Explaining the temperature-induced shift of the V-O charge transfer band experimentally and design of single-excitation ratiometric optical thermometry.

Abstract

Temperature-induced redshift of the V-O charge transfer band (CTB) is promising for designing high performance optical thermometry. The shift mechanism is considered as the thermal populations of high vibrational energy levels of the VO4 3- ground state. Direct experimental evidence for this, however, is still lacking. In this work, Tm3+-doped YVO4 with various doping concentrations was studied to achieve strong 1D2 emission of Tm3+. The temperature dependent CTB was studied at low temperatures to give direct evidence experimentally for the shift mechanism of the CTB using YVO4:20% Tm3+. It was found that the V-O CTB does not shift when the temperature is lower than a certain temperature (60 K), verifying the proposed shift mechanism experimentally. In addition, based on the temperature quenching of 1D2 emission of Tm3+ and the redshift of the CTB, single-excitation ratiometric thermometry was carried out using YVO4:30% Tm3+,6% Sm3+. High relative sensitivity was achieved with a maximal value reaching up to 3.86% K-1 at approximately 355 K.