The use of an Electrolyte-SiO2-Si system allows a detailed control of the electron injection from the electrolyte into SiO2 layer, and makes feasible to reach the electron heating in the conduction band of SiO2 before to take place the irreversible breakdown. The injected and heated electrons enhanced the probability of the SiO2 defect excitation as well as the Si-O bond breaking. Both features give raise to the relaxation processes which are responsible of the electroluminescence characteristics of the oxide. So, the measured electroluminescence spectrum presents straightforward information on the defect types, their nature and possible precursor defect behaviour. Results on silicon oxides obtained from different technological processes and treatments, corroborate the above analysis and show the electro-luminescence of SiO2 as an interesting and powerful method to evaluate the SiO2 properties.