Control of white light emission via co-doping of Dy3+ and Tb3+ ions in LiLuF4 single crystals under UV excitation

The lithium lutetium fluoride (LiLuF4) single crystals co-doped with fixed ~ 1.7 mol% Dy3+ and different concentrations of Tb3+ concentrations from 0 to 2.7 mol% were prepared by a Bridgman technique. Influence of Tb3+ ion concentration on the spectroscopic properties of Dy3+/Tb3+ co-doped LiLuF4 single crystal was explored with the help of optical absorption, luminescence, and decay curve. Dy3+ ion acts as a sensitizer for Tb3+ ion emission by the energy transfer process of Dy3+:F-4(9/2) + Tb3+:F-7(6) -> Dy3+:H-6(15/2) + Tb3+:D-5(4) under excitation of UV lights. Moreover, a fitting of the emission decay curve at 575 nm by the Inokuti-Hirayama expression suggested that the dipole-dipole energy transfer from Dy3+ to Tb3+ was dominated. The characteristic emission colors of the prepared crystal were estimated. An ideal white light emission with chromaticity coordinates of (0.328, 0.334) could be obtained and the emission color adjusted from the white to green region by varying Tb3+ ion concentrations under the excitation of UV light. In addition, the temperature-dependent fluorescence suggests that the Dy3+/Tb3+ co-doped LiLuF4 single crystal shows an excellent thermal stability.