Influence of adsorbed oxygen on the surface photovoltage and photoluminescence of ZnO nanorods

Abstract

ZnO nanorods have been prepared with sol–gel methods using zinc acetate dihydrate in ethanol in the presence of lithium hydroxide via alkaline hydrolysis. The electron transfer behaviour at the surface and interface in ZnO nanorods was investigated by means of the surface photovoltage technique. The influence of adsorbed oxygen on the surface photovoltage (SPV) response of ZnO nanorods was studied by surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (FISPS). The results of SPS demonstrate that for ZnO nanorods the built-in electric field should be a main driving force for the separation of the photogenerated electron–hole pairs and its ensuing SPV response. The method of photogenerated charge recombination was also studied with the aid of PL spectroscopy. It is shown that the two methods of energy relaxation in light-excited ZnO nanorods are competitive. When oxygen is adsorbed at the surface and the built-in electric field is formed, the SPV response should be the leading one. Nevertheless, when oxygen is absent, the energy relaxation is mostly carried out by radiative emission.