1. Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 China
2. Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials Hubei University Wuhan 430062 China
3. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 China
4. Laboratory of Solid State Microstructures Nanjing University Nanjing 210093 China
5. Department of Physics Boston College Chestnut Hill Massachusetts 02467 USA