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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 ...

It is impractical to plan the further work of the company without taking into account analytical data for previous production periods. Analytical accounting data allows managers to build a company's strategy or make changes to an existing development plan. The importance of accounting for the enterprise plays a large role at the planning stage of the further business strategy. A competent manager studies accounting data before making the next decision regarding the company's finances. The easiest way to streamline accounting documents and eliminate errors in it is to conduct an internal audit. Such an audit will protect the company from possible fines and problems with tax audits. It will help optimize accounting and document flow, and simplify relations with banks and counterparties. Economic analysis aims to turn economic and non-economic information into useful information for decision making. Logical processing, study, generalization of facts, their systematization, conclusions, proposals, search for reserves - all these tasks are solved within the framework of economic analysis, which is designed to ensure the validity of management decisions and increase its effectiveness. This monograph is a collective work of teachers and students of the Department of Economic Security, Accounting and Law of the Don State Technical University. It is devoted to the consideration of certain issues of accounting, audit and economic analysis at the enterprise in modern conditions.

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 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

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.

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.

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.

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.

Problems of forming an integrated mechanism of network accounting and management of the company's economic security based on the use of engineering tools and technologies are considered. The matter and peculiarities of network management in conjunction with the organization of accounting are disclosed. The model for organizing network accounting and managing economic security at the micro level is proposed.

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 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.

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.

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.

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.

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).

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.

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.

Bright emitters with photoluminescence in the spectral region of 800-1600 nm are increasingly important as optical reporters for molecular imaging, sensing, and telecommunication and as active components in electrooptical and photovoltaic devices. Their rational design is directly linked to suitable methods for the characterization of their signal-relevant properties, especially their photoluminescence quantum yield (Φ(f)). Aiming at the development of bright semiconductor nanocrystals with emission1000 nm, we designed a new NIR/IR integrating sphere setup for the wavelength region of 600-1600 nm. We assessed the performance of this setup by acquiring the corrected emission spectra and Φ(f) of the organic dyes Itrybe, IR140, and IR26 and several infrared (IR)-emissive Cd(1-x)Hg(x)Te and PbS semiconductor nanocrystals and comparing them to data obtained with two independently calibrated fluorescence instruments absolutely or relative to previously evaluated reference dyes. Our results highlight special challenges of photoluminescence studies in the IR ranging from solvent absorption to the lack of spectral and intensity standards together with quantum dot-specific challenges like photobrightening and photodarkening and the size-dependent air stability and photostability of differently sized oleate-capped PbS colloids. These effects can be representative of lead chalcogenides. Moreover, we redetermined the Φ(f) of IR26, the most frequently used IR reference dye, to 1.1 × 10(-3) in 1,2-dichloroethane DCE with a thorough sample reabsorption and solvent absorption correction. Our results indicate the need for a critical reevaluation of Φ(f) values of IR-emissive nanomaterials and offer guidelines for improved Φ(f) measurements.

Core-shell CdSe/CdS nanocrystals are a very promising material for light emitting applications. Their solution-phase synthesis is based on surface-stabilizing ligands that makes them soluble in organic solvents, like toluene or chloroform. However, solubility of these materials in water provides many advantages, such as additional process routes and easier handling. So far, solubilization of CdSe/CdS nanocrystals in water that avoids detrimental effects on the luminescent properties, poses a major challenge. This work demonstrates how core-shell CdSe/CdS quantum dot-in-rods can be transferred into water using a ligand exchange method employing mercaptopropionic acid (MPA). Key to maintaining the light-emitting properties is an enlarged CdS rod diameter, which prevents potential surface defects formed during the ligand exchange from affecting the photophysics of the dot-in-rods. Films made from water-soluble dot-in-rods show amplified spontaneous emission (ASE) with a similar threshold (130 microJ/cm2) as the pristine material (115 microJ/cm2). To demonstrate feasibility for lasing applications, self-assembled micro lasers are fabricated via the coffee-ring effect that display single-mode operation and a very low threshold of around 10 microJ/cm2. The performance of these micro lasers is enhanced by the small size of MPA ligands, enabling a high packing density of the dot-in-rods., 20 pages, 4 figures, published paper with supporting information

Hybrid materials formed by semiconductor quantum dots and J-aggregates of cyanine dyes provide a unique combination of enhanced absorption in inorganic constituents with large oscillator strength and extremely narrow exciton bands of the organic component. The optical properties of dendrite structures with fractal dimension 1.7-1.8, formed from J-aggregates integrated with CdTe quantum dots (QDs), have been investigated by photoluminescence spectroscopy and fluorescence lifetime imaging microscopy. Our results demonstrate that (i) J-aggregates are coupled to QDs by Förster-type resonant energy transfer and (ii) there are energy fluxes from the periphery to the centre of the structure, where the QD density is higher than in the periphery of the dendrite. Such an anisotropic energy transport can be only observed when dendrites are formed from QDs integrated with J-aggregates. These QD/J-aggregate hybrid systems can have applications in light harvesting systems and optical sensors with extended absorption spectra. © The Royal Society of Chemistry 2013., This research was supported by the ETORTEK 2011–2013 project “nanoIKER” from the Department of Industry of the Basque Government and by the Ministry of Education and Science of the Russian Federation Contract no. 8842 and 11.G34.31.0050. Financial support from the Portuguese Foundation for Science and Technology (FCT) and FEDER through Projects PTDC-FIS-113199-2009 and PEst-C/FIS/UI0607/2011 is gratefully acknowledged.

Further improvement of infrared single photon sources is a major challenge for future implementations of quantum information and quantum communication applications. In this paper, we give further insight into a recently presented, conceptually novel method for the generation of single photons. 1 The method is of particular interest for spectral domains where stable room temperature single photon sources are not available. For example, this is the presently the case for the near-infrared. This wavelength regime is important for data transfer over long distances where optical losses in fibers are minimal. The presented method is based on the following idea. The fundamental key requirement for single photon generation is the generation of a single excitation in an optically active system. It is not the presence of a single quantum system. The presented method is applied to realize a stable, non-blinking, room temperature infrared single photon source by converting visible single photons from a defect center in diamond to the near infrared. For the presented implementation, the theoretical conversion efficiency was estimated to be 26 %. In a first prove of principle experiment, a conversion efficiency of 0.1 % was achieved.

We report wavelength-dependent enormous enhancement of the nonlinear refractive index of wild-type bacteriorhodopsin in the presence of semiconductor quantum dots. The effect is strongest in the region just below the absorption edge of both constituents of this hybrid material and in samples that show strong Förster resonance energy transfer. We show that enhancements of up to 4000% can be achieved by controlled engineering of the hybrid structure involving variations of the molar ratio of the constituents. This new hybrid material with exceptional nonlinear properties will have numerous photonic and optoelectronic applications employing its photochromic, energy transfer, and conversion properties. © 2013 American Chemical Society., This work was funded by the Irish Research Council for Science, Engineering, and Technology (ICSET) under the Embark Initiative and by Science Foundation Ireland under Grant No. 08/IN.1/I1862. Partial support of the Ministry of Higher Education and Science of the Russian Federation under the Contract Nos. 8842 and 11.G34.31.0050 is also acknowledged.

ZnO@Zn3 P2 quantum dots (QDs) are synthesized, with emission from yellow to red. Photoelectrochemical investigations reveal that the current and voltage of the QD-derivatized electrodes show a response upon illumination. A photocurrent of ca. 8 nA cm(-2) for a monolayer of ZnO@Zn3 P2 QDs deposited on indium tin oxide (ITO) electrode is recorded.

Using electro-static assembly of complementary organic (cyanine dye) and inorganic (quantum dots) building blocks we report on formation of an advanced nanohybrid system with highly efficient nonradiative energy transfer properties. In contrast to previous approaches, formation of J-aggregates in cyanine dye solution was triggered by direct injection of as-synthesized colloidal CdTe quantum dots without any additional surface treatment. The optical properties of formed hybrid aggregates have been investigated by absorption and photoluminescence spectroscopy and fluorescence lifetime imaging microscopy. A quantum dot/J-aggregate system shows the enhanced absorption in visible and ultraviolet parts of the spectrum typical of quantum dots, along with the narrow emission linewidth and fast recombination rate characteristic of the J-band emitters. These quantum dot/J-aggregate hybrid systems may have applications in light harvesting systems with the extended spectral absorption as well as optical sensors and optoelectronic devices. © The Royal Society of Chemistry 2012., This work was in part financially supported by Ikerbasque Visiting Fellowship (NG). DS and YR acknowledge the support received from the European Science Foundation (activity PLASMON - BIONANOSENSE).

The incorporation of colloidal quantum dots (QDs) into ionic crystals of various salts (NaCl, KCl, KBr, etc.) is demonstrated. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Moreover, the ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment and as a result providing them with extraordinary high photo- and chemical stability. A prototype of a white light-emitting diode (WLED) with a color conversion layer consisting of this kind of mixed crystals is demonstrated. These materials may also find applications in nonlinear optics and as luminescence standards. © 2012 American Chemical Society.

Surface plasmon enhanced Forster resonant energy transfer (FRET) between CdTe nanocrystal quantum dots (QDs) has been observed in a multilayer acceptor QD–gold nanoparticle–donor QD sandwich structure. Compared to a donor–acceptor QD bilayer structure without gold nanoparticles, the FRET rate is enhanced by a factor of 80 and the Forster radius increases by 103%. Furthermore, a strong impact of the donor QD properties on the surface plasmon mediated FRET is reported.

Diatom-templated noble metal (Ag, Pt, Au) and semiconductor (CdTe) nanoparticle arrays were synthesized by the attachment of prefabricated nanoparticles of defined size. Two different attachment techniques-layer-by-layer deposition and covalent linking-could successfully be applied. The synthesized arrays were shown to be useful for surface-enhanced Raman spectroscopy (SERS) of components, for catalysis, and for improved image quality in scanning electron microscopy (SEM).

Forster resonant energy transfer (FRET) can be applied to create energy flow on the nano-scale for lightharvesting, colour conversion or sensing applications. The performance of such devices depends on the efficiency of the energy transfer process between the donors and acceptors. In order to achieve high FRET efficiencies, the FRET rate has to dominate over the other donor decay rates. The FRET rate depends on the donor-acceptor separation, the acceptor concentration and it has also been proposed that it can be strongly enhanced by localized surface plasmons supported by metal nanoparticles. The impact of these different parameters on the FRET rate in a CdTe quantum dot donor-acceptor bilayer structure is presented. The quantum dot structures, prepared by a layer-by-layer deposition technique, were characterized by steady-state photoluminescence (PL) and absorption spectroscopy as well as time-resolved PL measurements. The FRET rate of the different structures was determined from the time-resolved donor PL decays and its separation and concentration dependence was compared with FRET theory.

Colloidal nanocrystal quantum dots have attracted interest for use in light-harvesting and emitting devices. One of the key parameters for such applications is the quantum efficiency. Nanocrystal quantum dots exhibit reduced quantum yield in layers or solids compared with solutions. Optimizing the overall efficiency of the emission is an important goal. Here we report on a large enhancement of the quantum efficiency of mixed TGA-stabilised CdTe quantum dot in closely packed monolayers formed with nanocrystal QDs of two sizes. Energy is transferred from the smaller donor quantum dots to the larger acceptor quantum dots via Forster resonant energy transfer (FRET). The increased quantum efficiency is attributed to exciton recycling from the donor defect states. The acceptor emission enhancement and relative quantum efficiency are strongly dependent on the donor:acceptor concentration ratio. A relative quantum efficiency of 160% is achieved for the mixed quantum dot layer with a donor:acceptor ratio of 11∶1.

Spatial light modulator (SLM) is a key component of modern video projectors, beam shaping devices, laser beam combiners and optical information processors. Challenging tasks in SLM are optoelectronic integration, all-optical operation and phase modulation with low absorption. A possible improvement along these lines could be the use of new nano-materials with large and controllable optical nonlinearities, e.g. the quantum dots (QDs).

We propose and demonstrate a nanocomposite localized surface plasmon resonator embedded into an artificial three-dimensional construction. Colloidal semiconductor quantum dots are assembled between layers of metal nanoparticles to create a highly strong plasmon-exciton interaction in the plasmonic cavity. In such a multilayered plasmonic resonator architecture of isotropic CdTe quantum dots, we observed polarized light emission of 80% in the vertical polarization with an enhancement factor of 4.4, resulting in a steady-state anisotropy value of 0.26 and reaching the highest quantum efficiency level of 30% ever reported for such CdTe quantum dot solids. Our electromagnetic simulation results are in good agreement with the experimental characterization data showing a significant emission enhancement in the vertical polarization, for which their fluorescence decay lifetimes are substantially shortened by consecutive replication of our unit cell architecture design. Such strongly plasmon-exciton coupling nanocomposites hold great promise for future exploitation and development of quantum dot plasmonic biophotonics and quantum dot plasmonic optoelectronics. © 2011 American Chemical Society.

International audience; Purple membrane (PM) from bacteriaHalobacterium salinarumcontains a photochromic protein bacteriorhodopsin (bR)arranged in a 2D hexagonal nanocrystalline lattice (Figure 1). Absorption of light by the protein-bound chromophore retinal results inpumping the protons through the PM creating an electrochemical gradient which is then used by the ATPases to energize the cellularprocesses.1Energy conversion, photochromism, and photoelectrism are the inherent effects which are employed in many bR technicalapplications.2,3bR, along with the other photosensitive proteins, is not able to deal with the excess energy of photons in UV and bluespectral region and utilizes less than 0.5% of the energy from the available incident solar light for its biological function.4Here, weproceed with optimization of bR functions through the engineering of a “nanoconverter” of solar energy based on semiconductorquantum dots (QDs) tagged with the PM. These nanoconverters are able to harvest light from deep-UV to the visible region and totransfer this additionally collected energy to bR via Fo ̈ rster resonance energy transfer (FRET). We show that specific nanobio-opticaland spatial coupling of QDs (donor) and bR retinal (acceptor) provide a means to achieve FRET with efficiency approaching 100%.We have finally demonstrated that the integration of QDs within PM significantly increases the efficiency of light-driven transmembraneproton pumping, which is the main bR biological function. This new QD-PM hybrid material will have numerous optoelectronic,photonic, and photovoltaic applications based on its energy conversion, photochromism, and photoelectrism properties.KEYWORDSQuantum dot, bacteriorhodopsin, FRET, hybrid material, photovoltaic

In this work, we demonstrate the functionality of optical limiting obtained with CdTe nanocrystals embedded in polystyrene. This functionality relies on our experimentally observed large, saturable, and controlled nonlinear optical properties of CdTe nanocrystals with sizes around 2 nm, at laser wavelength of 532 nm. Our investigation is presenting an experimental proof of concept. The limiting threshold occurs at an average laser power of 10 mW. For laser beam diameter of 1 mm, the threshold intensity for this optical limiting device is ∼ 1 W/cm2.

The quantum dot (QD) concentration dependence of the optical properties of QD monolayers is shown to be dominated by F\"orster resonant energy transfer (FRET) from smaller to larger QDs in the ensemble. With increasing QD concentration a redshift of the peak emission wavelength, a shortening of the photoluminescence lifetime of the QDs on the high-energy side of the ensemble emission spectrum as well as increased difference in the lifetimes on the high- and low-energy sides are observed in the layer-by-layer deposited QD monolayers. There is also evidence of an increased rise time in the time-resolved photoluminescence decays on the low-energy side of the QD emission for two of the three samples presented in most detail. A theory of FRET in two dimensions is applied to explain the lifetime decrease on the high-energy side of the ensemble emission and confirms that the impact of the QD concentration on the optical properties is primarily due to FRET from the smaller to larger QDs in the ensemble. The concentration effects are stronger in QD samples which have a broader emission peak compared to the Stokes shift. Based on good agreement with FRET theory, the QD concentration and the overlap of the QD emission and absorption peaks can both be used to control the efficiency of the FRET process in monodispersed QD layers.

Colloidal semiconducting quantum dots ( QDs), also known as nanocrystals, offer a number of advantages in light generation, e.g., for solid-state lighting, biol ogical labeling, and bio -imaging.3 These applications typically necessitate high quantum eff iciencies in film, preferably with polarized emission in certain applications. One of the major problems encountered when working with films of these QDs is the decrease in their fluorescence quantum efficiency in the solid form. Another technical challenge is to obtain anis otropic emission from these QDs. Recently plasmonics has enabled a wide range of important applications related to nanocrystals including metal enhanced light generation and plasmonic biosensing.1,2 In this work, to address the se difficulties encountered with QD solids, we investigate and demonstrate anisotropic enhanced emission from semiconductor quantum dots placed in multilayered plasmon resonator nanocomposite s using strong plasmon-exciton interactions. In these metal nanoparticle (MNP) resonator architectures, we show that highly isotropic nature of QD emission c an desirably be altered through modifying emission kinetics by plasmon coupling, while also enhancing the overall QD emission.

A general synthetic strategy for the synthesis of nanocrystals of both visible and near infrared emitting materials is introduced. Further, the potential for these materials to be employed in a wide variety of applications is discussed.

We proposed and demonstrated architectural tuning of color chromaticity by controlling photoluminescence decay kinetics through nonradiative Förster resonance energy transfer in the heterostructure of layer-by-layer spaced CdTe nanocrystal (NC) solids. We achieved highly sensitive tuning by precisely adjusting the energy transfer efficiency from donor NCs to acceptor NCs via controlling interspacing between them at the nanoscale. By modifying decay lifetimes of donors from 12.05 to 2.96 ns and acceptors from 3.68 to 14.57 ns, we fine-tuned chromaticity coordinates from (x,y) = (0.575,0.424) to (0.632, 0.367). This structural adjustment enabled a postsynthesis color tuning capability, alternative or additive to using the size, shape, and composition of NCs. © 2009 American Institute of Physics.

In recent years, precisely tuning shades of white across color chromaticity diagram has become critically important in solid state lighting, especially to achieve application specific spectrally tuned illumination [1]. In this respect, semiconductor quantum dot nanocrystals (NCs) have attracted significant attention for their use as luminophors in light-emitting diodes (LEDs). This is mainly because it is possible to conveniently control the electronic structure of these nanocrystals by adjusting their size, shape, and composition [2]. However, such tuning is only limited to the process of nanocrystal synthesis in which the size, shape, and composition are controlled. Here we propose and demonstrate an alternative, post-synthesis, architectural approach to tune the color of nanocrystal emitters by controlling their radiative decay kinetics and steady state spontaneous emission using nonradiative Forster resonance energy transfer (FRET). For the proof-of-concept demonstration of such FRET-controlled tuning, we constructed nanocrystal solids that are layer by layer assembled with interlayer spacings between them precisely controlled at the nanoscale [3].

At present, there exist a number of on-demand single photon sources with high emission rates and stability even at room temperature. However, their emission wavelength is restricted to specific transitions in single quantum emitters. Single photon generation in the near infrared, possibly within the telecom band, though most urgently needed, is particularly crucial. In this paper, we suggest an experimental method to convert visible single photons from a defect center in diamond to the near infrared. The conversion relies on efficient absorption by colloidal quantum dots and subsequent Stokes-shifted emission. The desired target wavelength can be chosen almost arbitrarily by selecting quantum dots with a suitable emission spectrum. A hollow core photonic crystal fiber selectively filled with a solution of quantum dots was used to achieve at the same time a single photon absorption probability of near unity and a very high re-collection efficiency of Stokes-shifted fluorescence (theoretically estimated to be 26%). A total conversion efficiency of light of 0.1% is achieved. Experimental strategies to significantly enhance this number are presented.

The power conversion efficiency of a dye-sensitized solar cell with tailored squaraine dye enhanced by 47%, due to Forster resonance energy transfer from CdSe quantum dots to the squaraine dye. The incident photons to collection efficiency of electrons indicate panchromatic response from the visible to the near-infrared spectrum.