1. School of Materials and Energy Lanzhou University Lanzhou 730000 P. R. China
2. National & Local Joint Engineering Laboratory for Optical Conversion Materials and Technology Lanzhou University Lanzhou 730000 P. R. China
3. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 P. R. China
4. School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 P. R. China