1. State Key Laboratory of Powder Metallurgy, College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, P. R. China
2. Department of Physics and Institute of Advanced Materials Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, P. R. China
3. Key Laboratory of Solid State Optoelectronic Devices of Zhejiang Province, College of Physics and Electronic Information Engineering, Zhejiang Normal University, Jinhua, Zhejiang 321004, China
4. Department of Chemistry, Université Laval, Quebec City, Quebec, G1V 0A6, Canada
5. Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam-Golm, Germany