Superparamagnetic and light-emitting bifunctional nanocomposites of iron oxide and erbium or thulium doped yttrium orthovanadate

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Advances in biomedical research have increased interest in obtaining and studying new bifunctional materials for use in theragnostic. Here we describe in detail the preparation of new magnetic-fluorescent bifunctional (Y0.9Ln0.1VO4/Fe3O4)@SiO2 and [(Y0.9Ln0.1VO4 @SiO2)/Fe3O4)@SiO2] nanocomposites with Ln = Er or Tm. In addition, their magnetic and optical properties were carefully analyzed. The influence of Fe3O4 content and the silica shell thickness on the fluorescent emission in the VIS-NIR region of Y0.9Ln0.1VO4 cores was evaluated as well as their use as display systems with the possibility of directing them by means of external magnetic fields. Samples were prepared using wet chemistry methods involving low temperatures and short reaction times. Y0.9Ln0.1VO4 samples that are not easily oxidizable were prepared by a hydrothermal method, while Fe3O4 sample was synthesized by a coprecipitation process in which the mixture of precursors was treated at very low temperature to avoid oxidation. The powder amalgamation of both Y0.9Ln0.1VO4 and Fe3O4 samples was possible due to the silica polymeric network synthetized by a modified Stöber method. The purity of all samples was ensured by XRD and FTIR techniques. Diffraction profiles of Y0.9Ln0.1VO4 samples show diffraction maxima that can be indexed to a tetragonal symmetry of space group I41/amd, compatible with the zircon structure-type of YVO4 host. All reflections present in the diffraction profile of Fe3O4 sample can be indexed to a cubic symmetry of space group Fd3̅m, characteristic of an inverse spinel structure-type. The amorphous silica incorporation on the samples was also evaluated by TEM images. Studies of the magnetic behavior and luminescent emission intensity of the investigated samples showed their dependence on both, the silica coating thickness, and the contact or not between the luminescent samples and the magnetic powder.
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