1. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South P. R. China Academy of Advanced Optoelectronics, South P. R. China Normal University, Guangzhou 510006, P. R. China
2. National Center for International Research on Green Optoelectronics, South P. R. China Normal University, Guangzhou 510006, P. R. China
3. Department of Chemistry, City University of Hong Kong, Hong Kong 999077, P. R. China
4. Department of Radiology, The First Affiliated Hospital, Guangzhou Medical University, Guangzhou 510120, P. R. China
5. Department of Radiology, The First Affiliated Hospital, Sun Yat-Sen University, Guangzhou 510080, P. R. China