Highly Sensitive Optical Temperature Sensing Based on FIR of CaWO₄: Sm³⁺ Nanophosphor

Abstract In this study, the hydrothermal method is used to prepare CaWO 4 : 0.5 mol% Sm 3+ phosphors with different particle sizes using Na 3 Cit (Na 3 C 6 H 5 O 7 ) as a chelating agent. The experimental results show that when the sodium citrate content increases, particle size decreases. The temperature‐dependent emission spectra of different samples are measured and found that the WO 4 2− luminescence exhibits the conventional thermal quenching trend, whereas the luminescence intensity of Sm 3+ gradually enhances as the temperature increases. The anomalous thermal enhancement phenomenon of Sm 3+ luminescence arises from the increased energy transfer effect from WO 4 2− to Sm 3+ when the temperature increases. Since the luminescence thermal quenching trends of WO 4 2− and Sm 3+ are significantly different, the temperature can be characterized by the fluorescence intensity ratio (FIR) between WO 4 2− and Sm 3+ . Through the comparison of different samples, it is found that the relative sensitivity ( S r ) value increases as the particle size decreases. The maximum S r values for phosphors with particle sizes of 4.4 µm, 1.3 µm, and 63 nm all occur at 303 K, with 5.86% K −1 , 8.05% K −1 , and 9.26% K −1 , respectively. In summary, the CaWO 4 : 0.5 mol% Sm 3+ nanophosphor have a high relative sensitivity, suggesting their promising application in temperature sensing.