1. School of Materials and EnergyGuangdong University of Technology Guangzhou 510006 China
2. School of Physics and Optoelectronic EngineeringFoshan University Foshan 528000 China
3. LUMINOUS!Centre of Excellence for Semiconductor Lighting and DisplaysSchool of Electrical and Electronic EngineeringNanyang Technological University Nanyang Avenue 639798 Singapore
4. Institute of Polymer Optoelectronic Materials and DevicesState Key Laboratory of Luminescent Materials and DevicesSouth China University of Technology Guangzhou 510640 China