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+ (1G4 → 3H6) and Dy3+ (4F9/2 → 6H15/2) ions, and yellow band of 573 nm ascribed to Dy3+ (4F9/2 → 6H13/2) 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 ≈ 0.2836, y ≈ 0.3229, and color temperature Tc = 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.