A novel optical thermometry strategy: Based on the combined effects of red-shift charge transfer band and thermal coupling

The non-contact temperature measurement method based on the fluorescence intensity ratio of thermally coupled energy levels has emerged as a focal point of research in recent years due to its characteristics of short response time, suitability for extreme environments, and high sensitivity. The enhancement of relative sensitivity (Sr) is a key objective in refining ratio-metric optical thermometry. However, the Sr is limited by the thermometry strategies. Regarding excitation and monitoring methods, ratio-metric temperature measurement strategies typically adopt two distinct approaches: single-excitation dual-emission (S-D), and dual-excitation single-emission (D-S). In this study, we developed a dual-excitation dual-emission (D-D) thermometry strategy that theoretically and experimentally demonstrates higher Sr and reduced temperature uncertainty (δT). This advancement was achieved by analyzing thermal coupling energy levels (TCELs) and the red-shift charge transfer band (CTB) properties. YVO4:Er3+ was selected for experimental validation due to its pronounced thermal coupling and red-shift CTB effects. The experimental results show that the Sr(D-D) equal to the sum of Sr(S-D) and Sr(D-S), and 1/δT(D-D) equal to the sum of 1/δT(S-D) and 1/δT(D-S), which well verifies the theoretical expectations. Thus, the D-D strategy emerges as a novel and effective method for ratio-metric thermometry, promising enhanced precision in temperature measurements.