Trap depth engineering in MgGa2O4: Bi3+ for muticolor dynamic anti-counterfeiting, encryption and optical temperature sensing applications

Anti-counterfeiting and encryption are key technologies for information transmission in modern society. Whereas, most optical materials reported only provide single luminous color and fixed response mode, which limits their safety in advanced anti-counterfeiting applications. In this work, we reported a Bi3+-assisted trap depth engineering strategy to achieve a dual-mode dynamic photoluminescence response of MgGa2O4: Bi3+ with intriguing anti-counterfeiting and encryption performances. Upon the ultraviolet (UV) of 254 nm irradiation for 20 s, the color of MgGa2O4: x% Bi3+ (x = 0, 1.0, 2.0, 3.0, 5.0) samples showed dynamic transformation from green or near-infrared to bluish-white emission. Combined with the dynamic photoluminescent (PL) behavior of MgGa2O4: 2.0% Bi3+, high-level dynamic anti-counterfeiting and encryption properties of MgGa2O4: Bi3+ for tagging spies were investigated through powder filling followed by a masked screen printing method. On the other hand, the fluorescence intensity ratios (FIR) of I430 nm/I500 nm and I430 nm/I709 nm for MgGa2O4: 2.0% Bi3+ showed excellent temperature-dependent quenching behaviors in the temperature range of 283 to 393 K, and the relative temperature sensitivities for FIR of I430 nm/I500 nm and I430 nm/I709 nm are 2.18% and 2.98% K-1 at 283 K, respectively. These results inspired more flexible designs to safeguard information security and develop novel high-efficiency optical temperature detectors.