1. School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, P.R. China
2. Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin, Germany
3. School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou 434023, P.R. China
4. College of Physics and Electronic Information, Yan’an University, Yan’an 716000, P. R. China
5. State Key Lab of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, P.R. China