1. The State Key Laboratory of Luminescent Materials and Devices, Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques, Guangdong Engineering Technology Research and Development Center of Special Optical Fiber Materials and Devices, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, P. R. China
2. Department of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongwen Road, Chongqing 400065, China
3. College of Physics, Taiyuan University of Technology, 030024 Taiyuan, China
4. Laboratory of Crystal Physics, Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk 660036, Russia
5. World-Class Research Center “Advanced Digital Technologies”, University of Tyumen, Tyumen 625003, Russia
6. Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein ZA-9300, South Africa