The structure and photoluminescence properties of TiO2-coated ZnS nanowires

The structure and photoluminescence properties of TiO2-coated ZnS nanowires were investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powder and then coated with TiO2 by using the metal organic chemical vapor deposition (MOCVD) technique. We performed scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, and photoluminescence (PL) spectroscopy to characterize the as-synthesized and TiO2-coated ZnS nanowires. TEM and XRD analyses revealed that the ZnS core and the TiO2 coatings had crystalline zinc blende and crystalline anatase structures, respectively. PL measurement at room temperature showed that the as-synthesized ZnS nanowires had two emissions: a blue emission centered in the range from 430 to 440 nm and a green emission at around 515 nm. The green emission was found to be dominant in the ZnS nanowires coated with TiO2 by MOCVD at 350°C for one or more hours, while the blue emission was dominant in the as-synthesized ZnS nanowires. Also the mechanisms of the emissions were discussed.