Growth and Optical Spectra of Tb³⁺/Sm³⁺/Ce³⁺ Triply Doped LiYF₄Single Crystals for White-Light LEDs.

Abstract

The Tb³⁺/Sm³⁺/Ce³⁺ triply doped LiYF4 single crystals were grown by a modified Bridgman method. The absorption spectra, excitation spectra, and fluorescence spectra of Tb³⁺/Sm³⁺/Ce³⁺ ions in LiYF₄ crystals were measured. The fluorescence spectra of several bands, mainly located at purplish blue ~413 nm (⁵D₃ --> ⁷F₅), yellowish green ~542 nm (⁵D₄ --> ⁷F₅), and red ~643 nm (⁴G₅/₂ --> ⁶H₉/₂), were observed under excitation of ultraviolet light. White light could be generated by the mixture of the multicolor lights. The luminous intensities varied slightly with the excitation wavelength from 300 nm to 400 nm and doping Tb³⁺/Sm³⁺/Ce³⁺ ion concentration. The chromatic- ity coordinates of the crystal could be modified by changing the excitation wavelengths and the concentrations of Tb³⁺/Sm³⁺/Ce³⁺ ions. A near-ideal white light emission could be obtained from 1.25 mol% Tb³⁺, 1.98 mol% Sm³⁺, 0.44 mol% Ce³⁺ triply doped LiYF₄ single crystal with chro- maticity coordinates of x = 0.3090, y = 0.3223, color temperature Tc = 6777 K, color rendering index Ra = 77 and color quality scale Qa = 76 under the excitation of a 374 nm light.