1. State Key Laboratory of Rare Earth Materials Chemistry and Applications; College of Chemistry and Molecular Engineering; Peking University; 202 Chengfu Road Beijing 100871 P.R. China
2. CAS Key Laboratory of Materials for Energy Conversion Shanghai Institute of Ceramics; Chinese Academy of Sciences; 1295 Dingxi Road Shanghai 200050 P.R. China
3. Department of Chemistry and Biochemistry; Northern Illinois University; DeKalb Illinois 60115 USA