1. Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China
2. Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
3. Department of Chemistry & Key Laboratory of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China
4. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China