Tunable luminescence of Eu²⁺/Eu³⁺-activated La_5.5Ca_4.5P_2.5Si_3.5O₂₆ phosphors for ratiometric optical thermometry and...

To develop new phosphors for non-contact optical thermometry and high-level anti-counterfeiting, the dual-emission Eu³⁺-doped La_5.5Ca_4.5P_2.5Si_3.5O₂₆ (LCPS) phosphors were synthesized, and their luminescence properties were systematically investigated. The spectra reveal that the coexistence of bivalent states (Eu²⁺ and Eu³⁺) are successfully achieved by exploiting the incomplete reduction during the synthesis process. By systematically characterizing the excitation and emission spectra, the fluorescence intensity ratio (FIR) of the prepared phosphors with temperature was analyzed. Driven by the distinct thermal quenching behaviors of Eu²⁺ and Eu³⁺, the samples exhibit significant temperature response within the range of 298-498 K, yielding a maximum relative sensitivity (S_R) of 0.98% K^-1. Furthermore, the designed anti-counterfeiting device displays remarkable multimodal luminescence phenomena under natural light, various excitation wavelengths, and thermal stimuli. This study not only validates the potentiality of the LCPS-based phosphors for non-contact optical thermometry but also leverages the multivalent dynamic luminescence introduced by incomplete reduction for designing high-security and multi-stimulus-responsive anti-counterfeiting strategy.