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