1. College of Physics and Electronic Information Yunnan Normal University, Yunnan Kunming 650500, P. R. China
2. Yunnan Provincial Key Laboratory for Photoelectric Information Technology, Yunnan Normal University, Yunnan Kunming 650500, P. R. China
3. Key Laboratory of Advanced Technique & Preparation for Renewable Energy Materials, Ministry of Education Yunnan Normal University, Yunnan Kunming 650500, P. R. China