Dual-emission-center strategy in Ca3Ga4O9:Er3+/Sm3+ enables color-tunable afterglow for multimodal luminescent encryption materials

Abstract

Materials exhibiting long-persistent luminescence (LPL) in the visible spectrum hold pivotal importance for anti-counterfeiting and encryption. Nevertheless, conventional LPL materials generally possess a fixed afterglow color. 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.