1. Department of Chemical, Biological & Macromolecular Sciences; S. N. Bose National Centre for Basic Sciences, Block JD, Sector III; SaltLake, Kolkata 700 106 India
2. Solid State Physics Division; Bhabha Atomic Research Centre; Mumbai 400085 India
3. Department of Chemistry; West Bengal State University; Barasat, Kolkata 700126