1. Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), Jilin University, Changchun 130012, China
2. Key Laboratory for UV Light-Emitting Materials and Technology (Ministry of Education), Northeast Normal University, Changchun 130024, China
3. Department of Physics, College of Science, Yanbian University, Yanji 133002, China
4. Department of Materials Science & Engineering and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, United States