Effect of crystallinity on the optical thermometry sensitivity of Tm3+/Yb3+ codoped LiNbO3 crystal

Under 980 nm excitation, optical temperature sensing properties based on the upconversion emissions of Tm3+ in LiNbO3 polycrystal and single crystal are studied in the temperature range of 323-773 K. It is observed the 3F2,3 and 3H4 levels of Tm3+ are thermally coupled levels in both LiNbO3 polycrystal and single crystal, suggesting that the Tm3+-doped LiNbO3 crystals possess potential application in optical thermometry. Moreover, the crystallinity of host material greatly affects the optical thermometry sensitivity. The splitting degrees of upconversion emission spectra are changed with the crystallinities of LiNbO3 crystals, smaller splitting degree can result in higher absolute sensitivity. By optimizing the Tm3+ and Yb3+ ion concentrations, LiNbO3 single crystal is promising for optical high temperature sensor. These results reveal that the higher crystallinity of sensing material is beneficial to improve the sensitivity and resolution of optical temperature sensor.