Influence of the sintering temperature on the electrical and luminescent properties of Mn-doped ZnO

The electrical and luminescent properties of a series of ZnO pellets doped with 0.1% Mn, sintered at 1100, 1200, 1300 and 1400 °C and furnace cooled have been studied. The impedance spectra of the pellets can result from a grain boundary capacitance. The conductivity of the material increases with increasing sintering temperature. The electrical properties agree with the brick layer-grain boundary model put forward for ZnO-based varistors. All the pellets are photoluminescent with both an identical photoluminescence spectrum and an identical photoluminescence yield. Unlike the pellets sintered at 1100, 1200 and 1400 °C, the pellet sintered at 1300 °C is electroluminescent. This electroluminescence, which is observed at a voltage lower than the breakdown voltage, evidences the presence of field inhomogeneities and hot electrons inside the pellet.