resumo
A series of La1-xEuxVO4 samples with a different Eu³⁺ content was synthesized via a hydrothermal route. Increase in the dopant content resulted in 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 novel approach which involved displacement of the Eu ion. The force constants were then used to calculate charge donation factors g for each ligand atom. The chemical bond parameters and the geometries from DFT calculations were used to obtain theoretical Judd-Ofelt intensity parameters Ωλ. The effects of geometry changes caused by the dopant addition were analyzed in terms of Ωλ. The effects of distortions in interatomic angles of the Eu coordination geometry on the Ωλ were analyzed. Effects of distortions of atomic positions in the crystal lattice on the Ωλ and photoluminescence intensities of Eu³⁺ 4f-4f transitions were discussed. It was shown that ideal database geometry of LaVO4 corresponds to highly symmetric coordination geometry of Eu³⁺ and very low Ω2. On the contrary, experimental intensities of the ⁵D0 → ⁷F2 transition and the corresponding Ω2 parameter 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 earths ortovanadates.
autores
Andrii Shyichuk, Renaldo T. Moura Jr., Albano N. Carneiro Neto, Marcin Runowski, Mohammad S. Zarad, Agata Szczeszak, Stefan Lis, and Oscar L. Malta
nossos autores
