1. Wuhan National Laboratory for Optoelectronics; Huazhong University of Science and Technology; Wuhan 430074 P. R. China
2. Department of Chemistry and Biochemistry; University of California; Santa Cruz CA 95064 USA
3. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing; School of Materials Science and Engineering; Wuhan University of Technology; Wuhan 430070 P. R. China