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 it 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 mu m, 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 panicle 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 he 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.