OPTICAL AND HIGH-TEMPERATURE ELECTRICAL PROPERTIES OF PURE AND Sr-MODIFIED CdS NANOCRYSTALS

Nanoparticles of CdS-and Sr-doped CdS were synthesized through chemical precipitation method using a high-boiling solvent. X-ray diffraction confirms the nanocrystallinity of the prepared nanostructures. The mean crystal size obtained by full width half maxima analysis is 3.34 nm for CdS, 3.39 nm for CdS: Sr (2mM) and 3.41 nm for CdS: Sr (4 mM). The optical absorption analysis conducted in UV-vis range 200-900 nm reveals the transparency of these nanocrystals in the entire visible range but not in ultraviolet range. The results based on optical analysis yield bandgap values as 2.63 eV for CdS, 2.58 eV for CdS: Sr (2mM) and 2.52 eV for CdS: Sr (4mM) nanoparticles. This implies that pure CdS-and Sr-doped CdS are blue shifted with respect to the bulk CdS (2.42 eV), however Strontium modified CdS nanocrystals are red shifted with respect to pure CdS nanocrystals. The electrical conductivity data reveals semi-conducting behavior of both pure CdS-and Sr-doped CdS nanocrystals. Fitting of conductivity data in Mott's variable range hopping model shows that Strontium doping in CdS reduces gap parameters from 2.81 to 2.59 eV.