Identification of the transition responsible for the visible emission in ZnO using quantum size effects

The emission properties of suspensions of nanocrystalline ZnO particles wit h different particle sizes were studied. Two emission bands were observed, one being an exciton emission and the other the visible emission of ZnO. Th e energy of both emissions depends on the particle dimensions due to size q uantization. A linear relationship between the energetic maxima of the two emission bands is found. Because of the difference in effective masses of e lectrons and holes in ZnO, the slope of the linear relationship clearly ind icates that the visible emission is due to the transition of an electron fr om the conduction band to a deep trap. The nature of the deep trap is also considered. (C) 2000 Elsevier Science B.V. All rights reserved.