1. School of Materials Science and Engineering, Anhui Polytechnic University, Wuhu, AnHui 241000, P. R. China
2. Chemistry and Pharmaceutical Engineering College, Nanyang Normal University, Nanyang, Henan 473061, P. R. China
3. Faculty of Institute of Photoelectronics Thin Film Devices and Technique of Nankai University, Nankai University, Tianjin 30071, P. R. China