1. Beijing National Laboratory for Molecular Sciences (BNLMS); State Key Laboratory of Rare Earth, Materials Chemistry and Applications; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 PR China
2. Department of Physics; Yunnan University; 2 Cuihu Bei Lu Kunming 650091 PR China
3. Department of Materials Science and Engineering; University of Toronto; 184 College Street Toronto, Ontario Canada M5S 3E4