; Swapna, Nair S; Mercy, Mathews; Anantharaman, M R(Elsevier, May , 2005)
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Abstract:
Superparamagnetic nanocomposites based on Y-Fe2O3 and sulphonated polystyrene were synthesised by ion-exchange process
and the structural characterisation has been carried out using X-ray diffraction technique. Doping of cobalt in to the Y-Fe2O3 lattice
was effected in situ and the doping was varied in the atomic percentage range 1–10. The optical absorption studies show a band gap
of 2.84 eV, which is blue shifted by 0.64 eV when compared to the reported values for the bulk samples (2.2 eV). This is explained on
the basis of weak quantum confinement. Further size reduction can result in a strong confinement, which can yield transparent magnetic
nanocomposites because of further blue shifting. The band gap gets red shifted further with the addition of cobalt in the lattice
and this red shift increases with the increase in doping. The observed red shift can be attributed to the strain in the lattice caused by
the anisotropy induced by the addition of cobalt. Thus, tuning of bandgap and blue shifting is aided by weak exciton confinement
and further red shifting of the bandgap is assisted by cobalt doping.