We reported the observation of photoluminescence (PL) from low-temperature grown amorphous silicon oxynitride (a-SiNxOy) films with its peak location tunable in a wide range from 450 to 600 nm by controlling the Si/N ratios. The origin of luminescence from a-SiNxOy film has been thoroughly investigated. From the results of the optical absorbance spectrum, an oxygen-induced new luminescent defect state, which was characterized to be responsible for the light emission, was determined to locate at about 0.65 eV from the absorption edge. The measurements of Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectrum (XPS) has verified the existence of O-Si-N bonding configuration, which serves as this new luminescent defect state in this kind of material (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)