Luminescence and Thermometric Properties of Ba₂LaSbO₆:Eu³⁺/g-C₃N₄ Mixed Materials

In this study, a series of Ba₂La_1- xSbO₆:xEu³⁺ (x = 0, 5, 10, 15, 20, 25 mol%) phosphors and graphitic carbon nitride (g-C₃N₄) powders were synthesized via a high-temperature solid-phase method. Their structural and luminescent properties are characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence spectra. Upon excitation at 273 nm, Ba₂LaSO₆:Eu³⁺ exhibits pronounced red emission, demonstrating anti-thermal quenching behavior within the temperature range of 313-453 K. At 453 K, its emission intensity reaches 131.3% of its initial intensity measured at 313 K. In contrast, g-C₃N₄ shows rapid thermal quenching, with emission intensity dropping to 12.0% at 573 K compared to that at 313 K. A mixed material, composed of Ba₂LaSO₆:10 mol%Eu³⁺ and g-C₃N₄, demonstrates dual-mode thermometric performance. Using fluorescence intensity ratio (FIR), the maximum absolute sensitivity (S_a) and relative sensitivity (S_r) are determined to be 1.34% K^-1 (522 K) and 1.53% K^-1 (368 K), respectively. Temperature characterization using color coordinate (CIE) shifts achieves maximum S_a and S_r values of 0.16% K^-1 (313 K) and 0.63% K^-1 (313 K), respectively. Additionally, the mixed material exhibits excellent repeatability, achieving a repeatability parameter (R) of 98.8% for FIR and 98.9% for CIE measurements across five temperature cycles. These results underscore the potential of the mixed material for self-calibrating optical thermometers.