Structural, luminescent, and temperature-dependent luminescence of Tb³⁺-doped silicate phosphors for non-contact thermometry applications

Recent developments in luminescent materials doped with rare-earth ions, particularly for optical thermometry and lighting applications, have garnered considerable attention. However, integrating multiple functionalities into a single material remains a challenge due to the differing requirements for thermal responsiveness. This study addresses this challenge by synthesizing Ba₂ZnSi₂O₇: Tb³⁺ phosphors. X-ray diffraction analysis confirms that these phosphors have a monoclinic structure. Optical tests reveal their luminescent properties, with blue light emission at 417 nm and green light at 544 nm when excited at 240 nm. These emissions are linked to transitions of ⁵D₃➔⁷F₃ and ⁵D₄➔⁷F₄ energy levels of Tb³⁺ ions, which were optimized for dopant concentration. The temperature-dependent photoluminescence (PL) exhibits an unusual thermal quenching behavior. By exploiting these unique temperature-dependent PL features, a dual-mode optical thermometer was developed using this material, achieving maximum relative sensitivities of 1.36% K⁻¹ for fluorescence intensity ratio. Additionally, using an optimized phosphor with strong optical temperature measurement capabilities, a temperature measurement model based on fluorescence lifetime was established, resulting in a maximum sensitivity ratio (S_R-Lifetime) of 2.02% K⁻¹. As a result, the Tb³⁺-doped Ba₂ZnSi₂O₇ phosphors show significant potential for UV-excitable warm lighting applications and non-contact optical thermometry applications, as demonstrated by the experimental results.