High temperature sensing performance based on optical thermometry in ZnAl2O4:Eu3+-ZnTiO3:Mn4+ mixed composites

Multiphase phosphors have garnered increased attention for their notable photothermal sensing properties. The temperature sensitivity of multiphase composites is significantly influenced by heat treatment, which impacts the interfacial diffusion of emitting centers. This study delved into the structural and optical properties of ZnAl2O4:Eu3+-ZnTiO3:Mn4+ composites with varying annealing temperatures. Distinct photoluminescence spectra of Eu3+ were observed in ZnAl2O4 matrix, accompanied by a robust emission band corresponding to the 2Eg →4A2g transition of Mn4+ in cubic ZnTiO3 crystals. Notably, a sharp emission band at 714 nm emerged as the measurement temperature decreased, which is attributed to Mn4+ in hexagonal ilmenite ZnTiO3. The emission intensity of Mn4+ in mixed phosphors decreased with increasing annealing temperature. The temperature dependence of emission peaks was investigated in two temperature regions of 80–260 K and 300–390 K for the ZnAl2O4:Eu3+-ZnTiO3:Mn4+ mixed phosphors with varying annealing temperatures. A second heat treatment at different temperature significantly influenced the optical properties associated with Eu3+ and Mn4+. In low temperature region, the highest temperature relative sensitivity reached 2.83% K−1 @230 K for the composites annealed at 1073 K. In high temperature region, the maximum relative sensitivity of 4.86% K−1@300 K was achieved based on the FIR of I614 nm/IMn4+ in both the as-synthesized composites and those annealed at 1073 K. All the phosphors demonstrated excellent repeatability over 15 recycles. The findings suggested that ZnAl2O4:Eu3+-ZnTiO3:Mn4+ mixed phosphors had significant potential applications in optical thermometers.