Room-temperature ultraviolet ͑UV͒ laser emission of ZnO microcrystallite thin films is reported. The hexagonal ZnO microcrystallites are grown by laser molecular beam epitaxy. They are self-assembled and parallelly arrayed on sapphire substrates. The facets of the hexagons form natural Fabry-Pérot lasing cavities. The optical gain for the room-temperature UV stimulated emission is of an excitonic nature and has a peak value an order of magnitude larger than that of bulk ZnO crystal. The observation of room-temperature UV lasing from the ordered, nano-sized ZnO crystals represents an important step towards the development of nanometer photoelectronics.

We report the preparation of highly monodisperse ZnO nanoparticles using poly(vinyl pyrrolidone) (PVP) as the capping molecules. The surface-modified ZnO nanoparticles were found to be remarkably stable. The optical absorption shows distinct excitonic features. Markedly enhanced near-band-edge ultraviolet photoluminescence and significantly reduced defect-related green emission were also observed. We attribute this observation to the nearly perfect surface passivation of the ZnO nanoparticles by the PVP molecules. The third-order nonlinear optical response of these PVP-capped ZnO nanoparticles in a dilute solution was found to be significantly larger (by at least two orders of magnitude) than that of the bulk ZnO.

We have synthesized highly monodisperse wurtzite ZnO nanoparticles using poly-(vinylpyrrolidone) (PVP) as the capping molecules. The effect of surface modification on the size, structure, morphology, and optical properties of ZnO nanoparticles was investigated. It was found that many properties of the ZnO nanoparticles could be optimized by simply varying the molar ratio Zn(II)/PVP. The ZnO nanoparticles prepared under the optimum conditions are particularly stable, monodisperse, as well as small in size. The EXAFS result showed a structural contraction in the ZnO nanoparticles relative to the bulk. These nanoparticles exhibit distinct excitonic absorption features, markedly enhanced near-bandedge UV photoluminescence, and significantly reduced defect-induced green emission. The third-order nonlinear optical response of these PVP-capped ZnO nanoparticles in a dilute solution was found to be larger than that of the bulk ZnO by at least 2 orders of magnitude.