Theory of Electroluminescence

The theoretical basis for exciting luminescence by the application of an electric potential to a crystalline dielectric or semiconductor is considered. Three mechanisms of excitation are each shown to be theoretically feasible in appropriate solids and with suitable local field conditions: (1) the ionization of impurity systems directly by an electric field, (2) the acceleration of conduction electrons or positive holes in the valence band to kinetic energies sufficient to excite or ionize impurity systems or valence electrons by inelastic collisions, and (3) injection of charge carriers. Radiative de-excitation is feasible by two mechanisms: (a) direct recombination of conduction electrons and holes in the valence band, and (b) optical transitions characteristic of impurity systems known as activators. The characteristics of electroluminescence proceeding by these processes are examined theoretically.