Optical and structural properties of CdS:Pb$^{2+}$ nanocrystals

Abstract

The goal of this work is to study the effects of doping on structural, morphological and optical properties of CdS thin films as a function of Pb$^{2+}$ concentration. Thus, nanoparticles were synthesized by chemical bath and a thickness decrease of $\sim$575-200 nm range was observed. In Fourier-transform infrared spectroscopy, all the samples showed a sharp stretching mode observed at $\sim$1384 cm$^{-1}$ corresponding to the vibration mode of CO$_3^{-2}$. X-ray diffraction studies show that the size of crystallites is in the $\sim$33-12 nm range. The peaks belonging to primary phase are identified at the $2\theta = 26.5^{\circ}$ and $2\theta = 26.00^{\circ}$, corresponding to CdS and PbS respectively. Thus, a shift in maximum intensity peak from $2\theta = 26.4^{\circ}$ to 28.2$^{\circ}$ is observed. Likewise peaks at $2\theta = 13.57^{\circ}$, 15.91$^{\circ}$ correspond to lead perchlorate thiourea. The optical, absorption, and transmission properties of the films were determined by UV-vis spectrophotometry, optical energy gap was found to range from 2.1 to 2.4 eV. Raman spectroscopy on doped films showed a shifting of these modes that can be attributed to strain, stress effects, defects, phonon confinement, and variation in phonon relaxation with grain size.