Download or read book Synthesis and Characterization of Lead based Core shell shell Quantum Dots and Studies on Excitation dependent Quantum Yield Measurement written by Jieming Cao and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nano-sized semiconductors, known as quantum dots (QDs), are one of the hottest research areas in recent years. The energy gaps of QDs change with their diameters, giving them size-dependent optical properties. By controlling reaction conditions, people are able to make QDs that can emit in certain wavelength ranges. So far, QDs have shown great potential in telecommunication, bio-imaging, single-photon laser source, etc. This thesis starts with Chapter 1, which first introduces the finding of QDs and why they have such special properties. The quantum confinement and energy gap are discussed, followed by the absorption and emission of QDs. Moreover, the synthesis methods and mechanism involved are reviewed in brief.
Download or read book Core Shell Quantum Dots written by Xin Tong and published by Springer Nature. This book was released on 2020-07-01 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book outlines various synthetic approaches, tuneable physical properties, and device applications of core/shell quantum dots (QDs). Core/shell QDs have exhibited enhanced quantum yield (QY), suppressed photobleaching/blinking, and significantly improved photochemical/physical stability as compared to conventional bare QDs. The core-shell structure also promotes the easy tuning of QDs’ band structure, leading to their employment as attractive building blocks in various optoelectronic devices. The main objective of this book is to create a platform for knowledge sharing and dissemination of the latest advances in novel areas of core/shell QDs and relevant devices, and to provide a comprehensive introduction and directions for further research in this growing area of nanomaterials research.
Download or read book Process Dependent Properties in Colloidally Synthesized Giant Core Shell Nanocrystal Quantum Dots written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to their characteristic bright and stable photoluminescence, semiconductor nanocrystal quantum dots (NQDs) have attracted much interest as efficient light emitters for applications from single-particle tracking to solid-state lighting. Despite their numerous enabling traits, however, NQD optical properties are frustratingly sensitive to their chemical environment, exhibit fluorescence intermittency ('blinking'), and are susceptible to Auger recombination, an efficient nonradiative decay process. Previously, we showed for the first time that colloidal CdSe/CdS core/shell nanocrystal quantum dots (NQDs) comprising ultrathick shells (number of shell monolayers, n,> 10) grown by protracted successive ionic layer adsorption and reaction (SILAR) leads to remarkable photostability and significantly suppressed blinking behavior as a function of increasing shell thickness. We have also shown that these so-called 'giant' NQDs (g-NQDs) afford nearly complete suppression of non-radiative Auger recombination, revealed in our studies as long biexciton lifetimes and efficient multiexciton emission. The unique behavior of this core/shell system prompted us to assess correlations between specific physicochemical properties - beyond shell thickness - and functionality. Here, we demonstrate the ability of particle shape/faceting, crystalline phase, and core size to determine ensemble and single-particle optical properties (quantum yield/brightness, blinking, radiative lifetimes). Significantly, we show how reaction process parameters (surface-stabilizing ligands, ligand:NQD ratio, choice of 'inert' solvent, and modifications to the SILAR method itself) can be tuned to modify these function-dictating NQD physical properties, ultimately leading to an optimized synthetic approach that results in the complete suppression of blinking. We find that the resulting 'guiding principles' can be applied to other NQD compositions, allowing us to achieve non-blinking behavior in the near-infrared. Lastly, in addition to realizing novel light-emission properties by refining nanoscale architectures at the single-NQD level, we also investigate collective properties by assembling our core/shell NQDs into larger scale arrays.
Download or read book Synthesis and Characterization of Doped Core shell Quantum Dots written by Elizabeth J. Sodt and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The central theme of the research performed is the systematic modification of the optical properties of quantum dots by the formation of a shell of another quantum dot of a different band gap energy. Core/shell quantum dots such as CdS:Mn/CdS. CdS:Mn/ZnS, and ZnS:Mn/CdS with various concentrations of dopant Mn2 in the core and shell concentrations have been synthesized under mild conditions in the aqueous phase using stoichiometric amounts of the surfactant stabilizer dodecyl sulfate. These quantum dots exhibit UV-vis, emission, and electron paramagnetic resonance (EPR) spectral behavior that is dependent on the concentration of the shell and the dopant Mn2 in the core. The emission intensities of the core quantum dots do exhibit a systematic variation with Mn2 concentration. When a shell is added a systematic variation in the emission intensity and lifetime that are inversely proportional to the concentration of the shell is observed. When the large band gap ZnS is added as a shell to the small band gap CdS, the Mn2+ ions migrate from the core to the shell which is manifested in the emission and EPR spectra. Additionally the mixing of the valence and conduction band energy states of the large and small band gap shell and core respectively is also manifested in the emission spectra. In the reverse case, namely when CdS is added as a shell to ZnS the migration is not observed and the mixing of the valence and conduction band energy levels is minimum. The tunable optical properties of these core/shell quantum dots make them excellent platforms for the generation of nanosensors for nerve gas analogs.
Download or read book Synthesis and Characterization of Colloidal Lead Chalcogenide Quantum Dots and Progress Towards Single Photons On demand written by Keith Alexander Abel and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanometer-sized semiconductor crystals, termed 'quantum dots', are of fundamental interest because of their size-tunable properties. Three-dimensional quantum confinement of charge carriers by the small crystal size results in discrete atomic-like electronic states. This dissertation describes the synthesis and in-depth characterization of lead chalcogenide colloidal quantum dots for forthcoming applications as near-infrared single photon emitters. An efficient single photon source that operates at telecommunication wavelengths (between 1.3 and 1.6?m) is a basic requirement for many photonic quantum technologies, such as quantum computing and quantum cryptography. Chapters 1 and 2 of this work provide an introduction to colloidal quantum dots and their use as single photon emitters. It includes a description of photonic crystal microcavities and their ability to enhance the spontaneous emission rate of quantum dots. The synthesis and basic characterization of PbSe and PbS quantum dots is then discussed in chapter 3. In particular, a new synthetic method for the preparation of highly photoluminescent PbS quantum dots is presented. PbSe/CdSe core/shell quantum dots prepared by a cation exchange reaction are also described and a significant improvement in photo-stability is shown. Chapter 3 concludes with a description of three different surface modification techniques. PbSe core and PbSe/CdSe core/shell materials are investigated further in chapter 4 by advanced characterization techniques that include high-angle annular dark field (HAADF) imaging, energy-filtered transmission electron microscopy (EF-TEM) imaging, energy-dependent X-ray photo-electron spectroscopy (XPS), small angle X-ray scattering (SAXS), and small angle neutron scattering (SANS). The information obtained from these techniques is combined to form a structural model of the PbSe core and PbSe/CdSe core/shell quantum dots with greater complexity than previously reported. In chapter 5, the temperature-dependent photoluminescence from PbSe and PbSe/CdSe core/shell quantum dots is discussed and a thermal model is presented that accounts for the large (non-trivial) temperature dependence of the Stokes shift and photoluminescence lineshape over the entire temperature range (4.5 to 295 K). Chapter 6 examines two scalable methods to integrate the colloidal quantum dots into silicon two-dimensional photonic crystal slab microcavities (a requirement for efficient single photon emission). Finally, conclusions and possible future work are discussed in chapter 7.
Download or read book Cadmium Telluride Quantum Dots written by John Donegan and published by CRC Press. This book was released on 2016-04-19 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 dev
Download or read book Synthesis and Characterization of Infrared Quantum Dots written by Daniel Kelly Harris and published by . This book was released on 2014 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on the development of synthetic methods to create application ready quantum dots (QDs) in the infrared for biological imaging and optoelectronic devices. I concentrated primarily on controlling the size and size distribution of indium arsenide and cadmium arsenide QDs. In the nanocrystal community, classical nucleation and growth is often invoked to explain size focusing. However, this model lacks predictive power and contradicts what is known about the chemistry of QD growth. I try to relate my experimental approach and my conclusions to our understanding of the mechanism of particle growth. This approach led me to explore the role of precursor conversion rate in the growth of III-V QDs and to develop a continuous injection synthesis method that I used to make both III-V and cadmium arsenide QDs. Cadmium arsenide (Cd 3As 2 ) is a narrow gap semiconductor that can form QDs with tunable emission between 530nm and 2000nm. I developed a synthetic strategy to precisely control the size of Cd3As 2 QDs while maintaining a narrow size distribution. Continuous precursor injection was used to drive growth and suppress size broadening. The quantum yields of Cd3As 2 QDs produced using this method ranged as high as 80%, and their emission is tunable over a broad range with narrow linewidths. However, they were found to be unstable in ambient conditions. Nevertheless, by processing in inert conditions we were able to make a crude photodetector that demonstrates that Cd3As 2 QDs are sufficiently stable for use in optoelectronic devices. Although growth of a Cd3 P2 shell provided enough added stability to observe emission after ligand exchange into water, these core-shell structures do not seem to be robust enough for biological applications. Indium arsenide (InAs) QDs are more easily stabilized with a core-shell structure. However, the spectral linewidths are broad and existing synthetic techniques produce only small particles with limited spectral tunability. Models predicted that decreasing precursor reactivity would produce larger, more monodisperse particles. Therefore, I chemically modified the group-V precursor to reduce reactivity. I made a library of group-V precursors, and I developed a framework for comparing the QDs that they produced and measuring the kinetics of precursor conversion and particle growth. Although we successfully reduced precursor reactivity, we found that the effect on particle size was minimal and that the least reactive precursors produced particles with inferior size distributions. To find another way to try to improve III-V synthesis, I adapted the continuous injection method developed for making Cd3As 2. Using this strategy, I was able to produce InAs QDs with broadly tunable size and narrow spectral features. However, continuous injection ceases to drive particle growth beyond about 5nm in diameter. We examined why particle growth stops, and proposed a strategy to prolong growth and size focusing. Ultimately, the continuous injection technique allowed us to produce InAs QDs with infrared emission and narrow spectral features that were ideally suited for producing QDs optimized for deep tissue imaging in mice. By adding a shell of CdSe, CdS, or ZnSe, the quantum yield and stability were enhanced. These emitters allowed us to see biodistribution and biological processes occurring inside live mice. Although we found that precursor chemistry did not affect particle growth to the degree we hoped, we were able to produce application ready QDs via a continuous injection procedure. Continuous injection synthesis of QDs is a precise way to tune QD size while maintaining narrow size distributions. We have used this technique to produce QDs with the specifications required for high impact applications.
Download or read book Synthesis of Non blinking Semiconductor Quantum Dots Emitting in the Near Infrared written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Our previous work demonstrates that Quasi-Type II CdSe/CdS core-shell quantum dots with thick shells (3-5 nm) exhibit unique photophysical characteristics, including improved chemical robustness over typical thin-shelled core/shell systems and the elimination of blinking through suppression of nonradiative Auger recombination. Here we describe a new thick-shelled heterostructure, InP/CdS, which exhibits a Type II bandgap alignment producing near-infrared (NIR) emission. Samples with a range of shell thicknesses were synthesized, enabling shell-thickness-dependent study of the absorbance and emission spectra, fluorescence lifetimes, and quantum yields. InP/CdS/ZnS core/shell/shell structures were also synthesized to reduce cadmium exposure for applications in the biological environment. Single particle spectroscopy indicates reduced blinking and improved photostability with increasing shell thickness, resulting in thick-shelled dots that are appropriate for single-particle tracking measurements with NIR emission.
Download or read book Quantum Dots written by N. Thejo Kalyani and published by Woodhead Publishing. This book was released on 2023-01-18 with total page 612 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum dots: Emerging materials for versatile applications is an introduction to the fundamentals and important advances of research of this important category of semiconductor nanostructured materials. After a brief review of relevant nanotechnology concepts and the unique properties of nanomaterials, the book describes the fundamentals of quantum dots with definitions of the primary classifications of quantum dots. There is an emphasis on practical considerations of the commercial translation of quantum dots such as their toxicity, stability, and disposal. Moreover, the book focuses on a review of the advances in research in emerging quantum dot materials along with the latest innovations in materials design and fabrication methods. Quantum Dots is suitable for materials scientists and engineers in academia or industry R&D who are looking for an introduction to this research topic or a key reference on the latest advances and applications. Introduces the primary classifications, properties, synthesis, characterization and fabrication strategies of quantum dots Reviews the latest applications of quantum dots for LEDs, displays, energy storage devices, photovoltaic cells, medicine, and more Discusses the practical barriers to commercial translation of quantum dots, including toxicity, stability, and their safe disposal
Download or read book Synthesis and Structure of Colloidal Quantum Dots written by Ingrid Joylyn Paredes and published by American Chemical Society. This book was released on 2023-06-15 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanotechnology is an interdisciplinary field comprising materials scientists, chemists, physicists, and engineers dedicated to understanding the chemistry behind the associated synthesis, purification, modification, and applications. Already, nanotechnology has been instrumental to advances in medicine, electronics, catalysis, and cosmetics. The work of nanotechnologists has enabled society to move from the current “Silicon Age” into a new “Nano Age.” These alternatives to Si-based technologies are expected to combine the optoelectronic properties of bulk inorganic semiconductors with the benefits of additive device manufacturing—low cost, large area, and solution-based processes. This primer focuses on a class of nanomaterials known as colloidal quantum dots. Known for their solution processability and size-dependent optoelectronic properties, the study of colloidal quantum dots has garnered significant attention from the research community. The goal of this primer is to equip newcomers with the introductory knowledge and tools necessary to enter the field. As such, the scope of our work focuses on the synthesis and characterization of quantum dots; where possible, we point the reader to further reading specific to applications.
Download or read book Quantum Dots written by Inamuddin and published by Materials Research Forum LLC. This book was released on 2021-04-05 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book provides a thorough survey of current research in quantum dots synthesis, properties, and applications. The unique properties of these new nanomaterials offer multifunctional applications in such fields as photovoltaics, light-emitting diodes, field-effect transistors, lasers, photodetectors, solar cells, biomedical diagnostics and quantum computing. Keywords: Quantum Dots (QD), Photovoltaics, Light-emitting Diodes, Field-effect Transistors, Lasers, Photodetectors, Solar Cells, Biomedical Diagnostics, Quantum Computing, QD Synthesis, Carbon QDs, Graphene QDs, QD Sensors, Supercapacitors, Magnetic Quantum Dots, Cellular/Molecular Separation, Chromatographic Separation Column, Photostability, Luminescence of Carbon QDs, QD Materials for Water Treatment, Semiconductor Quantum Dots, QD Drug Delivery, Antibacterial Quantum Dots.
Download or read book Colloidal Quantum Dot Optoelectronics and Photovoltaics written by Gerasimos Konstantatos and published by Cambridge University Press. This book was released on 2013-11-07 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.
Download or read book Quantum Dots written by Rakshit Ameta and published by Elsevier. This book was released on 2022-09-20 with total page 393 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum Dots: Fundamentals, Synthesis and Applications compiles key information, along with practical guidance on quantum dot synthesis and applications. Beginning with an introduction, Part One highlights such foundational knowledge as growth mechanisms, shape and composition, electrochemical properties, and production scale-up for quantum dots. Part Two goes on to provide practical guides to key chemical, physical and biological methods for the synthesis of quantum dots, with Part Three reviewing the application of quantum dots and a range of important use cases, including photocatalysis, energy cells and medical imaging. Drawing on the knowledge of its expert authors, this comprehensive book provides practical guidance for all those who already study, develop or use quantum dots in their work. Presents the foundational information needed to effectively understand and manipulate quantum dot properties Consolidates key methods of quantum dot synthesis in a single volume Reviews both current and future practical applications of quantum dots across a range of important fields
Download or read book Semiconductor Quantum Dots written by Mark Green and published by Royal Society of Chemistry. This book was released on 2014-07-01 with total page 295 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum dots are nano-sized particles of semiconducting material, typically chalcogenides or phosphides of metals found across groups II to VI of the periodic table. Their small size causes them to exhibit unique optical and electrical properties which are now finding applications in electronics, optics and in the biological sciences. Synthesis of these materials began in the late 1980’s and this book gives a thorough background to the topic, referencing these early discoveries. Any rapidly-expanding field will contain vast amounts of publications, and this book presents a complete overview of the field, bringing together the most relevant and seminal aspects literature in an informed and succinct manner. The author has been an active participant in the field since its infancy in the mid 1990’s, and presents a unique handbook to the synthesis and application of this unique class of materials. Drawing on both his own experience and referencing the primary literature, Mark Green has prepared. Postgraduates and experienced researchers will benefit from the comprehensive nature of the book, as will manufacturers of quantum dots and those wishing to apply them.
Download or read book Understanding the Influence of Interfacial Chemistry in Core Core shell and Core shell shell Quantum Dots on Their Fluorescence Properties written by Omondi Benard Omogo and published by . This book was released on 2014 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal semiconductor nanocrystals (quantum dots) have received a great deal of attention due to their superior size tunable properties and promising applications in many areas. Some of the most practical areas of their applications include light emitting diodes (LED), photovoltaic and biological studies. Synthetic methods of these crystals is becoming more established with new strategies being reported every now and then. However, quantitative studies connecting the processes at the interface, namely core-ligand, core-shell and shell-shells, to the overall quantum dots fluorescence properties are not well understood. Specifically for cores, relating surface-atoms interactions, solvents, ligands nature, density and functional groups on quantum yields have not been exhaustively carried out. Furthermore, for the core/shell counterparts, the connection between the qualities of the starting core on its resulting core/shell quality have been left trivial without experimental back up. Here, we summarize the reports of experiments that have systematically investigated these effects on the properties of quantum dots. Combining systematic synthetic approach with characterization tools such as FTIR, X-ray photoelectron and diffraction together with time resolved visible spectroscopies, we observed that the density, nature and the orientation of the ligand functional groups play significant roles in determining the charge carrier dynamics that results on the various quantum yields and quality of the quantum dots. The experimental results also contradicted the trivial belief that starting with a high quality core material should result into high quality core/shell quantum dots. We further extended these studies by controlling both lattice mismatch and exciton confinement potential to design small, biologically friendly and highly stable core/shell/shell material. Blinking studies confirmed an interplay of both lattice strain and exciton confinement as the major factors responsible for the blinking dynamics of these core/shell/shell quantum dots. Therefore, by controlling these parameters, we were able to observe reduced blinking quantum dots with relatively moderate shell thickness. These observations will provide a useful insight while designing these particles and enhance their future applications.
Download or read book Relationships Between Processing Structure And Properties Of Nanocrystal Quantum Dots And Superlattices written by Kaifu Bian and published by . This book was released on 2015 with total page 421 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystal quantum dots are novel materials of great scientific and technological interests. The attractive features of quantum dots include size-tunable optoelectronic properties, high optical absorption cross section and ease of synthesis and deposition. These unique features qualify quantum dots as a promising material platform for emerging technological applications such as photovoltaic devices, sensors, light emitting diodes and bioimaging. In most of the proposed applications, individual quantum dots cannot be utilized until they form macroscopic assemblies. Under proper conditions quantum dots self-assemble into periodical superlattices. The properties and performance of quantum dot assemblies depend on not only the intrinsic properties of isolated dots but also their spatial arrangement or ordering. Consequently the relationships between processing, structure and properties of quantum dots and superlattices are of great importance in guiding the design and fabrication of novel nanomaterials with advantageous features using quantum as building blocks. In this dissertation, I present my graduate research studying such trilateral relationships in lead chalcogenide quantum dot systems. The first half of this dissertation discusses the relationship between processing and structure of self-assembled superlattices. An overview of how the ligand-ligand interaction as the major driving force along with factors including particle size, shape, ligand morphology, solvents and interfaces determine superlattice morphology is provided and followed by specific examples. (1) By tuning surface ligand morphology of PbS quantum dots and growth conditions, the effective particles shape was altered and therefore different symmetries (fcc, bcc and bct) of superlattice were achieved. (2) The translational and orientational orderings in an fcc superlattice of cuboctahedron PbS quantum dots was decoded by small and wide angle x-ray scatterings. The dots showed two distinct orientations as a result of the interplay between particle shape and ligand attractions. (3) Study of the nucleation, orientational alignment and symmetry transformations of PbS nanocubes at solvent-air and solvent-substrate interfaces is presented to demonstrate the role of interfaces as templates in guiding superlattice formation. Presented in the second half of this dissertation are my research works using high pressure, which efficiently tunes both superlattice and atomic structures without altering chemistry, to probe the relationships between structure and properties of quantum dots systems. (1) Difference in the pressure-induced atomic phase transition pressure indicated that dots in bcc superlattice are more mechanically stable than those in fcc due to translational and orientational orderings. (2) Elastic stiffness of PbS quantum dots were found to show size-dependence which is explained by a core-shell model. (3) Size-dependent variation of band gap of PbS quantum dot under elevated pressure was observed and correlated to changes of atomic structure. (4) Quantum dots were innovatively used as a nano-scaled tool to uniaxially compress organic molecule chains and measure the force-length relationship of single molecules.
Download or read book Metal and Semiconductor Nanocrystals written by Jing Zhao and published by Frontiers Media SA. This book was released on 2020-01-14 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt:
