1. Department of Physics, Victoria Institution (College), 78 B,
A. P. C. Road, Kolkata 700009, India
2. Department of Physics, Sammilani Mahavidyalaya, Baghajatin
Station, E. M. Bypass, Kolkata 700075, India
3. Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India