Electro- and photoluminescence of the Tm3+ ion in Tm3+- and Li+doped ZnO ceramics.: Influence of the sintering temperature

The electro- and photoluminescence properties of ZnO:Tm,Li pellets sintered between 900 and 1300 degrees C have been studied at room temperature. The photoluminescence spectra show the emissions arising from both the Tm3+ ions and ZnO itself whereas the electroluminescence spectra show only the emission arising from the Tm3+ ions. The dependence of the current, capacitance and luminescence intensity upon voltage was measured. As for the ZnO:Bi composites, the electro-optical properties of the ZnO:Tm,Li composites depend mainly upon the grain boundaries, but unlike for the ZnO:Bi composites, they cannot be interpreted in terms of a succession of grain boundaries barriers. It is concluded that the grain boundaries act as preferential conduction pathways. The Tm3+ ions are mainly located between the grains in intergranular layers where their luminescence acts as a probe, which evidences both the current flow and the presence of hot electrons. (C) 1999 Elsevier Science B.V. All rights reserved.