Opto/Thermoresponsive Multimode Luminescence in Eu- and Er-Activated CaF₂ Phosphor for High-Security...

As the landscape of information storage and security continues to evolve, the deployment of sophisticated anticounterfeiting strategies with robust security features and multimodal luminescent capabilities becomes imperative. In this work, Eu³⁺ and Er³⁺ ions are codoped into CaF₂ phosphors to achieve multimodel optical output. The self-reduction of Eu³⁺ within the CaF₂ matrix gives rise to the coexistence of Eu³⁺ and Eu²⁺ ions, which manifests as a color transition from orange to blue as the excitation wavelength is varied from 300 to 335 nm. Moreover, the distinct temperature-dependent behaviors of Eu³⁺ and Eu²⁺ ions underscore the material's visible temperature-sensitive luminescence properties, characterized by remarkable thermal sensitivity (S_a = 0.0156 K^-1, S_r = 0.83%K^-1). Additionally, the strategic introduction of Er³⁺ ions adds an extra dimension, enabling the realization of color-tunable upconversion luminescence through the fine-tuning of Er³⁺ concentration. This synergistic integration culminates in the establishment of an efficient three-path authentication model within the CaF₂ host matrix, facilitating a dynamic multicolor response to changes in the excitation wavelength and temperature. By harnessing these diverse luminescent modalities, the study delivers a versatile and potent anticounterfeiting solution, advancing the frontiers of information security.