1. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, P. R. China
2. Key Laboratory of Solid State Optoelectronic Devices of Zhejiang Province, College of Physics and Electronic Information Engineering, Zhejiang Normal University, Jinhua 321004, P. R. China
3. State Key Laboratory of Supermolecular Structure and Materials, Jilin University, Changchun 130012, P. R. China