Highly sensitive optical thermometry in Pr3+ doped CaWO4 nanophosphors

In this study, the CaWO₄: x% Pr³⁺ (x = 0.1, 0.3, 1) nanophosphors were synthesized using the hydrothermal method. The FE-SEM diagrams demonstrates that the sample consists of irregularly shaped nanoparticles, averaging 93–97 nm in size. Analysis of the variable-temperature emission spectra of samples reveals that the luminescence of WO₄²⁻ exhibits typical thermal quenching behavior, whereas the luminescence of Pr³⁺ initially increases and subsequently decreases with temperature increasing. The different temperature dependence of the luminescence of Pr³⁺ and WO₄²⁻ enables higher relative sensitivity when using their fluorescence intensity ratio (FIR) for temperature characterization. The samples prepared in this study can be used to characterize temperature by two sets of FIR (I₆₀₅/I₄₂₀ and I₆₄₉/I₄₂₀) of Pr³⁺ (¹D₂→³H₄ 605 nm and ³P₀→³F₂ 649 nm) and WO₄²⁻ (³T₂→¹A₁ 420 nm). The obtained results can mutually validate each other, thereby achieving self-calibration. When using the FIR of I₆₀₅/I₄₂₀ for temperature characterization, the CaWO₄: 0.1 % Pr³⁺ demonstrates a maximum relative sensitivity value of 6.17 % K⁻¹ at 303 K, that is very high in inorganic materials. The results of this paper show that, CaWO₄: Pr³⁺ nanophosphors exhibit excellent optical temperature sensing performance, demonstrating considerable potential for application in optical thermometry.