Yuzhen Wang,Yanbin Li,Chaoyang Ma,Zicheng Wen,Xuanyi Yuan,Yongge Cao
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.
Developing novel optical thermometry with ultrahigh relative sensitivity and temperature resolution has become a cutting-edge topic. For this purpose, under obeying Boltzmann distribution , a series of Li 2 Zn 0.9992-x A x Ge 3-y B y O 8 :0.08% Cr 3+ (B= Sc 3+ , In 3+ , A = Si 4+ ) phosphors were studied, which the luminescence intensity ratio between the transition of 4 T 2g → 4 A 2g emission and the R line based on thermally coupled energy levels constitutes a temperature sensing work with a relative sensitivity of 9.46% K −1 , 9.73% K −1 , and 10.38% K −1 , respectively. It is worth mentioning that the luminescence intensity of the R line (peak 1) increases significantly with the increase of temperature, while the transition of 4 T 2g → 4 A 2g (peak 2) with high intensity at low temperature gradually quenching, and this opposite trend is an important advantage for the design of excellent thermometers. Compared the best relative sensitivity of Li 2 Zn 0.9992-x A x Ge 3-y B y O 8 :0.08%Cr 3+ (B= Sc 3+ , In 3+ , A = Si 4+ ) with the crystal field Dq /B, it can be concluded that relative sensitivity increasing gradually with decreasing the intensity of crystal field. Finally, by testing the stability of the sample at 50 K, a thermal resolution of 0.082 K, 0.080 K and 0.077 K was obtained, respectively, which is one of the best thermal resolutions so far, while the repeatability of the sample stability at 50 K and 300 K cycles was higher than 99%. Our work is expected to provide guiding insights for optimizing the sensitivity of Cr 3+ -based luminescence intensity ratio thermometers.
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