Optical properties and Judd-Ofelt analysis of a novel Red-Emitting monoclinic Li$_{3}$Ba$_{2}$Gd$_{3}$(WO$_{4}$)$_{8}$: Eu$^{3+}$ phosphor

Red-emitting Li$_3$Ba$_2$Gd$_3$(WO$_4$)$_8$: x at.% Eu$^{3+}$ (0.5 ≤ x ≤ 10) phosphors were effectively produced using a con-
ventional solid-state reaction method at high temperature in air atmosphere. The phosphors exhibited mono-
clinic 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 V$_{calc}$ = 1275.748(2) Å$^{3}$. 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 asso-
ciated with the 5D0→7F2 electrical dipolar transition of Eu$^{3+}$. At the same time, the influence of different Eu$^{3+}$ ion
concentration on the photoluminescence intensity is also discussed. The optimal concentration of Eu3+ ions in
Li$_3$Ba$_2$Gd$_3$(WO$_4$)$_8$ 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 Eu$^{3+}$ ions was determined to be
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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 Eu$^{3+}$ cations. The
chromatic coordinates of Li$_3$Ba$_2$Gd$_3$(WO$_4$)$_8$: Eu$^{3+}$ 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 Li$_3$Ba$_2$Gd$_3$(WO$_4$)$_8$: Eu$^{3+}$ exhibited favorable thermal stability, characterized by an
activation energy of 0.219 eV. The aforementioned findings indicate that the phosphors Li$_3$Ba$_2$Gd$_3$(WO$_4$)$_8$ doped
with Eu$^{3+}$ have the potential to function as a red-emitting phosphor in near-ultraviolet-driven white light-
emitting diodes.