Lanthanide-doped nanoparticles have great potential as a new kind of luminescent material. In this thesis, we report the synthesis of Cerium-doped LaF₃ nanoparticles in dimethyl sulfoxide (DMSO) using chemical reaction at different temperatures. We found that the emission of nanoparticles in DMSO not only depends on reaction temperature but also reaction time. The emission of DMSO solution can be tuned by reaction time, from 490 nm to 650 nm. The formation of LaF₃:Ce³⁺ nanoparticles has been identified by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM results show that the average sizes of these nanoparticles are within 10 nm to 13 nm, which is consistent with the sizes we obtained from XRD measurement. The mechanisms for tunable emissions are being investigated. In most biological application, especially in vivo application, nanoparticles are required to be water soluble and biocompatible. Based on this concept, we have developed a simple chemical method for making high-quality, well-defined, water-soluble lanthanide-ions-doped LaF₃ nanoparticles. All the nanoparticles we synthesized are water soluble and emit very strong luminescence.