Electric and luminescent properties of ZnO-based ceramics containing small amounts of Er and Mn oxide

The electric and luminescent properties of a series of polycrystalline sintered ZnO pellets containing small amounts of Er and/or Mn oxide have been studied with reference to the brick layer-grain boundary model put forward for ZnO-based varistors. The pellets, which contain Er oxide, are electro- and triboluminescent with an emission spectrum characteristic of the Er3+ ion. The electroluminescence is observed at low applied voltage well below the breakdown voltage. It indicates the presence of hot electrons and field inhomogeneities inside the pellets. Since the classical grain boundary model of varistors is found unable to account for the electroluminescent properties, it is concluded that the electroluminescence is a consequence of current flows along the grain boundaries in Er-rich regions.