1. College of Physics and Materials Science , 12523 Tianjin Normal University , Tianjin 300387 , P.R. China
2. Yongjiang Laboratory , Ningbo 315202 , P.R. China
3. Department of Physics , University of Rome Tor Vergata , Via Della Ricerca Scientifica 1 , Rome I-00133 , Italy
4. Beijing National Laboratory for Molecular Sciences, Institute of Chemistry , Chinese Academy of Sciences , Beijing 100049 , P.R. China
5. School of Chemical Sciences , University of Chinese Academy of Sciences , Beijing 100049 , P.R. China