1,721,077 research outputs found
Efficient energy transfer in layered hybrid organic/inorganic nanocomposites: A dual function of semiconductor nanocrystals
Full text linkThe efficiency of energy transfer in hybrid organic/inorganic nanocomposites based on conjugated polymers and semiconductor nanocrystals is strongly dependent on both the energy transfer rate and the rate of the nonradiative recombination of the polymer. We demonstrate that the polymer nonradiative recombination can be reduced by the suppression of exciton diffusion via proper morphology engineering of a hybrid structure. In the layer-by-layer assembled nanocomposite of a conjugated polymer and CdTe nanocrystals the latter have a dual role: first, they are efficient exciton acceptors and, second, they reduce nonradiative recombination in the polymer by suppressing exciton diffusion across the layers.Fil: Lutich, Andrey A.. Ludwig Maximilians Universitat; AlemaniaFil: Pöschl, Andreas. Ludwig Maximilians Universitat; AlemaniaFil: Jiang, Guoxin. Ludwig Maximilians Universitat; AlemaniaFil: Stefani, Fernando Daniel. Ludwig Maximilians Universitat; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Susha, Andrei S.. City University of Hong Kong; ChinaFil: Rogach, Andrey L.. City University of Hong Kong; ChinaFil: Feldmann, Jochen. Ludwig Maximilians Universitat; Alemani
Optical processes in carbon nanocolloids
No full textIn recent years, carbon dots, graphene quantum dots, and other carbon nanocolloids have attracted a mounting interest as readily available, non-toxic, and tailorable carbon-based nanomaterials. One of the most fascinating features of carbon nanocolloids is their luminescence, the origin of which remains a source of dispute. The lack of understanding of the optical properties of carbon nanocolloids hampers their use in technological, environmental, and biomedical processes. Here, we review the current knowledge of excited states in carbon nanocolloids and related properties, inviting researchers to embrace the complexity of carbon nanocolloids. We point to the fundamental problems associated with their structure, photophysics, and photochemistry and highlight multiple directions of current and future research of this exciting class of nanomaterials.Fil: Ragazzon, Giulio. Università degli Studi di Trieste; ItaliaFil: Cadranel, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Ushakova, Elena V.. City University of Hong Kong; ChinaFil: Wang, Yichun. University of Michigan; Estados UnidosFil: Guldi, Dirk. Universitat Erlangen-Nuremberg; AlemaniaFil: Rogach, Andrey L.. City University of Hong Kong; ChinaFil: Kotov, Nicholas A.. University of Michigan; Estados UnidosFil: Prato, Maurizio. Università degli Studi di Trieste; Itali
Interplay between Auger and ionization processes in nanocrystal quantum dots
Full text linkWe study the interplay between Auger effects and ionization processes in the limit of strong electronic confinement in core/shell CdSe/ZnS semiconductor nanocrystal quantum dots. Spectrally resolved fluorescence decay measurements reveal a monotonic increase of the photoluminescence decay rate on excitation density. Our results suggest that Auger recombination accelerates ionization processes that lead to the occupation of dark, nonemissive nanocrystal states. A model is proposed in the quantized Auger regime describing these experimental observations and providing an estimate of the Auger assisted ionization rates
Efficient light harvesting in hybrid CdTe nanocrystal/bulk GaAs p-i-n photovoltaic devices
No full textA hybrid colloidal CdTe nanocrystal/bulk GaAs p-i-n heterostructure is demonstrated to have potential for highly efficient light harvesting photovoltaic devices. An array of rectangular channels is fabricated on the surface of the GaAs heterostructure penetrating through its active layer and subsequently filled with water soluble CdTe nanocrystals emitting in the near infrared. Photogenerated carriers in the highly absorbing colloidal nanocrystals are efficiently transferred by means of nonradiative energy transfer to the patterned heterostructure possessing high carrier mobility and converted to electrical current. A threefold enhancement of both photocurrent and monochromatic power conversion efficiency has been achieved.<br/
Mechanisms underlying toxicity induced by CdTe quantum dots determined in an invertebrate model organism
No full textA systematic and thorough quantitative analysis of the in vivo effects of inorganic nanoparticles is extremely important for the design of functional nanomaterials for diagnostic and therapeutic applications, better understanding of their non-specificity toward tissues and cell types, and for assessments of their toxicity. This study was undertaken to examine the impact of CdTe quantum dots (QDs) on an invertebrate freshwater model organism, Hydra vulgaris, for assessment of long term toxicity effects. The continuous exposure of living polyps to sub-lethal doses of QDs caused time and dose dependent morphological damages more severe than Cd2+ ions at the same concentrations, impaired both reproductive and regenerative capability, activated biochemical and molecular responses. Of remarkable interest, low QD doses, apparently not effective, caused early changes in the expression of general stress responsive and apoptotic genes. The occurrence of subtle genetic variations, in the absence of morphological damages, indicates the importance of genotoxicity studies for nanoparticle risk assessment. The versatility in morphological, cellular, biochemical and molecular responses renders Hydra a perfect model system for high-throughput screening of toxicological and ecotoxicological impact of nanomaterials on human and environmental health
Integrated Plasmonic Infrared Photodetector Based on Colloidal HgTe Quantum Dots
No full textThis paper presents a 2300 nm wavelength photodetector which comprises a spin-deposited colloidal HgTe quantum dot (QD) film on a metal-insulator-metal (MIM) plasmonic waveguide. This photodetector is an integrated device based on the complementary metal-oxide-semiconductor compatible silicon-on-insulator platform. The device employs input and output silicon waveguide grating couplers, and HgTe QDs are used as the infrared photosensing material. Infrared light is coupled to the strongly confined MIM waveguide mode, which shrinks the device footprint and improves the light detection efficiency simultaneously. A room temperature responsivity of 23 mA W−1 and a noise-equivalent power of 8.7 × 10−11 W Hz−1/2 at 2300 nm wavelength are achieved by the photodetector at 2.14 W mm−2 (measured at the input to the plasmonic waveguide) with a device footprint of 15 µm × 0.35 µm. The light intensity–dependent photocurrent, the current noise spectral density, and the 3 dB operation bandwidth are all characterized. The charge transfer properties of the organic HgTe QD films are further analyzed based on field effect transistor measurements
Room Temperature Synthesis of HgTe Quantum Dots in an Aprotic Solvent Realizing High Photoluminescence Quantum Yields in the Infrared
No full textA computer controlled, automated synthesis method has been used to grow HgTe quantum dots (QDs) entirely at room temperature, using an aprotic solvent, dimethyl sulfoxide. The growth is carried out with small iterative additions of the Te precursor, which allows frequent sampling of the products to assess the growth trajectory in terms of the relationship between the QD concentration and QD diameters as the reaction proceeds. As such, this approach is a useful tool to develop a detailed understanding of the growth process and to work toward optimizing the reaction conditions in terms of the quality of the resulting QDs. HgTe QDs with emission spectra ranging up to 3000 nm and with photoluminescence quantum yields of up to 17% at 2070 nm have been produced by this method. Although coupling of the exciton to ligand vibrations is inevitable in this energy range, attention to the growth conditions and QD quality can influence the detailed coupling mechanisms, with fewer carrier traps reducing the extent of polaron mediated coupling. The influence of reaction conditions such as ligand-to-cation ratios and rate of Te precursor addition upon the onset of QD aggregation has been also examined. The method is readily up-scalable and has been employed to produce HgTe QD materials for infrared photodetectors
Investigation of the Exchange Kinetics and Surface Recovery of CdxHg1-xTe Quantum Dots during Cation Exchange Using a Microfluidic Flow Reactor
No full textDetailed analyses of coupled photoluminescence, emission lifetime, and absorption measurements have been made on the products of cation exchange reactions between CdTe nanocrystals and Hg2+ salt/ligand solutions in a microfluidic flow reactor and capillary measurement cell to probe the reaction kinetics over the seconds to hours time scale and to establish the influence of the reaction conditions on the spatial distribution of the mixed cations within the resulting CdxHg1–xTe colloidal quantum dots. The establishment of the evolution of the radiative and nonradiative rates allowed the recovery of the emission quantum yield in CdxHg1–xTe quantum dots to be quantified to almost 50% and the necessary time scales to be determined for each set of reaction conditions. The reaction kinetics showed clear indication of a fast surface exchange process followed by a slower internal rearrangement of the cation distribution
Mercury Telluride Quantum Dot Based Phototransistor Enabling High Sensitivity Room Temperature Photodetection at 2000 Nanometers
No full textNear-to-mid-infrared photodetection technologies could be widely deployed to advance the infrastructures of surveillance, environmental monitoring, and manufacturing, if the detection devices are low-cost, in compact format, and with high performance. For such application requirements, colloidal quantum dot (QD) based photodetectors stand out as particularly promising due to the solution processability and ease of integration with silicon technologies; unfortunately, the detectivity of the QD photodetectors toward longer wavelengths has so far been low. Here we overcome this performance bottleneck through synergistic efforts between synthetic chemistry and device engineering. First, we developed a fully automated aprotic solvent, gas-injection synthesis method that allows scalable fabrication of large sized HgTe QDs with high quality, exhibiting a record high photoluminescence quantum yield of 17% at the photoluminescence peak close to 2.1 μm. Second, through gating a phototransistor structure we demonstrate room-temperature device response to reach >2 × 1010 cm Hz1/2 W–1 (at 2 kHz modulation frequency) specific detectivity beyond the 2 μm wavelength range, which is comparable to commercial epitaxial-grown photodetectors. To demonstrate the practical application of the QD phototransistor, we incorporated the device in a carbon monoxide gas sensing system and demonstrated reliable measurement of gas concentration. This work represents an important step forward in commercializing QD-based infrared detection technologies
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