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

Abstract

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⁺:³F_2,3 → ³H₆) and 650 nm (Tm³⁺:¹G₄ → ³F₄) 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.