1. South China Academy of Advanced Optoelectronics and International Academy of Optoelectronics at Zhaoqing South China Normal University Guangdong 510631 P. R. China
2. Department of Chemical Engineering Waterloo Institute of Nanotechnology University of Waterloo 200 University Ave West Waterloo Ontario N2L 3G1 Canada
3. School of Information and Optoelectronic Science and Engineering South China Normal University Guangdong 510006 China
4. Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education Jilin Normal University Changchun 130103 P. R. China