Nonlocal nonlinear optical response of PEGylated superparamagnetic Fe3O4 nanoparticles

PEGylated superparamagnetic Fe3O4 nanoparticles were prepared using co-precipitation method and analyzed by using X-ray diffraction (XRD), UV-Visible spectroscopy, Fourier-transform infrared (FTIR), Transmission electron microscopy (TEM), Dynamic light scattering (DLS), Vibrating sample magnetometer (VSM) and TG analysis. The XRD results showed that an FCC phase of the Fe3O4 structure was formed by an average lattice constant about 8.379 Å. From optical absorbance spectra, the linear absorption coefficient and the band gap of PEGylated Fe3O4 nanoparticles were measured 0.855 cm−1 and 2.27 eV, respectively. The magnetic characteristics indicated that the PEGylated Fe3O4 nanoparticles had the saturation magnetic moments of 61 emug−1. The measurements of nonlinear optical (NLO) properties of PEGylated Fe3O4 nanoparticles have been performed using a nanosecond Nd:YAG pulse laser at 532 nm by the Z-scan technique. Both bare and PEGylated Fe3O4 nanoparticles clearly were exhibited a negative NLO index of refraction at 532 nm. A nonlocality in NLO response of nanoparticles was observed after PEGylation. The NLO absorption of PEGylated Fe3O4 nanoparticles is attributed to 2-photon absorption. A good NLO absorption was observed for both bare and PEG-coated Fe3O4 nanoparticles at 532 nm. Moreover, the nonlinear susceptibility of PEG-coated Fe3O4 nanoparticles was determined by the Z-scan technique of the order of 10−9 esu. The outcomes suggest that PEGylated Fe3O4 nanoparticles may be a promising candidate for the NLO applications.