1. Hebei Key Laboratory of Optic-Electronic Information and Materials, College of Physics Science and Technology, Hebei University, Baoding 071002, People’s Republic of China
2. Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
3. Key Laboratory of Luminescence and Optical Information, Ministry of Education, School of Physical Science and Engineering, Beijing JiaoTong University, Beijing 100044, People’s Republic of China