1. College of Textiles, Zhongyuan University of Technology, Zhengzhou, Henan 450007, P. R. China
2. School of Material Science and Engineering, Zhengzhou University, Zhengzhou, Henan 450052, P. R. China
3. College of Physics and Optoelectronic Engineering, Zhongyuan University of Technology, Zhengzhou, Henan 450007, P. R. China