Affiliation: | 1. School of Chemistry and Chemical Engineering, Southeast University, , Nanjing, Jiangsu, 211189 PR China;2. Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, , Hefei, Anhui, 230026 PR China;3. Center for Excitonics, Research Laboratory for Electronics, Massachusetts Institute of Technology, , Cambridge, MA, 02139 USA |