ZnO tetrapod nanowires were prepared by thermal evaporation of Zn in the flow of different carrier gases (argon, nitrogen, humidified argon and humidified nitrogen). The optical properties of the tetrapod nanowires were investigated by low-temperature photoluminescence measurements, reflectance measurements and X-ray photoelectron spectroscopy (XPS). It was found that the type of gas significantly affects the optical properties of the fabricated tetrapod nanowires. The origin of the differences in the photoluminescence spectra of tetrapod nanowires fabricated with different carrier gases is discussed. The addition of water vapor to the carrier gas affected the photoluminescence and XPS spectra for both N-2 and Ar carrier gases, and the changes observed in the XPS spectra indicated possible incorporation of hydrogen in these samples. (c) 2006 Elsevier B.V. All rights reserved.