Effects of growth time on the material properties of CdTe/CdSe core/shell nanoparticles prepared by a facile wet chemical route

Abstract

This study presents a facile synthetic approach used to prepare CdTe/CdSe core/shell nanoparticles (NPs). The effects of reaction time on the material properties of the CdTe/CdSe NPs are reported. It was realized that the reaction time has significant impact on the CdSe shell growth on the CdTe core. Various techniques were used to characterize the as-prepared CdTe/CdSe NPs. The X-ray diffraction (XRD) was used to study the crystal structure and the possible growth of the CdSe shell on the CdTe core. The results obtained indicated the formation of zinc blende crystal structure which was transformed from a polycrystalline to single crystalline structure. The XRD pattern displayed features that are intermediate between the CdTe and CdSe, a sign of shell formation and not two separate compounds formed. This was also supported by high resolution transmission electron microscope images obtained. The crystallite sizes estimated using Scherrer formula were all less than 3 nm showing that the NPs are in quantum confinement regime. Scanning electron microscope was used to determine the surface topography while the energy X-ray dispersive spectrometer displayed the elemental composition of the as-prepared NPs. SEM and HRTEM images showed uniformly distributed spherical NPs with some agglomerations observed at longer duration of synthesis. The optical properties (photoluminescence (PL) and absorbance) investigated at different reaction times (20, 40, 60 and 80 min) presented novel features which show the formation of a thin CdSe shell on the CdTe core NPs. The PL emission wavelength was dramatically red shifted upon the growth of the CdSe shell on the CdTe core (from 541- 615 nm). Other unique features of the as-grown CdTe/CdSe NPs are discussed in detail. The obtained results displayed good material properties of the CdTe/CdSe NPs suitable for use in biomaging applications.

Effects of Reaction Temperature and Cadmium Source on the Optical, Morphological and Cytotoxic Properties of CdSe/ZnSe Quantum Dots

“…Bright rings shown in the SAED image (inset of Figure 6(i)) also confirmed the improved crystallinity of the sample QDs formed.The blurred HRTEM mages displayed in Figure 6(ii) is attributted to agglomeration of the QDs due to increased growth temperature causing the small particles to combine with each other to form large particles which are non-uniform and tends to be amorphous in nature as reported by Kiprotich et.al 2022. [22] Figure 7 shows HRTEM micrographs and EDS analysis of the octylamine capped CdSe/ZnSe QDs displaying the presence of nanocrystals with different particle sizes that exist within one sample. The EDS analysis displayed the expected elements present in the sample at a fair percentage composition.…”