Engineering of monodisperse core-shell up-conversion dendritic mesoporous silica nanocomposites with a tunable pore size.

Fabricating lanthanide doped up-conversion luminescence based nanocomposites has drawn increasing attention in nanoscience and nanotechnology. Although challenging in precise synthesis, structure manipulation and interfacial engineering, fabricating dendritic mesoporous silica coated up-conversion nanoparticles (UCNP@dMSNs) with a tunable pore size is of great importance for the functionalization and application of UCNPs. Herein, we report a strategy to prepare uniform monodisperse UCNP@dMSNs with a core-shell structure. The silica shell has tunable center-radial and dendritic mesoporous channels. The synthesis was carried out in the heterogeneous oil-water microemulsion phase of the Winsor III system reaction system, which allows silica to be deposited directly on hydrophobic UCNPs through the self-anchoring of micelle complexes on the oleic acid ligand. The average pore size of UCNP@dMSNs could be tailored from ∼10 to ∼35 nm according to the varied amounts of co-solvent in the mixture. The microemulsion approach could also be used to prepare hierarchical UCNP@dMSNs with a multi-generational mesostructure. The resultant UCNP@dMSNs exhibit the unique advantage of loading "guest" nanoparticles in a self-absorption manner. We proved that Cu1.8S NPs (∼10 nm), Au NPs (∼10 nm) and Fe3O4 NPs (∼25 nm) could be incorporated in UCNP@dMSNs, which in turn validates the high adsorption capacity of UCNP@dMSNs.