1. Photonics and Optoelectronics Group Department of Physics and CeNS; Ludwig-Maximilians-Universität München; Amalienstr. 54 80799 Munich Germany
2. Nanosystems Initiative Munich (NIM); Schellingstr. 4 80799 Munich Germany
3. Department of Chemistry and CeNS; Ludwig-Maximilians-Universität München Butenand; str. 11 81377 Munich Germany