* Corresponding authors

^a Wuhan National Laboratory for Optoelectronics, and College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan, China
E-mail: jun.zhou@mail.hust.edu.cn
Fax: +86-27-87792225
Tel: +86-27-87793105

^b MOE of the Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, China

^c State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, P. R. China

^d Instrumental Analysis & Research Center, Sun Yat-Sen University, Guangzhou, China

^e Bejing National Laboratory for Condensed Matter Physics Institute of Physics, Chinese Academy of Sciences, Beijing, China

^f School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
E-mail: zhong.wang@mse.gatech.edu
Fax: +1-404-894-8008
Tel: +1-404-894-9140