1. State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, P. R. China
2. University of Science and Technology of China, Hefei 230026, P. R. China
3. European Theoretical Spectroscopy Facility, Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Chemin des étoiles 8, bte L07.03.01, B-1348 Louvain-la-Neuve, Belgium