Stokes and anti-Stokes operating conditions dependent luminescence thermometric performance of Er3+-doped and Er3+, Yb3+ co-doped GdVO4 microparticles in the non-saturation regime

Abstract

Er3+-doped and Er3+-Yb3+ co-doped GdVO4 crystals with different Er3+ and Yb3+ concentrations have been synthesized by the high temperature solid-state reaction method. The X-ray powder diffraction patterns indicated that the obtained materials were pure tetragonal phase. The different performance of these luminescent thermometers in terms of thermal sensitivities and temperature uncertainties when operated under conditions of down or up-conversion were studied, in the non-saturation regime, using the self-referenced fluorescence intensity ratio technique. The calculated absolute and relative sensitivities and temperature uncertainties, in the 300–453 K temperature range can be found in the range 7.16–12.56 10−3 K−1, 0.83–1.34% K−1 and 0.37–0.60 K, respectively, with the low temperature bound determined to be 110–150 K. This work confirmed that a thermal effect generated by the excitation light can be ignored in the down-conversion luminescence process, while it has some implications in the upconversion luminecence mechanism. Therefore, the down-conversion emission gives rise to the highest thermal sensitivities and the best thermal resolution in comparison with the up-conversion emission, with values of 1.34% K−1 and 0.37 K at 300 K, respectively, in 2 at.% Er, 8 at.% Yb: GdVO4 MCs. These results reveal that it is preferable to operate these materials for luminescence temperature sensors under a down-conversion process to achieve the best performance.