1. Department of Physics , PSGR Krishnammal College for Women , Coimbatore 641004, Tamilnadu , India
2. Department of Physics , Karunya Institute of Technology and Sciences , Coimbatore 641114, Tamilnadu , India
3. Department of Physics , PSGR Krishnammal College for Women , Coimbatore 641004, Tamilnadu , India , Tel.: +91-7812844344