In this paper, the luminescence properties of thin, thermally grown SiO 2 layers implanted with silicon and carbon ions are explored. The doses and energies were chosen in such a way that the resulting peak concentration of excess Si and C amounts to 5–10% in a depth region of 60–180nm below the surface. The microstructure was investigated by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). Amorphous nanostructures with a size between 2 and 3.5nm were found in depth region between 80 and 150nm below the oxide surface. Strong photoluminescence (PL) around 2.1 and 2.7eV has been observed after excitation at 4.77eV. Si y C 1−y O x complexes with x<2 are assumed to cause the observed PL in the blue spectral region.