ANGEWANDTE CHEMIE, Issue 17 2010
Xian Guo
Ganz einfach lassen sich Filme aus Graphen- und Quantenpunkt(QD)-Schichten aus wässrigen Lösungen auf transparenten leitfähigen Indiumzinnoxid(ITO)-Substraten aufbringen. Graphen eignet sich dank seiner Struktur und günstigen Austrittsarbeit gut für die Sammlung und Übertragung durch Licht erzeugter Ladungen auf die Elektrode; als Resultat erhält man ein hocheffizientes Photovoltaikelement (siehe Bild; IPCE=Photostromeffizienz, SWNT=einwandige Kohlenstoffnanoröhre). [source]

Quantum Dot,Polymer Composites for Displays: Inkjet-Printed Quantum Dot,Polymer Composites for Full-Color AC-Driven Displays (Adv. Mater.

ADVANCED MATERIALS, Issue 21 2009
21/2009)
Vladimir Bulovic and co-workers show on p. 2151 that colloidal quantum dot-polymer composites are used for inkjet print-deposition of high resolution, patterned, multicolored thin films in the fabrication of robust, bright, full-color AC-driven displays. The inside cover shows an inkjet nozzle with a quantum dot solution and a completed device on a flexible substrate under UV illumination, with inset examples of the achievable high resolution and patterning. [source]

Inkjet-Printed Quantum Dot,Polymer Composites for Full-Color AC-Driven Displays

ADVANCED MATERIALS, Issue 21 2009
Vanessa Wood
Colloidal quantum dot,polymer composites are used for inkjet-print deposition of high-resolution, patterned, multicolored thin films in the fabrication of robust, bright, full-color AC-driven displays. The left panel shows a photograph of a complete device on a flexible substrate under UV illumination, while the right panel shows photographs of the electroluminescence of red, green, and blue 80 mm2 pixels. [source]

Photoluminescence Quenching Control in Quantum Dot,Carbon Nanotube Composite Colloids Using a Silica-Shell Spacer,

ADVANCED MATERIALS, Issue 4 2006
M. Grzelczak
One-dimensional nanocomposite colloids are prepared by means of electrostatic self-assembly of CdTe nanocrystals on both carbon nanotubes (CNTs) and silica-coated CNTs (see Figure). The dense coverage of these linear nanoparticle assemblies minimizes the spacing between the nanocrystals, thereby facilitating efficient electronic and energy transfer along the nanotubes. [source]

Quantum Dot-based Energy Transfer: Perspectives and Potential for Applications in Photodynamic Therapy

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2006
Anna C. S. Samia
ABSTRACT Quantum dots have emerged as an important class of material that offers great promise to a diverse range of applications ranging from energy conversion to biomedicine. Here, we review the potential of using quantum dots and quantum dot conjugates as sensitizers for photodynamic therapy (PDT). The photophysics of singlet oxygen generation in relation to quantum dot-based energy transfer is discussed and the possibility of using quantum dots as photosensitizer in PDT is assessed, including their current limitations to applications in biological systems. The biggest advantage of quantum dots over molecular photosensitizers that comes into perspective is their tunable optical properties and surface chemistries. Recent developments in the preparation and photophysical characterization of quantum dot energy transfer processes are also presented in this review, to provide insights on the future direction of quantum dot-based photosensitization studies from the viewpoint of our ongoing research. [source]

Binding energy of a hydrogenic donor impurity in an ellipsoidal finite-potential quantum dot

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007
M. Barati
Abstract In this article, the binding energy of a hydrogenic donor impurity in weakly oblate Ellipsoidal Quantum Dot (EQD), using the perturbation theory within the framework of effective mass approximation, is investigated. In this regard, the binding energies of 1S, 2S and 2P0 states for GaAs/AlxGa1,xAs structures, as functions of the dot radius and ellipticity constant, are calculated. Results show that variations of binding energies of a hydrogenic impurity with respect to the dot dimension are similar to the case of Spherical Quantum Dot (SQD). In addition, it is found that the binding energy is inversely proportional to the ellipticity constant. This behavior is more profound for 2P0 state, where, depending on the dot's dimensionality and ellipticity, the binding energy may become negative. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Living Yeast Cells as a Controllable Biosynthesizer for Fluorescent Quantum Dots

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Ran Cui
Abstract There are currently some problems in the field of chemical synthesis, such as environmental impact, energy loss, and safety, that need to be tackled urgently. An interdisciplinary approach, based on different backgrounds, may succeed in solving these problems. Organisms can be chosen as potential platforms for materials fabrication, since biosystems are natural and highly efficient. Here, an example of how to solve some of these chemical problems through biology, namely, through a novel biological strategy of coupling intracellular irrelated biochemical reactions for controllable synthesis of multicolor CdSe quantum dots (QDs) using living yeast cells as a biosynthesizer, is demonstrated. The unique fluorescence properties of CdSe QDs can be utilized to directly and visually judge the biosynthesis phase to fully demonstrate this strategy. By such a method, CdSe QDs, emitting at a variety of single fluorescence wavelengths, can be intracellularly, controllably synthesized at just 30°C instead of at 300°C with combustible, explosive, and toxic organic reagents. This green biosynthetic route is a novel strategy of coupling, with biochemical reactions taking place irrelatedly, both in time and space. It involves a remarkable decrease in reaction temperature, from around 300 °C to 30 °C and excellent color controllability of CdSe photoluminescence. It is well known that to control the size of nanocrystals is a mojor challenge in the biosynthesis of high-quality nanomaterials. The present work demonstrates clearly that biological systems can be creatively utilized to realize controllable unnatural biosynthesis that normally does not exist, offering new insights for sustainable chemistry. [source]

Plasma Nanoparticle Synthesis: Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Mater.
The cover picture shows a view into the plasma zone of a microwave plasma reactor, which is used to synthesize macroscopic quantities of single crystalline silicon nanoparticles with a very high production rate. These nanoparticles exhibit bright luminescence across the visible spectrum. On page 696, the authors report that the emission of such silicon nanoparticles can be tuned by changing their size and surface chemistry. [source]

Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Anoop Gupta
Abstract Aiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, a novel approach to produce luminescent silicon nanoparticles (Si-NPs) is developed. Single crystalline Si-NPs are synthesized by pyrolysis of silane (SiH4) in a microwave plasma reactor at very high production rates (0.1,10,g,h,1). The emission wavelength of the Si-NPs is controlled by etching them in a mixture of hydrofluoric acid and nitric acid. Emission across the entire visible spectrum is obtained by varying the etching time. It is observed that the air oxidation of the etched Si-NPs profoundly affects their optical properties, and causes their emission to blue-shift and diminish in intensity with time. Modification of the silicon surface by UV-induced hydrosilylation also causes a shift in the spectrum. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si-NPs. In addition, the amount of shift depends on the type of organic ligand on the silicon surface and the UV exposure time. The surface modification of Si-NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si-NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way towards their commercialization. [source]

Photosensitization of TiO2 Nanostructures with CdS Quantum Dots: Particulate versus Tubular Support Architectures

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
David R. Baker
Abstract TiO2 nanotube arrays and particulate films are modified with CdS quantum dots with an aim to tune the response of the photoelectrochemical cell in the visible region. The method of successive ionic layer adsorption and reaction facilitates size control of CdS quantum dots. These CdS nanocrystals, upon excitation with visible light, inject electrons into the TiO2 nanotubes and particles and thus enable their use as photosensitive electrodes. Maximum incident photon to charge carrier efficiency (IPCE) values of 55% and 26% are observed for CdS sensitized TiO2 nanotube and nanoparticulate architectures respectively. The nearly doubling of IPCE observed with the TiO2 nanotube architecture is attributed to the increased efficiency of charge separation and transport of electrons. [source]

Hydrothermal Route for Cutting Graphene Sheets into Blue-Luminescent Graphene Quantum Dots

ADVANCED MATERIALS, Issue 6 2010
Dengyu Pan
Water-soluble graphene quantum dots (GQDs, ca. 10 nm in diameter) that exhibit bright blue photoluminescence (PL) are prepared by hydrothermal (chemical) cutting of oxidized graphene sheets (see figure). The mechanisms of the cutting and luminescence are discussed. This discovery of PL of GQDs may extend the range of application of graphene-based materials to optoelectronics and biological labeling. [source]

Electroluminescent Cu-doped CdS Quantum Dots

ADVANCED MATERIALS, Issue 28 2009
Jan W. Stouwdam
Incorporating Cu-doped CdS quantum dots into a polymer host produces efficient light-emitting diodes. The Cu dopant creates a trap level that aligns with the valence band of the host, enabling the direct injection of holes into the quantum dots, which act as emitters. At low current densities, the luminance efficiency maximizes at 9,cd A,1, providing an external quantum efficiency of 5%. [source]

Quantum Dots: Self-Assembled Quantum Dot Molecules (Adv. Mater.

ADVANCED MATERIALS, Issue 25-26 2009
26/2009)
The cover shows a 2D photoluminescence intensity map from a self-assembled lateral quantum dot molecule in an electric field applied along the molecular axis. The coupling of the two quantum dots is evidenced by intricate spectral line anticrossings, indicated by dotted lines, as reported in the review by Lijuan Wang and co-workers on p. 2601. A 3D AFM image of a lateral quantum dot molecule overlapped with the ground-state electron wavefunction is shown in the inset. [source]

Highly Efficient Green-Light-Emitting Diodes Based on CdSe@ZnS Quantum Dots with a Chemical-Composition Gradient

ADVANCED MATERIALS, Issue 17 2009
Wan Ki Bae
Highly efficient green-light-emitting diodes (LEDs) based on CdSe@ZnS quantum dots (QDs) with a chemical-composition gradient are demonstrated. Through the moderate control of QD coverage in multilayered devices, excellent device performance has been achieved. The color-saturated green-light emission (see figure for Commission Internationale de l'Eclairage (CIE) co-ordinates) is mainly from the QD layers (more than 99% of total emission). [source]

Template-Guided Self-Assembly of Colloidal Quantum Dots Using Plasma Lithography

ADVANCED MATERIALS, Issue 12 2009
Michael Junkin
A plasma lithography technique is developed to guide the self-assembly of colloidal quantum dots and other nanoscale building blocks, including fluorescent nanoparticles, gold nanoparticles, salts, and proteins. Plasma lithography enables the self-assembly of nanoscale materials onto soft and polymeric substrates with feature sizes as small as 100,nm. [source]

Water-Soluble Silicon Quantum Dots with Wavelength-Tunable Photoluminescence

ADVANCED MATERIALS, Issue 6 2009
Zhenhui Kang
H-terminated Si quantum dots (Si QDs) with 3,nm diameter are converted to water-soluble uniform-sized Si QDs after controlled oxidation in an EtOH/H2O2 solution. These dots present Si/SiOxHy core/shell nanostructures, and can be finely tuned to emit light in seven different colors due to the quantum size effect in the Si cores, exhibiting excellent photocatalytic activity in the visible range. [source]

Aqueous Near-Infrared Fluorescent Composites Based on Apoferritin-Encapsulated PbS Quantum Dots,

ADVANCED MATERIALS, Issue 19 2008
Barbara Hennequin
PbS nanocrystals entrapped in the hollow core of apoferritin protein cages are synthesized in aqueous solution by both reassembly and nanoreactor routes. In both cases, apoferritin limits the size of the PbS quantum dot it can encapsulate to 8 nm and provides a route to the creation of a stable near-infrared fluorescent composite. [source]

Hybrid Light-Emitting Diodes from Microcontact-Printing Double-Transfer of Colloidal Semiconductor CdSe/ZnS Quantum Dots onto Organic Layers,

ADVANCED MATERIALS, Issue 10 2008
Aurora Rizzo
A novel dry deposition approach is developed to transfer arrays of colloidal quantum dots onto organic thin films, as illustrated in the figure. A red light-emitting device combining inorganic and organic components is fabricated based on this simple transfer protocol. [source]

GdIII -Functionalized Fluorescent Quantum Dots as Multimodal Imaging Probes,

ADVANCED MATERIALS, Issue 21 2006
H. Yang
Multimodal probes of GdIII -functionalized silica-coated CdS:Mn/ZnS quantum dots (see figure) that exhibit yellow fluorescence and strong paramagnetism are reported. High magnetic resonance imaging (MRI) contrast is exhibited by these quantum dots. These properties make for a probe that can operate in multiple modes, which is highly desirable for in,vivo bioimaging applications. [source]

Fabrication of Stable Low-Density Silica Aerogels Containing Luminescent ZnS Capped CdSe Quantum Dots,

ADVANCED MATERIALS, Issue 15 2006
L. Sorensen
Luminescent CdSe quantum dots of 2.5 and 6.0,nm dimension have been incorporated into a low-density silica aerogels matrix. The aerogels are formed from the supercritical CO2 extraction of an alcogel containing quantum dots surface passivated with 3-aminopropyltriethoxysilane. The resulting aerogels (see figure and cover) are low scattering and show intense, stable luminescence. [source]

Templated and Hierarchical Assembly of CdSe/ZnS Quantum Dots,

ADVANCED MATERIALS, Issue 15 2004
Y. Babayan
CdSe/ZnS nanocrystals have been assembled into mesoscale structures (see Figure). Templates with dimensions down to 100,nm are generated via phase-shifting photolithography using composite poly(dimethylsiloxane) masks. Upon removal of the template, the CdSe/ZnS structures are found to exhibit hierarchical order over square nanometers (self-assembly of nanocrystals), square micrometers (template shape), and square centimeters (arrays of template pattern). [source]

2nd International Conference on Semiconductor Quantum Dots (QD 2002) in Tokyo, Japan, 30 September,3 October 2002

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
R. Heitz
No abstract is available for this article. [source]

Dynamical symmetries and quantum transport through nanostructures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2007
*Article first published online: 18 JUN 200, M. N. Kiselev
Abstract We discuss the manifestation of dynamical symmetries in quantum transport through nanostructures. The dynamical symmetry SO (4) manifested in the singlet-triplet excitations is shown to be responsible for several exotic effects in nano-devices: non-equilibrium Kondo effect in T-shape Double Quantum Dots, phonon-induced Kondo effect in transition-metal-organic complexes, Kondo shuttling in Nano-Electromechanical Single Electron Transistor. We consider the interplay between charge U (1) and spin SU (2) fluctuations in the vicinity of Stoner instability point and a non-monotonic behavior of a Tunneling Density of States in metallic quantum dots. The experiments showing important role of dynamical symmetries in nanostructures are briefly reviewed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nonlinear piezoelectric properties of GaN quantum dots nucleated at the edge of threading dislocations

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
ewski
Abstract It was observed experimentally by Rouviere et al. that GaN/AlN Quantum Dots (QDs) nucleate at the edge of threading dislocations (Appl. Phys. Lett. 75, 2632 (1999) [1]). The preferred nucleation of QDs in this way is generally assumed to be due to the influence of the stress/strain field around the dislocation core, which in turn, gives the chemical and geometric conditions for nucleation of the QDs. We solve the finite element problem for QDs situated at the edge of threading dislocations where different lattice parameters, piezoelectric and spontaneous polarisation coefficients are assumed for the QD and its matrix. By solving the elastic and electric equilibrium problems we obtain both the residual stress and electric fields. The computational scheme employed here was obtained by linking two previous finite element algorithms described inreferences (P. D,u,ewski et al., Comput. Mater. Sci. 29, 379 (2004) [2]) and (G. Jurczak et al., phys. stat. sol. (c) 2, 972 (2005) and S.P. ,epkowski et al., Phys. Rev. B 73, 245201 (2005) [3, 4], respectively). This approach allows us to get a deeper physical insight into the mechanics and electrical properties of QDs and ultimately determine the efficiency of light emission from these objects. [source]

Proceedings of the 2nd International Conference on Semiconductor Quantum Dots (QD2002)

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003
Y. Arakawa
The International Conference on Semiconductor Quantum Dots (QD2002) was held at Komaba Campus of University of Tokyo, Japan, from Monday, 30 September, through Thursday, 3 October 2002. The purpose of the QD2002 was to bring together scientists from different fields of physics and chemistry to discuss topics of common interest and significance in such growing areas including semiconductor quantum dots, nanocrystals, and clusters. The conference was focused on the optical and electronic properties of three-dimensionally confined nanostructures grown both by epitaxial methods and chemical preparation routes. The QD2002 was the second in a series which started in Munich, Germany, in 2000. The scope of the QD2002 covered various research fields including novel fabrication techniques of nanoheterostructures, electronic structures, optical properties, electronic properties/single electron tunneling processes, molecular dots, nanocrystals, device applications such as lasers and memories, coherent processes/quantum computations, and biomedical applications. [source]

Fluorescent Quantum Dots as Artificial Antennas for Enhanced Light Harvesting and Energy Transfer to Photosynthetic Reaction Centers,

ANGEWANDTE CHEMIE, Issue 40 2010
Prof. Igor Nabiev
Bio-Nano: Quantenpunkte (QDs) können mit photosynthetischen Reaktionszentren (RCs) so markiert werden (siehe Bild), dass der FRET vom QD zum RC eine annähernde Verdreifachung der Geschwindigkeit, in der Excitonen im RC erzeugt werden, zur Folge hat. Es werden sogar noch größere Verstärkungen vorhergesagt, was dafür spricht, dass solche Komplexe die Effizienz der Photosynthese erheblich steigern könnten. [source]

Circularly Polarized Luminescent CdS Quantum Dots Prepared in a Protein Nanocage,

ANGEWANDTE CHEMIE, Issue 39 2010
Dr. Masanobu Naito
In Ferritin (einem ,-Helix-reichen, rhombischen, dodekaedrischen Protein) hergestellte CdS-Quantenpunkte (CdS-QDs) zeigen linkshändige circular polarisierte Lumineszenz (CPL) aus einem direkten Übergang und aus Oberflächenstörstellen, die relativ große Anisotropiefaktoren aufweisen. Bei Laser-Photoätzen findet man mit abnehmender QD-Größe eine Blauverschiebung der PL/CPL-Banden von Oberflächenstörstellen, und die Bande des direkten Übergangs verschwindet. [source]

Glucose-Mediated Assembly of Phenylboronic Acid Modified CdTe/ZnTe/ZnS Quantum Dots for Intracellular Glucose Probing,

ANGEWANDTE CHEMIE, Issue 37 2010
Weitai Wu Dr.
Effektive Punkte: Die Emission von Quantenpunkten (QDs) wird durch reversibles kovalentes Binden von Glucose an Boronsäuren auf der QD-Oberfläche moduliert (siehe Bild). Die hoch selektive ratiometrische Sonde sprach auf Glucose im physiologisch wichtigen Konzentrationsbereich 0.4,20.0,mM an und wurde genutzt, um den Glucosegehalt in lebenden Zellen zu bestimmen. [source]

Water-Soluble Fluorescent Carbon Quantum Dots and Photocatalyst Design,

ANGEWANDTE CHEMIE, Issue 26 2010
Haitao Li
Größenkontrolliert: Eine einstufige Alkalimetall-unterstützte elektrochemische Methode zur Herstellung von Kohlenstoff-Quantenpunkten (CQDs) mit größenabhängiger Lumineszenz wird vorgestellt (siehe Bild). Die Upconversion-Lumineszenz der CQDs könnte als Grundlage für die Entwicklung neuer Photokatalysatoren dienen. [source]

Self-Controlled Monofunctionalization of Quantum Dots for Multiplexed Protein Tracking in Live Cells,

ANGEWANDTE CHEMIE, Issue 24 2010
Changjiang You Dr.
Die Funktionalisierung von Quantenpunkten (QDs) gelang, wenn die Oberflächendichte an funktionellen Gruppen durch elektrostatische Abstoßung eingestellt wurde. Solche QDs konjugierten in vitro und in lebenden Zellen durch Selbstorganisation mit His-markierten Proteinen und konnten dann ohne weitere Fraktionierung zur Zweifarbenbildgebung von Zelloberflächenrezeptoren eingesetzt werden (siehe Schema). [source]