Ultra-thin ZnO nanowire (NW)/nanotube (NT) arrays have been formed on ZnO film-coated Si substrates by a hydrothermal. growth method. The individual nanostructures are single crystal ZnO, with diameters, d, in the range 10 - 30 nm, and length of several microns. Most nanostructures with d > 20 nm are tubular, while those with d = 10 - 20 nm tend to be solid NWs. The NW/NT diameters can be controlled by the precursor concentrations. Room temperature photoluminescence spectra of as-grown and annealed samples are studied, and variations discussed in terms of differences in the extent and composition of the surface depletion layer. (c) 2006 Elsevier B.V. All rights reserved.