In order to investigate the influence of Yb3+concentration on the up-converted blue fluorescence intensity of Tm3+ ions,the fluorescent materials of Tm3+ and Yb3+ codoped LaF3 nanoparticles are prepared using hydrothermal method with NaF and La(NO3)3 as raw materials.The result of X-ray diffraction shows that the crystal structure of the prepared nanoparticles is hexagonal.The image of the transmission electron microscopy suggents that the particles are uniformly distributed and have a good dispersity.Up-converted blue emissions at 474 nm and 450 nm,which correspond to the transitions of 1G4→3H6 and 1D2→3F4 respectively,are observed when the samples are excited with 800 nm lasers.The influence of Yb3+ concentration on the fluorescence properties of Tm3+ ions is investigated by adjusting the Yb3+ concentration in Tm3+/Yb3+:LaF3 nanoparticles.It is found that for fluorescence emission at 474 nm,when the concentration of the Yb3+ increases,the fluorescence intensity also increases due to inverse energy transfer process.But the fluorescence intensity will decrease after it reaches a certain value.For the fluorescence emission at 450 nm,its intensity does not change obviously with the concentration of Yb3+ ions，but its fluorescence intensity is increasing firstly and then decrease like 474 nm fluorescence.