Self-Structural Regulation-Oriented Adjustable Optical Properties of SrGa₂Si₂O₈: Mn²⁺, Cr³⁺ toward Anticounterfeiting, Encryption, and Optical Thermometry Applications

Unlike static anticounterfeiting that is easily replicated, dynamic multimode photoluminescence (PL) technology has a brighter application prospect in anticounterfeiting/encryption. Yet, the majority of dynamic PL phosphors currently still rely solely on the optical storage mechanism, resulting in a scarcity of diversification, and can easily be decoded. Herein, a series of SrGa2Si2O8: Mn2+/Cr3+ (SGS: Mn/Cr), synthesized via a facile solid-state reaction, is designed to explore interrelationships among entangled changes in the host structure, crystallographic site occupancy, dynamic multimode PL, and multiapplications in anticounterfeiting, encryption, and optical thermometry, based on theoretical calculations and experimental analyses. Although pristine SGS only provides 7(Sr)- and 4(Ga, Si)-fold sites for dopants to occupy, highly efficient characteristic broadband red-NIR emission at ∼765 nm from Cr3+ in 6-fold crystallographic position is obtained as a result of fine-tuning of the local site from [GaO4] to [Ga(Cr)O6] and the close ionic radius in the same valence. Based on the spectral superposition of Mn2+ simultaneously from [Ga(Mn)O4], [Sr(Mn)O7], and Mn–Mn dimers, broadband PL in the green region with a summit of ∼530 nm is gained. The green- and red-NIR afterglows from Mn2+ and Cr3+ with wide and continuous multiple traps are also studied. Owing to the combined PL from the codoped SGS: Mn/Cr, which shows strong correlations with excitation wavelength, doping content, composition, temperature, and detecting time, dynamic multimode PL is realized under distinct test conditions, and the corresponding applications are achieved in the laboratory. This study gives new cogitations in structural adaptabilities for Cr-activated phosphors and their related actual applications.