1. Department of Physics, Ahmedabad Institute of Technology, Ahmedabad 380 060, Gujarat, India
2. Department of Science & Humanities, Government Polytechnic, (Gujarat Technological University, Ahmedabad), Dahod 389 151, Gujarat, India
3. Department of Physics, M K Bhavanagar University, Bhavanagar 364 001, Gujarat, India
4. Department of Physics, School of Science, Gujarat University, Ahmedabad 380 009, Gujarat, India