Surfactant mediated phase transformation of CdS nanoparticles

In this paper, we report an observation of phase transition of CdS nanoparticles as a function of surfactant concentration. We used different concentrations of a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) to monitor phase change in CdS nanoparticles. The effect of surfactant on phase transition was investigated by several characterization techniques. To investigate the structural properties we employed X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman techniques. XRD spectrum exhibited the phase transition from hexagonal to mixed cubical phase with increasing surfactant concentration. This was also accompanied by a reduction in particle size. Raman spectra indicated blue shift in fundamental optical phonon mode (1LO) as well as increase in full width at half maxima (FWHM) corresponding to 1LO with decreasing particle size. Intensity ratio of 2LO mode of phonon to the 1LO phonon mode (I2LO/I1LO) was also found to be sensitive to particle size. UV–visible (UV–vis) absorption spectra showed the blue shift in absorption edge with increasing surfactant concentration. Photoluminescence (PL) spectra were recorded to investigate the presence of interstitial sulphur (IS) as well as interstitial cadmium (ICd) in our samples.