1. Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory for the Physical Chemistry of Solid Surfaces; Xiamen University; Xiamen Fujian 361005 P.R. China
2. Engineering Research Centre of Environment-Friendly Functional Materials, Ministry of Education. Fujian Provincial Key Laboratory of Photoelectric, Functional Materials, Institute of Materials Physical Chemistry; Huaqiao University; No.668 Jimei Avenue Xiamen Fujian 361021 P.R. China