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

A series of La1-xEuxVO4 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 g for each ligand atom. The chemical bond parameters and the geometries from DFT calculations were used to obtain theoretical Judd-Ofelt intensity parameters Omega(lambda). The effects of geometry changes caused by the dopant addition were analyzed in terms of Omega(lambda). The effects of distortions in interatomic angles of the Eu3+ coordination geometry on the Omega(lambda) were analyzed. Effects of distortions of atomic positions in the crystal lattice on the Omega(lambda) 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 Omega(2). On the contrary, experimental intensities of the D-5(0) -> F-7(2) transition and the corresponding Omega(2) 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.