Eu³⁺-based dual-excitation single-emission luminescent ratiometric thermometry

Recently, single-band ratiometric (SBR) thermometry becomes a hot-spot in the research field of optical thermometry. Here we propose a new SBR thermometry by combining the temperature-induced red shift of charge transfer state (CTS) of W-O and Eu-O with the ground state absorption (GSA) and excited state absorption (ESA) of Eu³⁺. The emitting intensity of the ⁵D₀-⁷F₂ transition of Eu³⁺ is monitored under CTS, GSA and ESA excitations at different temperatures. It is found that the SBR thermometry, depending on the combination of [GSA + CTS] of Eu³⁺ doped calcium tungstate, has the highest relative sensitivity of 1.25% K^-1 at 573 K, higher than conventional luminescent ratiometric thermometry such as the ²H_11/2 and ⁴S_3/2 thermally coupled states of Er³⁺.