1. Department of Physics, Abdul Wali Khan University, Mardan, 23200, Pakistan
2. National University of Sciences and Technology (NUST), Islamabad, Pakistan
3. Department of Physics, College of Science, King Saud University, P. O. Box 2455, Riyadh 11451, Saudi Arabia
4. Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, People's Republic of China