Investigation on Two Forms of Temperature-Sensing Parameters for Fluorescence Intensity Ratio Thermometry Based on Thermal Coupled Theory

Abstract

Absolute temperature sensitivity (S_a) reflects the precision of sensors that belong to the same mechanism, whereas relative temperature sensitivity (S_r) is used to compare sensors from different mechanisms. For the fluorescence intensity ratio (FIR) thermometry based on two thermally coupled energy levels of one rare earth (RE) ion, we define a new ratio as the temperature-sensing parameter that can vary greatly with temperature in some circumstances, which can obtain higher S_a without changing S_r. Further discussion is made on the conditions under which these two forms of temperature-sensing parameters can be used to achieve higher S_a for biomedical temperature sensing. Based on the new ratio as the temperature-sensing parameter, the S_a and S_r of the BaTiO₃: 0.01%Pr³⁺, 8%Yb³⁺ nanoparticles at 313 K reach as high as 0.1380 K^-1 and 1.23% K^-1, respectively. Similarly, the S_a and S_r of the BaTiO₃: 1%Er³⁺, 3%Yb³⁺ nanoparticles at 313 K are as high as 0.0413 K^-1 and 1.05% K^-1, respectively. By flexibly choosing the two ratios as the temperature-sensing parameter, higher S_a can be obtained at the target temperature, which means higher precision for the FIR thermometers.