Confined growth of CdSe quantum dots in colloidal mesoporous silica for multifunctional nanostructures

We report a new and convenient strategy for incorporating fluorescent semiconductor nanocrystals into silica hosts for the synthesis of multifunctional nanostructures. Mesoscale porosity was first created in conventional Stober silica spheres by chemical etching under the protection of polymeric ligands. Uniform and highly luminescent CdSe nanocrystals were then directly grown in the porous silica network by reacting the silica spheres in a growth solution at high temperature. The confinement of silica network led to slower nanocrystal growth and subsequently smaller CdSe dots with blue shifted fluorescence compared with those without confinement. The loading number of CdSe nanocrystals can be easily tuned by changing the degree of porosity of the silica. The advantages of this strategy include simplicity as no special surface treatment processes are needed, general applicability to silica hosts of various shapes and sizes, high flexibility in tuning the dimensions of both the active nanocrystals and host particles, and ample opportunities for incorporating multiple functionalities. With the demonstration of a porous Fe3O4@SiO2/CdSe composite structure with combined magnetic and optical properties, we believe this strategy may provide a platform for the fabrication of a large variety of multifunctional composite nanostructures.