Investigation on direct-current-driven inorganic electroluminescence in rare-earth and Li co-doped ZnO pellets

The phenomena involved in direct-current-driven electroluminescence (DC EL) was investigated, which occurred in the sintered pellets of ZnO doped with rare-earth (RE) and lithium. The microstructural observation revealed that the morphology of loosely-packed small-grains was advantageous for the DC EL, where the doped RE3+ was homogeneously dispersed over the ZnO matrix as small RE2O3 grains. The EL color was dependent on the type of the doped RE3+ and green, blue, or red EL was observed with Er3+, Tm3+, or Eu3+. The EL emission was recognized on the anode side. That brought a new multilayered structure concentrating RE3+ on the anode side to enhance the EL intensity. The occurrence of the EL on the anode side in the presence of an acceptor-type dopant lithium suggested the involvement of holes in the DC EL emission.