Full-Color Magnetic Nanoparticles Based on Holmium-Doped Polymers

Here, we have demonstrated the production of colorless and full-color magnetic nanoparticles based on holmium (Ho)-doped polymers, which could not be achieved with conventional dark brown iron oxide magnetic nanoparticles. The coordination of Ho, a lanthanide with low colorability and a strong magnetic moment, with a poly­(2-acetoacetoxy ethyl methacrylate) brush built on the surface of submicron-sized silica particles allowed for the formation of colorless magnetic nanoparticles. Additionally, bright and full-color magnetic nanoparticles were obtained by mixing different colored magnetic nanoparticles that were prepared by copolymerization of 2-acetoacetoxy ethyl methacrylate and dye monomers. Various colors, including transparency, were demonstrated by means of the present method, which determines the presence or absence of magnetism by Ho doping. The bright and magnetically controllable colored nanoparticles presented herein may have a significant impact on practical substances and applications, such as ink and biomedical and device applications.