Highly sensitive optical thermometry based on upconversion emissions in Tm^3+/Yb^3+ codoped LiNbO_3 single crystal

Under 980 nm excitation, upconversion emissions originating from 3F(2,3)→3H(6) and 3H(4)→3H(6) transitions of Tm3+ ion in LiNbO3 single crystal were studied as a function of temperature in the range of 323-773 K. The 3F(2,3) and 3H(4) levels of Tm3+ ion are confirmed to be thermally coupled levels. By using fluorescence intensity ratio technique, the sensitivity of optical temperature sensor achieved in our work is higher than other reported temperature sensors. Additionally, this optical temperature sensor is well suited to high operating temperature. Tm3+/Yb3+ codoped LiNbO3 is a promising candidate for fabricating excellent optical temperature sensors.