1. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, 27 South Taoyuan Road, Taiyuan, Shanxi 030001, P. R. China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, No. 19 (A) Yuquan Road, Shijingshan
District, Beijing 100049, P. R. China
3. School of Physics and Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Jianshe North Road, Chengdu 610054, P. R. China