1. Chair for Photonics and Optoelectronics, Nano-Institute Munich Department of Physics Ludwig-Maximilians-Universität München (LMU) Königinstrasse 10 80539 Munich Germany
2. Nanosystems Initiative Munich (NIM) and Center for NanoScience (CeNS) Schellingstrasse 4 80799 Munich Germany
3. Department of Materials Science and Engineering, and Centre for Functional Photonics (CFP) City University of Hong Kong 83 Tat Chee Avenue, Kowloon Hong Kong S.A.R. China
4. Department of Chemistry Ludwig-Maximilians-Universität München Butenandtstrasse 5–13 (E) 81377 Munich Germany