Er³⁺ upconversion fluorescence of ErNbO₄ phosphor for optical temperature sensing

Er³⁺ upconversion (UC) fluorescent characteristics of ErNbO ₄ phosphor were studied for temperature sensing purposes. This letter shows that the ErNbO₄ phosphor emits more UC fluorescence than the Er³⁺-doped LiNbO₃ single-crystal and Er ₃NbO₇ phosphor. Both energy-transfer UC and excited state absorption play a role in the UC emission. Both the peak and integrated UC intensities decrease with the raised temperature, and the 530, 560, and 670 nm UC intensities reduce by ~26%, 42%, and 34%, respectively, with the temperature rise of only 57 °C from 21 °C, implying that the phosphor is applicable to temperature sensing based upon either the 560- or 670-nm emission. The feasibility to realize the temperature sensing is discussed from the application requirements of smartness and low-cost, suggesting that not only the single 560- or 670-nm band, but the combined 530- and 560-nm bands can be also utilized.