Ternary afterglow and dynamic anti-counterfeiting applications of self-activated zinc germanate

Abstract

Up to now, there is still a lack of understanding of luminescence and afterglow in connection with native defects in self-activated zinc germanate (Zn₂GeO₄, abbreviated as ZGO). In this paper, a series of zinc–germanate (Zn/Ge) samples with various ratios were prepared via a high temperature solid-state method under different sintering atmospheres to analyze their self-activated luminescence characteristics. All ZGO samples exhibited ternary persistent luminescence with blue (430 nm), green (530 nm), and near-infrared (NIR, 800 nm) emissions, each with different decay rates, and a NIR afterglow with higher intensity than green emission was observed for the first time in undoped ZGO materials. By studying the effects of different synthesis conditions, native luminescence linked with ternary persistent luminescence bands was discussed; consequently, a reasonable afterglow mechanism was proposed for the self-activated system. Furthermore, aliovalent Al³⁺-doped self-activated ZGO (abbreviated as ZAGO) showed better luminescence and afterglow properties, with yellow (632 nm) light emission enhanced by 10 times and green (530 nm) light afterglow increased by 18.5 times compared with ZGO. Finally, taking advantage of the unique yellow light and enhanced green afterglow, dynamic anti-counterfeiting applications were achieved.