Local charge regulation by doping Li+ in BaGa2O4:Bi3+ to generate multimode luminescence for advanced optical Morse code

In the field of advanced anti-counterfeiting research, it is a hot issue to develop a multimodal anti-counterfeiting material with adjustable luminescence characteristics. Here, persistent luminescent materials of BaGa2O4:xBi3+ (x = 0-0.02) and BaGa2O4:0.005Bi3+,yLi+ (y = 0.001–0.02) were synthesized by a solid state reaction at high temperature. BaGa2O4: Bi3+ exhibited a broad blue emission at ∼470 nm (transition from [GaO4]) and a sharp NIR emission at ∼710 nm (3P1→1S0 transition of Bi3+), upon UV excitation at 250 nm. Incorporation of Li+ in BGO: 0.005Bi3+ induced the emission color shifting from blue to green. After stoppage of UV excitation, the BGO:0.005Bi3+ exhibited white afterglow with emission peaks at the range of 500–700 nm. However, incorporation of Li+ leaded to a stronger green afterglow and a weaker NIR afterglow. When the afterglow disappeared, the sample outputted afterglow again after heating processing. The prepared samples exhibited time- and temperature-dependent multimode luminescence, so they were used as components, combined with Morse code to realize multi-modal dynamic anti-counterfeiting. The outcomes in this work indicate that the prepared luminescent materials have broad prospects in advanced anti-counterfeit applications.