1. Department of Chemistry, UGC-Centre for Advanced Studies-I, Guru Nanak Dev University, Amritsar 143005, India
2. Faculty of Science and Engineering, Division of Chemistry and Environmental Sciences, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester M15 6BH, U.K.
3. Département de Physique, ULB, CP 238, av. F. D. Roosevelt, Bruxelles B-1050, France
4. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
5. School of Engineering, Newcastle University, Merz Court, Newcastle upon Tyne NE17RU, U.K.