In this work we have studied the structural, electrical and optical properties of MOS devices, where the dielectric layer consists of a SiO x ( x<2) thin film prepared by plasma enhanced chemical vapor deposition and implanted with rare earth ions. As deposited SiO x films were annealed at high temperature (>1000 °C) to induce the separation of the Si and SiO 2 phases with the formation of Si nanocrystals embedded in the insulating matrix. Devices based on this system present a strong light emission at room temperature at a wavelength of about 900 nm. Devices emitting at different wavelengths have been fabricated by implanting SiO x films with Er or Tm. Devices based on Er-doped Si nanoclusters film exhibit an intense 1.54 μm room temperature electroluminescence (EL). We have calculated the excitation cross-section for Er ions in presence of Si nanoclusters under electrical pumping and the value is ∼1 × 10 −14 cm 2, comparable to the value found for the electrical excitation of undoped Si nanocrystals. Finally, devices based on Tm-doped Si nanoclusters exhibit two EL peaks at 0.78 and 1.7 μm.