Eulytite-type Ba3Yb(PO4)3:Tm/Er/Ho as a high sensitivity optical thermometer over a broad temperature range

Abstract

Application of optical thermometers requires maintaining high sensitivity over the entire temperature range. Based on the Eulytite-type host Ba₃Yb(PO₄)₃, we have successfully constructed four different up-conversion (UC) phosphors by individually doping Tm, Er, and Ho and co-doping Tm/Er/Ho. The UC luminescence spectra, color purity, brightness, and energy transfer mechanisms of these four phosphors were thoroughly investigated. The optical temperature sensing properties of the four phosphors were evaluated using thermally coupled or non-thermally-coupled fluorescence intensity ratio (FIR). Our optical thermometer, which can maintain high sensitivity (S_r > 0.65% K⁻¹) over the whole temperature measurement range of 303–603 K, was successfully designed by selecting and using temperature-sensitive energy level transitions from different active ions in Ba₃Yb(PO₄)₃:Tm/Er/Ho phosphors. These results confirm that Ba₃Yb(PO₄)₃:Tm/Er/Ho is a material with application potential in optical temperature measurement.