Noninjection, One-Pot Synthesis of Photoluminescent Colloidal Homogeneously Alloyed CdSeS Quantum Dots

Abstract

Colloidal photoluminescent CdSeS quantum dots (QDs) were readily prepared via a noninjection, one-pot approach, with air-stable compounds cadmium acetate dihydrate (Cd(OAc)2·2H2O), elemental selenium (Se), and elemental sulfur (S) as Cd, Se, and S source compounds, respectively. The homogeneously alloyed CdSeS QDs were synthesized at 240 °C in a reaction flask containing the source compounds together with myristic acid, 2,2′-dithiobisbenzothiazole (MBTS), and 1-octadecene (ODE). All of these chemicals were loaded at room temperature with this newly developed approach. The effects of Cd/Se/S and S/MBTS feed molar ratios affecting the growth of the CdSeS QDs were investigated, via monitoring the temporal evolution of the optical properties (namely, absorption and emission) of the growing nanocrystals. The resulting ternary nanocrystals can be tuned easily to emit in the range of 470−550 nm of the electromagnetic spectrum; such an emission window is hard to manage with binary CdS and CdSe QDs alone. The bandgap engineering was accomplished readily via tuning the different Cd/Se/S and S/MBTS feed molar ratios. High Cd/Se/S feed molar ratios lead to an increase in both size and Se composition of the resulting CdSeS nanocrystals and, thus, a small bandgap; it is the composition that plays a relatively important role as compared to the size. Low S/MBTS feed molar ratios also lead to CdSeS QDs with a small bandgap, which is due to a high S activity, resulting in a fast growth in size. The CdSeS QDs were characterized by TEM, XPS, and XRD: they are homogeneous alloys with a cubic crystal structure. This noninjection, one-pot approach developed in our laboratories, which is the first regarding the synthesis of CdSeS QDs, features easy handling and large-scale production with excellent synthetic reproducibility.