1. State Key Laboratory on Integrated Optoelectronics, and College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
2. Department of Physics and Materials Science and Centre for Functional Photonics, City University of Hong Kong, Hong Kong
3. State Key Laboratory of Superhard Materials, and College of Physics, Jilin University, Changchun 130012, China
4. Department of Chemistry and Physics, Louisiana State University, Shreveport, Louisiana 71115, USA