1. School of Physics and Optoelectronic Engineering; Guangdong University of Technology; Guangzhou 510006 P. R. China
2. Shanghai Institute of Optics and Fine Mechanics; Chinese Academy of Sciences; Shanghai 201800 P. R. China
3. Department of Biomedical Engineering; School of Basic Medical Sciences; Guangzhou Medical University; Guangzhou 510182 P. R. China
4. Department of Biochemistry and Molecular Pharmacology; University of Massachusetts Medical School; Worcester Massachusetts 01605 USA
5. State Key Laboratory of Luminescent Materials and Devices; School of Materials Science and Technology; South China University of Technology; Guangzhou 510640 P. R. China
6. State Key Laboratory of Modern Optical Instrumentation; College of Optical Science and Engineering; Zhejiang University; Hangzhou Zhejiang 310058 P. R. China