1. College of Electronic Information and Optical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2. College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
3. Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong 999077, China
4. Department of Physics, City University of Hong Kong, Kowloon, Hong Kong 999077, China
5. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States