Optical properties of the deposited germanium-oxide (Ge-O) prepared from the laser ablation of GeO2 were investigated. When the GenOm clusters, having the compositions mainly at n = m, were deposited onto a substrate as a precursor, 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 component of the oxidation state of Ge2+, which shows the contributions from 1:1 composition of Ge2+-O2-. Correspondingly, the electronic structures of the 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 molecular orbital gap of the corresponding neutral GenOn clusters experimentally, 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 the GenOn clusters can be ascribed to the origin of the visible photoluminescence.
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