Dependence of spectroscopic and electrical properties on the size of cadmium sulfide nanoparticles

Cadmium sulfide (CdS) nanoparticles with different sizes were synthesized using chemical precipitation method. The change of particle size, morphologies and crystal structures with the molar ratio of cadmium to sulfide salt was obtained from transmission electron microscopy (TEM) and X-ray diffraction pattern results. It should be noted that, the CdS nanoparticles were formed with different size, normal distribution and cubic phase. The effect of particle sizes on the optical properties was confirmed from UV–visible and fluorescence spectroscopic data. The optical band gap decreases from 2.9 to 2.51 eV with increasing the particle size from 5 to 9.25 nm due to the change of the molar ratio of CdCl2 to Na2S from (16:1) to (1:16). The electrical results obtained show that, DC conductivity increase with decreasing the particle sizes. The conduction mechanisms were discussed at low and high applied voltage. All samples have semiconducting behavior and can be used in the field of light emitting diodes.