Catalyst driven optical properties of the self-assembled ZnS nanostructures

In this paper, we present the effect of different catalysts (Mn, Au and Sn) on the room temperature photoluminescence and Raman spectra of VLS grown ZnS nanostructures. The catalysts found to self-dope the ZnS nanostructures during its growth were confirmed by XRD and XPS results. The extent of self-doping, which depended on the type and size of catalysts, was observed strongly to have affected the optical properties of ZnS nanostructures, particularly intrinsic defects like S and Zn vacancies. Intense broad bands in the visible due to intrinsic defects, namely Zn and S vacancies were observed, which were quite different for each catalyst as well as for the size of the catalyst. Au and Mn catalyzed ZnS nanostructures also showed creation of catalyst related defects, which were absent in the case of Sn. From the PL spectra, an estimation of the Zn and S vacancies was made for each type of catalyzed ZnS nanostructures. Surface optic (SO) phonon modes of the ZnS nanostructures were also observed to behave differently for the three catalysts. The dielectric continuum model was applied to determine the correlation length and variation in the surface potential modulations in these nanostructures. It was deduced from optical studies that the location of dopant in self-doped ZnS nanostructures strongly affected the luminescence properties. Finally it was concluded that self-doping using a suitable catalyst can be a simple and controllable way to dope ZnS nanostructures with tailored optical characteristics.