Multi-color afterglow of the LiGa5O8:Tb3+/Sm3+ co-doped gallosilicate glass via energy transfer and trap sharing for optical anti-counterfeiting†

Long afterglow materials with excellent optical properties and stable performance are urgently required, particularly in the fields of anti-counterfeiting and encryption. Nowadays, glass ceramics are promising candidates for afterglow, due to their good ability to capture photons and robust chemical stability. Here, a series of Tb³⁺/Sm³⁺ co-doped gallosilicate glass precursors were prepared via a high-temperature melting method, forming transparent glass ceramics containing LiGa₅O₈ nanocrystals by heat-treatment. The afterglow phenomenon was observed in these samples after turning off UV irradiation, and subsequent investigation showed that, by controlling the concentration of two rare earth ions Tb³⁺ and Sm³⁺, the afterglow could be transitioned from green (LiGa₅O₈:Tb³⁺) to orange (LiGa₅O₈:Sm³⁺) and then to yellow (LiGa₅O₈:Tb³⁺,Sm³⁺). Structural analysis reveals that Tb³⁺ and Sm³⁺ ions have occupied the octahedral sites (Ga sites) in the LiGa₅O₈ anti-spinel structure, which makes them close to intrinsic defects beneficial for the afterglow. Furthermore, the process of energy transfer from Tb³⁺ to Sm³⁺ ions and the sharing of oxygen vacancy defects are importantly outlined in order to elucidate the mechanism behind the multi-color afterglow phenomenon. The tunable afterglow-emitting glass ceramics provide a novel approach for optical anti-counterfeiting and information encryption, thereby enriching the visual diversity of displayed information.