1. School of Chemistry Beihang University Beijing 100191 P.R. China
2. School of Physics Hubei University Wuhan Hubei 430062 P.R. China
3. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences College of Materials Science and Opto-Electronic Technology University of Chinese Academy of Sciences Beijing 100190 P.R. China
4. Ningbo Institute of Materials Technology and Engineering Chinese Academy of Sciences Ningbo 315201 P.R. China
5. School of Optical and Electronic Information Huazhong University of Science and Technology Wuhan Hubei 430074 P.R. China