Colloidal Multi-Dot Nanorods

Colloidal nanorod heterostructures consisting of multiple quantum dots within a nanorod (n-DNRs, where n is the number of quantum dots within a nanorod) are synthesized with alternating segments of CdSe "dot" and CdS "rod" via solution heteroepitaxy. The reaction temperature, time dependent ripening, and asymmetry of the wurtzite lattice and the resulting anisotropy of surface ligand steric hindrance are exploited to vary the morphology of the growing quantum dot segments. The alternating CdSe and CdS growth steps can be easily repeated to increment the dot number in unidirectional or bidirectional growth regimes. As an initial exploration of electron occupation effects on their optical properties, asymmetric 2-DNRs consisting of two dots of different lengths and diameters are synthesized and are shown to exhibit a change in color and an unusual photoluminescence quantum yield increase upon photochemical doping.

Room-Temperature Interconversion Between Ultrathin CdTe Magic-Size Nanowires Induced by Ligand Shell Dynamics

The formation mechanisms of colloidal magic-size semiconductor nanostructures have remained obscure. Herein, we report the room temperature synthesis of three species of ultrathin CdTe magic-size nanowires (MSNWs) with diameters of 0.7 ± 0.1 nm, 0.9 ± 0.2 nm, and 1.1 ± 0.2 nm, and lowest energy exciton transitions at 373, 418, and 450 nm, respectively. The MSNWs are obtained from Cd(oleate)₂ and TOP-Te, provided diphenylphosphine and a primary alkylamine (RNH₂) are present at sufficiently high concentrations, and exhibit sequential, discontinuous growth. The population of each MSNW species is entirely determined by the RNH₂ concentration [RNH₂] so that single species are only obtained at specific concentrations, while mixtures are obtained at concentrations intermediate between the specific ones. Moreover, the MSNWs remain responsive to [RNH₂], interconverting from thinner to thicker upon [RNH₂] decrease and from thicker to thinner upon [RNH₂] increase. Our results allow us to propose a mechanism for the formation and interconversion of CdTe MSNWs and demonstrate that primary alkylamines play crucial roles in all four elementary kinetic steps (viz., monomer formation, nucleation, growth in length, and interconversion between species), thus being the decisive element in the creation of a reaction pathway that leads exclusively to CdTe MSNWs. The insights provided by our work thus contribute toward unravelling the mechanisms behind the formation of shape-controlled and atomically precise magic-size semiconductor nanostructures.

Luminescence studies in cadmium telluride nanocrystals grown on glass substrates

The thermal evaporation method can easily be employed to fabricate hybrid inorganic-organic LEDs and the emission properties can be controlled by varying the thickness of the nanocrystalline CdTe film. The fabrication of CdTe nanocrystals on glass substrates was demonstrated using a thermal evaporation method. Films were characterised using various experimental tools, such as SEM, TEM, AFM, UV-Vis and PL spectroscopy. The formation of nanoparticles with diameters from 1.5 nm up to 9 nm was observed in the nanocrystalline thin films. The organic light emitting diodes (OLEDs) based on these nanocrystals as an emissive layer exhibit electroluminescence (EL) in the green to yellow region of the visible spectrum, which is ascribed to the varying size dependent EL from the nanocrystals of CdTe present in the thin film. The method demonstrates an easy and convenient way to incorporate inorganic CdTe nanocrystals inside the organic light emitting devices.

CdTe thin films deposited using vacuum thermal evaporation and incorporated inside OLEDs. A shift in electroluminescence peak observed with increasing film thickness. The method can be employed to control emission properties by varying film thickness.