Manipulating photon absorption and trap energy supply for multimode dynamic anti-counterfeiting†

Developing advanced fluorescence anti-counterfeiting technologies can enhance the effectiveness of current anti-counterfeiting strategies by addressing their limitations. To meet this demand, an afterglow material Y₂CaSnGa₄O₁₂:Pr³⁺ (YCSG:Pr³⁺) exhibiting photochromic phenomena was engineered. This design capitalizes on the opposite effects of traps and color centers on emission intensity, thus ingeniously achieving excitation wavelength-dependent modifications in luminescence intensity. A thorough analysis of the energy conversion processes before and after irradiation by ultraviolet light was undertaken to discern the dominant role of color centers and traps under varying excitation conditions. Thereby, the dynamic energy conversion processes from traps and color centers to the luminescence center are established, showing a variety of output modes related to wavelength, irradiation time and distance. Furthermore, discrepancies in energy transfer efficiency from traps to different energy levels result in temperature-dependent spectral variations, consequently manifesting distinct colors in afterglow and luminescence at each temperature. This pioneering approach serves as a valuable blueprint for the development of multimode dynamic anti-counterfeiting materials capable of adapting to changes in temperature, irradiation time and irradiation distance by leveraging the synergy between traps and color centers.