1. School of Materials Science and Engineering; University of New South Wales; Sydney NSW 2052 Australia
2. Materials Sciences Division; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA
3. Department of Physics; University of California, Berkeley; Berkeley CA 94720 USA
4. Department of Materials Science and Engineering; University of California, Berkeley; Berkeley CA 94720 USA
5. Department of Materials; ETH Zurich; Wolfgang-Pauli-Strasse 10 8093 Zurich Switzerland
6. Department of Materials Science and Engineering; University of Michigan; Ann Arbor MI 48109 USA
7. Center for Nanophase Materials Science; Oak Ridge National Laboratory; Oak Ridge TN 37831 USA
8. Institute of Applied Photophysics; Technische Universität Dresden; 01062 Dresden Germany