Optical thermometry of a Tm3+/Yb3+ Co-doped LiLa(MoO4)2 up-conversion phosphor with a high sensitivity

Well-crystallized LiLa(MoO4)(2) co-doped with 20% Yb3+ and 0.5% Tm3+ was successfully synthesized by a sol-gel method and the temperature dependence of its up-conversion (UC) luminescence was investigated systematically. The fluorescence intensity ratio between the UC emission bands centered at around 700 (Tm3+:F-3(2,3)-> H-3(6)) and 650 nm (Tm3+:(1)G(4) -> F-3(4)) from Tm3+ was measured as a function of temperature in the range of 303-543 K under 980 nm diode laser excitation. The maximum of the relative temperature sensitivity reaches 3.85% K-1 at 300 K, which is superior to other previously reported results based on the FIR technique using the thermally coupled energy levels. This result indicates that the phosphor LiLa(MoO4)(2): 0.5% Tm3+, 20% Yb3+ is a promising candidate for accurate optical temperature sensors with a higher relative sensitivity.