Electroluminescence from alumina ceramics surface under low AC electric field in vacuum

The electroluminescence (EL) from a planar metal-alumina-metal structure was investigated under ac voltage applied in vacuum. Two kinds of electrode contacts, i.e., with/without sputtered gold films, showed quite different optical phenomena. For the non-sputtered samples (type A), no luminescence was detected below 4.5 kV. While for the sputtered samples (type B), from low applied voltage, there was faint and stable light emission due to EL observed. The characteristics of EL were examined in detail. It is supposed that the different electrode contacts are responsible for the interesting phenomena. A model has been proposed to distinguish their metal-alumina interface. For samples of type B, a marked reduction of the potential barrier between electrodes and alumina surface would be conducted. Thus compared with samples of type A, charge carriers can be more easily injected from the electrodes into the surface states of alumina, and EL will emit due to the radiative recombination of electrons and holes