The Creation of Multimode Luminescent Phosphor through an Oxygen Vacancy Center for High-Level Anticounterfeiting

Integrating multimode optical properties into a single material simultaneously is promising for improving the security level of fluorescent anticounterfeiting. However, there has been a lack of affirmative principles and unambiguous mechanisms that guide the design of such material. Herein, we achieve color-tunable photoluminescence, long-lived persistent emission, thermally stimulated luminescence, and reversible photochromism in a Tb³⁺-activated Mg₄Ga₈Ge₂O₂₀ phosphor by employing the F-like color center as an energy reservoir. It is experimentally revealed that the role of oxygen vacancies in the lattice of Mg₄Ga₈Ge₂O₂₀ is assumed as the main trap for the photogenerated electronic carriers, which is the origin of metastable F-like color centers. The formed color centers with the estimated depths of 0.48-0.95 eV could suppress the recombination of electron-hole pairs, thus giving rise to good photochromism and persistent emission properties, while under various modes of stimulation such as thermal attack or photo radiation, a quick recombination of electron holes happens, accounting for the bright thermally stimulated luminescence and the accompanied color bleaching. Finally, we fabricate a flexible phosphor/polymer composite by encapsulating the developed phosphor into a polydimethylsiloxane matrix, and conceptual demonstration of the composite for the high-security fluorescent anticounterfeiting technology, by virtue of multimode optical phenomena as authentication signals.