Size dependent optical temperature sensing properties of Y₂O₃: Tb³⁺, Eu³⁺ nanophosphors

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The sizes of the sample particles were controlled by changing the molar ratio of the urea and rare earth ions. The microstructure and crystallographic structure of the sample were determined through powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FE-SEM). The test results show that the sample is body centered cubic. As the molar ratio of urea to rare earth ions increases, the size of the sample particles decreases. The temperature-dependent emission spectra of Tb³⁺, Eu³⁺ co-doped Y₂O₃ phosphors with different particle sizes were measured. The results showed that because the fluorescence intensity ratio (FIR) of Tb³⁺ and Eu³⁺ varies with temperature, it can be used to visually reflect changes in temperature. In addition, the temperature sensing sensitivity of Tb³⁺ and Eu³⁺ co-doped Y₂O₃ phosphors increased upon a decrease in the particle size, but the relative sensitivity decreased with a decrease in the particle size. The physical mechanism of the sensitivity and relative sensitivity changes with the size of the sample particles was also explained.