1. Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices
2. Institute of Opto-electronic Materials and Technology
3. South China Normal University
4. Guangzhou 510631
5. China
6. Department of Physics
7. The University of Hong Kong
8. State Key Laboratory of Optoelectronic Materials and Technologies
9. School of Physics
10. Sun Yat-Sen University
11. Guangzhou 510275
12. Institute of Microelectronics
13. Tsinghua University
14. Beijing 100084