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

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 BaTiO 3: 0.01%Pr 3+, 8%Yb 3+ 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 BaTiO 3: 1%Er 3+, 3%Yb 3+ 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.