Enhancement in the photoluminescence of ZnS nanowires by TiO2 coating and thermal annealing

Influences of the TiO2 coating and thermal annealing on the photoluminescence (PL) properties of ZnS nanowires were investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powder and then coated with TiO2 by using the sputtering technique. The PL emission of ZnS nanowires can be significantly enhanced without nearly changing the wavelength of the emission by coating them with a TiO2 layer with an appropriate thickness and then annealing them in an Ar atmosphere. The optimum TiO2 coating layer thickness for the highest PL emission enhancement was found to be about 6.5 nm. The PL emission of the ZnS-core/TiO2-shell coaxial nanowires is degraded by annealing in an oxygen atmosphere whereas it is enhanced by annealing in an argon atmosphere.