1. Institute of Semiconductors, South China Normal University, Guangzhou 510631, China
2. State Key Laboratory of Optic Information Physics and Technologies, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
3. Jiangxi Key Laboratory of Nanomaterials and Sensors, School of Physics, Communication and Electronics, Jiangxi Normal University, Nanchang 330022, China
4. Department of Physics, College of Science, Nanchang University, Nanchang 330031, China