1. Key Laboratory of Photo‐electronic Materials Ningbo University Ningbo Zhejiang 315211 P. R. China
2. State Key Laboratory on Integrated Optoelectronics College of Electronic Science and Engineering and College of Physics Jilin University Changchun Jilin 130012 P. R. China
3. Department of Physics Dalian Maritime University Dalian Liaoning 116026 P. R. China