indicate that persistent phosphors have great potential for use in advanced, optical anti-counterfeit materials, owing to their ability to afford higher security.