1. Department of Physics, Bishop Moore College, Mavelikara, Alappuzha 690110, Kerala, India
2. Centre for Molecular and Biophysics Research, Department of Physics, Mar Ivanios College, Thiruvananthapuram 695 015, Kerala, India
3. National Physical Laboratory, New Delhi 110 012, India
4. Raman Research Institute, Bangalore 560080, India