Effects of Dopant Addition on Lattice and Luminescence Intensity Parameters of Eu(III)-Doped Lanthanum Orthovanadate

A series of La_1–<i>x</i>Eu_<i>x</i>VO₄ samples with a different Eu³⁺ content was synthesized via a hydrothermal route. An increase in the dopant content resulted in a decrease in lattice constants of the materials. Plane-wave DFT calculations with PBE functional in CASTEP confirmed this trend. Next, CASTEP calculations were used to obtain force constants of Eu–O bond stretching, using a novel approach which involved displacement of the Eu³⁺ ion. The force constants were then used to calculate charge donation factors <i>g</i> for each ligand atom. The chemical bond parameters and the geometries from DFT calculations were used to obtain theoretical Judd–Ofelt intensity parameters Ω_λ. The effects of geometry changes caused by the dopant addition were analyzed in terms of Ω_λ. The effects of distortions in interatomic angles of the Eu³⁺ coordination geometry on the Ω_λ were analyzed. Effects of distortions of atomic positions in the crystal lattice on the Ω_λ and photoluminescence intensities of Eu³⁺ 4f–4f transitions were discussed. It was shown that the ideal database geometry of LaVO₄ corresponds to the highly symmetric coordination geometry of Eu³⁺ and very low Ω₂. On the contrary, experimental intensities of the ⁵D₀ → ⁷F₂ transition and the corresponding Ω₂ parameters were high. Consequently, distortions of crystal structure that reduce the symmetry play an important role in the luminescence of the LaVO₄:Eu³⁺ materials and probably other Eu³⁺-doped phosphors based on zircon-type rare earth orthovanadates