1. Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India
2. Department of Physics, M. G. Mahavidyalaya, Bhupatinagar, Midnapore (East), West Bengal 721 425, India
3. Department of Chemistry, Jadavpur University, Kolkata 700 032, India
4. Department of Chemistry, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5, 07122 Palma de Mallorca (Baleares), Spain