Preparation and luminescence characteristics of LiYF4: Tm3+/Dy3+ single crystals for white-light LEDs

Tm3+ /Dy3+ co-doped LiYF4 single crystals were synthesized by using vertical Bridgman method in sealed Pt crucibles. When excited by a proper UV-light, the crystals show blue emission band centered at 485 nm, which overlaps between the transition of Tm3+ ((1)G(4) -> H-3(6)) and Dy3+ (F-4(9/2) -> H-6(15/2)) ions, and yellow band of 573 nm ascribed to Dy3+ (F-4(9/2) -> H-6(13/2)) ions. Both chromaticity coordinates and photoluminescence intensity vary with the excitation wavelengths and the concentration of rare earth dopants. A white light can be achieved from Tm3+ (0.6 mol%), Dy3+ (2.25 mol%) co-doped LiYF4 crystal with chromaticity coordinates of x a parts per thousand 0.2836, y a parts per thousand 0.3229, and color temperature T (c) = 8419 K by the excitation of a 350 nm light. It indicates that this crystal can be a potential candidate for the UV-light excited white-light emitting diodes.