1. College of Materials and Chemical Engineering, Xi’an Technological Univ., Xi’an, P. R. C. 710021, CN (Corresponding author), e-mail: niuxl0123@163.com
2. School of Photoelectrical Engineering, Xi’an Technological Univ., Xi’an, P. R. C., 710021, CN.
3. College of Physics and Information Technology, Shaanxi Normal Univ., Xi’an, Shaanxi, P. R. C., 710062, CN.