1. School of Physics and Electronic Engineering, Xinxiang University, Xinxiang, Henan 453003, P. R. China
2. School of Chemistry and Material Engineering, Xinxiang University, Xinxiang, Henan 453003, P. R. China
3. School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074, P. R. China