Analysis of Optical Temperature Sensing Performance of Alkali Metal Doped Na_0.5Gd_0.5TiO₃: Yb, Er Based on Judd‐Ofelt Theory and First Principles Calculations

Abstract In alkali metal‐doped optical temperature measurement materials, the influence of the electronegativity difference of alkali metal ions on optical temperature measurement performance is rarely reported. This study investigates and analyzes the performance of optical temperature measurement of Na_0.5Gd_0.5TiO₃: Yb, Er doped with Li⁺ and K⁺ ions, utilizing the Judd‐Ofelt theory and the first‐principles method. The results reveal that the sensitivities increase with the increase of atomic number of doped alkali metal ions. The reason is that a difference in ionic radius between the dopant and the replaced ion decreases the symmetry of the crystal field and increases the value of Ω₂. The doping K⁺ with low electronegativity leads to an increase in the s orbital electron density of rare earth ions, thereby repelling the d orbital electrons, reducing the d electron density, and decreasing the value of Ω₆. Based on the Judd‐Ofelt theory, a combination of a large Ω₂ and a small Ω₆ is expected to enhance the absolute sensitivity of optical temperature‐measuring materials doped with rare earth ions. Therefore, it can be concluded that doping an ion with low electronegativity and a significant radius difference from the substitution site is beneficial for enhancing the optical temperature sensitivity.