1. Key Laboratory of Luminescence and Optical InformationMinistry of EducationSchool of ScienceBeijing Jiaotong University Beijing 100044 China
2. Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic InformationHuazhong University of Science and Technology Wuhan 430074 China
3. Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of EducationDepartment of ChemistryTsinghua University Beijing 100084 China