1. Egerton University, Department of Physics, P.O. Box 536-20115, Egerton, Kenya
2. Universidade Federal de Itajuba, Av. BPS, 1303, 37500-903 Itajuba, MG, Brazil
3. Universitat Politecnica de Valencia, 46022, Valencia, Spain
4. Sao Paulo State University, Advanced Materials Group, Bauru Campus, Av. Luiz Edmundo Carrijo Coube N°14-01, Vargem Limpa Bauru-SP CEP: 17033-360, Brazil