Multimode-Responsive Luminescence of Er3+ Single-Activated CaF2 Phosphor for Advanced Information Encryption

The current optical anticounterfeit strategies that rely on multimode luminescence in response to the photon or thermal stimuli have significant importance in the field of anticounterfeiting and information encryption. However, the dependence on light and heat sources might limit their flexibility in practical applications. In this work, Er³⁺ single-doped CaF₂ phosphors that show multistimuli-responsive luminescence have been successfully prepared. The as-obtained CaF₂:Er³⁺ phosphor exhibits green photoluminescence (PL) and color-tunable up-conversation (UC) luminescence from red to green due to the cross-relaxation of Er³⁺ ions. Additionally, as-obtained CaF₂:Er³⁺ phosphors also display green mechano-luminescence behavior, which is induced by the contact electrification between the CaF₂ particles and PDMS polymers, enabling the phosphor to flexibly respond to mechanical stimuli. Moreover, feasible anticounterfeiting schemes with the capability of multistimuli-responsive and flexible decryption have been constructed, further expanding the application of optical materials in the field of advanced anticounterfeiting and information encryption.