1. Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology No.1037 Luoyu Road Wuhan 430074 P.R. China
2. Department of Physics Department of Materials Science and Engineering, and Department of Biomedical Engineering City University of Hong Kong Tat Chee Avenue Hong Kong P.R. China
3. China-EU Institute for Clean and Renewable Energy Huazhong University of Science and Technology No.1037 Luoyu Road Wuhan 430074 P.R. China
4. The Key Laboratory of Refractories and Metallurgy and Institute of Advanced Materials and Nanotechnology Wuhan University of Science and Technology No. 947, Heping Avene Wuhan 430081 P.R. China