1. Department Chemie and Biochemie and CeNS, Ludwig-Maximilians-Universität München, 81377 München, Germany, Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970 Brazil, Department of Materials Science and Engineering and Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3108, and The Institute of Optics, University of Rochester, Rochester, New York 14627