The Dy3+ doped α-NaYF4 single crystals were synthesized by a modified Bridgman method under the conditions of taking KF as an assistant flux and a temperature gradient (70~90 ℃/cm) at the solid-liquid interface.X-ray diffraction,absorption spectra,excitation spectra,and emission spectra were measured to investigate the phase and spectrum properties of the crystals.The chromaticity coordinates and color temperature of crystals were calculated based on Colorimetry theories.Many growing experiments demonstrate that the chemical compositions of 30NaF-18KF-52YF3 (molar ratio) are beneficial to obtain big α-NaYF4 single crystals.The introduction of KF changed the phase equilibrium between NaF and YF3 completely and lowered the melting point of α-NaYF4,resulting into crystallization of α-NaYF4 just from the mixture when it is cooled.Most of KF was excluded on the top of crystals which grew at the final stage of crystal growth.The introduction of flux KF did not change the structure of α-NaYF4 single crystals.The emission blue 479 nm,yellow 571 nm and weak red 659 nm could be obtained simultaneously under the excitation of ultraviolet lights.A white light emission from the coupling of the above three lights with chromaticity coordinates of x=0.285,y=0.338,color temperature Tc=8 065 K could be obtained from 1.299 mole% Dy3+ doped α-NaYF4 single crystal when excited by a 348 nm light.This indicates that Dy3+ doped α-NaYF4 single crystals can be a potential candidate for white light emitting diode excited by ultraviolet light.