Control Over the Crystallinity and Defect Chemistry of YVO4 Nanocrystals for Optimum Photocatalytic Property

This work reports on the kinetic control over the crystallinity and defect chemistry of YVO4 nanoparticles for the optimization of their photocatalytic performance. YVO4 nanoparticles were prepared at room temperature via a precipitation method and then annealed in air at selected temperatures <= 500 degrees C to tune their crystallinity and defect features. By systematic evaluation of the sample characterizations, it has been found that the as-prepared samples crystallized in a pure tetragonal zircon-type structure, and the surfaces of the particles are hydrated. Upon annealing, all YVO4 nanoparticles became dehydrated, which increased the crystallite sizes and improved the crystallinity of the samples. In contrast to many other oxide nanoparticles reported in literature, the increase in crystallite size of YVO4 nanoparticles led to a lattice expansion, as observed by enhancement of the covalency of the V-O bonds and the systematic shifts in the Raman frequency modes, owing to the generation of oxygen vacancies on particle surfaces. The presence of oxygen vacancies not only introduced a deep acceptor level in the electronic structure that gives rise to a slightly narrowed band-gap and a broad visible emission, but also improved the photocatalytic activity of the particles; this latter effect is also a consesqence of the improved crystallinity of the samples.