Multimodal synergistic thermometry: designing wide-range optical thermometers via Eu³⁺/Er³⁺ co-doped YVO₄

In this paper, a five-mode synergistic thermometry system based on Eu³⁺/Er³⁺ co-doped YVO₄ fluorescent material was developed. By utilizing the spectral properties of the phosphor, two luminescence intensity ratio (LIR) and two excitation intensity ratio (EIR) thermometry modes were established, and the luminescence lifetime thermometry (τ) mode of Eu^{3+ 5}D₀ → ⁷F₂ was also introduced into this system. The S_r values of both Er³⁺- and Eu³⁺/Er³⁺-based LIR modes decrease with increasing temperature, and the maximal value of S_r (S_rmax) is 0.98% K^-1 at 300 K. Similarly, the EIR mode via V-O charge transfer (monitoring Er³⁺ emissions) shows a declining S_r trend, and the S_rmax of the EIR mode via V-O charge transfer (monitoring Er³⁺ emissions) is 1.01% K^-1 at 300 K. Unlike conventional LIR systems, the EIR mode based on Eu³⁺ (⁷F₀ → ⁵D₄/⁷F₀ → ⁵L₆) exhibits a distinctly different temperature dependence in its S_r value, and at 500 K the S_rmax of S_r of YVO₄:Eu³⁺,Er³⁺ can reach 0.65% K^-1. The S_rmax of the τ mode can reach 0.71% K^-1 at 500 K, which is superior to that of other systems. Notably, the EIR and τ modes address the limited high-temperature sensitivity of Boltzmann-type thermometry. In short, the YVO₄:Eu³⁺,Er³⁺ phosphor exhibits excellent thermometric performance and application potential.