Simple synthesis, structural and optical properties of cobalt ferrite nanoparticles

Abstract

Cobalt ferrite (CoFe2O4) nanoparticles have been successfully synthesised by simple and economic co-precipitation method at 90 °C for 2h using a biodegradable surfactant (starch), and by annealing at 500 °C for 1, 2, and 6h. The XRD patterns reveal spinel CoFe2O4 phase for as-synthesized and annealed samples without any impurity phase. FTIR spectra also demonstrate the characteristic absorption bands of CoFe2O4 phase and starch surfactant. SEM images display nearly spherical morphology for all the samples and the average particle size increases when annealed at 500 °C and for prolonged durations at the same temperature. The direct band gap of CoFe2O4 nanoparticles decreases with increasing particle size and the direct band gap values are attributed to spin-allowed d to d on-site transitions. The PL spectra exhibit peaks associated with transitions of charge carriers to near edge, surface, and defect states. The PLE peaks suffer blue shift when annealed at 500 °C for 1h and then red shift on further prolonging the annealing time to 2 and 6h at the same temperature. Such results offer new opportunities for optimizing and enhancing the performance of cobalt ferrite where the optical properties are decisive.