1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 (Singapore)
2. Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4J3 (Canada)
3. Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore 117602 (Singapore)
4. State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022 (P. R. China)