1. Department of Physics The Chinese University of Hong Kong New Territories Hong Kong 999077 China
2. State Key Laboratory of Modern Optical Instrumentation Center for Chemistry of High‐Performance & Novel Materials Department of Chemistry Zhejiang University Hangzhou Zhejiang 310030 China
3. Center for Advanced Low‐dimension Materials State Key Laboratory for Modi cation of Chemical Fibers and Polymer Materials College of Materials Science and Engineering Donghua University Shanghai 201620 China
4. School of Materials Science and Engineering Peking University Beijing 100871 China
5. School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081 China
6. Fluorescence Research Group Singapore University of Technology and Design Singapore 487372 Singapore