1. Key Laboratory of Theoretical Chemistry of Environment, Ministry of Education, School of Chemistry, South China Normal University, Guangzhou 510006, P. R. China
2. Institute for Advanced Materials, South China Academy of Advanced Optoelectronics and Guangdong Provincial Key Laboratory of Optical Information Materials and Technology, South China Normal University, Guangzhou 510006, P. R. China
3. Institute of Semiconductor Science and Technology, South China Normal University, Guangzhou 510631, P. R. China