Download or read book Investigating Photophysics in Colloidal Semiconductor Quantum Dots Through Photon correlation Methods written by Weiwei Sun (Chemist) and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal semiconductor quantum dots (QDs) exhibit interesting photophysical properties due to their quantum-confined nature. Due to their bright and stable photoluminescence, they have been widely used in a variety of applications, including lasing, light emitting diodes (LEDs), solar cells, biological imaging, and most recently quantum information science. Numerous efforts have been made to optimize these QDs to improve their performance, which all require the establishment of an efficient feedback loop between optical properties and synthesis. Spectroscopic studies on their PL properties would inform us about the nature of QD emission and point new directions for future design and optimization of QDs. In this thesis, I will use photon-correlation-based spectroscopy, a powerful toolkit with both high temporal and spectral resolutions, to investigate the exciton photo-physics inside these QDs to build a complete understanding of the exciton dynamics in cesium lead halide and CdSe/CdS quantum dots. In the first two chapters, I will build a foundation on the understanding of semiconductor quantum dots, quantum emitters, and single particle spectroscopic techniques. In the next two chapters, I will use photon-correlation Fourier spectroscopy (PCFS) to investigate single particle optical coherence properties, to demonstrate cesium lead halide perovskite quantum dots (PQDs) as the next-generation quantum emitter materials for quantum information science, and investigate their dephasing mechanisms at cryogenic temperatures. In the next chapter, I will switch gears to CdSe/CdS quantum dots to develop the first-time all-optical deterministic blinking control method and explain the mechanisms behind it. Finally, I will present a few interesting and unexplored ideas in understanding the nature of fine structure states in PQDs and the integration of nanophotonic cavities to achieve true transform-limited single quantum emitters and large-scale generation.

Download or read book Unraveling the Interplay Between Structure and Photophysics in Colloidal Quantum Dot Nanostructures written by Kemar Reid and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal quantum dots (QDs) make up a class of nanomaterials that provide a remarkable platform for engineering photophysical properties tailored to a range of applications of considerable technological value, including energy-efficient LEDs, robust biological probes, low-threshold solution-processed lasers, advanced photocatalysts and single-photon sources for quantum technologies. Underpinning these uses of QDs lay more fundamental investigations into the role of structure on absorption, energy relaxation, charge separation and charge recombination in order to achieve complete control over their photophysical behavior. However, with complex interfaces and diverging morphologies in synthetic products, QDs are remarkably complex nanostructured materials. It is therefore challenging to develop detailed structure-function relationships at the ensemble scale--where the properties of an array of structures are simultaneously determined. To decode this information, it is necessary to study QD nanostructures one at a time. In this work, single QD investigations were applied to three different QD systems to better understand the interplay between structure and photophysics in these materials. From revealing the role of strain-induced structural changes on the color purity of CdSe-CdS core-shell QDs, to a thick-shell in suppressing random intermittent emission in cadmium-free InP QD nanostructures, these investigations continually point to the negative impact of structural heterogeneity on the properties of the ensemble. The implementation of a correlative technique to measure the structure and photophysics of the same QD facilitated a detailed examination of this heterogeneity in semiconductor nanorods--revealing the detrimental effects of surface roughness on the quantum efficiency of the material. The advanced characterization of QDs afforded by this technique also has far-reaching implications for QD development and could be used to inform methods to orchestrate the assembly of QD nanostructures with precisely tuned photophysical properties.

Download or read book On the Origin of Photons written by Thomas Stanley Bischof and published by . This book was released on 2015 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on studies of exciton and multiexciton dynamics in colloidal semiconductor nanocrystals. I concentrated primarily on the development of correlation spectroscopies for the measurement of the statistics and dynamics of multiexciton emission. Under most conditions, the emission properties of nanocrystals are dominated by the photophysics of the single-exciton state. However, due to high density of states nanocrystals can readily undergo several successive excitations, leading to multiexcitonic states with distinct dynamics. As nanocrystals are more frequently used under conditions of high excitation ux for light-emitting applications, the often destructive nature of multiexcitons are increasingly relevant. Prior work on multiexcitons has largely focused on the biexciton, and here we develop tools to directly study triexciton emission. First, we develop the theoretical and analytical apparatus for studying multiexciton emission. The model and software are general to arbitrary numbers of excitons and provide the framework for further correlation-based methods. The software is general and may be used in any photon-timing application. InAs is a promising candidate material as an infrared emitter for down-shifting and biological applications. In one study, we characterize the excitonic dynamics of individual InAs nanocrystals. We nd that the nanocrystals qualitatively behave like CdSe nanocrystals, in that they exhibit blinking, monoexponential radiative dynamics, and (generally) low biexciton quantum yield. In a separate set of experiments, we study the temperature-dependent exciton emission dynamics of InAs quantum dots and nd that their emission is well-described by existing excitonic ne-structure models. CdSe is the classical colloidal quantum dot material, and is the ideal testing ground for methods development. We apply new high-order correlation methods to study the emission statistics and dynamics of the triexciton, biexciton, and monoexciton at the single-molecule level. We nd that multiexcitonic states have no memory: the relaxation of a biexciton yields a monoexciton which behaves identically to one formed by a single-photon excitation. We discuss a few examples of materials which may exhibit exotic biexcitonic states. Next, we explore the use of infrared-emitting nanocrystals for deep-tissue imaging in biological research. Earlier work on the subject involved the use of emitters with significantly lower quantum yield, and we demonstrated a variety of applications which make use of the high quantum yield and chemical functionality of colloidal nanocrystals. We used the unique combination of chemical functionality and high emission quantum yield to perform studies in mice: non-invasive measurement of vital signs in awake mice; real-time metabolic imaging of lipoproteins in an intact mouse; vascular imaging and blood velocimetry in a mouse with a cranial window model. Finally we discuss a few project ideas which arose during the work on this thesis, but were not successfully completed.

Download or read book Semiconductor Quantum Dots written by Y. Masumoto and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductor quantum dots represent one of the fields of solid state physics that have experienced the greatest progress in the last decade. Recent years have witnessed the discovery of many striking new aspects of the optical response and electronic transport phenomena. This book surveys this progress in the physics, optical spectroscopy and application-oriented research of semiconductor quantum dots. It focuses especially on excitons, multi-excitons, their dynamical relaxation behaviour and their interactions with the surroundings of a semiconductor quantum dot. Recent developments in fabrication techniques are reviewed and potential applications discussed. This book will serve not only as an introductory textbook for graduate students but also as a concise guide for active researchers.

Download or read book Synthesis Photophysics and Applications of Colloidal Semiconductor Quantum Dots written by Kelly Loraine Sowers and published by . This book was released on 2016 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Colloidal semiconductor nanocrystals, commonly known as quantum dots (QDs), have been the source of much interest recently, as three-dimensional quantum confinement allows for size-dependent optical properties. Since particle size, shape, composition, and surface passivation are all easily controlled (and thus, particle photophysics) in the initial synthesis and post-synthetic reactions, the made-to-order nature of QDs allows them to be potentially useful in a wide range of applications, particularly in photocatalyitic systems. This work will touch on some of the fundamental synthetic methods of cadmium chalcogenide QDs, the resulting photophysics of surface composition, and efficacy as a photosensitizer. QDs are synthesized and subsequently shelled using secondary phosphine chalcogens, which enables particular control over the surface composition of CdSe/CdS core/shell QDs. Interestingly, this surface tuning can be used to control the fluorescence properties of the QD in a precise manner, wherein sulfur-rich surfaces demonstrate quenched fluorescence quantum yields, and cadmiumrich surfaces reversibly recover fluorescence. DFT calculations demonstrate that hole trap states arising on sulfur-rich surfaces act to diminish radiative recombination processes. The surface effects on trap states provide constructive insight into necessary features of QDs for various applications, including use in a solar hydrogen generation scheme."--Page vii.

Download or read book Quantum Dot Optoelectronic Devices written by Peng Yu and published by Springer Nature. This book was released on 2020-04-16 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book captures cutting-edge research in semiconductor quantum dot devices, discussing preparation methods and properties, and providing a comprehensive overview of their optoelectronic applications. Quantum dots (QDs), with particle sizes in the nanometer range, have unique electronic and optical properties. They have the potential to open an avenue for next-generation optoelectronic methods and devices, such as lasers, biomarker assays, field effect transistors, LEDs, photodetectors, and solar concentrators. By bringing together leaders in the various application areas, this book is both a comprehensive introduction to different kinds of QDs with unique physical properties as well as their preparation routes, and a platform for knowledge sharing and dissemination of the latest advances in a novel area of nanotechnology.

Download or read book Understanding Colloidal Quantum Dot Excitation with Solution Photon Correlation Fourier Spectroscopy written by Stephanie Leigh Heathcote and published by . This book was released on 2015 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal quantum dots (CQDs) have useful absorption and emission properties but exist in inhomogenous batches. Solution photon correlation fourier spectroscopy (S-PCFS) combines interferometry with fluorescence correlation spectroscopy (FCS) to measure the spectral correlation of the average single fluorophore in a solution. With S-PCFS, the intrinsic emission linewidth of CQDs can be assessed. This linewidth information is related to phonon coupling and gives insight into the separation of holes and electrons in excited CQDs. Experimental considerations and recommendations for troubleshooting a S-PCFS apparatus are also presented here.

Download or read book Three pulse Photon Echo Studies of Colloidal Semiconductor Quantum Dots written by Mayrose Ramos Salvador and published by . This book was released on 2007 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents ultrafast spectroscopic studies and theoretical modelling of the origins of the lineshape and linewidth in colloidal semiconductor quantum dots. Three-pulse photon echo peak shift experiments were employed to separate the inhomogeneous line broadening from the homogeneous line broadening. We first verified that this technique is capable of separating the two broadening mechanisms by investigating two samples with different static inhomogeneity associated with the size-distribution of the sample. The homogeneous linewidth was then investigated by doing 3PEPS and steady-state measurements at various temperatures. Results showed an anomalous temperature dependence of the optical gap and Stokes shift. The measurements were also performed on various nanocrystal size, crystal structure, capping group, embedding polymer matrix, and shape to better understand the role of exciton-phonon coupling, spectral diffusion within the fine structure, and disorder on the lineshape of the nanocrystals. To interpret our 3PEPS signals, non-linear response functions using a two-level model were formulated and numerically evaluated. The effect of excited state absorption in our peak shift measurement, was investigated by formulating the three-level response functions, including biexciton contributions as the third level. Numerical calculations revealed that the excited state absorption can give an initial fast decay on the peak shift. Finally, we show that exciton-exciton scattering contribution can also significantly decay the peak shift and including it in our numerical simulation allows us to fit our REPS data even with weak exciton-phonon coupling.

Download or read book Quantum Dot Devices written by Zhiming M. Wang and published by Springer. This book was released on 2012-05-25 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum dots as nanomaterials have been extensively investigated in the past several decades from growth to characterization to applications. As the basis of future developments in the field, this book collects a series of state-of-the-art chapters on the current status of quantum dot devices and how these devices take advantage of quantum features. Written by 56 leading experts from 14 countries, the chapters cover numerous quantum dot applications, including lasers, LEDs, detectors, amplifiers, switches, transistors, and solar cells. Quantum Dot Devices is appropriate for researchers of all levels of experience with an interest in epitaxial and/or colloidal quantum dots. It provides the beginner with the necessary overview of this exciting field and those more experienced with a comprehensive reference source.

Download or read book Quantum Dot Molecules written by Jiang Wu and published by Springer Science & Business Media. This book was released on 2013-10-28 with total page 383 pages. Available in PDF, EPUB and Kindle. Book excerpt: A quantum dot molecule (QDM) is composed of two or more closely spaced quantum dots or “artificial atoms.” In recent years, QDMs have received much attention as an emerging new artificial quantum system. The interesting and unique coupling and energy transfer processes between the “artificial atoms” could substantially extend the range of possible applications of quantum nanostructures. This book reviews recent advances in the exciting and rapidly growing field of QDMs via contributions from some of the most prominent researchers in this scientific community. The book explores many interesting topics such as the epitaxial growth of QDMs, spectroscopic characterization, and QDM transistors, and bridges between the fundamental physics of novel materials and device applications for future information technology. Both theoretical and experimental approaches are considered. Quantum Dot Molecules can be recommended for electrical engineering and materials science department courses on the science and design of advanced and future electronic and optoelectronic devices.

Download or read book Spectral Dynamics of Single Quantum Dots written by Lisa Faye Marshall and published by . This book was released on 2011 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: Conventional single-molecule fluorescence spectroscopy is limited in temporal resolution by the need to collect enough photons to measure a spectrum, in frequency resolution by the dispersing power of the spectrometer, and by environmental conditions by the need to immobilize the chromophore on a substrate. In this thesis, we use the recently developed technique of photon-correlation Fourier spectroscopy (PCFS) to circumvent each of these limitations. PCFS combines the high temporal resolution of photon correlation measurements with the high frequency resolution of Fourier spectroscopy. The experimental setup consists of a Michelson interferometer where the two outputs are detected with avalanche photodiodes and cross-correlated with a hardware autocorrelator card. The interferometer maps spectral changes into intensity changes which can be measured with high temporal resolution by the autocorrelator. The distribution of spectral changes between photons with a given temporal separation determines the degree of correlation in the interferogram. By measuring the intensity correlation at different interferometer positions while dithering one mirror, a time dependent spectral correlation function is obtained. From this, we learn about the temporal evolution of the emission line shape at timescales approaching the lifetime of the emitter. In this body of work, we both apply PCFS to study low temperature colloidal quantum dots and extend the technique to extract spectral lineshapes and dynamics of single quantum dots freely diffusing in solution. In solution, spectral correlations originating from the same quantum dot are statistically enhanced and separable from the ensemble using intensity fluctuations from diffusion. We are able to use spectral correlations from many diffusing chromophores to determine the average single chromophore spectral correlation. This thesis begins with a review of spectral dynamics in quantum dots in Chapter 1. Chapters 2 and 3 describe the theoretical and experimental implementation of PCFS. Chapters 4 and 5 cover numerical simulations and experimental demonstrations of the extension of PCFS to single quantum dots obscured by an ensemble in solution. Finally, chapter 6 applies PCFS to single quantum dots at liquid helium temperatures.

Download or read book Photo physics and Applications of Colloidal Quantum Dots written by Stuart Stubbs and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Photon Interactions with Semiconductor Quantum Dot Devices for Quantum Communication Applications written by Jason Phoenix and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A major goal in the field of quantum communication is to achieve long-distance (>100 km) transmission of quantum information, which would allow for the formation of a global quantum network. Devices called 'quantum repeaters' will enable delicate quantum states to be transmitted over long distances without succumbing to the signal losses inherent in the use of optical fibres. This thesis presents my work on a new type of hybrid quantum repeater design, which will combine both the photonic and spin qubit platforms to achieve more robust and efficient quantum communication. The focus of this work is on the optical aspects of this 'photon-to-spin' system, specifically the development of a method for delivering fibre-coupled single photons through an optical fibre to a lateral quantum dot device in a dilution refrigerator while preserving their polarisation states.

Download or read book Photo physics and Applications of Colloidal Quantum Dots written by Stuart Stubbs and published by . This book was released on 2010 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Time Resolved Correlation Spectroscopy of Single Photons from Semiconductor Quantum Dots written by Udi Mizrahi and published by . This book was released on 2003 with total page 78 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 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.