1. Department of Electronic Engineering The Chinese University of Hong Kong Shatin, New Territories Hong Kong SAR P. R. China
2. Department of Physics The Chinese University of Hong Kong Shatin, New Territories Hong Kong SAR P. R. China
3. School of Materials Sun Yat-sen University Guangzhou 510275 P. R. China
4. Instrumental Analysis and Research Centre Sun Yat-sen University Guangzhou 510275 P. R. China
5. School of Environment and Energy State Key Laboratory of Luminescent Materials and Devices National Engineering Laboratory for VOCs Pollution Control Technology and Equipment Guangdong Provincial Key Laboratory of Solid Wastes Pollution Control and Recycling South China University of Technology Guangzhou 510006 P. R. China
6. Materials Science and Technology Research Center The Chinese University of Hong Kong Shatin, New Territories Hong Kong SAR P. R. China