1. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic SystemsSchool of Materials Sciences & EngineeringBeijing Institute of Technology Haidian District Beijing 100081 P. R. China
2. Department of Physics of Complex SystemsFaculty of PhysicsWeizmann Institute of Science Rehovot 7610001 Israel
3. Key Laboratory for Special Functional Materials of Ministry of EducationHenan University Longting District Kaifeng 475004 P. R. China
4. State Key Laboratory of Luminescent Materials and Devices and Institute of Optical Communication MaterialsSouth China University of Technology Guangzhou 510641 P. R. China
5. Shenzhen Research InstituteBeijing Institute of Technology Nanshan District Shenzhen 518057 P. R. China