Tm3+/Dy3+ co-doped LaF3 nanocrystals have been synthesized by the co-precipitation method and the luminescence properties under UV light excitation examined. Tunable light emission containing blue (450 nm), yellow (570 nm), and red (660 nm) light components was observed. The excitation spectrum was investigated and the optimum excitation UV wavelength determined. The excitation mechanism responsible for the generation of the multicolor emission indicated that Tm-Dy energy-transfer plays a major role in the process. Tuning of the overall white-light emission was accomplished via variation of the Tm and Dy active ions contents in the nano-powder samples. The CIE chromaticity coordinates show that the Tm3+/Dy3+ co-doped LaF3 may be an excellent candidate for white light emitting diode devices.