Comparative studies of structure, spectroscopic properties and intensity parameters of tetragonal rare earth vanadate nanophosphors doped with Eu(III)

Abstract

Hydrothermal method was applied in order to synthesize nanocrystalline YVO4, LaVO4 and GdVO4 materials doped with Eu3+ ions. The conditions of synthesis were chosen to allow control of the process based on precipitation reaction in an autoclave, at elevated temperature and pressure. The prepared materials crystallized as single phase spherical-like nanocrystals of the tetragonal I41/amd structure. The average size of the particles was in the range of 7–10 nm in the YVO4- and GdVO4-based products and about 32 nm when LaVO4 was the host compound. The excitation spectra of the materials prepared revealed a broad and intense band in the UV region. The band resulted from charge transfer phenomena: excitation of the VO43+ groups was followed by the energy transfer to Eu3+ ions. Intense, red emission of the samples was a result of electronic transitions in Eu3+ dopant ions. The theoretical Judd-Ofelt intensity parameters Ωλ, obtained using the novel approach to the calculation of Eu-O bond stretching force constant and subsequently charge factors, were compared to the experimental Ωλ. Forced electric dipole part of Ωλ was calculated from scratch (using Eu3+ coordination geometry in REVO4 from DFT calculations), while a single parameter in the dynamic coupling part was fitted to the experimental data. The issues related to the force constant calculation are discussed. Crucial influence of crystal lattice distortions on Ωλ and Eu3+ emission intensities of the materials was shown.