Synthesis and characterization of monodisperse core-shell colloidal spheres of zinc sulfide and silica

We report on a new type of composite particles consisting of a zinc sulfide (ZnS) core and a silica (SiO₂) shell or vice versa. We developed and optimized these particles for photonic applications, because ZnS has a large refractive index and does not absorb light in the visible and both ZnS and SiO₂ can be easily doped with fluorophores. Both kinds of morphologies were created using a seeded growth procedure using monodisperse seeds on which homogeneous layers with a well-defined thickness were grown. Moreover, the ZnS and SiO₂ cores could be completely dissolved leaving SiO₂ and ZnS shells, respectively, filled with solvent or air after drying. The particle morphology was investigated by electron microscopy. The optical properties were studied by extinction measurements and angle resolved light scattering and compared to scattering theory.