INFLUENCE OF SYNTHESIS METHOD ON THE STRUCTURE AND PROPERTIES OF La1-xEuxVO4 (0£x£0,3)

UDC 546.05^'65'88

Abstract

Rare earth orthovanadates are widely used in optical electronic devices due to their interesting optic, magnetic and electrophysical properties. It is known that properties of composite oxides can essentially depend on method of synthesis. Choosing one or other method of preparation enables one to influence the structural and morphological characteristics (degree of crystallinity, porosity, grain size) as well as optical and electrical properties. Therefore, aim of our work is to investigate dependencies of spectral properties on method of synthesis. The samples La_1-xEu_xVO₄  obtained by the solid-state reaction and co-precipitation method. The La_1-xEu_xVO₄ (0 £x £0.3) compounds were identified using x-ray diffraction (XRD). It was found that the samples obtained by the solid state method are single phase, as well as those obtained using co-precipitation of components. The crystal structure of pure lanthanum ortovanadates LaVO₄ is monoclinic, space group P2₁/n with a = 0.7045(1) nm, b = 0.7281(1) nm, c = 0.6725(1) nm, β = 104.854(1) for solid state synthesis method and a = 0.7043(3) nm, b = 0.7280(1) nm, c = 0.6722(2) nm, b = 104.855(1) for co-precipitation synthesis method. In two series of the La_1‑xEu_xVO₄ solid solutions with increasing component concentration of europium at substitution lanthanum on europium the changing from monoclinic phase to tetragonal (space group I41/amd) is observed. We have studied the morphology (that may consist of one or several crystallites) and size of particles using scanning electron microscopy (SEM). Luminescence of the Eu³⁺ ions can be excited in the La_1‑xEu_xVO₄ solid solutions directly by inner transitions in the impurity ions. Energy transfer from the crystal matrix to the Eu³⁺ ions takes place. Efficiency of energy transfer from matrix to the Eu³⁺ ions depends on method of synthesis of and on concentration of the Eu³⁺ ions. We consider that features of crystal microstructures and neighbor surrounding of the Eu³⁺ ions influence on efficiency of energy transfer to centers of the Eu³⁺ emission.