Cadmium Telluride Quantum Dots

Cadmium Telluride Quantum Dots

Among nanomaterials, CdTe holds special technological importance as the only known II-VI material that can form conventional p-n junctions. This makes CdTe very important for the dev

Author: John Donegan

Publisher: CRC Press

ISBN: 9789814316095

Category: Science

Page: 248

View: 192

In the last two decades, semiconductor quantum dots—small colloidal nanoparticles—have garnered a great deal of scientific interest because of their unique properties. Among nanomaterials, CdTe holds special technological importance as the only known II–VI material that can form conventional p–n junctions. This makes CdTe very important for the development of novel optoelectronic devices such as light-emitting diodes, solar cells, and lasers. Moreover, the demand for water-compatible light emitters and the most common biological buffers give CdTe quantum dots fields a veritable edge in biolabeling and bioimaging. Cadmium Telluride Quantum Dots: Advances and Applications focuses on CdTe quantum dots and addresses their synthesis, assembly, optical properties, and applications in biology and medicine. It makes for a very informative reading for anyone involved in nanotechnology and will also benefit those scientists who are looking for a comprehensive account on the current state of quantum dot–related research.
Categories: Science

The Anticoagulant Properties of Cadmium Telluride Quantum Dots

The Anticoagulant Properties of Cadmium Telluride Quantum Dots

Abstract: The size‐dependent optical properties of quantum dots (QDs) are frequently exploited for use in medical imaging and labelling applications.

Author:

Publisher:

ISBN: OCLC:1052076459

Category:

Page:

View: 474

Abstract: The size‐dependent optical properties of quantum dots (QDs) are frequently exploited for use in medical imaging and labelling applications. Similarly, presented here, they also elicit profound size‐dependent anticoagulant properties. Cadmium telluride quantum dot (QDs) (3.2nm) were shown to have a dramatic anticoagulant effect centred on around the intrinsic coagulation pathway, compared to their 3.6 nm counterparts. Several clinically relevant diagnostic tests were carried out over a concentration range of the QDs and demonstrated that the 3.2 nm QDs elicited their response on the intrinsic pathway as a whole, yet the activity of the individual intrinsic coagulation factors was not affected. The mechanism appears also to be strongly influenced by the concentration of calcium ions and not cadmium ions leached from the QDs. Static and shear‐based primary haemostasis assays were also carried out, demonstrating a profound anticoagulant effect which was independent of platelets and phospholipids. The data presented here suggest that the physical–chemical properties of the QDs may have a role in the modulation of haemostasis and the coagulation cascade, in a yet not fully understood mechanism. This study has implications for the use of similar QDs as diagnostic or therapeutic tools in vivo, and for the occupational health and safety of those working with such materials. Abstract : Cadmium telluride quantum dots (3.2nm) exhibit a profound anticoagulant response centred on the intrinsic pathway. The mechanism appears also to be strongly influenced by the concentration of calcium ions and not the presence of cadmium ions.
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CdTe Quantum Dot Fluorescence Thermometry of Rolling Bearing

CdTe Quantum Dot Fluorescence Thermometry of Rolling Bearing

Temperature is one of the most important parameters affecting the service life and performance of a rolling element bearing component.

Author: Ke Yan

Publisher:

ISBN: OCLC:1154307562

Category: Science

Page:

View: 434

Temperature is one of the most important parameters affecting the service life and performance of a rolling element bearing component. In this paper, a nonintrusive method is developed to monitor the temperature variation of the inner raceway during bearing operation utilizing CdTe quantum dots as the temperature sensors. The CdTe quantum dots were synthesized and were used in constructing a sensor film by means of layer-by-layer electrostatic self-assembly method on an ultrathin glass slice. The peak wavelength shift of the fluorescence spectrum of the sensor film shows a linear and reversible relationship with temperature, and it is used to sense the temperature of the inner raceway. The resolution of the CdTe optothermal sensor is determined to be 0.14 nm/°C. The temperature measurement of rolling element bearing was conducted on a bearing test rig incorporated with an optical fiber fluorescence spectrum detecting system. To verify the accuracy of the temperature obtained by quantum dots sensor film, a thermocouple was used to test the temperature of the inner raceway right before and after the operation. Results show that the temperature obtained by the CdTe quantum dots film sensor is consistent with that by the thermocouple, with an error typically below 10% or smaller.
Categories: Science

Effect of Ascorbic Acid on CdTe Quantum Dots and Investigation of Different Chemical Sensors on CdTeHg Quantum Dots

Effect of Ascorbic Acid on CdTe Quantum Dots and Investigation of Different Chemical Sensors on CdTeHg Quantum Dots

The objective of my thesis is to investigate the effect of ascorbic acid on CdTe quantum dots, which is an antioxidant.

Author: Yamini Chitrala

Publisher:

ISBN: OCLC:822585334

Category:

Page:

View: 483

The objective of my thesis is to investigate the effect of ascorbic acid on CdTe quantum dots, which is an antioxidant. It was observed that the quantum dots recovered their luminescence intensity after the interaction of the ascorbic acid, where the intensity was quenched by the photosensitizer. The luminescence intensity increased gradually for 0.1mM- 0.5mM concentration of ascorbic acid and remained stable with higher concentrations of the antioxidant. Also, it was observed that under some reaction conditions like pH, temperature and concentration, ascorbic acid had a great influence on its photoluminescence. In the second part of the research project, I studied the influence of different chemicals on the luminescence intensity of CdTeHg (NIR) quantum dots. The interaction of certain chemical agents like bleach, dimethyl methyl phosphonate (DMMP), with these quantum dots had quenching effect on the luminescence intensity, whereas with the common background chemicals like ethanol could not quench the luminescence intensity of the quantum dots. Studies were carried out to find out the reasons behind this quenching and whether it is the singlet oxygen generated by these chemicals.
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Poly oxonorbornene coated CdTe Quantum Dots as Antibacterial Agents

Poly oxonorbornene  coated CdTe Quantum Dots as Antibacterial Agents

The increasing prevalence of multidrug resistant bacteria is a global human health challenge.

Author: Denise N. Williams

Publisher:

ISBN: OCLC:1163850298

Category:

Page:

View: 761

The increasing prevalence of multidrug resistant bacteria is a global human health challenge. Unfortunately, the development of traditional small molecules against drug resistant bacterial strains has been unable to fill the drug pipeline with treatments ready for clinical use. For this reason scientists are taking new approaches to antibacterial drug design, including the one pursued in our research: combining antimicrobial polymers and antibacterial nanoparticles into conjugates that could lead to synergistic activity against bacterial growth. The polymers we use are a series of synthetic mimics of antimicrobial peptides based on poly(oxanorbornene)s (PONs) which alone have selective, tunable, broad-spectrum activity against bacteria -including against some bacterial strains for which we are observing increasing cases of drug resistance. The nanoparticles in this study are 2.4eV bandgap CdTe quantum dots (QDs) which have optimal light-activated antibacterial activity compared to other QD materials and sizes, and also have demonstrated activity against some drug-resistant bacterial strains. We conjugated PONs of varying amine/alkyl ratios to CdTe QDs, and then compared the conjugatesu2019 activity against Escherichia coli and human red blood cells to that of free PONs and CdTe QDs. The conjugates -particularly those of higher amine density- had significantly lower minimum inhibitory concentrations than the free PONs or QDs. Equally important, the conjugates had decreased hemolytic activity compared to free PONs, leading to higher therapeutic indexes against E. coli. These outcomes highlight the potential for higher (and therefore more effective) concentrations of PONs to be used in antibacterial treatments while in conjugate form, with less concern for off-target effects.
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Probing Electronic and Vibronic States in CdTe Self assembled Quantum Dots and CdS Nanowires Using Room Temperature Resonant Raman Scattering

Probing Electronic and Vibronic States in CdTe Self assembled Quantum Dots and CdS Nanowires Using Room Temperature Resonant Raman Scattering

This is consistent with the interdiffusion of Zn and Cd which makes the confining potential shallower and the average diameter of the quantum dots larger.

Author:

Publisher:

ISBN: OCLC:76833110

Category:

Page: 141

View: 303

Resonant Raman scattering (RRS) is a sensitive means to probe electronic and vibrational states in semiconductor nanostructures, even when such states are not accessible either through photoluminescence or transport techniques. In this thesis, resonant Raman scattering is used to probe the electronic and vibronic states of CdTe/ZnTe quantum dots and CdS nanowires at room temperature. In case of the CdTe/ZnTe quantum dots, the sensitivity of the ZnTe longitudinal optical phonon (LO) resonance is used to probe the excited state in the CdTe quantum dots. In addition, this technique is utilized to study the energy shifts due to post growth rapid thermal annealing. Due to annealing, both the ground and excited state energies of the quantum dots move to a higher value. This is consistent with the interdiffusion of Zn and Cd which makes the confining potential shallower and the average diameter of the quantum dots larger. In the case of the CdS nanowires, the 1-LO and 2-LO resonance is readily observed above the broad photoluminescence (PL) background. The lineshape of the integrated intensity of the 1-LO and 2-LO resembles the PL spectrum suggesting that the RRS probes the electronic states in both the ensemble and in single nanowires. In addition, the energy separation between the peaks of the 1-LO and 2-LO resonance of the ensemble CdS nanowires was found to be 34 meV which is comparable to the 37 meV value measured in bulk samples. We also show that spatially-resolved Raman scattering at resonance probes the structural uniformity in a single CdS nanowire and is able to identify the layers of the CdTe/ZnTe quantum dots sample. We found RRS intensity of single CdS nanowire strongly depends on the morphology of the wire. In conclusion, we have shown that RRS at room temperature is a sensitive and nondestructive tool to probe electronic and vibration sates as well as structural uniformity in semiconductor nanostructures.
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Evaluation of CdTe CdS ZnS Core shell shell Quantum Dot Toxicity on Three dimensional Spheroid Cultures1

Evaluation of CdTe CdS ZnS Core shell shell Quantum Dot Toxicity on Three dimensional Spheroid Cultures1

Abstract : In this work, three-dimensional (3D) spheroid cultures of human adipose-derived mesenchymal stem cells (hAD-MSCs), with tissue-mimetic morphology through well developed cell–cell and cell–matrix interactions and distinct ...

Author:

Publisher:

ISBN: OCLC:1051803999

Category:

Page:

View: 187

Abstract : Three-dimensional hAD-MSCs spheroid cultures, with the ability to resemble closely in vivo tissue structures, were assessed for evaluation of dose-dependent cytotoxicity effects of CdTe/CdS/ZnS quantum dots. Abstract : In this work, three-dimensional (3D) spheroid cultures of human adipose-derived mesenchymal stem cells (hAD-MSCs), with tissue-mimetic morphology through well developed cell–cell and cell–matrix interactions and distinct diffusion/transport characteristics, were assessed for dose-dependent toxic effects of red-emitting CdTe/CdS/ZnS quantum dots (Qdots). Morphological investigations and time-resolved microscopy analysis in addition to cell metabolic activity studies revealed that 3D spheroid cultures are more resistant to Qdot-induced cytotoxicity in comparison to conventional 2D cultures. The obtained results suggest the presence of two distinct cell populations in 2D cultures with different sensitivity to Qdots, however that effect wasn't observed in 3D spheroids. Our investigations were aimed to improve the prediction of nanotoxicity of Qdot on tissue-level and provide the essential screening steps prior to any in vivo application. Moreover, penetration ability of highly fluorescent Qdots to densely-packed spheroids will fortify the biological application of developed Qdots in tissue-like structures.
Categories:

Nanomaterials

Nanomaterials

Improved performance Quantum dot light emitting of silicon nanowire/cadmium
telluride electrochemical cell hybrid device ... Size of CdTe quantum dots controls
the CdTe quantum dots decorated n-ZnO nanorods/p-GaN light-emitting diodes.

Author: Simona Clichici

Publisher: BoD – Books on Demand

ISBN: 9781789846164

Category: Technology & Engineering

Page: 246

View: 175

In the last decade, nanomaterials have become a double-edged sword. On one hand, nanomaterials have proven their limitless potential not only for technological applications, but also for medical ones. On the other hand, the increasing use of these nanomaterials has raised concerns regarding their safety for environmental and human health, due to their potential toxicity. The toxic effects of nanomaterials depend on their type, surface geometry, diameter, length and function. This book intends to provide a comprehensive evidence-based overview of nanomaterial toxicity, from their synthesis and characterization, environmental impact, tests to assess their toxicity in vitro and in vivo, ways to modulate their impact on living organisms, to their beneficial use in biomedical applications.
Categories: Technology & Engineering

Semiconductor Nanocrystal Quantum Dots

Semiconductor Nanocrystal Quantum Dots

Ann Rev Biomed Eng 7: 55–76 [39] Byrne SJ, Corr SA, Rakovich TY, Gunko YK,
Rakovich YP, Donegan JF, Mitchell S, Volkov Y (2006) Optimisation of the
synthesis and modification of CdTe quantum dots for enhanced live cell imaging.

Author: Andrey Rogach

Publisher: Springer Science & Business Media

ISBN: 9783211752371

Category: Technology & Engineering

Page: 372

View: 570

This is the first book to specifically focus on semiconductor nanocrystals, and address their synthesis and assembly, optical properties and spectroscopy, and potential areas of nanocrystal-based devices. The enormous potential of nanoscience to impact on industrial output is now clear. Over the next two decades, much of the science will transfer into new products and processes. One emerging area where this challenge will be very successfully met is the field of semiconductor nanocrystals. Also known as colloidal quantum dots, their unique properties have attracted much attention in the last twenty years.
Categories: Technology & Engineering

Green Metal Nanoparticles

Green Metal Nanoparticles

Ananth, D.A., Rameshkumar, A., Jeyadevi, R., Jagadeeswari, S., Nagarajan, N.,
Renganathan, R., Sivasudha, T., Antibacterial potential of rutin conjugated with
thioglycolic acid capped cadmium telluride quantum dots (TGA-CdTe QDs).

Author: Suvardhan Kanchi

Publisher: John Wiley & Sons

ISBN: 9781119418238

Category: Technology & Engineering

Page: 720

View: 893

The use of biological sources such as microbes and plants can help in synthesizing nanoparticles in a reliable and eco-friendly way. The synthesis of nanoparticles by these natural sources is characterized by processes that take place near to ambient temperature and pressures and also near neutral pH. This edited volume authored by subject specialists, provides all the latest research and builds a database of bioreduction agents to various metal nanoparticles using different precursor systems. The book also highlights the different strategies such as simplicity, cost-effectiveness, environment-friendly and easily scalable, and includes parameters for controlling the size and shape of the materials developed from the various greener methods. In order to exploit the utmost potential metal nanoparticles synthesis from the different sources such as agricultural waste, flora and fauna, food waste, microbes and biopolymer systems, it is also crucial to recognize the biochemical and molecular mechanisms of production of nanoparticles and their characterization.
Categories: Technology & Engineering

Chemosensors

Chemosensors

A new nanobiosensor for glucose based on the FRET between concanavalin A (
ConA)modified CdTe quantum dots and B-CD-modified gold nanoparticles has
been recently reported [64]. Quantum dots such as CdS, CdTe, and ZnS ...

Author: Binghe Wang

Publisher: John Wiley & Sons

ISBN: 1118019571

Category: Science

Page: 524

View: 137

A thorough, accessible, and general overview of chemosensors Providing a comprehensive overview of chemosensors—organic molecules designed to bind and sense small molecules or metal ions—and their applications, Chemosensors: Principles, Strategies, and Applications is an accessible one-stop resource for analysts, clinicians, and graduate students studying advanced chemistry and chemosensing. Chemosensors function on a molecular level, generating a signal upon binding. The book reviews their synthesis, design, and applications for detecting biological and organic molecules as well as metal ions. The text highlights applications in drug discovery and catalyses that have not been well covered elsewhere. Covering such topics as molecular recognition, detection methods, design strategies, and important biological issues, the book is broken into four sections that examine intermolecular interactions, strategies in sensor design, detection methods, and case studies in metal, saccharide, and amino acid sensing. An indispensable source of information for chemical and biomedical experts using sensors, Chemosensors includes case studies to make the material both accessible and understandable to chemists of all backgrounds.
Categories: Science

Rapid Preparation of Self assembled CdTe Quantum Dots Used for Sensing of DNA in Urine

Rapid Preparation of Self assembled CdTe Quantum Dots Used for Sensing of DNA in Urine

Abstract : In this article, the authors report a systematic study of the self-assembly of CdTe quantum dots (QDs) stabilized by mercaptosuccinic acid (MSA) at laboratory temperature (25 °C) or after thermal treatment (90 °C).

Author:

Publisher:

ISBN: OCLC:1051850510

Category:

Page:

View: 433

Abstract : In this article, the authors report a systematic study of the self-assembly of CdTe quantum dots (QDs) stabilized by mercaptosuccinic acid (MSA) at laboratory temperature (25 °C) or after thermal treatment (90 °C). Abstract : In this article, the authors report a systematic study of the self-assembly of CdTe quantum dots (QDs) stabilized by mercaptosuccinic acid (MSA) at laboratory temperature (25 °C) or after thermal treatment (90 °C). It was found that QD/MSA can be synthesized spontaneously under mild laboratory conditions (25 °C and 70 hours) without any further instrumentation or they can be treated using an increased temperature (90 °C and 8 min) to achieve the same fluorescence intensity. These QDs were used for the preparation of a fluorescent (off–on) probe based on methylene blue as a quencher for the specific determination of nucleic acid from urine. The whole process was monitored using stationary spectroscopy (absorbance and fluorescence measurement) and capillary electrophoresis (CE) with laser-induced fluorescence detection. The average size of the prepared QDs (approximately 3 nm) was determined using transmission electron microscopy and it was proven that the presented fluorescent probe combined with the CE method can be used for the sensitive determination of DNA (LOD 3 ng mL −1 ).
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Issues in Chemistry and General Chemical Research 2011 Edition

Issues in Chemistry and General Chemical Research  2011 Edition

(2010 JAN 29) Bhabha Atomic Research Center, Maharashtra: Ultrafast Charge
Carrier Relaxation and Charge Transfer Dynamics of CdTe/CdS Core-Shell
Quantum Dots as Studied by Femtosecond Transient Absorption Spectroscopy “
We ...

Author:

Publisher: ScholarlyEditions

ISBN: 9781464963292

Category: Science

Page: 6580

View: 419

Issues in Chemistry and General Chemical Research: 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Chemistry and General Chemical Research. The editors have built Issues in Chemistry and General Chemical Research: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Chemistry and General Chemical Research in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Chemistry and General Chemical Research: 2011 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Categories: Science

Comprehensive Nanoscience and Technology

Comprehensive Nanoscience and Technology

Synthesis of cadmium telluride quantum wires and the similarity of their effective
band gaps to those of equidiameter cadmium telluride quantum dots. Journal of
the American Chemical Society. 2008;130:7997–8005. Yu H, Li JB, Loomis RA, ...

Author:

Publisher: Academic Press

ISBN: 0123743966

Category: Science

Page: 2774

View: 593

From the Introduction: Nanotechnology and its underpinning sciences are progressing with unprecedented rapidity. With technical advances in a variety of nanoscale fabrication and manipulation technologies, the whole topical area is maturing into a vibrant field that is generating new scientific research and a burgeoning range of commercial applications, with an annual market already at the trillion dollar threshold. The means of fabricating and controlling matter on the nanoscale afford striking and unprecedented opportunities to exploit a variety of exotic phenomena such as quantum, nanophotonic and nanoelectromechanical effects. Moreover, researchers are elucidating new perspectives on the electronic and optical properties of matter because of the way that nanoscale materials bridge the disparate theories describing molecules and bulk matter. Surface phenomena also gain a greatly increased significance; even the well-known link between chemical reactivity and surface-to-volume ratio becomes a major determinant of physical properties, when it operates over nanoscale dimensions. Against this background, this comprehensive work is designed to address the need for a dynamic, authoritative and readily accessible source of information, capturing the full breadth of the subject. Its six volumes, covering a broad spectrum of disciplines including material sciences, chemistry, physics and life sciences, have been written and edited by an outstanding team of international experts. Addressing an extensive, cross-disciplinary audience, each chapter aims to cover key developments in a scholarly, readable and critical style, providing an indispensible first point of entry to the literature for scientists and technologists from interdisciplinary fields. The work focuses on the major classes of nanomaterials in terms of their synthesis, structure and applications, reviewing nanomaterials and their respective technologies in well-structured and comprehensive articles with extensive cross-references. It has been a constant surprise and delight to have found, amongst the rapidly escalating number who work in nanoscience and technology, so many highly esteemed authors willing to contribute. Sharing our anticipation of a major addition to the literature, they have also captured the excitement of the field itself in each carefully crafted chapter. Along with our painstaking and meticulous volume editors, full credit for the success of this enterprise must go to these individuals, together with our thanks for (largely) adhering to the given deadlines. Lastly, we record our sincere thanks and appreciation for the skills and professionalism of the numerous Elsevier staff who have been involved in this project, notably Fiona Geraghty, Megan Palmer and Greg Harris, and especially Donna De Weerd-Wilson who has steered it through from its inception. We have greatly enjoyed working with them all, as we have with each other.
Categories: Science

Quantum Dot Sensors

Quantum Dot Sensors

Consisting of six chapters, written by experts in their field, this book charts the progress made in the use of quantum dots as the signaling component in optical sensors since their discovery in the early 1980s.

Author: John Callan

Publisher: CRC Press

ISBN: 9789814364614

Category: Science

Page: 230

View: 663

Consisting of six chapters, written by experts in their field, this book charts the progress made in the use of quantum dots as the signaling component in optical sensors since their discovery in the early 1980s. In particular, it focuses on CdS-, CdSe-, and CdTe-type QDs due to their emission in the visible region of the electromagnetic spectrum. The book begins by detailing the range of methods currently used for the preparation and passivation of core/core–shell quantum dots and follows with a discussion on their electrochemical properties and potential toxicity. The book culminates by focusing on how electron and energy transfer mechanisms can be utilized to generate a range of quantum dot-based probes. This is the first text of its kind dedicated to quantum dot-based sensors and will appeal to those readers who have an interest in working with these versatile nanoparticles.
Categories: Science

Spectroscopic Investigations of Excited Charge Carriers in II VI Nanoparticles

Spectroscopic Investigations of Excited Charge Carriers in II VI Nanoparticles

Furthermore, through collaborations with the research group of William E. Buhro, we can also make high quality samples of CdTe QW that enable their quantum-mechanical properties and resultant dynamics to be carefully characterized.

Author: William Matthew Sanderson

Publisher:

ISBN: OCLC:1190714733

Category: Electronic dissertations

Page: 253

View: 225

The large absorption cross sections and the tunability of the energetic spacings between the states in the conduction (CB) and valence band (VB) within a semiconductor nanoparticle (NP) make them promising media for capturing electromagnetic radiation and converting it into charge carriers, or electricity. In photovoltaic devices that incorporate semiconductor NPs, it would be ideal if every photon could be absorbed by a NP and the carriers could be collected with perfect efficiency and without loss of energy. The relaxation pathways of the carriers within the NPs down to the band edge and their fate at the band edge contribute significantly to this ideal goal. For samples of NPs that are not in a device, but are suspended in solution, the carriers (electrons and holes) would relax to states near the band edge of the CB and VB, and if there are no competing pathways, they would recombine radiatively, and give off light or emission. The specific relaxation mechanisms and their efficiencies depend on many factors including chemical composition, local environment, and the dimensionality of the NP. In this dissertation, I describe the results obtained from a barrage of optical spectroscopy experiments aimed at characterizing the energetics and the relaxation dynamics of photogenerated charge carriers in semiconductor NP samples. Particular focus was placed on samples of one-dimensional (1D) cadmium telluride (CdTe) quantum wires (QWs) as they offer the tunability of their energetics through adjustment of their diameters as well as the length dimensions for efficient charge transport over macroscopic distances. Furthermore, through collaborations with the research group of William E. Buhro, we can also make high quality samples of CdTe QW that enable their quantum-mechanical properties and resultant dynamics to be carefully characterized. In order to probe the role of the densities of the quantum-mechanical states on the relaxation of electrons and holes down to those at the band edge, the dependencies of the efficiency for radiative recombination on the excess energy with which the carriers are prepared was investigated on numerous samples of NPs with varying dimensionality. These samples included cadmium selenide (CdSe) quantum dots (QDs), CdSe quantum platelets (QPs), CdTe QWs, and surface-passivated CdTe QWs. We identified two common trends of the efficiency on excitation energy without distinct differences associated with the dimensionality of the NPs. (1) The overall efficiency of radiative recombination decreases with increasing excitation energy. (2) There are often local minima in the efficiencies when exciting at energies between the spectral features present in the absorption spectra. We were able to conclude that it is not just how high above the band gaps the electrons and holes are prepared, but that at specific energies used to excite these charge carriers, competing, non-radiative relaxation pathways are opened. The relaxation dynamics of the electrons and holes were further investigated in CdTe QWs using time-resolved transient absorption (TA) spectroscopy. In order to untangle the complicated TA signals, we developed a model, termed quantum-state renormalization (QSR), that accounts for the shifting of the quantum-confinement states that occurs due to the change in electron density caused by photoexcitation. The QSR model enabled us to directly probe the population of the electrons and holes through the different states, as well as track their changing energies with time. Several noteworthy results were obtained. The photogenerated holes relax to the band edge on very fast, instrument-limited timescales, and the electrons relax more slowly with a rate of ~0. 6 eV ps−1. The prominent relaxation mechanism was concluded to be a phonon-coupling mechanism, where the carriers relax by converting the kinetic energy associated with quantum confinement to vibrational or phonon modes of the CdTe QW. Lastly, the emission lifetimes of the CdTe QWs were measured as a function of the emission efficiency, or photoluminescence (PL) quantum yield ([phi]PL). The lifetimes for CdTe QW samples with photoluminescence quantum yields > 4% were nearly an order of magnitude greater than the radiative lifetime of CdTe QDs, >̲200 ns versus ~25 ns. We propose these long lifetimes are a consequence of the conservation of momentum that must be maintained during radiative recombination. The photogenerated electron-hole pairs relax to the lowest quantum confinement states, and in these high-quality QWS, the pairs remain bound as 1D excitons. These 1D excitons have a thermal distribution of translational kinetic energy along the long, unconfined dimension of the QWs, and thus they contain significant momentum. This momentum cannot be conserved during radiative recombination, and this channel is closed. Only when the 1D excitons become localized can they emit. These results suggest that long charge carrier lifetimes coupled with the dimensionality of these high-quality semiconductor QWs offer distinct advantages for use in photovoltaics.
Categories: Electronic dissertations

Journal of Nano Research

Journal of Nano Research

This volume of the journal will be useful and interesting for a wide range of engineers, scientists and students whose activity is related with creation and using of nanomaterials and nanotechnologies in the different branches of human ...

Author: Trans Tech Publications, Limited

Publisher: Trans Tech Publications Ltd

ISBN: 9783035733433

Category: Technology & Engineering

Page: 136

View: 185

The 50th volume of the journal "Journal of Nano Research" presents to readers the collection of the peer-reviewed papers by results of the research from field of syntesis of the various nanomaterials and nanostructures, applied nanotechnologies in the engineering and chemical production. This volume of the journal will be useful and interesting for a wide range of engineers, scientists and students whose activity is related with creation and using of nanomaterials and nanotechnologies in the different branches of human activity.
Categories: Technology & Engineering

Ethylamines Advances in Research and Application 2012 Edition

Ethylamines   Advances in Research and Application  2012 Edition

Southwest University, Chongqing: Characterization of the interaction between
mercaptoethylamine capped CdTe quantum dots with human serum albumin and
its analytical application “CdTe quantum dots (QDs) were synthesized in
aqueous ...

Author:

Publisher: ScholarlyEditions

ISBN: 9781481604024

Category: Science

Page: 158

View: 177

Ethylamines—Advances in Research and Application: 2012 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Ethylamines. The editors have built Ethylamines—Advances in Research and Application: 2012 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Ethylamines in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Ethylamines—Advances in Research and Application: 2012 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Categories: Science