1. School of Physics and Technology, Xinjiang University, Urumqi 830017, P. R. China
2. School of Mechanical and Electrical Engineering, Wuhan Institute of Technology, Wuhan 430205, P. R. China
3. College of Physics and Electronics, Hunan Institute of Science and Technology, Yueyang 414000, P. R. China
4. China-EU Institute for Clean and Renewable Energy, Huazhong University of Science and Technology, Wuhan 430074, P. R. China