Luminescence Property, Color Tunability, and Optical Thermometry Behavior of Bismuth-Europium Codoped Strontium-Anorthite-Type Phosphors

Developing Bi³⁺-doped inorganic phosphors has aroused great interest in pursuing luminescent materials for optoelectronic and thermometrical applications. Herein, a new Sr₂Ga₂SiO₇:Bi³⁺,Eu³⁺ phosphor with a Ga-substituted strontium anorthite host had been synthesized and investigated. The Bi³⁺ singly doped phosphor exhibited asymmetry emission under UV excitation at 298 and 80 K despite the fact that there is only one Sr²⁺ site for Bi³⁺ to occupy from the crystal structure analysis. The X-ray photoelectron spectroscopy, luminescence–concentration relation, and metal-to-metal charge-transfer (MMCT) empirical analysis were used as tools to analyze the origin of the emission, which rule out the Bi²⁺, Bi³⁺ cluster, and MMCT emission and make us ascribe the asymmetric spectra to Bi³⁺ substituting for Sr²⁺ sites with different crystal environments because of the charge imbalance. By codoping the Bi³⁺ and Eu³⁺ in the host and utilizing the Bi³⁺–Eu³⁺ energy transfer, CIE coordinates as well as the emission color of the phosphors have been tuned. Moreover, based on the different response of emission intensity of the sensitizer and activator on the working temperature, the optical thermometry behavior of prepared Sr₂Ga₂SiO₇:Bi³⁺,Eu³⁺ has been investigated. At 503 K, the absolute and relative sensitivities of the sample with good cyclicity were calculated to be 0.0023 K^–1 and 0.56%K^–1, respectively, indicating that the obtained sample has potential value in being utilized as a phosphor for optical thermometers.