Zirconium oxynitride (ZrNxOy) thin films were prepared by d.c. magnetron sputtering using air as a reactive gas. Replacing conventionally used N-2/O-2 with air as a reactive gas allows the process to perform at high base pressures (low vacuum), which could drastically reduce the processing time. The color of the obtained films changed from light golden and dark golden for low air/Ar flow ratios, to dark violet and bright cyan for high air/Ar ratios. X-ray diffraction patterns show that the films transformed from ZrN and Zr2ON2 mixed phases to a Zr2ON2 phase, and then an m-ZrO2 phase. The thickness of the films decreased slightly with increasing the air/Ar flow ratio. ZrNxOy films possessed a mixture of Zr-N-O, Zr-N and Zr-O chemical binding states determined from X-ray photoelectron spectroscopy. ZrNxOy films with mainly a Zr2ON2 phase exhibited the band gap of 1.96-2.26 eV, while the m-ZrO2 films with slight nitrogen incorporation had a band gap of 2.32 eV, evaluated from transmittance spectra. By varying the air/Ar ratio during deposition, the nitrogen/oxygen content of the films could be controlled and hence, the color, crystal structure, atomic composition, and band gap of the films could be tailored. (C) 2010 Elsevier B.V. All rights reserved.