THE ROLE OF SURFACE-STATES AND SURFACE COMPLEXES IN ELECTROLUMINESCENCE CHARACTERISTICS OF SEMICONDUCTOR ELECTRODES

The roles of surface states, surface complexes, and donor states in electroluminescence characteristics were investigated by impurity (Nb)-doped and defect-doped polycrystalline TiO2. Due to intense light emission which resulted in consumption of electroactive species at the electrode surface, luminescence intensity decayed exponentially with time. In order to separate the contribution from the mass transport in the electrolyte, rotating disk electrode was used. Oxygen defects were found to play the decisive role in luminescence characteristics. They constitute a variety of energy states: the oxygen defect locating in the bulk acts as a donor, the energy level of which lies about 0.3 eV below the conduction band edge while the oxygen defect locating at the surface constitutes donor-type surface states.