1. School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong, P. R. China
2. Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-sen University, Guangzhou 510275, Guangdong, P. R. China
3. State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, Guangdong, P. R. China