1. Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
2. CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology of China, Beijing 100190, P. R. China
3. College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
4. Center for Advanced Quantum Studies, Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, P. R. China
5. University of Chinese Academy of Sciences, Beijing 100049, P. R. China