1. School of Optoelectronic Engineering and Institute of Advanced Materials; Nanjing University of Posts and Telecommunications; Nanjing 210023 China
2. School of Energy Science and Engineering; Harbin Institute of Technology, National Engineering Laboratory for Reducing Emissions from Coal Combustion; Harbin 150001 China
3. Philips Lighting Research China; Shanghai 200233 China
4. School of Materials Science and Engineering; Tianjin University; Key Laboratory of Advanced Ceramics and Machining Technology, Ministry of Education; Tianjin 300354 China
5. Department of Optical Science and Engineering; Fudan University; Shanghai 200433 China