Temperature sensing properties of NaYTiO4: Yb/Tm phosphors based on near-infrared up-conversion luminescence

In this study, NaYTiO 4 : Yb/Tm phosphors with different concentrations of Yb 3+ and Tm 3+ ions were synthesized by conventional solid-state reaction. Upon a 980 nm laser excitation, the up-conversion luminescence properties in a wide temperature range (303–823 K) were investigated. By employing the fluorescence intensity ratio (FIR) techniques based on the robust near-infrared emissions of thermally coupled 3 F 2,3 / 3 H 4 energy levels and 3 H 4(1) / 3 H 4(2) Stark energy levels, the calculated absolute sensitivity (S a ), relative sensitivity (S r ), and temperature uncertainty (δT) values demonstrated good temperature sensing properties. For the 3 F 2,3 / 3 H 4 energy levels, the maximum S r and minimum δT values are 1.04% K −1 and 0.010 K at 463 K, respectively. Moreover, the maximum S a is 0.32 × 10 −3  K −1  at 823 K. In addition, the thermally coupled 3 H 4 Stark energy levels present the maximum S a , S r and the minimum δT are 0.88 × 10 −3  K −1 , 0.60% K −1 and 3.17 K at 303 K, respectively. Besides, due to the ratio of blue to red emission varying with elevated temperature, the NaYTiO 4 : Yb/Tm phosphors are expected to be applied as an intuitive high-temperature indicator.