Optical and magnetic properties of zinc vanadates: synthetic design of colloidal Zn₃V₂O₇(OH)₂(H₂O)₂, ZnV₂O₄ and Zn₃V₂O₈ nanostructures

Colloidal hierarchical self-assembled Zn₃V₂O₇(OH)₂(H₂O)₂ superstructures, were synthesized via a simple and large-scale production route and then was converted into ZnV₂O₄ and Zn₃V₂O₈ by calcination with retaining Zn₃V₂O₇(OH)₂(H₂O)₂ original morphology and hydrophilicity. Prepared compounds were characterized by X-ray diffraction, energy dispersive X-ray analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The optical, magnetic and photoluminescence properties of Zn₃V₂O₇(OH)₂(H₂O)₂, ZnV₂O₄ and Zn₃V₂O₈ were explored by ultraviolet–visible spectroscopy, vibrating sample magnetometer and emission/excitation spectroscopy, respectively. According to the scanning electron and transmission electron microscopy results, the as-prepared samples were crystallized with a flower-like morphology for the optimized materials. The hierarchical self-assembled flower-like particles were composed of a large number of similar nanosheets with a thickness of 10–70 nm. The photophysical properties investigation of Zn₃V₂O₇(OH)₂·2H₂O demonstrated that this sample has a wide band gap with photoabsorption ability only in the UV region. The magnetic properties of the ZnV₂O₄ nanostructures were evaluated, and results showed sample has a ferromagnetic behavior at room temperature. Finally, the optical study of the Zn₃V₂O₈ nanostructure showed a very pronounced red-shifted PL emission for the two excitation wavelengths of 237 and 340 nm in their photoluminescence spectra.