In this study, flame aerosol processes were used to synthesize M-SiO2 composite nanoparticles (M=Fe, Eu, Tb, Dy, Tm). These particles are characterized by TEM, XRD, and fluorescence spectroscopy. The Fe/SiO2 nanoparticles contain separate phases of amorphous SiO2 and crystalline gamma-Fe2O3. The lanthanides exist in the silica matrix as a separate amorphous phase. All lanthanide/silica particles are fluorescent, with photoluminescence peak wavelength at 544, 574, 616, and 657 nm (Tb, Dy, Eu and Tm respectively). The particles generally do not have a core-shell structure. The iron- or lanthanide-rich phases randomly distribute in the silica matrix. When on the edge of the nanoparticles, these phases may be dissolved in 4% sulfuric acid at room temperature.
In conclusion, flame aerosol synthesis can be used to generate silica-based composite nanoparticles for magnetic or fluorescent properties. These particles can be potentially used in biomedical imaging. However, with this method making core-shell structures with full encapsulation by silica remains a challenge. The toxicity of these particles needs to be examined before they can be used in biomedical applications.