Frequency upconversion of Tm3+ and Yb3+ codoped YLiF4 synthesized by hydrothermal method

In this paper, YLiF4 codoped with Tm3+ and Yb3+ ions was synthesized by hydrothermal method. Yb3+ concentration is fixed at 1.5%, and Tm3+ concentration is changed from 0.1 to 0.4%. Intense upconversion luminescence is observed when the samples are excited by 980 nm. The dependence of upconversion luminescence on Tm3+ concentrations is presented. The results show that upconversion luminescence increases with the Tm+ concentration and gets its peak at 0.3 mol%. Under the excitation of 980 nm, the blue emission of 479 nm and the red emission of 647 nm are both duo to two photons process, and the UV emission of 361 nm is attributed to the three photons process. We also analyse the upconversion mechanism and process.