1. College of Chemistry and Chemical EngineeringCentral South University Changsha 410083 P. R. China
2. Beijing National Laboratory for Molecular SciencesCAS Key Laboratory of Organic SolidsInstitute of ChemistryChinese Academy of Sciences Beijing 100190 P. R. China
3. Department of Physics and Institute of Advanced MaterialsHong Kong Baptist University Kowloon Tong Hong Kong SAR 999077 P. R. China
4. Department of PhysicsThe Chinese University of Hong Kong New Territories Hong Kong 999077 P. R. China
5. State Key Laboratory of Luminescent Materials and DevicesSouth China University of Technology Guangzhou 510640 P. R. China
6. Department of ChemistryUniversité Laval Quebec City Quebec G1V 0A6 Canada