1. College of Chemistry and Molecular Engineering; Zhengzhou University; Zhengzhou 450001 Henan Province P. R. China
2. Department of Physics; The Chinese University of Hong Kong; Shatin Hong Kong SAR P. R. China
3. Institute of Nanostructured Functional Materials; Huanghe Science and Technology College; Zhengzhou 450006 Henan Province P. R. China
4. College of Chemistry and Chemical Engineering; Xiamen University; Xiamen 361005 Fujian Province P. R. China