1. State Key Laboratory of High Performance Complex Manufacturing College of Mechanical and Electrical Engineering Central South University Changsha 410000 P. R. China
2. School of Electronic and Electrical Engineering Zhaoqing University Zhaoqing Road, Duanzhou District Zhaoqing Guangdong 526061 P. R. China
3. Key Laboratory for UV‐Emitting Materials and Technology of Ministry of Education Northeast Normal University Changchun 130024 P. R. China