Electroluminescence ( EL) and photoluminescence ( PL) measurements were conducted on Si-implanted SiO2 layers as a function of process and measurement parameters. Measurable light emission was observed from the metal oxide semiconductor light emitting diode ( MOS-LED) when holes are injected from the substrate. It was shown that major PL and EL emissions have the same origin. However, two important differences were observed between EL and PL spectra. The first one is the light emission from the Si substrate due to the recombination of electrons supplied by the front contact and holes that were accumulated in the inversion region at the substrate/SiO2 interface. This might be a factor reducing the contribution of Si nanocrystals to the EL emission of the MOS-LED structure as a result of decrease in the number of holes in the inversion layer. The second difference is that EL emission peaks stay at a slightly higher energy than PL peaks. It was observed that the EL peak shifts towards the PL peak with increasing bias voltage. This behaviour is explained by considering the size distribution of nanocrystals formed by ion implantation.