1. Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, P. R. China
2. Chongqing University of Technology, Chongqing 400054, P. R. China
3. Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095, United States
4. Department of Optoelectronic Engineering, Chongqing University, Chongqing 400044, P. R. China