1. School of Physics, Nanjing University of Science and Technology, Nanjing 210094, P. R. China
2. MIIT Key Laboratory of Advanced Display Materials and Devices, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China
3. Department of Basic Science and Humanities, Dawood University of Engineering and Technology, Karachi, Sindh 74800, Pakistan
4. Wet Chemistry Laboratory, Department of Metallurgical Engineering, NED University of Engineering and Technology, University Road, Karachi 75270, Pakistan