1. School of Microelectronics, Xidian University , Xi’an 710071 , P.R. China
2. School of Physics and Optoelectronic Engineering, Xidian University , Xi’an 710071 , P.R. China
3. College of Physics and Optoelectronic Technology, Baoji University of Arts and Sciences , Baoji 721013 , P.R. China
4. College of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences , Baoji 721013 , P.R. China
5. College of Mechanics and Optoelectronic Physics, Anhui University of Science and Technology , Huainan 232001 , P.R. China