1. State Key Laboratory
of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, P. R. China
2. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, P. R. China
3. State Key Laboratory of Rare Earth Materials Chemistry and Applications,
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China