1. School of Sciences, Xi’an University of Architecture and Technology , Xi’an, Shaanxi 710043 , P.R. China
2. School of Physics and Optoelectronic Engineering, Xidian University , Xi’an, Shaanxi 710071 , P.R. China
3. College of Chemistry and Chemical Engineering, Guangxi University , Nanning, Guangxi 530004 , P.R. China