Synthesis and Characterization of Lead-based Core-shell-shell Quantum Dots and Studies on Excitation-dependent Quantum Yield Measurement - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis and Characterization of Lead-based Core-shell-shell Quantum Dots and Studies on Excitation-dependent Quantum Yield Measurement write by Jieming Cao. This book was released on 2015. Synthesis and Characterization of Lead-based Core-shell-shell Quantum Dots and Studies on Excitation-dependent Quantum Yield Measurement available in PDF, EPUB and Kindle. 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.
Core/Shell Quantum Dots
Core/Shell Quantum Dots - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Core/Shell Quantum Dots write by Xin Tong. This book was released on 2020-07-01. Core/Shell Quantum Dots available in PDF, EPUB and Kindle. 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.
Synthesis and Characterization of Doped Core/shell Quantum Dots
Synthesis and Characterization of Doped Core/shell Quantum Dots - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis and Characterization of Doped Core/shell Quantum Dots write by Elizabeth J. Sodt. This book was released on 2007. Synthesis and Characterization of Doped Core/shell Quantum Dots available in PDF, EPUB and Kindle. 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.
Process-Dependent Properties in Colloidally Synthesized?Giant? Core/Shell Nanocrystal Quantum Dots
Process-Dependent Properties in Colloidally Synthesized?Giant? Core/Shell Nanocrystal Quantum Dots - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Process-Dependent Properties in Colloidally Synthesized?Giant? Core/Shell Nanocrystal Quantum Dots write by . This book was released on 2012. Process-Dependent Properties in Colloidally Synthesized?Giant? Core/Shell Nanocrystal Quantum Dots available in PDF, EPUB and Kindle. 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.
Synthesis and Characterization of Colloidal Lead Chalcogenide Quantum Dots and Progress Towards Single Photons On-demand
Synthesis and Characterization of Colloidal Lead Chalcogenide Quantum Dots and Progress Towards Single Photons On-demand - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis and Characterization of Colloidal Lead Chalcogenide Quantum Dots and Progress Towards Single Photons On-demand write by Keith Alexander Abel. This book was released on 2011. Synthesis and Characterization of Colloidal Lead Chalcogenide Quantum Dots and Progress Towards Single Photons On-demand available in PDF, EPUB and Kindle. 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.
