We have studied the effect of annealing on the electroluminescence (EL) spectrum of Si-SiO₂ structures containing excess ion-implanted silicon in the oxide layer. The implantation of 150-keV silicon ions to doses in the range from 5 × 10¹⁶ to 3 × 10¹⁷ cm ^-2 leads to the appearance of an intense emission band at 2.7 eV in the EL spectrum. The postimplantation annealing leads to a decrease in the intensity of this band and to the appearance of a new EL band at 1.6 eV assigned to radiative transitions in defect centers formed at the boundaries between silicon nanoclusters and silicon dioxide.