Green-emitting LaF3:Ce, Tb phosphor nanoparticles were synthesized by a simple hydrothermal method and characterized by XRD, TEM and fluorescence spectra. The prepared samples had a hexagonal shape, fine size (30 nm), and high brightness under ultraviolet, and the structure of LaF3 remained unchanged after being doped with Ce3+ and Tb3+ ions. The blue Ce3+ emission centered at 261 nm is efficiently quenched in the samples of LaF3:Ce, Tb, in which the dominant emission is in the green at 544 nm, originating from the doped Tb3+ ions' transition of (5)D4 to (7)F5. Excitation spectra of the LaF3:Ce, Tb, observed at 544 nm, consist of both contributions from Ce3+ and Tb3+ ions. There is energy transfer of Ce3+ --> Tb3+ in this system. The energy transfer mechanism was discussed. Above all, the phosphor nanoparticles have high photoluminescence intensity even without any calcination, about twice that of bulk materials prepared by high temperature solid synthesis, and the intensity is also stronger than calcined phosphor nanoparticles.