Optical properties and Judd-Ofelt analysis of a novel Red-Emitting monoclinic Li3Ba2Gd3(WO4)8: Eu3+ phosphor

Abstract

Red-emitting Li3Ba2Gd3(WO4)8: x at.% Eu3+ (0.5 ≤ x ≤ 10) phosphors were effectively produced using a conventional solid-state reaction method at high temperature in air atmosphere. The phosphors exhibited monoclinic crystalline structure with the C2/c space group and 2/m point group. The unit cell parameters determined from the Rietveld refinement for 3 at.% doped sample are a = 5.2149(4) Å, b = 12.7447(1) Å, c = 19.2058(3) Å, α = γ = 90°, β = a^c = 91.9315(1)° and Vcalc = 1275.748(2) Å3. Photoluminescence spectra, lifetimes, colour coordinates and purity, and temperature-dependent emission spectra have been systematically studied. Upon excitation at 395 nm, the phosphors displayed red emission with a peak centered at 614 nm, which was associated with the 5D0→7F2 electrical dipolar transition of Eu3+. At the same time, the influence of different Eu3+ ion concentration on the photoluminescence intensity is also discussed. The optimal concentration of Eu3+ ions in Li3Ba2Gd3(WO4)8 was found to be 3 at.%. The mechanism behind concentration quenching was ascribed to dipole–dipole interactions, and the critical distance for energy transfer among Eu3+ ions was determined to be 7.409 Å. The Judd–Ofelt theory was utilized to assess the intensity parameters and radiative properties. The fluorescence decay times were also determined for the different concentration levels of Eu3+ cations. The chromatic coordinates of Li3Ba2Gd3(WO4)8: Eu3+ were found to be (0.653, 0.345), closely resembling the standard red light (0.670, 0.330) and demonstrated high colour purity (98.42 %) under excitation at 395 nm. Moreover, the phosphors Li3Ba2Gd3(WO4)8: Eu3+ exhibited favorable thermal stability, characterized by an activation energy of 0.219 eV. The aforementioned findings indicate that the phosphors Li3Ba2Gd3(WO4)8 doped with Eu3+ have the potential to function as a red-emitting phosphor in near-ultraviolet-driven white light-emitting diodes.