Ultra-sensitive low-temperature thermometer regulated by the crystal field strength

Abstract

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 Li2Zn0.9992-xAxGe3-yByO8:0.08% Cr3+ (B= Sc3+, In3+, A = Si4+) phosphors were studied, which the luminescence intensity ratio between the transition of 4T2g→4A2g 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 4T2g→4A2g (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 Li2Zn0.9992-xAxGe3-yByO8:0.08%Cr3+ (B= Sc3+, In3+, A = Si4+) 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 Cr3+-based luminescence intensity ratio thermometers.