1. Institute for Advanced Materials (IAM) Academy of Advanced Optoelectronics; South China Normal University; Guangzhou 510006 China
2. School of Physics and Telecommunication Engineering; South China Normal University; Guangzhou 510006 China
3. Department of Physics Boston College, Chestnut Hill; Massachusetts 02467 USA
4. Department of Physics and TcSUH; University of Houston; Houston, Texas 77204 USA
5. NanoLab, Inc; Waltham Massachusetts 02451 USA
6. Department of Chemistry UAM; Poznan Poland
7. Department of Physics Freie Universität Berlin Berlin 14195 , Germany Department of Physics; Freie Universität Berlin; Berlin 14195 Germany