1. State Key Laboratory of Luminescent Materials and Devices; School of Materials Science and Engineering; South China University of Technology; Wushan Road 381 Guangzhou 510641 P. R. China
2. Department of Physics; Zhejiang Normal University; Jinhua Zhejiang 321004 P. R. China
3. Department of Physics; South China University of Technology; Guangzhou 510640 China
4. State Key Laboratory of Modern Optical Instrumentation; College of Materials Science and Engineering; Zhejiang University; Hangzhou Zhejiang 310027 P. R. China