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We report on a near-infrared (NIR) emitting semiconductor nanocrystal (NC) heterostructure with tunable optical properties. This heterostructure is built of two different semiconductor sections in ...

The material-efficient monolayers of transition-metal dichalcogenides (TMDs) are a promising class of ultrathin nanomaterials with properties ranging from insulating through semiconducting to metallic, opening a wide variety of their potential applications from catalysis and energy storage to optoelectronics, spintronics, and valleytronics. In particular, TMDs have a great potential as emerging inexpensive alternatives to noble metal-based catalysts in electrochemical hydrogen evolution. Herein, we report a straightforward, low-cost, and general colloidal synthesis of various 2D transition-metal disulfide nanomaterials, such as MoS2, WS2, NiSx, FeSx, and VS2, in the absence of organic ligands. This new preparation route provides many benefits including relatively mild reaction conditions, high reproducibility, high yields, easy upscaling, no post-thermal annealing/treatment steps to enhance the catalytic activity, and, finally, especially for molybdenum disulfide nanosheets, high activity in the hydrogen evolution reaction. To underline the universal application of the synthesis, we prepared mixed CoxMo1-xS2 nanosheets in one step to optimize the catalytic activity of pure undoped MoS2, which resulted in an enhanced hydrogen evolution reaction performance characterized by onset potentials as low as 134 mV and small Tafel slopes of 55 mV/dec.

Nanocrystal micro/nanoarrays with multiplexed functionalities are of broad interest in the field of nanophotonics, cellular dynamics, and biosensing due to their tunable electrical and optical properties. This work focuses on the multicolor patterning of two-dimensional nanoplatelets (NPLs) via two sequential self-assembly and direct electron-beam lithography steps. By using scanning electron microscopy, atomic force microscopy, and fluorescence microscopy, we demonstrate the successful fabrication of fluorescent nanoarrays with a thickness of only two or three monolayers (7-11 nm) and a feature line width of ∼40 nm, which is three to four NPLs wide. To this end, first, large-area thin films of red-emitting CdSe/ZnyCd1-yS and green-emitting CdSe1-xSx/ZnyCd1-yS core/shell NPLs are fabricated based on Langmuir-type self-assembly at the liquid/air interface. By varying the concentration of ligands in the subphase, we investigate the effect of interaction potential on the film's final characteristics to prepare thin superlattices suitable for the patterning step. Equipped with the ability to fabricate a uniform superlattice with a controlled thickness, we next perform nanopatterning on a thin film of NPLs utilizing a direct electron-beam lithography (EBL) technique. The effect of acceleration voltage, aperture size, and e-beam dosage on the nanopattern's resolution and fidelity is investigated for both of the presented NPLs. After successfully optimizing EBL parameters to fabricate single-color nanopatterns, we finally focus on fabricating multicolor patterns. The obtained micro/nanoarrays provide us with an innovative experimental platform to investigate biological interactions as well as Forster resonance energy transfer.

We introduce new oxygen- and moisture-proof polymer matrixes based on polyisobutylene (PIB) and its block copolymer with styrene [poly(styrene-block-isobutylene-block-styrene), PSt-b-PIB-b-PSt] for...

We report a synthesis route to two-dimensional PbSe, HgSe, ZnSe, SnSe, and Cu-Zn-Sn-Se (CZTSe) nanomaterials based on cation exchange (CE) reactions. This approach includes two steps: it starts with the synthesis of hexagonal, up to several micrometers large yet approx. 5 nm-thick CuSe nanosheets (NSs), followed by CE of the host copper ions with the desired guest cation (Pb2+, Hg2+, Zn2+, or Sn4+). In the case of CZTSe, both guest cations can be added simultaneously since the variation of the guest cation ratio and reaction time can lead to various compositions. Mild reaction conditions allow for a preservation of the size and the 2D shape of the parent NSs accompanied by corresponding changes in their crystal structure. We furthermore demonstrate that the crystal structure of CuSe NSs can be rearranged even without addition of guest cations in the presence of tri-n-octylphosphine. Thus, the obtained NSs were further subjected to ligand exchange reactions in order to replace insulating bulky organic molecules on their surface with compact iodide and sulfide ions, a step crucial for the application of nanomaterials in (opto)electronic devices. The resulting NS dispersions were processed into thin films by spray-coating onto commercially available interdigitated platinum electrodes. Light response measurements of PbSe and CZTSe NS-films demonstrated their potential for applications as light-sensitive materials in photodetection or photovoltaics.

Cation exchange emerged as a versatile tool to obtain a variety of nanocrystals not yet available via a direct synthesis. Reduced reaction times and moderate temperatures make the method compatible with anisotropic nanoplatelets (NPLs). However, the subtle thermodynamic and kinetic factors governing the exchange require careful control over the reaction parameters to prevent unwanted restructuring. Here, we capitalize on the research success of CdSe NPLs by transforming them into PbSe NPLs suitable for optoelectronic applications. In a two-phase mixture of hexane/Nmethylformamide, the oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH4I and a cation exchange reaction to PbSe. Their morphology and crystal structure are well-preserved as evidenced by electron microscopy and powder X-ray diffraction. We demonstrate the successful ligand exchange and associated electronic coupling of individual NPLs by fabricating a simple photodetector via spray-coating on a commercial substrate. Its optoelectronic characterization reveals a fast light response at low operational voltages.

Funding: This work was supported by the EU Horizon 2020 Project MiLEDi (779373) and by the Belarusian Republican Foundation for Fundamental Research (grant X21MC-007). D. I. Shiman, E. Ksendzov, E. A. Bolotina, and S. V. Kostjuk acknowledge the support by the Erasmus+ Traineeship Programme for Higher Education. Photoluminescent quantum dots (QDs) are a prominent example of nanomaterials used in practical applications, especially in light-emitting and light-converting devices. Most of the current applications of QDs require formation of thin films or their incorporation in solid matrices. The choice of an appropriate host material capable of preventing QDs from degradation and developing a process of uniform incorporation of QDs in the matrix have become essential scientific and technological challenges. In this work, we developed a method of uniform incorporation of Cu–Zn–In–S (CZIS) QDs into a highly protective cross-linked polyisobutylene (PIB) matrix with high chemical resistance and low gas permeability. Our approach involves the synthesis of a methacrylate-terminated three-arm star-shaped PIB oligomeric precursor capable of quick formation of a robust 3D polymer network upon exposure to UV-light, as well as the design of a special ligand introducing short PIB chains onto the surface of the QDs, thus providing compatibility with the matrix. The obtained cross-linked QDs-in-polymer composites underwent a complex photostability test in air and under vacuum as well as a chemical stability test. These tests found that CZIS QDs in a cross-linked PIB matrix demonstrated excellent photo- and chemical stability when compared to identical QDs in widely used polyacrylate-based matrices. These results make the composites developed excellent materials for the fabrication of robust, stable and durable transparent light conversion layers. Publisher PDF

In this work we present a technique of incorporation of semiconductor CdTe nanocrystals (NCs) into metal oxide matrices prepared by inorganic sol-gel method. As the matrices, we chose alumina and aluminum tin oxide, which are optically transparent in the visible region. Among them the first is electrically insulating, while the second is conductive and thus can be used in optoelectronic devices. We found optimal synthetic parameters allowing us to maintain optical properties of the NCs in both matrices even after heating up to 150°C in air. Therefore, in our approach we overcame a common problem of degradation of the optical properties of semiconductor NCs in oxide matrices as a result of the incorporation and subsequent interaction with the matrix. The resulting materials were characterized in detail from the point of view of their optical and structural properties. Based on the results obtained, we suggest the formation mechanism of these materials. Semiconductor NCs embedded in robust and optically transparent metal oxides offer promising applications in optical switching, optical filtering, waveguides, light emitting diodes, and solar concentrators.

In the past decades cadmium-free quantum dots (QDs), among which are quaternary colloidal Cu-Zn-In-S/ZnS (CZIS/ZnS) core/shell nanocrystals (NCs), have attracted great scientific interest. Particularly, their low toxicity and the possibility to tune their photoluminescence (PL) properties by varying the composition in the multicomponent system make them highly attractive for applications in light-emitting diodes (LEDs). Thus, the demands for high quality CZIS/ZnS QDs and methods to process them into bulk materials stimulate investigations of these nanomaterials. Herein, we demonstrate the synthesis of CZIS/ZnS core/shell NCs via a surfactant induced nucleation process, which emit in various colors covering the range from 520 nm to 620 nm possessing high photoluminescence quantum yields (PLQYs) up to 47%. Furthermore, the as synthesized NCs were successfully integrated into two different salt matrices [Na2B4O7 (Borax) and LiCl] using two different approaches. The commonly used incorporation of the NCs into Borax salt led to salt crystals emitting from 540 nm to 600 nm with PLQYs up to 24%. By encapsulating the QDs into LiCl, brightly emitting NCs-in-LiCl powders with the PL covering a range from 520 nm to 650 nm with PLQYs of up to 14% were obtained. As a proof of concept, the fabrication of a color conversion LED using NCs encapsulated into LiCl demonstrated the applicability of the encapsulated NCs.

We present a general strategy for a facile synthesis of complex multifunctional nanoscale materials via colloidal atomic layer deposition (c-ALD). The c-ALD technique is based on self-limiting half-reactions of ionic precursors on the surface of a nanocrystal (NC) occurring at room temperature. Using this technique, uniform layers of CdS and ZnS semiconductor shells were epitaxially grown on CdSe semiconductor cores with different shell combinations, leading to the precise control of the optical properties of these heterostructures. All core-shell multicomponent nanoparticles preserve narrow size distributions, phase crystallinity, and shape homogeneity of the initial NCs. Furthermore, we attempted to extend the toolbox of the c-ALD to combine materials with intrinsically different properties, such as Au/CdS core/shell structures with substantial lattice mismatch. The results presented in this work demonstrate great opportunities for creating functional materials with programmable properties for electronics and optoelectronics.

Frontiers in Chemistry, 7, ISSN:2296-2646

We demonstrate high-mobility solution-processed inorganic field-effect transistors (FETs) with ultra-short channel (USC) length using semiconductor CdSe nanocrystals (NCs). Capping of the NCs with hybrid inorganic-organic CdCl

In this work, we present a new synthetic approach to colloidal PbS nanoplatelets (NPLs) utilizing a cation exchange (CE) strategy starting from CuS NPLs synthesized via the hot-injection method. Whereas the thickness of the resulting CuS NPLs was fixed at approx. 5 nm, the lateral size could be tuned by varying the reaction conditions, such as time from 6 to 16 h, the reaction temperature (120 °C, 140 °C), and the amount of copper precursor. In a second step, Cu+ cations were replaced with Pb2+ ions within the crystal lattice via CE. While the shape and the size of parental CuS platelets were preserved, the crystal structure was rearranged from hexagonal covellite to PbS galena, accompanied by the fragmentation of the monocrystalline phase into polycrystalline one. Afterwards a halide mediated ligand exchange (LE) was carried out in order to remove insulating oleic acid residues from the PbS NPL surface and to form stable dispersions in polar organic solvents enabling thin-film fabrication. Both CE and LE processes were monitored by several characterization techniques. Furthermore, we measured the electrical conductivity of the resulting PbS NPL-based films before and after LE and compared the processing in ambient to inert atmosphere. Finally, we fabricated field-effect transistors with an on/off ratio of up to 60 and linear charge carrier mobility for holes of 0.02 cm2 V−1 s−1.

We present a colloidal synthesis of quaternary Cu–Zn–In–S (CZIS) nanoplatelets (NPLs) by means of partial cation exchange. Starting with the synthesis of highly monodisperse binary CuS NPLs with lateral dimensions of ∼64 nm and thickness of ∼5 nm, we further performed a cation exchange reaction in which copper was partly replaced by indium, leading to Cu–In–S NPLs. To enhance the stability of the resulting NPLs and to improve their optical properties, we carried out the ZnS shell growth via both the heterogeneous nucleation of ZnS on the NPLs and via partial cation exchange on the surface of the particles. The latter reaction resulted, however, in rather an alloyed than the core/shell structure, whereas the reaction between zinc and sulfur precursors yielded unusual cookie-like hexagonal shaped structure, in which ZnS trigonal extensions grew only on one of the basal planes of the plates along the thickness direction. Upon ZnS growth, the lateral dimensions of the resulting core/shell CZIS/ZnS and alloyed CZIS NPLs distinctly increased to ∼80 and ∼75 nm, respectively. The analysis of the optical properties of the alloyed CZIS NPLs showed photoluminescence (PL) in the range from 780 to 820 nm depending on the reaction time and temperature. This PL signal originated mainly from small nanoparticles formed as a byproduct in the synthesis. In contrast to the alloyed NPLs, PL measurements of the core/shell CZIS/ZnS platelets showed a weak emission in the near-infrared region (PL maximum at approx. 1110 nm), which so far has rarely been reported for the copper chalcogenide-based two-dimensional structures.

Atomically flat colloidal semiconductor CdSe nanoplatelets (NPLs) with precisely controlled thickness possess a range of unique optoelectronic properties. Here, we study the growth of CdSe, CdTe, and CdS NPLs with the aim of synthesizing thicker NPLs in order to extend their optical activity further into the lower energy/larger wavelength range. We employ cadmium halides, which lead to faster reaction kinetics as confirmed by control experiments with cadmium hydroxide as a Cd-precursor. Addition of halides in all cases led to the formation of thicker NPL species, as compared with the corresponding syntheses without these additives. Analysis of a recent theoretical model of the platelet growth mechanism confirms an earlier suggestion that reducing both the reaction enthalpy and the surface energy of CdSe, by replacing acetate ligands with chloride ions, should indeed lead to thicker NPLs as observed. We noticed a formation of Cd0-metal nanoparticles in the first stage of the synthesis by preparing the Cd-precursor, which is another key finding of our work. We assume that these particles can serve as an active cadmium source facilitating the growth of the NPLs. The resulting 6 ML CdSe NPLs exhibited bright photoluminescence with quantum yield of up to 50%, exceptionally narrow spectrum centered at 582 nm with full width at half-maximum of approx. 11 nm, and small Stokes shift of 2 nm. Moreover, we demonstrated the synthesis of heterostructured core/shell CdSe/CdS NPLs based on 6 ML CdSe platelets, which also exhibited bright fluorescence. This work shows the possibility to overcome energetic barrier limiting the size (thickness) control by using appropriate promoters of the growth of CdSe, CdTe, and CdS 2D structures.

Quasi-two-dimensional (2D) CdSe nanoplatelets (NPLs) are distinguished by their unique optical properties in comparison to classical semiconductor nanocrystals, such as extremely narrow emission line widths, reduced Auger recombination, and relatively high absorption cross sections. Inherent to their anisotropic 2D structure, however, is the loss of continuous tunability of their photoluminescence (PL) properties due to stepwise growth. On top of that, limited experimental availability of NPLs of different thicknesses and ultimately the bulk band gap of CdSe constrain the achievable PL wavelengths. Here, we report on the doping of CdSe NPLs with mercury, which gives rise to additional PL in the red region of the visible spectrum and in the near-infrared region. We employ a seeded-growth method with injection solutions containing cadmium, selenium, and mercury. The resulting NPLs retain their anisotropic structure, are uniform in size and shape, and present significantly altered spectroscopic characteristics due to the existence of additional energetic states. We conclude that doping takes place by employing elemental analysis in combination with PL excitation spectroscopy, X-ray photoelectron spectroscopy, and single-particle fluorescence spectroscopy, confirming single emitters being responsible for multiple distinct emission signals.

Semiconductor colloidal nanoplatelets (NPLs) are a promising new class of nanostructures that can bring much impact on lightning technologies, light-emitting diodes (LED), and laser fabrication. Indeed, great progress has been made in optimizing the optical properties of the NPLs for the visible spectral range, which has already made the implementation of a number of effective devices on their basis possible. To date, state-of-the-art near-infrared (NIR)-emitting NPLs are significantly inferior to their visible-range counterparts, although it would be fair to say that they received significantly less research attention so far. In this study, we report a comprehensive analysis of steady-state and time-dependent photoluminescence (PL) properties of four monolayered (ML) PbSe NPLs. The PL measurements are performed in a temperature range of 78&ndash, 300 K, and their results are compared to those obtained for CdSe NPLs and PbSe quantum dots (QDs). We show that multiple emissive states, both band-edge and trap-related, are responsible for the formation of the NPLs&rsquo, PL band. We demonstrate that the widening of the PL band is caused by the inhomogeneous broadening rather than homogeneous one, and analyze the possible contributions to PL broadening.

Wir berichten über eine Weiterentwicklung auf Grundlage der analytischen Ultrazentrifugation, durch welche Partikelgrößen direkt in Lösung mit Sub-nm-Auflösung charakterisiert werden können. Erreicht wird diese Auflösung durch die simultane Messung von UV/Vis-Spektren, während die einzelnen Komponenten der Mischung hydrodynamisch aufgetrennt werden. Durch die Aufrüstung der analytischen Ultrazentrifuge mit einem neuartigen Multiwellenlängendetektor wird der traditionellen hydrodynamischen Charakterisierung eine weitere spektrale Dimension hinzugefügt, was den Informationsgehalt vervielfacht. Die Leistungsfähigkeit der Messmethode wird durch die Charakterisierung von CdTe-Nanopartikeln verdeutlicht, wobei keine Aufreinigung und Fraktionierung der Nanopartikeln in einzelne, scheinbar monodisperse Fraktionen erforderlich ist. Durch unsere Untersuchungen konnten wir zum ersten Mal die reinen spektralen Eigenschaften und Bandlücken von diskreten CdTe-Nanopartikelspezies in einer Mischung messen. published

We report on an efficient assembly approach to a variety of electrostatically stabilized all-inorganic semiconductor nanocrystals (NCs) via their linking with appropriate ions into multibranched gel networks. These all-inorganic non-ordered 3D assemblies can combine strong interparticle coupling which facilitates charge transport between the NCs with their diverse morphology, composition, size, and functional capping ligands. Moreover, the resulting dry gels (aerogels) are highly porous monolithic structures, which preserve the quantum confinement of their building blocks. The inorganic semiconductor aerogel made of 4.5 nm CdSe colloidal NCs, capped with iodide ions and bridged with Cd2+ ions, exhibited a surface area as high as 146 m2/g.

A novel colloidal synthesis of copper selenide nanosheets (NSs) with lateral dimensions of up to 3 μm is developed. This material is used for the fabrication of flexible conductive films prepared via simple drop-casting of the NS dispersions without any additional treatment. The electrical performance of these coatings is benchmarked against copper selenide spherical nanocrystals (SNCs) in order to demonstrate the advantage of 2D morphology of the NSs for flexible electronics. In this contest, Cu2−xSe SNC films exhibit higher conductivity but lower reproducibility due to the formation of cracks leading to discontinuous films. Furthermore, the electrical properties of the films deposited on different flexible substrates following their bending, stretching and folding are studied. A comparison of Cu2−xSe SNC and CuSe NS films reveals an increased stability of the CuSe NS films under mechanical stress applied to the samples and their improved long-term stability in air.

We proposed and demonstrated the first account of large-area, semi-transparent, tandem photosensitive nanocrystal skins (PNSs) constructed on flexible substrates operating on the principle of photogenerated potential buildup, which avoid the need for applying an external bias and circumvent the current-matching limitation between junctions. We successfully fabricated and operated the tandem PNSs composed of single monolayers of colloidal water-soluble CdTe and CdHgTe nanocrystals (NCs) in adjacent junctions on a Kapton polymer tape. Owing to the usage of a single NC layer in each junction, noise generation was significantly reduced while keeping the resulting PNS films considerably transparent. In each junction, photogenerated excitons are dissociated at the interface of the semi-transparent Al electrode and the NC layer, with holes migrating to the contact electrode and electrons trapped in the NCs. As a result, the tandem PNSs lead to an open-circuit photovoltage buildup equal to the sum of those of the two single junctions, exhibiting a total voltage buildup of 128.4 mV at an excitation intensity of 75.8 mu W cm(-2) at 350 nm. Furthermore, we showed that these flexible PNSs could be bent over 3.5 mm radius of curvature and cut out in arbitrary shapes without damaging the operation of individual parts and without introducing any significant loss in the total sensitivity. These findings indicate that the NC skins are promising as building blocks to make low-cost, flexible, large-area UV/visible sensing platforms with highly efficient full-spectrum conversion.

The n‐type semiconductor system Bi2Te3Bi2Se3 is known as a low‐temperature thermoelectric material with a potentially high efficiency. Herein, a facile approach is reported to synthesize core/shell heterostructured Bi2Te2Se/Bi2Te3 nanosheets (NSs) with lateral dimensions of 1–3 μm and thickness of about 50 nm. Bi2Te3 and Bi2Se3, as well as heterostructured Bi2Te2Se/Bi2Te3 NSs are obtained via colloidal synthesis. Heterostructured NSs show an inhomogeneous distribution of the chalcogen atoms forming selenium and tellurium‐rich layers across the NS thickness, resulting in a core/shell structure. Detailed morphological studies reveal that these structures contain nanosized pores. These features contribute to the overall thermoelectric properties of the material, inducing strong phonon scattering at grain boundaries in compacted solids. NSs are processed into nanostructured bulks through spark plasma sintering of dry powders to form a thermoelectric material with high power factor. Electrical characterization of our materials reveals a strong anisotropic behavior in consolidated pellets. It is further demonstrated that by simple thermal annealing, core/shell structure can be controllably transformed into alloyed one. Using this approach pellets with Bi2Te2.55Se0.45 composition are obtained, which exhibit low thermal conductivity and high power factor for in‐plane direction with zT of 1.34 at 400 K.

We developed a three-step colloidal synthesis of near-infrared (NIR) active Cu–In–Se (CISe)-based nanocrystals (NCs) via a sequential partial cation exchange realized in one pot. In the first step, binary highly copper deficient Cu2–xSe NCs were synthesized, followed by a partial cation exchange of copper to indium ions, yielding CISe NCs. This reaction allows for a precise control of the composition of the resulting NCs through a simple variation of the ratio between guest-cation precursors and parent NCs. To enhance the stability and the photoluminescence (PL) properties of the NCs, a subsequent ZnS shell was grown in the third step, resulting in CISeS/ZnS core/shell particles. These core/shell hetero-NCs exhibited a dramatic increase in size and a restructuring to trigonal pyramidal shape. The shell growth performed at a relatively high temperature (250 °C) also led to anion exchange, in which sulfur replaced part of selenium atoms close to the surface of the NCs, forming alloyed CISeS core structure. ...

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Hierarchical superstructures formed by self-assembled nanoparticles exhibit interesting electrochemical properties that can potentially be exploited in Li-ion batteries (LIBs) as possible electrode materials. In this work, we tested two different morphologies of CuS superstructures for electrodes, namely, tubular dandelion-like and ball-like assemblies, both of which are composed of similar small covellite nanoparticles. These two CuS morphologies are characterized by their markedly different electrochemical performances, suggesting that their complex structures/morphologies influence the electrochemical properties. At 1.12Ag-1, the cells made with CuS tubular structures delivered about 420mAhg-1, and at 0.56Ag-1, the capacity was as high as about 500mAhg-1 with good capacity retention. Their ease of preparation and processing, together with good electrochemical performance, make CuS tubular dandelion-like clusters attractive for developing low-cost LIBs based on conversion reactions.

In this work, we developed a method to study in situ the optical properties of Cu2-xSe and CuS nanocrystals upon electrochemical reduction and oxidation. Both these materials possess a strong localized surface plasmon resonance (LSPR) in the near-infrared region. First, the nanoparticles were embedded into a transparent film made of a perfluorinated sulfonic-acid copolymer Nafion deposited onto an ITO-coated glass. This substrate was employed as a working electrode for chronoamperometry and cyclic voltammetry measurements directly in a transparent cell allowing for simultaneous acquisition of absorption spectra of the system upon its charging/discharging. We observed that LSPR of the Cu2-xSe NCs can be well-controlled and tuned in a wide range simply by potentiostatic potential switching. Starting with an intensive plasmon of the initial as-synthesized Cu2-xSe NCs we were able to completely damp it via reduction (electron injection). Moreover, this electrochemical tuning was demonstrated to be reversible by subsequent oxidation (extracting electrons from the system). At the same time, CuS NCs did not exhibit such prominent LSPR modulation upon the same experimental conditions due to their more metallic-like electronic structure. Hence, our findings demonstrate for the first time a reversible tuning of the LSPR of copper chalcogenide NCs without any chemical or structural modification. Such a wide LSPR tunability is of paramount importance, for example in applications of these materials in photovoltaics to amplify light absorption, in systems involving plasmon-exciton interactions to controllably quench/enhance light emission, and in electrochromic devices to control their transmittance. Fil: Benavente Llorente, Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Technische Universität Dresden; Alemania Fil: Dzhagan, Volodymyr M.. Technische Universität Chemnitz; Alemania Fil: Gaponik, Nikolai. Technische Universität Dresden; Alemania Fil: Iglesias, Rodrigo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Zahn, Dietrich R. T.. Technische Universität Chemnitz; Alemania Fil: Lesnyak, Vladimir. Technische Universität Dresden; Alemania

We report on a simple and effective technique of tuning the colloidal solubility of inorganic-capped CdSe and CdSe/CdS core/shell nanocrystals (NCs) from highly polar to nonpolar media using n-butylamine molecules. The introduction of the short and volatile organic amine mainly results in a modification of the labile diffusion region of the inorganic-capped NCs, enabling a significant extension of their dispersibility and improving the ability to form long-range assemblies. Moreover, the hybrid n-butylamine/inorganic capping can be thermally decomposed under mild heat treatment, making this approach of surface functionalization well-compatible with a low-temperature, solution-processed device fabrication. Particularly, a field-effect transistor-based on n-butylamine/Ga-I-complex-capped 4.5 nm CdSe NC solids shows excellent transport characteristics with electron mobilities up to 2 cm2/(V·s) and a high current modulation value (>104) at a low operation voltage (

We modeled a prototype of a photovoltaic window, a passive source of clean energy, using a Monte Carlo ray-tracing method. We considered different geometries, material properties, and edge solar cells to determine the optimal conditions and possible electrical power yield. The modeled photovoltaic window prototype was based on colloidal luminescent low-toxic I–III–VI quantum dots (core/shell CuInS2/ZnS nanocrystals) with large Stokes shifts, high quantum yields, and tunable spectral properties. We also showed the influence of the quantum dot absorption/emission spectra on the resulting spectrum of transmitted light (i.e., the visual appearance of the photovoltaic window) using a chromaticity diagram.

We report the synthesis of alloyed quaternary and quinary nanocrystals based on copper chalcogenides, namely, copper zinc selenide-sulfide (CZSeS), copper tin selenide-sulfide (CTSeS), and copper zinc tin selenide-sulfide (CZTSeS) nanoplatelets (NPLs) (∼20 nm wide) with tunable chemical composition. Our synthesis scheme consisted of two facile steps: i.e., the preparation of copper selenide-sulfide (Cu2-xSeyS1-y) platelet shaped nanocrystals via the colloidal route, followed by an in situ cation exchange reaction. During the latter step, the cation exchange proceeded through a partial replacement of copper ions by zinc or/and tin cations, yielding homogeneously alloyed nanocrystals with platelet shape. Overall, the chemical composition of the alloyed nanocrystals can easily be controlled by the amount of precursors that contain cations of interest (e.g., Zn, Sn) to be incorporated/alloyed. We have also optimized the reaction conditions that allow a complete preservation of the size, morphology, and crystal structure as that of the starting Cu2-xSeyS1-y NPLs. The alloyed NPLs were characterized by optical spectroscopy (UV-vis-NIR) and cyclic voltammetry (CV), which demonstrated tunability of their light absorption characteristics as well as their electrochemical band gaps.

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.

Here we report a facile approach to synthesize copper chalcogenide (Cu2–xS, Cu2–xSeyS1–y and Cu2–xTeyS1–y) nanocrystals without employing hot-injection, at moderate reaction temperatures (200–220 °C) and free of phosphines. Scaling up of the synthesis yields monodisperse nanoparticles without variations in their morphology. We have observed the formation of alloyed copper selenide-sulfide and telluride-sulfide nanocrystals due to the incorporation of sulfur by using 1-dodecanethiol as a ligand along with oleic acid. The materials obtained possess localized surface plasmon resonances in the near-infrared region, which are demonstrated to be widely tunable via a controlled oxidation generating copper vacancies. Copper sulfide nanoparticles with well-defined initial chalcocite crystal phase were subjected to oxidation followed by structural characterization. Structural rearrangement of the oxidized chalcocite Cu2–xS crystal lattice to roxbyite by aging is proven to release the copper vacancies. Further oxida...

Mixed metal–semiconductor nanocrystal aerogels are fabricated, which are light-emitting and highly porous macroscopic monoliths. Thiol-stabilized CdTe and Au nanoparticles from aqueous synthesis act as building blocks for the hybrid material. The Au colloids undergo a surface-modifi cation to enhance the particle stability and achieve thiol functionalities. A photochemical treatment is applied for the gelation process which is found to be reversible by subsequent addition of thiol molecules. Via supercritical drying aerogels are formed. The variation of the initial CdTe to Au nanoparticle ratio permits a facile tuning of the content and the properties of the resulting aerogels. The obtained structures were characterized by means of optical spectroscopy, electron microscopy, elemental analysis, and nitrogen physisorption.

The influence of gold nanoparticle concentration on signatures of localized surface plasmon mediated Forster resonant energy transfer is investigated in a quantum dot–gold nanoparticle sandwich structure. At lower gold nanoparticle concentrations, localized surface plasmon mediated Forster resonant energy transfer enhancement of the acceptor emission is observed. At higher gold nanoparticle concentrations, the acceptor emission is reduced despite faster localized surface plasmon enhanced Forster resonant energy transfer rates being achieved. This is attributed to competition between localized surface plasmon mediated Forster resonant energy transfer and gold nanoparticle quenching effects.

Plasmon-enhanced nonradiative energy transfer is demonstrated in two inorganic semiconductor systems. The first is comprised of colloidal nanocrystal CdTe donor and acceptor quantum dots, while the second is a hybrid InGaN quantum well-CdSe/ZnS quantum dot donor-acceptor system. Both structures are in a planar geometry. In the first case a monolayer of Au nanospheres is sandwiched between donor and acceptor quantum dot monolayers. The largest energy transfer efficiency is seen when the donor is ~3 nm from the Au nanopshere. A plasmon-enhanced energy transfer efficiency of ~ 40% has been achieved for a separation of 3 nm between the Au nanopshere monolayer and the acceptor monolayer. Despite the increased energy transfer efficiency these conditions result in strong quenching of the acceptor QD emission. By tuning the Au nanosphere concentration and Au nanosphere-acceptor QD separation the acceptor QD emission can be increased by a factor of ~2.8. The plasmon-enhanced nonradiative energy transfer is observed to extend over larger distances than conventional Forster resonance energy transfer. Under the experimental conditions reported herein, it can be described by the same d-4 dependence but with a larger characteristic distance. Using a Ag nanobox array plasmonic component plasmon-enhanced nonradiative energy transfer has also demonstrated from an InGaN quantum well to a ~80 nm thick layer of CdSe/ZnS colloidal quantum dots. An efficiency of ~27% is achieved, with an overall increase in the QD emission by ~70%.

Multiexciton Generation (MEG) enabled by the photogeneration of more than one electron-hole pairs upon the absorption of a single photon observed in colloidal semiconductor nanocrystals (NCs) is an essential key to high efficiency when operating in large enough photon energy regimes. Here, we report a newly designed class of solution-processed highly sensitive MEG-assisted photosensors of CdHgTe NCs, in which the charge accumulation is dramatically enhanced for photon energies greater than two times the bandgap of the employed NCs. We fabricated and comparatively studied five types of devices based on different NC monolayers of selected quantum-confined bandgaps resulting in different levels of photovoltage buildup readouts. Among these photosensitive platforms, MEG is distinctly observed for CdHgTe NCs, as the number of electrons trapped inside these NCs and the number of holes accumulating into the interfacing metal electrode were increased beyond a single exciton per absorbed photon. Furthermore, we conducted time-resolved fluorescence measurements and confirmed the occurrence of MEG in the CdHgTe NC monolayer of the photosensor. These findings pave the way for engineering of multiexciton kinetics in high-efficiency NC-based photosensors and photovoltaics.

In this work, we have developed novel hybrid quantum dot gels based on the controllable and reversible assembly of nanoparticles via metal-tetrazole complexation. Combining in one hybrid network nanocrystals of different semiconductors (ZnSe and CdTe) as well as quantum dots of different sizes (green and red emitting CdTe) with different band gaps, we have examined energy relations within these systems and act out a facile route to the color design of the resulting gels. Efficient energy pumping from donor quantum dots to acceptors leads to a remarkable enhancement of the emission intensity of the gel. Furthermore, by integrating three different quantum dot types into one network, we obtained a white-light-emitting aerogel.

Four alternating arylamino-functionalized copolymers were synthesized in a Suzuki copolymerization applying 4, 4′-(2,7-dibromo-9H-fluorene-9,9-diyl)dianiline, 4,4′-(2,7-dibromo-9H-fluorene-9,9-diyl)bis(N,N-diphenylaniline), 4-(3,6-dibromo-9H- carbazol-9-yl)aniline and 4-(3,6-dibromo-9H-carbazol-9-yl)-N,N-diphenylaniline in combination with 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(1,3,2-dioxaborinane). The resulting novel alternating copolymers were fully characterized. The copolymers revealed blue light emission and wide optical bandgaps of at least 2.93 eV for the fluorene-based and 3.07 eV for the carbazole-based polymers. The amino-functions allow to tie semiconducting CdTe nanocrystals (NCs) and to synthesize a series of composites with CdTe NCs. Moreover, tuning the emission color over a wide range by tying these CdTe NCs results in a facile preparation of organic–inorganic semiconductor composites with emission colors “a la carte.” © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Random side-chain functionalized copolymers were synthesized, utilizing a facile Yamamoto protocol by applying 2,7-dibromo-9,9-bis(6-bromohexyl)-9H-fluorene, (E)-1,2-bis(4-bromophenyl)ethene, 2,7-dibromo-9,9-dioctyl-9H-fluorene as comonomers. The precursor copolymers were post-functionalized utilizing di-n-propylamine and the resulting target copolymers were fully characterized. The optical classification parameters have been determined in solutions and in thin films as well. The copolymers revealed blue light emission, wide optical bandgaps Egopt of at least 2.84 eV and remarkable quantum yields up to 0.78 in chloroform solutions. The amino-functional copolymers allowed tying semiconductor CdTe nanocrystals.

5 páginas, 5 figuras.-- et al., A novel all-inorganic electroluminescent device is demonstrated based on highly luminescent CdTe nanocrystals intercalated within a laminar hydrotalcite-like structure. The laminar scaffold acts to both support and distribute the CdTe nanocrystals. The device is synthesized using simple wet chemical processes at room temperature in ambient conditions. It has high thermal stability, operating continuously up to 90 °C, and a maximum efficiency at J = 0.12 A cm−2. The device is targeted at the automotive industry., The authors acknowledge funding from the EU FP6 project “Stabilight” (Grant No. 017328).

Physikalische Chemie/Elektrochemie, TU Dresden, Bergstr. 66b, 01062 Dresden, GermanyIn this work we report on the development of novel hybrid material with enhanced photodynamicproperties based on methylene blue and CdTe nanocrystals. Absorption spectroscopy, visible photo-luminescence spectroscopy and ”uorescence lifetime imaging of this system reveal ef“cient chargetransfer between nanocrystals and the methylene blue dye. Near infra-red photoluminescencemeasurements provide evidence for an increased ef“ciency of singlet oxygen production by themethylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were alsoperformed, they point towards an improvement in the cell kill ef“ciency for the methylene blue-semiconductor nanocrystals hybrid system.

In this paper, we report on a convenient and quick self-assembly of thioglycolic acid (TGA)-capped CdTe nanocrystals (NCs) into three-dimensional (3D) nanostructures in solution, in which large-scale nanowires are found as building blocks. The wet 3D nanostructures can be further dried by critical CO2 to obtain solids with a volume of about 1 cm3 and a density of about 1/2500th of bulk CdTe. By SEM, EDS, and HRTEM characterization, it is found that the nanowires actually are CdTe@Cd−TGA complex hybrid nanostructures in which many well-separated CdTe NCs are uniformly distributed. The hybrid nanowires can reach several micrometers in length and 25 ± 8 nm in width. As a result of the CdTe NCs with their integrity and effective protection by the Cd−TGA complex, the hybrid nanowires and 3D nanostructures still show visually bright luminescence and retain the size-quantized properties of the CdTe NCs. This new kind of QD-based nanostructures may be suitable for subsequent processing into quantum-confined super...

We have studied the photodynamic properties of novel CdTe quantum dots—methylene blue hybrid photosensitizer. Absorption spectroscopy, photoluminescence spectroscopy, and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near-infrared photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point toward an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.

In the present study, we report a method for preparing a fluorescent thermosensitive hybrid material based on monodisperse, thermosensitive poly(N-isopropyl acrylamide) (PNIPAM) microgels covered with CdTe nanocrystals of 3.2 nm diameter. The CdTe nanocrystals were covalently immobilized on the surface of PNIPAM microgels. The chemical environment around the CdTe nanocrystals was modified by changing the temperature and inducing the microgel volume-phase transition. This change provoked a steep variation in the nanocrystal photoluminescence (PL) intensity in such a way that when the temperature was under the low critical solution temperature (LCST) of the polyrner (36 degrees C) the PL of the nanocrystals was strongly quenched, whereas above the LCST the PL intensity was restored. Langmuir

We report on a generic approach for immobilizing quantum dots (CdTe nanoparticles) on thin, fluid films consisting of poly(acrylic acid) (PAA) polymer chains tethered by one end to an underlying substrate in a polymer brush configuration. The protocol involves covalent bonding (amide linkage) between amino groups present on the surface of CdTe nanoparticles and carboxylic groups of PAA polymer chains. The thickness of the PAA polymer brush employed (∼4.5 nm) is comparable to the nanoparticle size. Exploitation of such a thin polymer brush was found to suppress nanoparticle aggregation and facilitates complete surface coverage. Atomic force microscopy (AFM) was used to study the film morphology. Covalent linkage between nanoparticles and polymer brushes was proven by X-ray photoelectron spectroscopy (XPS). The change in the optical properties of the quantum dots after immobilization was studied by photoluminescence spectroscopy and fluorescence microscopy. The results suggest a simple, effective and highly versatile method for modification of various surfaces with different nanoscopic particles.

Capping agents play an important role in the colloidal synthesis of nanomaterials because they control the nucleation and growth of particles, as well as their chemical and colloidal stability. During recent years tetrazole derivatives have proven to be advanced capping ligands for the stabilization of semiconductor and metal nanoparticles. Tetrazole-capped nanoparticles can be prepared by solution-phase or solventless single precursor approaches using metal derivatives of tetrazoles. The solventless thermolysis of metal tetrazolates can produce both individual semiconductor nanocrystals and nanostructured metal monolithic foams displaying low densities and high surface areas. Alternatively, highly porous nanoparticle 3D assemblies are achieved through the controllable aggregation of tetrazole-capped particles in solutions. This approach allows for the preparation of non-ordered hybrid structures consisting of different building blocks, such as mixed semiconductor and metal nanoparticle-based (aero)gels with tunable compositions. Another unique property of tetrazoles is their complete thermal decomposition, forming only gaseous products, which is employed in the fabrication of organic-free semiconductor films from tetrazole-capped nanoparticles. After deposition and subsequent thermal treatment these films exhibit significantly improved electrical transport. The synthetic availability and advances in the functionalization of tetrazoles necessitate further design and study of tetrazole-capped nanoparticles for various applications.