1. Physics and Chemistry of Nanostructures, Ghent University, Ghent B-9000, Belgium
2. Department of Chemistry, Basel University, Basel 4058, Switzerland
3. Sol−gel Centre for Research on Inorganic Powders and Thin films Synthesis, Ghent University, Ghent B-9000, Belgium
4. Center for Nano and Biophotonics, Ghent University, Ghent B-9000, Belgium