Structural and Optical Properties of Polystyrene CdS Nanocomposite Prepared by a Soft Chemistry Method

Cadmium sulfide nanocrystals were prepared by the hydrothermal method. X-ray diffraction patterns have presented a small broadening of the diffraction peaks. This broadening is due to the nanometric size of cadmium sulfide powders. The patterns also confirmed that cadmium sulfide crystallizes in the wurtzite structure (P6_3mc crystallographic group) and that crystallite sizes are nanometric. Polystyrene cadmium sulfide nanocomposite has been fabricated by soft chemistry method. This involves mixing a solution of cadmium sulfide (1 g of cadmium sulfide poured in 10 mL of chloroform) with a solution of 1 g of polystyrene dissolved in 30 mL of chloroform. After including the CdS nanopowders into the polystyrene, a decrease in size was observed, going from 20.90 nm to 16.68 nm. The SEM image revealed that the surface of the polystyrene presents pores and these pores have been filled during the fabrication of polystyrene CdS nanocrystals composite. Raman spectra show, in addition to the Raman peaks of polystyrene, the characteristic peak of the longitudinal optical phonon (LO) mode of CdS. UV-visible spectroscopy showed that the composite exhibited high transparency in the Visible region. The optical absorption spectrum at room temperature shows a shift of the absorption edge towards high energies. The energy bandgap has been obtained using second derivative curve. The value of band gap energy has been found to be 2.52 eV. The emission spectrum of polystyrene shows no luminescence, whereas the signal of the photoluminescence at room temperature of the composite polystyrene/CdS nanocrystals is formed by two bands situated respectively at 2.51 eV and 2.31 eV. The first band has been assigned to the band-to-band transition, while the second is attributed to the deep level emission.