1. School of Physics and Opto-Electronic Technology, Baoji University of Arts and Sciences, Baoji, Shaanxi 721016, P. R. China
2. College of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, P. R. China
3. Baoji Key Laboratory of Micro-Nano Optoelectronics and Terahertz Technology, Baoji, Shaanxi 721016, P. R. China
4. Т. F. Gorbachev Kuzbass State Technical University, Kemerovo 650000, Russia