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Mn2+-doped Zn2SiO4 phosphors with nanoellipsoid or nanowire morphologies were synthesized at low temperature <200 °C by a hydrothermal method without any surfactants. The morphologies of the phosphors were easily tailored by varying the amount of hydroxide ions in the precursor solution before the hydrothermal reaction. Absolute ethanol was used as a solvent instead of distilled water to explore the effects of hydroxide ions on the morphology and crystal structure. We adjusted the amount of hydroxide ions by changing the pH of the precursor solution. Sheaves of powders with an ellipsoid shape were synthesized at low pH values of 7 and 9, at which only a few hydroxide ions were present, whereas powders with a nanowire shape were produced at a high pH of 11, at which many hydroxide ions were present. In addition to its morphology, the hydroxide ions also affect the crystal structure of the synthesized powder. Whereas a Zn2SiO4 phase with a willemite structure was formed at pH 7 and 9, a Zn4Si2O7(OH)2·H2O phase with a hemimorphite structure was formed at pH 11. The as-prepared powders with a willemite structure showed an intense green emission (λ ≈ 525 nm) under 254 nm excitation, whereas the as-prepared powders with a hemimorphite structure did not show any emission. However, all of the powders showed a willemite structure while retaining their original shape after annealing at 900 °C under a reducing atmosphere. The annealed sheaves of willemite with an ellipsoid shape showed a more intense green emission with a longer decay time than the phase-transformed willemite nanowires. These results were discussed in terms of the surface defects and dopant concentration.

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We demonstrated the formation of monodispersed spherical aluminum hydrous oxide precursors with tunable sizes by controlling the variables of a forced hydrolysis method. The particle sizes of aluminum hydrous oxide precursors were strongly dependent on the molar ratio of the Al(3+) reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al(2)O(3)) and finally to α-Al(2)O(3) through thermal dehydrogenation were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). After annealing the amorphous aluminum hydrous oxide in air at 900 °C and 1100 °C for 1 h, we observed complete conversion to phase-pure γ- and α-Al(2)O(3), respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al(2)O(3) were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m(2) g(-1), respectively, based on the Brunauer-Emmett-Teller (BET) measurement.