Visible photoluminescence of the deposited germanium-oxide prepared from clusters in the gas phase

Optical properties of the deposited germanium-oxide (Ge-O) prepared from th e laser ablation of GeO2 were investigated. When the GenOm clusters, having the compositions mainly at n=m, were deposited onto a substrate as a precu rsor, strong visible photoluminescence peaked at 500 nm was observed under the excitation of 325 nm laser light. X-ray photoelectron spectroscopy for the deposited Ge-O on the substrate consistently shows the substantial comp onent of the oxidation state of Ge2+, which shows the contributions from 1: 1 composition of Ge2+-O2-. Correspondingly, the electronic structures of th e germanium-oxide cluster were studied by using photoelectron spectroscopy in gas phase. Our developed method of the halogen atom doping enables us to determine the highest occupied molecular orbital-the lowest unoccupied mol ecular orbital gap of the corresponding neutral GenOn clusters experimental ly, and it was found that the gap of the GenOn (n=2-5) clusters reasonably corresponds to the energy of the visible light. These results imply that th e GenOn clusters can be ascribed to the origin of the visible photoluminesc ence. (C) 2000 American Institute of Physics. [S0021-8979(00)03522-2].