Nonstoichiometry-Induced Self-Activated Phosphors for Dynamic Anti-counterfeiting Applications

Optical signals with distinctive properties, such as contactless, fast response, and high identification, are harnessed to realize advanced anti-counterfeiting. However, the simultaneous attainment of multi-color, -temporal, and -modal luminescence performance remains a compelling and imperative pursuit. In our work, a temperature/photon-responded dynamic self-activated luminescence originating from nonstoichiometric Zn₂GeO₄ is developed with the modulation of intrinsic defects. The increased concentration of oxygen vacancies (V_O^••) contributes to an enhanced recombination of Zn_Ge^″-V_O^••, ultimately improving the self-activated luminescence performance. Additionally, the photoluminescence (PL) color of the representative Zn_2.2GeO₄ sample changes from green to blue-white with the increased ultraviolet (UV) irradiation time. Concurrently, the emission color undergoes a variation from blue to green as the ambient temperature raises from 280 to 420 K. Remarkably, green long persistent luminescence (LPL) and photostimulated luminescence (PSL) behaviors are observed. Herein, this study elucidates a sophisticated anti-counterfeiting approach grounded in the dynamic luminescent attributes of nonstoichiometric Zn₂GeO₄, presenting a promising frontier for the evolution of anti-counterfeiting technologies.