High-sensitivity optical thermometry in CaWO₄: Bi³⁺, Pr³⁺ phosphors based on distinct thermal quenching behaviors

Within the present investigation, varying-concentration Bi³⁺, Pr³⁺ co-doped CaWO₄ samples were prepared via the hydrothermal approach. The present comprehensive investigation was performed into their optical temperature sensing characteristics. Experimental results indicate that, in the CaWO₄ host, the emission characteristics of Bi³⁺ shows a pronounced tendency toward thermal luminescence quenching, while the thermal luminescence quenching process of Pr³⁺ emission is significantly slower in comparison with Bi³⁺. Therefore, the FIR of Pr³⁺ and Bi³⁺ rises markedly as the temperature elevates, a property that allows it to be employed for temperature characterization, and achieved a relatively higher sensitivity. The prepared phosphors can achieve temperature characterization through two sets of FIR: I_602.5/I₄₄₃ and I₆₄₉/I₄₄₃, corresponding to Pr³⁺ (¹D₂ → ³H₄, ³P₀ → ³F₂) and Bi³⁺ (³P₁ → ¹S₀). The acquired results can cross-verify one another, thus enabling the realization of self-calibration. In the case where the FIR of I_602.5/I₄₄₃ is used for temperature characterization, exhibits the highest S_r of 4.36% K^-1 (in the CaWO₄ co-doped with 5 mol% Bi³⁺ and 0.5 mol% Pr³⁺ phosphor at 298 K). When the FIR of I₆₄₉/I₄₄₃ is used for temperature characterization, exhibits the highest S_r of 4.06% K^-1 (in the CaWO₄ co-doped with 5 mol% Bi³⁺ and 0.5 mol% Pr³⁺ phosphor at 298 K). Furthermore, with an increase in temperature, the emission color of the phosphors gradually changes from the blue region to the orange-red region, this luminescent color change allows for the rough estimation of temperature. Findings from the present investigation demonstrate that CaWO₄: Bi³⁺, Pr³⁺ phosphors possess considerable practical application value in the realm of luminescence thermometry.