Multimodal synergistic thermometry: designing wide-range optical thermometers <i>via</i> 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 (<i>τ</i>) mode of Eu^{3+ 5}D₀ → ⁷F₂ was also introduced into this system. The <i>S</i>_r values of both Er³⁺- and Eu³⁺/Er³⁺-based LIR modes decrease with increasing temperature, and the maximal value of <i>S</i>_r (<i>S</i>_rmax) is 0.98% K^-1 at 300 K. Similarly, the EIR mode <i>via</i> V-O charge transfer (monitoring Er³⁺ emissions) shows a declining <i>S</i>_r trend, and the <i>S</i>_rmax of the EIR mode <i>via</i> 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 <i>S</i>_r value, and at 500 K the <i>S</i>_rmax of <i>S</i>_r of YVO₄:Eu³⁺,Er³⁺ can reach 0.65% K^-1. The <i>S</i>_rmax of the <i>τ</i> mode can reach 0.71% K^-1 at 500 K, which is superior to that of other systems. Notably, the EIR and <i>τ</i> 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.