Understanding the power of luminescence ratiometric thermal history indicators driven by phase transitions: the case of Eu 3+ doped LaVO 4 .

Finding thermal history phosphors with high sensitivity and a consistent readout is required for reliable thermal history determination with high temperature resolution. This work presents a new thermal history phosphor based on the luminescence of Eu 3+ ions in LaVO 4 to meet these requirements. As demonstrated, raising the annealing temperature causes a structural phase transition from a low-temperature tetragonal phase to a high-temperature single-stranded phase. The associated change in the local point symmetry of the crystallographic site occupied by Eu 3+ ions result in a significant decrease in the emission intensity ratio of the 5 D 0 → 7 F 2 band relative to the 5 D 0 → 7 F 1 band, which enables the development of the ratiometric thermal history phosphor with the relative sensitivity of 0.38% °C -1 at 800 °C. Its applicative potential for thermal history readout was proved in the proof-of-concept experiment.