The system of the nanoinclusions of Si in the SiO2 and Al2O3 matrix (SiO2:Si, Al2O3:Si) attracts great attention due to its ability of the luminescence in visible and near-IR range of spectrum. The influence of the P ion alloying on the electronic structure of nanocomposites was investigated. The P ion doping and post-annealed at T= 1000 degrees C (2 h) results in the enhancement of the photoluminescence (PL) peak connected with the Si nanocrystals. The electronic structure was investigated by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy losses spectroscopy (HREELS) methods. Ion surface modification and annealing forms the special nanostructure with Si nanocrystals in SiO2 and Al2O3 matrix having high density of interfaces with special atomic structure and various degree of oxidation of Si atoms on the boundaries. HREELS investigations show that the P ion doping increases the probability of interband transitions in SiO2:Si and Al2O3:Si composites. (c) 2006 Published by Elsevier B.V.