1. College of Railway Transportation, Hunan University of Technology, Zhuzhou 412008, China
2. Qinghai Provincial Key Laboratory of Nanomaterials and Nanotechnology, Qinghai Minzu University, Qinghai 810007, China
3. Shandong Provinical Key Laboratory of Optical Communication Science and Technology, School of Physical Science and Information Technology, Liaocheng University, Liaocheng 252059, China
4. Department of physics, Guangxi Minzu University, Nanning, 530006, China