1. Center of Materials Science and Optoelectronics Engineering College of Materials Science and Opto-Electronic Technology &, CAS Center for Excellence in Topological Quantum Computation &, CAS Key Laboratory of Vacuum Physics University of Chinese Academy of Sciences Beijing 100049 P. R. China
2. Department of Physics, Chemistry and Biology (IFM) Linköping University 58183 Linköping Sweden
3. Key Laboratory of Luminescence and Optical Information Ministry of Education School of Science Beijing Jiaotong University Beijing 100044 P. R. China
4. Beijing National Laboratory for Molecular Sciences CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences Institute of Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
5. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Center of Smart Materials and Devices School of Chemistry, Chemical Engineering and Life Science Wuhan University of Technology Wuhan 430070 P. R. China
6. Department of Physics The Chinese University of Hong Kong New Territories Hong Kong P. R. China