Effect of solvent-induced structural modifications on optical properties of CdS nanoparticles

Abstract

We have investigated the effects of solvent used during synthesis on structural and optical properties of CdS quantum dots. Different methods of synthesis for the production of CdS quantum dots are presented. These are: (a) wet chemical co-precipitation in non-aqueous medium (i.e. methanol); (b) wet chemical co-precipitation in aqueous medium (deionized water) and (c) solid state reaction. It is demonstrated that the use of methanol as solvent leads to a strong enhancement of PL intensity of CdS quantum dots for use in optoelectronic devices. These products were characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The change in bandgap with size-quantization was investigated by UV-VIS absorption spectroscopy. CdS nanocrystals prepared in non-aqueous medium have narrow size distribution than those prepared in aqueous medium and solid state reaction. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure was observed in methanol solution. The formation of CdS/Cd(OH) 2 nanostructure was also confirmed using X-ray diffraction pattern. This suggests that the strong enhancement of the PL intensity may have originated from the remarkable reduction of non-radiative recombination process, due to surface defects of quantum dots. The red shift of the Raman peaks compared to that for bulk CdS may be attributed to optical phonon confinement.

Structural and Optical Properties of Nanocrystalline Pb1-xCdxS Thin Films Prepared by Chemical Bath Deposition

“…This blue shift in absorption is also a signature of nanostructure formation. Similar behaviors have been reported for CBD, PbS, and CdS films Thangavel et al (2010) and Chawla et al (2010). Furthermore, the increase in α with decreasing λ shows a sharp change, which may be related to the increase in crystallinity of the films and the occurrence of direct optical transitions αhυ allowed direct ws a plot of (α material has a ields the energ 0.6, respectivel et al 2007…”

“…The variation in the optical absorption coefficient (α) with λ is shown in Figure 4. All films show higher absorptions (α ≥10 4 cm -1 ) at the shorter wavelength side, indicating that the films undergo direct optical electronic transitions Chawla et al (2010). The spectra in Figure 4 show that absorbance edges are blue shifted with respect to the bulk Pb 1-x Cd x S and with increasing x, that is, with doping by Cd.…”

Biogenic synthesis and photocatalytic activity of CdS nanoparticles

“…This is because of their size dependent properties due to the high surface to volume ratio. 7 CdS nanoparticles are also utilized an ideal materials to investigate the optical and electronic properties of quantum conned semiconductors. 8 Due to such unique properties and a large number of technical applications, a number of routes have been utilized for the synthesis of CdS nanoparticles such as solvothermal 9 and hydrothermal 10 methods.…”

Multi-color carbon dots for white light-emitting diodes

“…According to previous reports, this may be due to solvent effect between CDs and ethanol. 29,30 To know more details about the surface chemistry, the CDs are further analyzed with XPS. The elemental content analysis in Table S1 (ESI †) demonstrates that all four CDs have the same elemental composition (i.e.…”