Shape- and size-controlled synthesis of monoclinic ErOOH and cubic Er2O3 from micro- to nanostructures and their upconversion luminescence

A general approach has been developed for the synthesis of monoclinic ErOOH and cubic Er2O3 structures with high yield and controlled size and shape via the solvo-hydrothermal reaction of erbium nitrate in water/ethanol/decanoic acid media. The monoclinic ErOOH phase was formed at relatively low temperature (120-140 degrees C); however, the cubic Er2O3 phase was obtained at higher temperature (160-180 degrees C). By simply tuning different experimental parameters, such as the reaction temperature, the concentration of decanoic acid and erbium precursor etc., different sizes from 3 nm to 3 microm, and a variety of shapes including cores/dots to spheres, wrinkle-surfaced spheres, flowers, dog bonds, wires, rods, bundles, straw sheaves, and brooms can be achieved. The particle size of products decreased from micro- to nanometer as the decanoic acid concentration increased from 0.038 to 0.190 M. Furthermore, by using anhydrous ethanol instead of water-ethanol solvents, the particle size significantly decreased from 18 nm spheres to 3 nm cores. At high precursor monomer concentrations (76.25-152.50 mM), the nanorods were also obtained due to the anisotropic growth. On the basis of this study, a correlation between the experimental parameters and the phase, shape, and size of the products was proposed. The upconversion luminescence properties depend not only on crystalline phase but also on particle size of the products. The luminescence intensity increases with the decrease of particle size from micro- to nanometers.

Shape-controlled synthesis of highly crystalline titania nanocrystals

A versatile synthetic method based on solvothermal technique has been developed for the fabrication of TiO(2) nanocrystals with different shapes such as rhombic, truncated rhombic, spherical, dog-bone, truncated and elongated rhombic, and bar. The central features of our approach are the use of water vapor as hydrolysis agent to accelerate the reaction and the use of both oleic acid and oleylamine as two distinct capping surfactants which have different binding strengths to control the growth of the TiO(2) nanoparticles. We also show that the presence of an appropriate amount of water vapor along with the desired oleic acid/oleylamine molar ratio plays a crucial role in controlling size and shape of TiO(2) nanocrystals.

Monodisperse samarium and cerium orthovanadate nanocrystals and metal oxidation states on the nanocrystal surface

A new solvothermal method has been developed for the synthesis of monodisperse SmVO4 and CeVO4 nanocrystals with controlled size and shape. The obtained materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) techniques. The results reveal that uniform nanocrystals and pure tetragonal phase of SmVO4 and CeVO4 can be achieved. To investigate the oxidation states of the metals on the mixed oxide nanocrystal surface, the XPS technique was employed. The results exhibit that only one oxidation state of samarium, cerium, and vanadium for each metal (e.g., Sm3+, Ce3+, V5+) was surprisingly well stable on the particle surface at the nanoscale, even after calcination, while the existence of two oxidation states of these metals is observed (e.g., Sm3+/Sm2+, Ce4+/Ce3+, V5+/V4+) in the corresponding single metal oxide nanocrystals.