Structural, optical and magnetic properties of Co doped CdS nanoparticles

Pure and cobalt doped CdS nanoparticles were successfully synthesized by surfactant assisted simple chemical co-precipitation method. Size of the particles around 3 nm and cubic zincblende structure were revealed by the X-ray diffraction pattern. From TEM images particle size was found be around 4-5 nm. Redshift of absorption edge and bandgap narrowing (from DRS spectra) can be attributed to increase in the carrier concentration by the inclusion of cobalt ions and creation of defect levels in the bandgap. Three characteristic reflectance minima only in cobalt doped samples can be related to d-d transitions 4A2(F) → 3/2U1, 4A2(F) → E11 and 4A2(F) → 5/2U1. Strong green emission was exhibited by all the samples through photoluminescence studies can be attributed to the transitions of trapped electrons from donor levels to the valance band or mid gap surface states. Intensity of the luminescence peak was found to be maximum for 2% and quenching was observed beyond 2%. Well defined room temperature ferromagnetic hysteresis loop was observed for 4% Co doped CdS nanoparticles. Saturation of magnetization MS and retentivity MR mounts up with cobalt content up to 4% and then decreases.