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

Abstract

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⁺:⁴F_9/2 + Tb³⁺:⁷F₆ → Dy³⁺:⁶H_15/2 + Tb³⁺:⁵D₄ 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.