1. The Beijing Municipal Key Laboratory of New Energy Materials and Technologies; School of Materials Sciences and Engineering; University of Science and Technology Beijing; Beijing 100083 P. R. China
2. Anhui Key Laboratory of Optoelectric Materials Science and Technology; Department of Physics; Anhui Normal University; Wuhu Anhui 241000 P. R. China
3. State Key Laboratory of Luminescent Materials and Devices and Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques; South China University of Technology; Guangzhou 510641 P. R. China