1. Department of Materials Science and EngineeringCity University of Hong Kong 83 Tat Chee Avenue Kowloon Hong Kong 999077 P. R. China
2. School of Advanced Materials and NanotechnologyXidian University Xi'an 710071 P. R. China
3. National Engineering Research Center for Advanced Polymer Processing TechnologyZhengzhou University Zhengzhou Henan 450002 P. R. China
4. Centre for Functional Photonics (CFP)City University of Hong Kong 83 Tat Chee Avenue Kowloon Hong Kong 999077 P. R. China