Tunable luminescence in Eu³⁺/Sm³⁺ doped Na₂YMg₂V₃O₁₂ for WLEDs and optical thermometry

In recent years, it has become a development trend to design multi-application luminescent materials with rare earth ion doping. In this work, a series of Eu³⁺/Sm³⁺ doped self-activated Na₂YMg₂V₃O₁₂ (NYMVO) phosphors were synthesized through a simple high-temperature solid-state reaction method. Interestingly, due to the energy transfer (ET) from the matrix to the activators, the luminescence color of the phosphors changed from turquoise to orange-red and yellow-green under near-ultraviolet (n-UV) 365 nm excitation. Based on the fluorescence intensity ratio of the matrix to Eu³⁺/Sm³⁺, the optical thermometry performances of the NYMVO:0.20Eu³⁺ and NYMVO:0.06Sm³⁺ phosphors were described. Notably, the maximum absolute sensitivity (S_a) values for NYMVO:0.20Eu³⁺ and NYMVO:0.06Sm³⁺ phosphors were 0.30 K^-1 and 0.032 K^-1, respectively. Correspondingly, the maximum relative sensitivity (S_r) values were 2.17 %K^-1 and 1.22 %K^-1, respectively. Moreover, the light-emitting devices based on NYMVO:0.20Eu³⁺ and NYMVO:0.06Sm³⁺ phosphors had excellent optical properties, with correlated color temperature (CCT) of 4552 K and 4470 K, and color-rendering index (CRI) of 84.6 and 88.5. These results suggested that the two vanadate phosphors prepared had potential applications in both warm white light-emitting diodes (WLEDs) and optical thermometry.