Photodarkening effect and optical properties of nanocomposite material polymer/Fe_3O_4 magnetic nanoparticles

摘要

Materials with combined ferroelectric and ferromagnetic properties or magneto-electric coupling effects are promising candidates for information technology, photosensoring, and device fabrication. Preparation and characterization of multiferroic materials in which ferroelectricity and ferromagnetism coexist attracted much interest in research for functionalized materials and devices. They present a possibility to electrically control magnetic memory devices and, conversely, magnetically manipulate electric devices. In this work we considered Fe_3O_4 magnetic nanoparticles with and without a protective SiO_2/TiO_2 double-layer coating embedded into the carbazole-based, namely, poly-epoxypropylcarbazole (PEPC) thin (500 nm) film. Optical characterization of the PEPC films was performed using light irradiation in the UV7VIS and NIR ranges. A shift in the optical absorption edge toward a higher wavelength region of the spectrum took place for all irradiated samples: the polymer film, as well as for the samples with Fe_3O_4 and Fe_3O_4/SiO_2/TiO_2 nanoparticles inside of the polymer matrix. We suggest that changes in the UV/VIS/NIR spectra took place as a function of the degree of structural changes and stabilizing of the atomic matrix, as well as due to change in the values of the refractive index following irradiation, calculated from the spectral data. In such a way photo-structural modifications induced by the UV irradiation and the implantation of the magnetic nanoparticles make these materials perspective for optical recording media. We conclude, therefore, that Fe_3O_4 and Fe_3O_4/SiO_2/TiO_2 nanoparticles considerably affect the optical properties of the PEPC thin film, and result in the enhancement of the photodarkening effect following the UV irradiation.