1. Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and DevicesSchool of Information and Optoelectronic Science and EngineeringSouth China Normal University Guangzhou 510006 P. R. China
2. School of Optoelectronic EngineeringGuangdong Polytechnic Normal University Guangzhou 510665 P. R. China
3. Department of Electronic EngineeringCollege of Information Science and TechnologyJinan University Guangzhou 510632 P. R. China
4. School of Chemistry and EnvironmentSouth China Normal University Guangzhou 510006 P. R. China