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

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.