Effect of core size on the luminescence properties of cadmium telluride/zinc sulphide core-shell quantum dots

Abstract

In the present work, cadmium telluride/zinc sulphide (CdTe/ZnS) Core-Shell Quantum Dots (QDs) were prepared and the effects of core size on the luminescence possessions of CdTe QDs were investigated. For this purpose, the CdTe QDs was coated with ZnS from aqueous phase. Post growths, the synthesized QDs (CdTe & CdTe/ZnS) were characterized by photo-physical spectra for analyzing the characteristic changes in the samples. The photo-physical analysis revealed the shifts in absorption peaks of both the samples (CdTe and CdTe/ZnS). In UV–Visible analysis, due to increase in particle size, the absorption peak of CdTe QDs red shifts to higher wavelength with respect to the refluxing time. Even in the case of CdTe/ZnS core-shell QDs, the emission wave length red shifts to longer wavelength. X-Ray Diffraction (XRD) revealed the crystal structure of the synthesized CdTe QDs and CdTe/ZnS core-shell QDs. The peaks of CdTe/ZnS QDs shift towards greater angles and it is the development of shell structure ZnS over CdTe QDs. HRTEM studies revealed the presence of core and shell from the synthesized materials In HRTEM images, the additional stretch everywhere from the core particles confirmed the compressive strain developed from ZnS. This was qualitatively considered and attributed into the successive establishment of ZnS shells on the core CdTe QDs surface. And these prepared CdTe/ZnS core-shell QDs are having the increase of average size. In XPS analysis for the CdTe/ZnS Core-Shell layering were confirmed, through the intensity signal of Cd (3d), Te (3d), Zn (2p) and S (2s).