Enhanced Optical Properties of Core/Shell/Shell CdTe/CdS/ZnO Quantum Dots Prepared in Aqueous Solution

Abstract

New quantum dots (QDs) were fabricated with a core/shell/shell structure consisting of CdTe core/CdS shell/ZnO shell. Despite the high lattice mismatch between CdS and ZnO, a ZnO shell was successfully introduced by basic hydrolysis of Zn(OAc)2 at the surface of core/shell CdTe/CdS QDs stabilized by 3-mercaptopropionic acid (MPA). The core/shell/shell CdTe/CdS/ZnO@MPA QDs exhibited a significant redshift of emission peaks (up to 50 nm for green-emitting CdTe/CdS QDs) when the shell grew. By changing the size of the core or the thickness of the ZnO shell, the emission colors of the obtained nanocrystals can be tuned between the green and red regions of the spectrum following an identical procedure. The influence of ZnO shell growth on photoluminescence (PL) quantum yields was found to be more pronounced for CdTe/CdS samples with green or yellow emission for which quantum yields increased up to three times. The epitaxial growth of the ZnO shell was confirmed by X-ray photoelectron spectroscopy and luminescence decay experiments. Because of the passivation of surface defects, a PL lifetime of 33.6 ns was measured for core/shell/shell CdTe/CdS/ZnO QDs prepared with a Zn/Cd ratio of 0.8, while it was only 17.7 ns for core/shell CdTe/CdS QDs.

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Highly Luminescent PbS/ZnS Nanoparticles Synthesized by a Microwave Method

“…In addition Figure 4b shows the PL spectra for pure PbS and PbS/ZnS nanoparticles where a dramatically increase of the PL intensity is obtained after the formation of the ZnS shell. The sharp luminescence produced by particles with cycling heating profiles is an evidence of the efficiency of the ZnS shell for stabilize the PbS core by decreasing the surface traps and confining the charge carries generated during the exciton formation [Aldeek et al, 2009]. The quantum yield (QY) of PbS/ZnS nanoparticles, synthesized by microwave method was determined by using Rhodamine 6G in ethanol as standard.…”

Preparation of polymer–nanocrystals hybrid solar cells through aqueous approaches

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