Ge nanoparticles of 2.3-5.0 nm size embedded in ZnO matrix were prepared by rf alternate sputtering and subsequent annealing technique. Raman and infrared (IR) absorption spectroscopy were used to characterize the Ge/ZnO nanocomposite films. Raman spectra of the composite films revealed 300 cm(-1) Ge-Ge transverse optic (TO) vibrational band of Ge nanocrystals, which shifted towards lower frequencies on decreasing the size of Ge nanocrystals due to phonon confinement in smaller crystallites. IR spectra of the composite films revealed that the Ge nanocrystals remain with elemental core surrounded by oxidized cap-layer. The thickness of the oxide cap-layer decreased with the increase of annealing temperature. (c) 2004 Elsevier B.V. All rights reserved.