1. a Department of Physics , PES College of Science , Mandya , INDIA
2. b Department of Studies in Physics , University of Mysore , Manasagangotri, Mysore , 570 006 , INDIA
3. c Department of Chemistry , University of Mysore , Manasagangotri, Mysore , 570 006 , INDIA
4. d Department of Physics , N E R I S T , Itanagar , INDIA