1. Department of Physics and Materials Science, Maseno University, P. O. Box 333-40105, Maseno, Kenya
2. Department of Physics, University of Eldoret, P. O. Box 1125-30100, Eldoret, Kenya
3. Department of Physics and Mathematics, Moi University, P. O. Box 3900-30100, Eldoret, Kenya
4. Department of Physics and Materials Science, Maseno University of Eldoret, P. O. Box 333-40105, Eldoret, Kenya