1. School of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, China
2. School of Physics, Shandong University, Jinan 250100, China
3. Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
4. Material and Opto-Electronic Research Center, University of Chinese Academy of Sciences, Beijing 100039, China