Electronic structure of AgBr(111) twin boundaries

The structure and the electrical and luminescence properties of polycrystalline sintered ZnO pellets containing small amounts of Bi, Mn and Er oxides have been studied. The electric behaviour of the pellets not containing Bi2O3 is ohmic or nearly ohmic, whereas the pellets containing Bi2O3 show a strong increase in their conductivity with the applied voltage. Compared to the Er2O3-free pellets, the pellets containing Er2O3 are highly conducting. The photoluminescence spectrum of all the pellets is the broad classical spectrum of ZnO. The pellets containing Er2O3 are electroluminescent and show mainly the emission spectrum of the Er3+ ion. The electroluminescence intensity increases with the applied voltage and follows a power law, whereas the relative intensity of the different bands of the electroluminescence spectrum of the Er3+ ion is independent of the applied voltage. The field inhomogeneities predicted by the classical model of varistors are unable to account for the observed electroluminescence results. It is concluded that the excitation of the Er3+ ions results either from an indirect process such as a hot electron impact-ionisation of Er2O3 in the boundaries or from a direct impact by hot electrons, the energy of which is controlled by the material.