Garnet-structured persistent luminescence phosphor Ca₃Al₂Ge₃O₁₂:Cr³⁺ for dynamic anticounterfeiting applications

Abstract

Fluorescent materials have gradually become a hot spot in the field of anti-counterfeiting. Multifunctional phosphors used in anti-counterfeiting designs still have the problems of disordered reading sequences, difficulty in detection, and easy forging. To resolve these problems, we propose a new flexible dual-mode anti-counterfeiting design using a series of phosphors Ca₃Al₂Ge₃O₁₂:Cr³⁺ (CAG) with deep red persistent luminescence peaking at 722 nm. By adjusting the doping concentration of Cr³⁺ from 2% to 6%, deep red persistent luminescence with different afterglow intensities and durations can be achieved. By performing a series of thermoluminescence (TL) experiments under different conditions, the defects in materials were comprehensively and systematically analyzed. The defects contributed to the deep and shallow traps; this led to an obvious improvement in its long persistent luminescence (LPL). Such a dual-mode system with flexibility and simplicity properties is a good choice not only for anti-counterfeiting, but also for multi-layer information encryption, and a series of demo experiments based on the digital tube, Moss code, QR code, bar-code, school celebration pattern, and love letter information encryption design were implemented. Their dynamic anti-counterfeiting applications have been demonstrated, which provides a new way to rationally design multi-functional luminescent materials.