Design of Fe3O4@SiO2@mSiO2-organosilane carbon dots nanoparticles: Synthesis and fluorescence red-shift properties with concentration dependence

Organosilane-functionalized carbon dots (SiCDs) immobilized silica composite nanoparticles (Fe3O4@SiO2@mSiO2-SiCDs) with dually emissive properties have been prepared by a modified sol-gel method. Such Fe3O4@SiO2@mSiO2-SiCDs nanoparticles solution exhibits blue light emission with a maximum wavelength of 470 nm at lower concentrations, and red-shifts to yellow-green light emission with maximum wavelength of 565 nm at higher concentrations, which is different with traditional carbon dots composite materials displaying strong emission only in the blue-light region. The SiCDs are immobilized in the outer mesoporous silica layer by covalent bonds via proper blending ration, which enables the nanoparticles solution to possess excellent fluorescence stability. The Fe3O4@SiO2@mSiO2-SiCDs nanoparticles show good stability, high surface area (483.19 m2/g), high saturation magnetization (22.1 emu/g) and low remanence (0.217 emu/g). When the concentration of nanoparticles solution is increased, the distance between the nanoparticles decreases and exhibits the concentration-mediated scattering phenomena, which result in the red-shift of fluorescent peaks. The specific structure of the Fe3O4@SiO2@mSiO2-SiCDs nanoparticles and the concentration-mediated scattering phenomena play key roles in the red-shift appearing.