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

Abstract

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.