Upconversion luminescence of NaYF₄: Yb³⁺, Er ³⁺ for temperature sensing

Rare earth doped luminescent materials are promising candidates for temperature sensing. In this paper, pure β-NaYF₄:20%Yb ³⁺, 2%Er³⁺ microprisms were synthesized by hydrothermal method. The temperature dependence of the fluorescence intensity ratio (FIR) of emission bands centered at 525 nm and 545 nm was measured in the temperature range of 160-300 K under excitation of a 980 nm diode laser. The monotonous increase of FIR with temperature shows that this material can be used for temperature sensing. The dependence of the FIR on temperature is fitted with an exponential function and the effective energy difference obtained is 752 cm ^-1, which gives further a temperature sensitivity of 1.20% K ^-1 at 300 K. The FIR technique was then used to study the effect of heating caused by laser excitation under various powers.