1. Department of Chemistry, Faculty of Science, Okayama University of Science, 1-1 Ridaicho, Okayama 700-0005, Japan
2. Advanced Materials Institute and Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jyonan-ku, Fukuoka 814-0180, Japan
3. Laboratoire Léon Brillouin (CEA-CNRS), CE Saclay, 91191 Gif-sur-Yvette Cedex, France