Enhanced Fluorescence Emission from Core-Shell Mesoporous Silica Nanoparticles with Amine-Functionalized Silica as Cores

In this paper, N-(3-Trimethoxysilylethyl) ethylenediamine (TMSEEDA) has been immobilized on silica nanoparticles (NPs) with diameter smaller than 100 nm by covalent bond grafting technique. The as-made particles can be used as cores to prepare core-shell mesoporous silica composites, which are encapsulated with a layer of ordered mesoporous silica through a surfactant-assembly method, resulting to uniform core-shell NPs denoted as SiO2-NH2@mSiO(2). Low angle X-ray diffraction (XRD), scanning, electron microscopy (SEM), transmission electron microscopy (TEM), N-2 adsorption-desorption, and photoluminescence (PL) spectra were used to characterize the sample, respectively. The results show that the nanocomposites with 74 nm core size and 7 nm shell thickness have typical ordered mesoporous characteristics (2.8 nm) and spherical morphology with the surface area as high as 445 m(2)/g and the pore volume as large as 0.29 cm(3)/g. Additionally, a broad and faint blue emission at 410 nm was observed for silica NPs under 300 nm exaction at room temperature. Importantly, it is found that a quantitative comparison of PL intensity of silica NPs covalently grafted with TMSEEDA to the only silica NPs yields an enhancement of approximately an order of magnitude with the same peak position. This observation indicates, most likely, formation of more defect centers due to the functionalization of small molecules TMSEEDA. On the other hand, luminescence intensity is enhanced 3 times again after coating of mesoporous silica shells. The origin of the PL and enhanced mechanism are also discussed.