1. Photonics and Optoelectronics Group; Department of Physics and Center for NanoScience (CeNS); Ludwig-Maximilians-Universität München; Amalienstrasse 54 80799 Munich Germany
2. Nanosystems Initiative Munich (NIM); Schellingstrasse 4; Munich 80799 Germany
3. Institute for Technical Physics and Materials Science; HAS Centre for Energy Research; P.O. Box 49 H-1525 Budapest Hungary
4. National Institute for Cellular Biotechnology; School of Chemical Sciences; Dublin City, Glasnevin Dublin 9 Ireland
5. School of Chemistry; University College Dublin; Belfield Dublin 4 Ireland