Synthesis and characterization of shaped ZnS nanocrystals in water in oil microemulsions

Shaped zinc sulfide nanocrystals were synthesized in W/O microemulsions by using cyclohexane/Triton X-100/n-pentanol/water system. Under different synthetic conditions appearance of two distinct morphologies of ZnS nanocrystals, either cubes or nanowires, was proven by transmission electron microscopy (TEM). The ZnS cubes have an average size of about 25 nm, while the ZnS nanowires have 25 Å diameter and length ranging from several hundred nanometers up to a few microns. The X-ray diffraction analysis (XRD) revealed formation of ZnS with cubic zinc blende crystal structure. Due to two dimensional confinement the exciton of ZnS nanowires is blue shifted compared to the bulk material. Four well-resolved photoluminescence bands in visible spectral region were observed upon excitation of cubic ZnS particles, while in the case of ZnS nanowires emission band was observed at 421 nm. The origin of photoluminescence bands was discussed in details.