Ultraviolet lasing of ZnO whiskers prepared by catalyst-free thermal evaporation

ZnO nanowire lasers

The pathway towards the realization of optical solid-state lasers was gradual and slow. After Einstein's paper on absorption and stimulated emission of light in 1917 it took until 1960 for the first solid state laser device to see the light. Not much later, the first semiconductor laser was demonstrated and lasing in the near UV spectral range from ZnO was reported as early as 1966. The research on the optical properties of ZnO showed a remarkable revival since 1995 with the demonstration of room temperature lasing, which was further enhanced by the first report of lasing by a single nanowire in 2001. Since then, the research focussed increasingly on one-dimensional nanowires of ZnO. We start this review with a brief description of the opto-electronic properties of ZnO that are related to the wurtzite crystal structure. How these properties are modified by the nanowire geometry is discussed in the subsequent sections, in which we present the confined photon and/or polariton modes and how these can be investigated experimentally. Next, we review experimental studies of laser emission from single ZnO nanowires under different experimental conditions. We emphasize the special features resulting from the sub-wavelength dimensions by presenting our results on single ZnO nanowires lying on a substrate. At present, the mechanism of lasing in ZnO (nanowires) is the subject of a strong debate that is considered at the end of this review.

Antibiotic-inspired zinc oxide with morphology-dependent photocatalytic activity

ZnO materials with different morphologies (hexahedron, coneflowerlike, cauliflowerlike, and nanorods) have been synthesized via a bioinspired method, which is effective and facile for the controlled synthesis of ZnO. Zinc acetate and ammonia were used as growth precursors, and ampicillin was used as the morphology-directing agent. X-ray diffraction (XRD) data showed that the obtained ZnO with different morphologies displayed different crystal growth habits. Photodegradation of Orange G was used as a model reaction to test the photocatalytic activity of ZnO samples. Different morphologies exhibited different activities to Orange G degradation. The cauliflowerlike ZnO sample showed the best photocatalytic performance compared with the others. The influence of the morphology-directing agent and pH on the morphology of ZnO samples and the effect of the morphologies on the photocatalytic activity are tentatively discussed.

Fast synthesis of ZnO nanostructures by laser-induced decomposition of zinc acetylacetonate

A CO2 laser (lambda = 10.6 microm) was used to heat a solution of water and alcohol saturated by Zn(AcAc)2 on a fused quartz substrate in open air. After only a few seconds of irradiation, various zinc oxide (ZnO) nanostructures including nanorods and nanowires are formed near the center of the irradiated zone, surrounded by a porous thin film of ZnO nanoparticles. The type of structures produced and their localization on the substrate can be varied by selecting adequate irradiation time and laser power ranges. The deposits have been analyzed using SEM, TEM, EDS, XRD, and Raman spectroscopy, revealing that the nanorods (aspect ratio ~6) and nanowires (aspect ratio ~94) are single-crystalline structures which grow along the c axis of wurtzite ZnO. The nanoparticles are also single-crystalline and have an average diameter of 16 nm. A qualitative model for nanostructure growth is proposed, based on previous studies of aqueous solution and hydrothermal processing.