Luminescence of Tb3+/Eu3+ codoped LiYF4 single crystals under UV excitation for white-light LEDs

The absorption spectra, excitation spectra, and emission spectra of Tb3+/Eu3+ ions in LiYF4 single crystals synthesized by an improved Bridgman method are measured. The emission spectra of several bands, mainly located at blue similar to 487 nm (Tb:D-5(4) -> F-7(6)), yellowish green similar to 542 nm (Tb:D-5(4) -> F-7(5)) and red similar to 611 nm (Eu:D-5(0) -> F-7(2)) wavelengths, are observed under excitation by UV light. An ideal white light emission as a result of simultaneous combination of these emissions can be obtained from 1.11 mol% Tb3+ and 0.9 mol% Eu3+ co-doped LiYF4 single crystals with chromaticity coordinates of = 0.3242, y = 0.3389, color temperature T-c = 5878 K, color rendering index R-a = 77, and color quality scale Q(a) = 75 under excitation of 384 nin light. The chromaticity coordinate, color rendering index, and color quality scale can be modified by the change of the concentration of rare-earth dopants and the excitation wavelength.