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We present a solution-phase preparation method for the synthesis of ZnO in an open reactor (with constant stirring) or in a closed reactor (autoclave). The method is based on a combination of the polyol method and the homogeneous precipitation of zinc nitrate with urea. ZnO particles with a rod-like shape and with a regular bipod structure were prepared in an open reactor, while needle-like shapes were prepared in the autoclave. A detailed characterization of the planar base-plane and prismatic defects obtained in the hexagonal ZnO bipod particles with electron microscopy revealed that in the middle of the bipod the planar defects contain a small amount of silicon. A rough estimation indicated that there was a single atomic layer of silicon at the defect. From convergent-beam electron-diffraction experiments, we found that these planar defects were inversion domain boundaries (IDBs) with a head-to-head orientation of the polar axis. In the needle-like particles, besides IDBs on the basal planes, prismatic IDBs with a small amount of silicon were also found. The formation mechanism for the prismatic IDB was thought to be the overgrowth of one part of the bipod over another. In this case, not just the head-to-head arrangement of the polar axis, but also the tail-to-tail arrangement, must be able to occur.

ZnO nanorods were prepared at relatively low temperatures by homogeneous precipitation from zinc nitrate and urea in a water/ethylene glycol mixture. Crystal size and morphology are controlled by growth time and solvent composition. We observed a strong correlation between nanocrystals’ size/morphology and their optoelectronic defect-related properties. Smaller crystallites exhibited intense deep-defect luminescence and enhanced emission related to near-surface excitonic recombination. Longer growth times lead to formation of well-defined nanorods with hexagonal symmetry exhibiting reduced defect emission.