1. School of Materials Science and Engineering, Central South University, 932 Lushan Road South, Changsha 410083, Hunan, China
2. School of Physics and Electronic Information, Yunnan Normal University, 768 Juxian Street, Kunming 650500, Yunnan, China
3. Yunnan Key Laboratory of Optoelectronic Information Technology, Yunnan Normal University, Kunming 650500, Yunnan, China