1. Institute of Polymer Optoelectronic Materials & DevicesState Key Laboratory of Luminescent Materials & DevicesSouth China University of Technology Guangzhou 510640 P. R. China
2. Institute of Optical Communication MaterialsState Key Laboratory of Luminescent Materials & DevicesSouth China University of Technology Guangzhou 510640 P. R. China
3. School of Physics and OptoelectronicsSouth China University of Technology Guangzhou 510640 P. R. China
4. School of Physics and Telecommunication EngineeringSouth China Normal University Guangzhou 510006 P. R. China