Multifunctional visible/near-infrared luminescent core–shell magnetic silica structured nanocomposites

Abstract

In this paper, we report the fabrication and characterization of magnetic silica nanospheres covalently bonded with near-infrared (NIR) and ultraviolet-visible (UV-vis) luminescent lanthanide complexes [denoted as Fe₃O₄@SiO₂@Ln–PABI/SiO₂ (Ln = Nd, Eu)]. Fe₃O₄@SiO₂@Ln–PABI/SiO₂ (Ln = Nd, Eu) nanospheres with an average size of 150–200 nm were synthesized via incorporation of the chelate ligand PABI (N-(4-benzoic acid-yl)-N′-(propyltriethoxysilyl) urea) with Ln (Nd, Eu) into a framework of magnetic silica (denoted as Fe₃O₄@SiO₂), followed by a modified Stöber method and a layer-by-layer assembly technique. The morphological, structural, textural, magnetic, NIR luminescence and UV luminescence properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometry, and photoluminescence spectroscopy. These multifunctional nanocomposites exhibit superparamagnetic behavior, and the characteristic NIR emission and UV emission of Nd³⁺ and Eu³⁺, respectively. Such materials with superparamagnetic and lanthanide-based near-infrared and UV luminescence properties have several advantages for potential applications in optical imaging or as biological luminescent labels.