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. Institute of Electronic Paper Displays; Academy of Advanced Optoelectronics; South China Normal University; Guangzhou 510006 China
3. Department of Physics; Boston College; Chestnut Hill MA 02467 USA
4. School of Chemistry & Environment; South China Normal University; Guangzhou 510006 China
5. Laboratory of Solid State Microstructures; Nanjing University; Nanjing 210093 China