Large-scale ZnO nanotube bundles were successfully synthesized by a single solution method at lower temperature. Every ZnO nanotube bundle is composed of closely packed nanotubes, with inner diameters of ∼350 nm and wall thicknesses of ∼60 nm, and forms radiating structures. The influence of the reaction time on the size and shapes of the ZnO samples was studied in detail, and the results revealed that the reaction time plays an important role in determining final morphologies of the samples. The formation of the tubular structure may be due to the selective dissolution of the metastable Zn-rich (0001) polar surfaces, and a possible growth model was proposed. Optical properties of the ZnO nanotube bundles were also investigated by photoluminescence (PL) spectroscopy. It was found that the UV emission peak of the nanotube bundles did not change its position, while the visible emission band showed an obvious red shift when the nanotube bundles were annealed in ambient oxygen. Moreover, the UV emission was further identified to originate from the radiative free exciton recombination by the temperature-dependent PL.

Yttrium-doped ZnO thin films were deposited on silica glass substrates by the sol–gel method. The structural, electrical and optical properties of yttrium-doped ZnO thin films were investigated systematically and in detail. All the thin films have a preferred (0 0 2) orientation. When compared with the electrical resistivity values of films without annealing treatment, the values of films annealed in the reducing atmosphere were decreased by about three orders of magnitude. The lowest electrical resistivity value was 6.75 × 10−3 Ω cm, which was obtained in the 0.5 at% yttrium-doped ZnO thin film annealed in nitrogen with 5% hydrogen at 500 °C. In room-temperature photoluminescence (PL) spectra, two PL emission peaks are found in the pure ZnO thin film; one is the near-band-edge (NBE) emission at 3.22 eV and the other is a green emission at about 2.38 eV. Nevertheless, the green emission is not found in the PL of the yttrium-doped ZnO thin films. The low-temperature PL spectrum of the undoped ZnO thin film at 83 K is split into well-resolved free and bound excition emission peaks in the ultraviolet region, but the NBE emission of the 5 at% yttrium-doped ZnO thin film at 83 K has only one broad emission peak.

Large-scale uniform dumbbell-like ZnO microcrystals were successfully synthesized via a facile solution method under mild conditions. The as-prepared dumbbells, with lengths of 3.5-5.4 microm and diameters of 1.3-1.8 microm, possess a single-crystal hexagonal structure and grow along the [0001] direction. The influence of the reactant concentration on the size and shapes of the ZnO samples had been studied, and the results revealed that the reactant concentration plays a crucial role in determining final morphologies of the samples. Moreover, the evolution process of the dumbbell-like ZnO microcrystals was viewed by field-emission scanning electron microscopy (FE-SEM) characterization, and a possible formation mechanism was proposed. In addition, optical properties of the ZnO samples prepared at different reaction times were also investigated by photoluminescence (PL) spectroscopy. The room-temperature PL spectrum of the dumbbell-like ZnO microcrystals shows a strong UV emission peak. The UV emission is further identified to originate from the radiative free-exciton recombination by the temperature-dependent PL.

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Self-organized oxide nanotube arrays have been prepared by a facile two-electrode electrochemical anodization on Ti-2Al-1.5Mn alloy in a 0.5 wt % NH4F aqueous electrolyte. The surface morphology, structure, elemental analysis, and optical and photoelectrochemical behaviors of the nanotubular films are considered. The morphology greatly depends on the applied voltage and anodization time. The as-formed nanotubes under the optimized condition, at 20 V for 3 h, are highly ordered with ∼500 nm in length and the average tube diameter is about 90 nm. The possible “oxide growth and dissolution” mechanism is also discussed. By annealing the initially amorphous films at different temperatures, the importance of the crystalline nature is confirmed. A continuously remarkable red-shift of the absorption edge has been observed with increasing annealing temperature, which is related to the increasing crystallization and the possible new energy bands formed in the TiO2 band gap. The photoelectrochemical properties are investigated and the highest photocurrent of 3.11 mA/cm2 is obtained under AM1.5 100 mW/cm2 illumination at 0.65 V (vs Ag/AgCl). Significantly, a considerable and sustained water splitting behavior has also been observed, and the present convenient synthesis technique can also be extended to other binary or ternary oxide compositions for various applications.