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⁺ (⁴F_9/2 → ⁶H_15/2) ions, and yellow band of 573 nm ascribed to Dy³⁺ (⁴F_9/2 → ⁶H_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 ≈ 0.2836, y ≈ 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.