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Simin Kuang and Yadong Lia) Department of Chemistry, Tsinghua University, Beijing, 100084, People’s Republic of China (Received 11 November 2010; accepted 20 January 2011)

A facile ethylene glycol–based solvothermal method was developed for the synthesis of lanthanide orthovanadate LnVO4 (Ln 5 La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, Lu) nanoparticles with relatively uniform size and morphologies. The LnVO4 nanoparticles ranged from 100 to 500 nm and changed from spheres to ellipses and platelet–shaped particles depending on the ionic size. Radius of the Ln ions affected crystal structure. The particles with larger ions form monoclinic-type structure for LaVO4 and with smaller ions form zircon-type structure for LnVO4 (Ln 5 Pr-Yb). A nucleation and aggregates formation mechanism of LnVO4 nanomaterials was proposed to illustrate the crystal growth. The morphologies of LnVO4 nanoparticles could be turned by pH value and molar ratio of reactants. Spherical LaVO4 and PrVO4 nanoparticles were obtained at pH 6, whereas elliptical nanoparticles were obtained at pH 3. Eu3+-, Dy3+-, and Sm3+-doped zircon-type YVO4 nanoparticles exhibit strong luminescence typical of doped ions. I. INTRODUCTION

Address all correspondence to this author. e-mail: [email protected] This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy Supplemental files can be viewed online by visiting http://journals. cambridge.org/jmr. DOI: 10.1557/jmr.2011.36

morphology of LnVO4 nanoparticles. Recently, an oleic acid–assisted method has been developed for the synthesis of monodisperse square-like rare earth orthovanadate nanoparticles with hydrophobic surface.14,15 To the best of our knowledge, a facile method that does not use complex surfactants and additions for the synthesis of monodisperse LnVO4 nanoparticles has not been reported until now. Most reports on the synthesis of LnVO4 nanoparticles focused on a single compound, such as YVO4 or LaVO4 nanoparticles. There are few reports about the general approaches of the synthesis of LnVO4 nanoparticles. We believe that the lanthanide contraction effect, which greatly influences the crystal structures and physical properties of lanthanide compounds, is worthy for in-depth investigation. LnVO4 is an ideal model for the systematic study of the influence of lanthanide contraction, which would reveal some general rules underlying the crystal nucleation and growth process and further guide the synthesis of other lanthanide compound nanoparticles. In this article, we report a facile solvothermal method for the synthesis of hydrophilic monodisperse rare earth orthovanadate nanoparticles in ethylene glycol (EG) without the need for surfactants. EG, as an important solvent, has many unique characteristics, such as high viscosity, water-miscibility, and adequate coordination effect with metal ions. These characteristics endow EG with great advantages in th