Dual-Emission-Center Strategy in Ca3Ga4O9:Er3+/Sm3+ Enables Color-Tunable Afterglow for Multimodal Luminescent Encryption Materials

Materials exhibiting long-persistent luminescence (LPL) in the visible spectrum hold pivotal importance for anti-counterfeiting and encryption. Nevertheless, conventional LPL materials typically only exhibit single-color afterglow emission. This constraint makes it imperative to develop multimodal luminescent systems featuring spectrally tunable afterglow. Herein, the Er3+/Sm3+ co-doped Ca3Ga4O9 phosphors achieve multicolor photoluminescence (PL), upconversion luminescence (UCL), and color-tunable LPL by responding to multiple excitations modes ranging from ultraviolet (UV) to near-infrared radiation (NIR). Spectral analysis reveals a green-to-orange multicolor afterglow by varying the relative concentrations of Er3+ and Sm3+ ions. To unravel the mechanism of multicolor afterglow, afterglow spectra and thermoluminescence (TL) spectra are systematically employed to probe the trap distribution mediated by Er3+ and Sm3+ co-doping. Finally, their prospective application in optical anti-counterfeiting and information encryption is also systematically investigated based on the color-tunable LPL. This successful integration of multicolor, multimodal luminescence with color-tunable afterglow in a single host provides a novel platform for anti-counterfeiting and encryption, significantly expanding the visual diversity of displayable information.