Optical thermometry based on upconversion luminescence in Yb3+/Ho3+ co-doped NaLuF4

Short wavelength upconversion luminescence of Ho3+ was investigated for temperature sensing with fluorescence intensity ratio (FIR) technique in Yb3+/Ho3+ co-doped β-NaLuF4 hexagonal microprisms synthesized by hydrothermal method. The origins of two emission peaks located at 482.0 nm and 443.6 nm were identified for the first time. Further study on temperature dependence of 980 nm-excited upconversion FIR between two thermally coupled multiplets (5F1/5G6 and 5F2,3/3K8) was carried out from 390 K to 780 K. The FIR increases with temperature monotonously and the experimental data are well fitted with a theoretical function. A large energy difference (1438 cm−1) is obtained from the fitting curve, which could account for a higher relative sensitivity in this system than most RE3+ doped FIR-based temperature sensors, making this optical material a promising candidate for high-sensitive temperature sensing.