A high-precision thermometry strategy by replacing the infrared with visible light for detection.

We have developed a high-precision thermometry strategy based on I-I (I) and S-I (I) transitions of Er, after replacing the measurement of the I-I (I) transition with the S-I transition, i.e., using visible light for detection instead of infrared. Through rate equation model analysis, (I) and I can be substituted for each other under certain conditions. Further, because the I and I levels of Er are thermally coupled, a new idea of ratiometric thermometry is proposed based on the ratio of (I) and I, which has the advantages of anti-interference of excitation light source fluctuation and background-free detection. The feasibility of the idea was verified by researching the power-dependent emission spectra at different temperatures and temperature-dependent emission spectra of a CaWO:Er,Yb sample under 980-nm laser excitation. The maximum relative sensitivity for the new ratiometric thermometry reaches up to 7.4% K and the optimal temperature uncertainty calculated is 0.03 K at 303 K. This study provides guidance for solving the problem of a weak response of an infrared detector.