Aliaksei Dubavik

Shedding light on vacancy-doped copper chalcogenides: shape-controlled synthesis, optical properties, and modeling of copper telluride nanocrystals with near-infrared plasmon resonances.

Size- and shape-controlled synthesis of copper chalcogenide nanocrystals (NCs) is of paramount importance for a careful engineering and understanding of their optoelectronic properties and, thus, for their exploitation in energy- and plasmonic-related applications. From the copper chalcogenide family copper telluride NCs have remained fairly unexplored as a result of a poor size-, shape-, and monodispersity control that is achieved via one-step syntheses approaches. Here we show that copper telluride (namely Cu(2-x)Te) NCs with well-defined morphologies (spheres, rods, tetrapods) can be prepared via cation exchange of preformed CdTe NCs while retaining their original shape. The resulting copper telluride NCs are characterized by pronounced plasmon bands in the near-infrared (NIR), in analogy to other copper-deficient chalcogenides (Cu(2-x)S, Cu(2-x)Se). We demonstrate that the extinction spectra of the as-prepared NCs are in agreement with theoretical calculations based on the discrete dipole approximation and an empirical dielectric function for Cu(2-x)Te. Additionally we show that the Drude model does not appropriately describe the complete set of Cu(2-x)Te NCs with different shapes. In particular, the low-intensity longitudinal plasmon bands for nanorods and tetrapods are better described by a modified Drude model with an increased damping in the long-wavelength interval. Importantly, a Lorentz model of localized quantum oscillators describes reasonably well all three morphologies, suggesting that holes in the valence band of Cu(2-x)Te cannot be described as fully free particles and that the effects of localization of holes are important. A similar behavior for Cu2-xS and Cu(2-x)Se NCs suggests that the effect of localization of holes can be a common property for the whole class of copper chalcogenide NCs. Taken altogether, our results represent a simple route toward copper telluride nanocrystals with well-defined shapes and optical properties and extend the understanding on vacancy-doped copper chalcogenide NCs with NIR optical resonances.

3D assembly of semiconductor and metal nanocrystals: hybrid CdTe/Au structures with controlled content.

A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods.

Penetration of Amphiphilic Quantum Dots through Model and Cellular Plasma Membranes

In this work we demonstrate progress in the colloidal synthesis of amphiphilic CdTe nanocrystals stabilized by thiolated PEG oligomers with the aim of facilitating cellular uptake of the particles. High-boiling, good coordinating solvents such as dimethylacetamide and dimethylformamide accelerate the growth of the nanoparticles yielding stable colloids of which photoluminescence maxima can be tuned to cover the region of 540-640 nm with quantum yields of up to 30%. The CdTe nanocrystals capped by thiolated methoxypolyethylene glycol are shown to penetrate through the lipid bilayer of giant unilamellar vesicles and giant plasma membrane vesicles which constitute basic endocytosis-free model membrane systems. Moreover, the penetration of amphiphilic particles through live cell plasma membranes and their ability to escape the endocytic pathway have been demonstrated.

Enantioselective cellular uptake of chiral semiconductor nanocrystals

The influence of the chirality of semiconductor nanocrystals, CdSe/ZnS quantum dots (QDs) capped with L- and D-cysteine, on the efficiency of their uptake by living Ehrlich Ascite carcinoma cells is studied by spectral- and time-resolved fluorescence microspectroscopy. We report an evident enantioselective process where cellular uptake of the L-Cys QDs is almost twice as effective as that of the D-Cys QDs. This finding paves the way for the creation of novel approaches to control the biological properties and behavior of nanomaterials in living cells.

One-phase synthesis of gold nanoparticles with varied solubility.

We developed a straightforward synthesis of gold nanoparticles with diameters in the range 2.1-7.0 nm which display solubility in both aqueous and nonpolar (toluene, chloroform) media. This versatile solubility of the nanoparticles is achieved by the use of a thiolated PEG capping agent. Their plasmon resonance band is virtually unaltered in different media.

Influence of the stabilizing ligand on the quality, signal-relevant optical properties, and stability of near-infrared emitting Cd1−xHgxTe nanocrystals

Bright and stable near-infrared (NIR) and infrared (IR) emitting chromophores are in high demand for applications in telecommunication, solar cells, security barcodes, and as fluorescent reporters in bioimaging studies. The best choice for wavelengths >750 nm are semiconductor nanocrystals, especially ternary or alloy nanocrystals like CdHgTe, which enable size and composition control of their optical properties. Here, we report on the influence of growth time and surface chemistry on the composition and optical properties of colloidal CdHgTe. Up to now, these are the only NIR and IR emissive quantum dots, which can be synthesized in high quality in water, using a simple one-pot reaction. For this study we utilized and compared three different thiol ligands, thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and glutathione (GSH). Aiming at the rational design of bright NIR- and IR-emissive alloy materials, special emphasis was dedicated to a better understanding of the role of the surface ligand and adsorption–desorption equilibria on the photoluminescence quantum yield and stability. In this respect, dilution and protonation studies were performed. Our results show that with this simple synthetic procedure, strongly fluorescent CdHgTe colloids can be obtained with MPA as stabilizing ligand revealing quantum yields as high as 45% independent of particle concentration.

Optical properties of ordered superstructures formed from cadmium and lead chalcogenide colloidal nanocrystals

The optical properties of three-dimensional ordered superstructures formed on glass substrates by self-assembly of cadmium selenide or lead sulfide nanocrystals (NCs) are investigated and compared to the optical properties of the initial NC colloidal solutions. The formation of the superstructures is strongly correlated to the presence of oleic acid molecules on the surface of the NCs. It is found that the absorption band of the NCs in the superstructures is broadened and shifted to shorter wavelengths in comparison with the absorption band of the NCs in solution. The luminescence spectra of the NCs in the superstructures also differ from the spectra of the NCs in solution. The observed modification of optical properties of superstructures is a manifestation of interactions between the NCs and the chemical environment within the superstructures.

A Versatile Approach for a Variety of Amphiphilic Nanoparticles: Semiconductor – Plasmonic – Magnetic

Abstract In this work we summarize last achievements of the colloidal synthesis and applications of different amphiphilic nanoparticles, among which are semiconductor, metal and metal oxide materials. All these nanoparticles have been obtained employing polyethylene glycol based stabilizers which provide compatibility with a wide variety of media from nonpolar organics to water. Owing to their versatile solubility, the materials obtained have the ability of spontaneous multiphase transfer. Moreover, they have been shown to permeate through cell membranes avoiding endocytosis which makes them particularly interesting for bio-applications.

Study of the Optical Properties of CdZnSe/ZnS-Quantum Dot–Au-Nanoparticle Complexes

The interaction of gold nanoparticles (NPs) and semiconductor alloyed CdZnSe/ZnS quantum dots (QDs) in colloidal solutions is studied. It is shown that the photoluminescence intensity of QDs in a mixture decreases compared to that in the initial QD solution, which is caused by resonance nonradiative energy transfer from QDs to Au NPs in spontaneously formed aggregates. To control the formation of pairs of interacting QDs and Au NPs, we proposed have a method for creating QD–Au NP complexes bound by special molecules—ligands. It is shown that the morphology and optical properties of the samples obtained depend on the method of their preparation, in particular, on the chemical environment of QDs. It is found that the complexes form in the case of addition of hydrophilic Au NPs to hydrophobic QDs and that this almost does not change the optical properties of the latter compared to those of quasi-isolated QDs in colloidal solution.

A highly luminescent porous metamaterial based on a mixture of gold and alloyed semiconductor nanoparticles

Understanding the different processes in modern multicomponent metamaterials is a crucial task for their development. This includes the investigation of superstructures that can be formed by nanoparticle self-assembly. Here we present a destabilization-based synthetic protocol for the preparation of porous superstructures with flower, sphere, and spike-like shapes. This approach is universal for nanoparticles of various natures and compositions. We have prepared superstructures of the same architecture from alloyed quantum dots and their mixtures with gold nanoparticles. It was found that the concentration of gold nanoparticles strongly affects the QD optical properties in the superstructure: a 2.5-times PL enhancement for a 2% Au nanoparticle content is reported. We offer a detailed model describing the stages of superstructure formation and reveal the mechanisms behind this. Material-indifferent means of control over the shape and properties of self-assembled superstructures give us a new functional tool for developing metamaterials with potential applications in sensorics.