1. College of Materials Science and Opto-Electronic TechnologyCenter of Materials Science and Optoelectronics EngineeringCAS Center for Excellence in Topological Quantum ComputationCAS Key Laboratory of Vacuum Physic University of Chinese Academy of Sciences Beijing 100049 P. R. China
2. Key Laboratory of Luminescence and Optical InformationMinistry of EducationSchool of Science Beijing Jiaotong University Beijing 100044 P. R. China
3. Department of PhysicsChemistry and Biology (IFM) Linköping University 58183 Linköping Sweden
4. Center for Excellence in Nanoscience (CAS)Key Laboratory of Nanosystem and Hierarchical Fabrication (CAS) National Center for Nanoscience and Technology Beijing 100190 P. R. China
5. Institute of Polymer Optoelectronic Materials and DevicesState Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640 P. R. China
6. Beijing Key Laboratory for Optical Materials and Photonic DevicesDepartment of Chemistry Capital Normal University Beijing 100048 P. R. China