Luminescence properties and energy transfer behavior of novel KGd(WO4)2: Tb3 + , Eu3+ phosphors for ultraviolet-excited white light-emitting diodes

Abstract

A series of KGd(WO₄)₂: Tb³⁺ phosphors and Tb³⁺, Eu³⁺ co-doped KGd(WO₄)₂ phosphors were synthesized by high-temperature solid-state method. The structure, luminescence properties and energy transfer mechanism of the synthesized phosphors were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), excitation spectra and emission spectra. Under 315 nm excitation, the optimal doping concentration of Tb³⁺ was 0.04 mol. Beyond this concentration, the luminescence intensity of Tb³⁺ gradually decreased due to the concentration quenching effect. In KGd(WO₄)₂: Tb³⁺ samples, the dominant energy transfer mechanism was determined to be the dipole-dipole interaction. In addition, energy transfer from Tb³ ⁺ to Eu³ ⁺ was observed in the Tb³ ⁺/Eu³ ⁺-doped KGd(WO₄)₂ emission spectra, which was further verified by the fluorescence lifetime measurements of Tb³ ⁺. Calculations based on the CIE chromaticity coordinates revealed that luminescence color of the phosphors gradually shifted from green to yellow-green with the increase of Eu³⁺ doping concentration, realizing effective tunability of the luminescence color. The temperature-dependent emission spectra also indicated that KGd(WO₄)₂: Tb³⁺, Eu³⁺ phosphors had excellent thermal stability. The as-packaged white LED device exhibited an outstanding color rendering index of 96.4. The results mentioned above show that all the synthesized phosphors have potential application value in near-ultraviolet excited white light-emitting diodes.