Optical and electrical properties of pure and Ni-modified ZnS nanocrystals

Abstract

ZnS and Ni doped ZnS nanoparticles were synthesized through chemical precipitation method using a high-boiling solvent. The nanocrystillanity of the prepared nanostructures is confirmed by X-ray diffraction (XRD). The mean crystal size obtained by full width half maxima (FWHM) analysis is 3.2 nm for ZnS and 4.3 nm for ZnS:Ni. An optical absorption study conducted in UV-vis range 150-800 nm reveals the transparency of these nanocrystals in entire visible range but not in ultraviolet range. The results based on optical analysis yield band gap values as 3.92 eV for ZnS and 3.88 eV for ZnS:Ni nanoparticles. The electrical resistivity data reveals semiconducting behaviour to both compositions. Fitting of resistivity data in Mott's variable range hopping model (VRH) shows that nickel (1.5%) doping in ZnS reduces gap parameters from 4.78 to 4.22 eV. Based on this model the carrier density, energy gap and hopping distances are calculated for both pure and Ni modified nanocrystals.