Multiple encrypted dynamic fluorescent anti-counterfeiting and optical temperature detection of Ca2Ge7O16:Cr3+, Mn2+

In this study, Ca2Ge7O16:Mn2+, Cr3+ is successfully synthesized using the solid phase method. Mn2+ ions occupy the Ca2+ cationic site, while Cr3+ ions occupy the octahedral Ge4+ cationic site within the Ca2Ge7O16 lattice. The crystal field strength of the Cr3+ ion is calculated, yielding a Dq/B value of 2.46. Spectral and fluorescence lifetime indicate efficient energy transfer from Mn2+ to Cr3+ ions with the efficiency to 33.5% as the concentration of Cr3+ ions increases. The energy transfer mechanism is determined to result from nearest-neighbor ion interactions. Temperature-dependent spectra reveal that the maximum absolute sensitivity (Sa) is 1.045% K-1 at 373 K, and the maximum relative sensitivity (Sr) is 0.75% K-1 at 303 K with a temperature resolution of 0.0315 K as an optical thermometer. Furthermore, Ca2Ge7O16:Mn2+, Cr3+ exhibit a prominent afterglow. As the Cr3+ ion increases, the emitted color of Ca2Ge7O16:Mn2+, Cr3+ changes from orange to deep red. The emissions and afterglow change with the temperature, which enables multiple encrypted dynamic fluorescence anticounterfeiting under 222 nm excitation.