1. Integrated Center for Applied Physics and Photonic Materials (IAPP) and Center for Advancing Electronics Dresden (cfaed) Technische Universität Dresden Nöthnitzer Straße 61 Dresden 01187 Germany
2. Department of Materials Science and Engineering, and Centre for Functional Photonics (CFP) City University of Hong Kong 83 Tat Chee Avenue Kowloon Hong Kong SAR P. R. China