Site-Selective Occupancy of Mn²⁺ Enabling Adjustable Red/Near-Infrared Multimode Luminescence in Olivine for Dynamic Anticounterfeiting and Encryption

Transition metal Mn2+ ion activated luminescent materials with tunable visible emission and high color purity features are crucial for mondern lighting and displays and so forth. Herein, in contrast to the conventional visible emission of Mn2+, an olivine phosphor, Mg2GeO4:Mn2+, with adjustable red (centered at ∼ 650 nm)/NIR (centered at∼ 735 nm) emissions is demonstrated by doping Mn2+ ions into two different distorted octahedral MgO6 sites guided by theory simulation. By varying the doping content of Mn2+ ions, the red/NIR dual-wavelength emissions to a pure-NIR emission can be easily achieved in this system, and the luminescence properties are in good agreement with the theoretical analysis. Morevoer, when suitable defect traps are introduced in the band gap of Mg2GeO4 via Yb3+ ion codoping, adjustable red/NIR persistent luminescence and photostimulated luminescence are further realized in both Mg2GeO4:Mn2+,Yb3+ phosphor, and the ceramics. A reliable anticounterfeiting/dymamic information encryption technique is presented by the combination of as-prepared Mg2GeO4:Mn2+ and Mg2GeO4:Mn2+,Yb3+. This study not only provides a multimode luminescent material for dynamic anticounterfeiting and encryption, but also provides insights into the NIR emission of Mn2+.