Up-conversion thermometry based on Tm3+/Yb3+ co-doped Ba5Gd8Zn4O21 phosphors

Optical thermometry based on fluorescence intensity ratio of rare earth ions has attracted widespread attention due to its non-contact, fast response time, immune to interference and high sensitivity. In this study, we developed Tm³⁺/Yb³⁺ doped Ba₅Gd₈Zn₄O₂₁ phosphors for temperature sensing purposes. The structure, morphology and luminescent performances of these phosphors were comprehensively explored using X-ray diffraction, scanning electron microscopy and photoluminescence techniques. Furthermore, we explored the temperature-dependent fluorescence intensity ratio of Tm³⁺ (¹G₄ → ³H₆ and ³F₂ → ³H₆) with a temperature range of 303–573 K. Our results demonstrate excellent relative sensitivity and resolution for high-temperature sensing applications (S_R = 1.94 % K⁻¹, ΔT = 0.61 K). Overall, our findings highlight the promising potential of BGZO:Tm³⁺/Yb³⁺ phosphors in optical thermometry sensing.