Download or read book Exciton Dynamics in Semiconductor Confined Systems written by Carlo Piermarocchi and published by . This book was released on 1998 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Semiconductor Nanocrystal Quantum Dots written by Andrey Rogach and published by Springer Science & Business Media. This book was released on 2008-09-02 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Using Time resolved Photoluminescence Spectroscopy to Examine Exciton Dynamics in II VI Semiconductor Nanostructures written by Laura M. Robinson and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We use photoluminescence spectroscopy to investigate the optical properties of two different II-VI semiconductor nanostructure systems: ZnMnSe/ZnSe multiple quantum wells and self-assembled CdSe quantum dots. The behavior of excitons in ZnMnSe quantum wells is examined using polarized magneto-photoluminescence, while (temperature-dependent) time-resolved photoluminescence is used to study the dynamics of excitons confined to quantum dot structures. When Zn0.86Mn0.14Se/ZnSe multiple quantum wells are placed in an external magnetic fields, the spin-down holes become confined to the ZnMnSe "barriers," while the electrons remain in the ZnSe "wells." This spatial separation of electrons and holes results in weak electron-hole overlap, which should result in a large increase of the radiative lifetime of the spin-down exciton. As a result, we see the formation of exciton magnetic polarons (EMP) which lower their energy by spontaneously aligning the magnetic impurities in the exciton Bohr radius. We find that the EMP polarization approaches 100% in fields as small as 200 mT in these spatially indirect EMP, which is consistent with their extremely long recombination lifetime (%7E10 ns). This contrasts with previous measurements on other magnetic quantum well systems for which the polarization of short-lived spatially direct EMP never saturates. Time-resolved photoluminescence measurements of excitons confined to CdSe self-assembled quantum dots (SAQDs) reveal the existence of two different exciton decay times: a short 450 ps lifetime and a much longer (> 4 ns) lifetime. While the emission resulting from the short lifetime excitons persists to room temperatures, the longlifetime component decreases in intensity with increasing temperature and is nearly completely gone by 60 K. Time-resolved spectra further reveal that the long lifetime component arises from spectrally sharp features (%7E200eV), while the rapid decay results from an underlying broad emission (%7E60 meV). Further analysis reveals that both states exhibit an activated behavior with activation energies that differ by over an order of magnitude for the two components. These interesting differences may reflect the complex nature of the electron and hole wave functions confined to these CdSe structures.

Download or read book Exciton Dynamics in Lead Halide Perovskite Nanocrystals written by Bernhard Johann Bohn and published by Springer Nature. This book was released on 2021-05-18 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: Less than a decade ago, lead halide perovskite semiconductors caused a sensation: Solar cells exhibiting astonishingly high levels of efficiency. Recently, it became possible to synthesize nanocrystals of this material as well. Interestingly; simply by controlling the size and shape of these crystals, new aspects of this material literally came to light. These nanocrystals have proven to be interesting candidates for light emission. In this thesis, the recombination, dephasing and diffusion of excitons in perovskite nanocrystals is investigated using time-resolved spectroscopy. All these dynamic processes have a direct impact on the light-emitting device performance from a technology point of view. However, most importantly, the insights gained from the measurements allowed the author to modify the nanocrystals such that they emitted with an unprecedented quantum yield in the blue spectral range, resulting in the successful implementation of this material as the active layer in an LED. This represents a technological breakthrough, because efficient perovskite light emitters in this wavelength range did not exist before.

Download or read book Confinement Effects on Multiexciton Dynamics in Semiconductor Nanocrystals written by Katherine Emily Shulenberger and published by . This book was released on 2019 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal semiconductor nanocrystals are a promising platform for a number of technological developments in a wide variety of lighting applications. They also are an incredibly useful model system to interrogate fundamental carrier interactions in crystalline semiconductor lattices. This thesis investigates the properties of multiexciton states in semiconductor nanocrystals to build an understanding of what drives their emission dynamics and efficiency. A complete understanding of the processes which dominate in a wide variety of nanocrystal systems sheds light on electron-hole and exciton-exciton interactions and provides guidance on how to engineer nanocrystals for particular applications. In the first two chapters, I will build a foundation of understanding of semiconductor nanocrystal systems, and how to build up an intuitive understanding of the states in question from both fundamental modeling and chemical intuition. I also present a variety of methods which are used to interrogate the luminescent properties of these materials, with a particular focus on those utilized in this thesis. In the second chapter in particular, I focus on how photoluminescence measurements can go astray, how to identify artifacts or background signal which could bias or invalidate data, and how to eliminate these artifacts. The next chapter details the biexciton and triexciton emission dynamics and efficiency in CdSe nanocrystals. Utilizing a well-established and well-studied semiconductor systems allows nuanced interpretation of the emission dynamics, and the identification of perhaps some unexpected material properties to enhance how we imagine these highly excited states. Chapter four employs a suite of methods to begin to understand carrier-carrier interactions in cesium lead halide perovskite nanocrystals. This system provides a particularly interesting platform to investigate the effect of confinement and lattice mobility on excitonic properties. Finally, I present a few experimental directions and ideas which have not yet been explored and would provide an excellent continuation of this work.

Download or read book Excitons in Confined Systems written by Rodolfo Del Sole and published by Springer. This book was released on 1988 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains the proceedings of the International Meeting on Confined Excitons held in Rome in April 1987. The aim of the meeting was to discuss excitons confined in a variety of systems from semi-infinite solids to quantum wells. In the part on excitons in semi-infinite solids, the long-running discussion on exciton reflectance, involving the concepts of additional boundary conditions and the dead layer, is summarized and extended. The papers on excitons in thin films and in "thick" quantum wells bridge the gap between semi-infinite semiconductors and the usual quantum wells, presenting interesting results on exciton quantization. The third part reports many new results in the recently developed area of excitons in quantum wells and on the very new topic of excitons in quantum wires. Knowledge of the quantum well properties is an important aspect in the determination of exciton states, so tutorial articles on the growth and band structure of quantum wells are also included.

Download or read book Proceedings of 2000 International Conference on Excitonic Processes in Condensed Matter written by Kikuo Cho and published by World Scientific. This book was released on 2001 with total page 506 pages. Available in PDF, EPUB and Kindle. Book excerpt: At Yamada Conference LIII, papers on many novel materials and on novel phenomena in condensed matter physics were presented OCo for instance, the achievement of simultaneous creation of excitons and free-electron-hole pairs in rare gas solids, and a low frequency fluctuation of the spectral shift of indirect excitons in GaAs coupled quantum wells. Single molecule spectroscopy is a powerful tool for studying molecules including biological systems; the study of delocalization of excitons in the photosynthetic light harvesting antenna system was also reported. The proceedings thus contain many excellent papers dealing with current research topics on the excitonic processes in bulk, quantum wells, quantum dots and other confined systems. This book will serve as an excellent source of recent references and reviews for a wide range of researchers in physics, chemistry, engineering and biological sciences. The proceedings have been selected for coverage in: . OCo Index to Scientific & Technical Proceedings (ISTP CDROM version / ISI Proceedings). Contents: Dynamical Process of Photoionization in Semiconductor Nanocrystals (M Y Shen et al.); Excitons on a 1D Periodic Conjugated Polymer Chain: Two Electronic Structures of Polydiacetylene Chains (C Lapersonne-Meyer); Anomalous Spectral Shifts of Indirect Excitons in Coupled GaAs Quantum Wells (D W Snoke et al.); Infrared Absorption by Excitons in Cuprous Oxide (M GAppert et al.); Theory of Excitation-Energy Transfer Processes Involving Optically Forbidden Exciton States in Antenna Systems of Photosynthesis (K Mukai et al.); Transient Grating Induced by Excitonic Polaritons in Thin Film Semiconductors (K Akiyama et al.); Excitonic Photoluminescence of Pentacene Single Crystal (T Aoki-Matsumoto et al.); Scanning Near-Field Optical Microspectroscopy of Single Perylene Microcrystals (J Niitsuma et al.); and other papers. Readership: Condensed matter physicists, materials scientists, chemists and biologists."

Download or read book Exciton Relaxation and Electron Transfer Dynamics of Semiconductor Quantum Dots written by Cunming Liu and published by . This book was released on 2015 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Quantum dots (QDs) exhibit unique electronic and optical properties arising from their three-dimensional confinement and strongly enhanced coulomb interactions. Developing a detailed understanding of their exciton relaxation dynamics is important not only for the sake of exploring the fundamental physics of quantum confinement processes, but also for their potential applications. Ultrafast transient absorption (TA) spectroscopy, which has been proven as a powerful tool to explore the relaxation dynamics of excitons, was employed to characterize the hot single/multiexciton relaxation dynamics at the first four exciton states 1Se-1S3/2 (1S), 1Se-2S3/2 (2S), 1Pe-1P3/2 (1P) and 1Se-2S1/2 (2SH) of CdSe/CdZnS QDs. We found all exciton states can accomplish their initialization in sub-ps timescales. And, the 1S single exciton mainly relaxes to surface trapping state with a lifetime of 0.90 ł 0.02 ns. A 74 ł 2 ps Auger recombination occurs to nonradiatively annihilate 1S multiexctions under higher pump fluence. We also observed for the first time that the 2S hot hole can relax via two possible pathways-intraband multiple phonon coupling (2S3/2-1P3/2 or 2S3/2-1S3/2) and the intrinsic defect trapping, with a lifetime of 7 ł 2 ps. Owing to the overlap between highly energetic 1P and 2SH exciton states, their probed dynamics both show the characteristics of 1P and 2SH exciton states. Surprisingly, an ultra-short component of 8 ł 1 ps, directly associated with the Auger recombination at the 1P exciton state, was discovered under higher pump fluence. After finishing the studies of exciton relaxation inside QDs, ultrafast TA spectroscopy was further applied to explore the electron transferring outside from QDs. By employing a novel photocatalytic system consisting of water-soluble CdSe QDs and Ni-dihydrolipoic acid (Ni-DHLA) catalyst, which has represented a robust photocatalysis of H2 from water, the photoinduced electron transfer (ET) dynamics between QDs and catalyst, one of most primary steps during H2 generation, was studied. We found that smaller bare CdSe QDs exhibit a better ET performance with an amplitude-weighted average lifetime of 69 ł 2 ps. And, nearly ~90% of TA signal in the presence of Ni-DHLA can be attributed to the ET process. CdS shelling on the bare CdSe QDs worsens the ET between QDs and Ni-DHLA catalysts. Under higher pump fluence, the ET performance with CdSe/CdS core-shell QDs is improved because of the Auger recombination in CdSe cores strongly suppressed by CdS shelling, which is contrary with bare CdSe QDs. These studies may supply potential ways to optimize the QDs sensitized photocatalytic systems for H2 production. Finally, by virtue of effective mass approximation (EMA) method and Marcus theory, the mechanism of ET between CdSe QDs and Ni-DHLA catalysts was clarified in theory. Additionally, photoluminescence (PL) quenching and time-resolved PL measurements were used to demonstrate that the main pathway for ET between QDs and Ni-DHLA catalysts is through dynamic collisions. As Ni-DHLA concentration increases, the static attachment between QDs and Ni-DHLA catalyst molecules can occur to further speed up the ET process from QDs to Ni-DHLA catalysts."--Pages vi-vii.

Download or read book Radiationless Transitions written by Sheng Lin and published by Elsevier. This book was released on 2012-12-02 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radiationless Transitions is a critical discussion of research studies on the theory and experiments in radiationless transitions. This book is composed of nine chapters, and begins with discussions on the theory and experiment of photophysical processes of single vibronic levels and/or single rovibronic levels. The subsequent chapters deal with the spectroscopic investigations of intramolecular vibrational relaxation; the dynamics of molecular excitation by light; and the photophysical processes of small molecules in condensed phase. The discussions then shift to the high pressure effects on molecular luminescence and the internal conversion involving localized excitations, presenting one qualitative and one quantitative example, as well as the intersystem crossing with localized excitations. A chapter explores the energy transfer processes that occur after a molecule in solution is excited by light, with an emphasis on solid solutions in which the large amplitude molecular motion is largely quenched. This chapter also looks into the liquid solutions in which the molecules can translate and rotate under the influence of fluctuating forces from the liquid. The concluding chapter focuses on ultrafast processes. Researchers in the fields of physics, chemistry, and biology will benefit from this book.

Download or read book Ultrafast Investigations of Exciton Dynamics in 0D and 2D Hybrid Semiconductor Nanomaterials written by Eric R. Powers and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of hybrid organic-inorganic semiconductor nanomaterials represents a major advance towards highly tunable and efficient optoelectronic devices. These materials are comprised of multiple chemical constituents arranged in nanoscale geometries, and they exhibit emergent properties such as quantum confinement and enhanced Coulombic interactions. Photoactive nanomaterials have potential applications in lighting, solar, lasing, and quantum information. However, their complex chemistry and nanometer-scale dimensionality present a barrier to understanding and controlling their structure-function relationships. In this thesis, I utilize ultrafast pump-probe spectroscopy to study the fundamental properties of hybrid semiconductor nanomaterials. This technique allows the electronic and vibrational dynamics of these materials to be investigated with femtosecond time resolution, providing new insights into their underlying physics. I first employ impulsive vibrational spectroscopy to study exciton-phonon interactions in silver phenyl selenolate (AgSePh), a recently discovered hybrid 2D semiconductor. Combining this time-domain Raman technique with frequency-domain non-resonant Raman scattering, I measure the vibrational landscape of the system and identify a subset of vibrational modes that couple strongly to excitonic transitions. Density functional theory calculations are then utilized to pinpoint specific atomic displacements which couple to the excitonic transition. An investigation of temperature-dependent photoluminescence reveals the connection between atomic scale dynamics and macroscopic properties, showing the 99 cm−1 mode strongly impacts emission frequency and linewidth in AgSePh. Finally, temperature-dependent impulsive vibrational spectroscopy is employed to probe vibrational anharmonicity in this material. These findings provide a roadmap for controlling exciton-phonon coupling in hybrid organic-inorganic semiconductors. Next, I study charging and neutralization processes in lead halide perovskite nanocrystals (quantum dots) with transient absorption spectroscopy. A temperature-dependent study of CsPbBr3 nanocrystals reveals that charging occurs in a significant fraction of photoexcited nanocrystals (>10%), which then exhibit a microsecond neutralization lifetime at cryogenic temperatures. The temperature-dependent dynamics are modeled to extract a ~100 meV energy barrier to re-neutralization. Additionally, photocharging shows a sublinear fluence dependence, excluding Auger recombination as the initiator of this process, in contrast with traditional nanocrystal systems. These results help illuminate the underlying mechanism of charging in perovskite nanocrystals, guiding future synthetic advances to improve nanocrystal performance in lighting and quantum information applications.

Download or read book Nanostructured and Photoelectrochemical Systems for Solar Photon Conversion written by Mary D. Archer and published by World Scientific. This book was released on 2008 with total page 781 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this book, expert authors describe advanced solar photon conversion approaches that promise highly efficient photovoltaic and photoelectrochemical cells with sophisticated architectures on the one hand, and plastic photovoltaic coatings that are inexpensive enough to be disposable on the other. Their leitmotifs include light-induced exciton generation, junction architectures that lead to efficient exciton dissociation, and charge collection by percolation through mesoscale phases. Photocatalysis is closely related to photoelectrochemistry, and the fundamentals of both disciplines are covered in this volume.

Download or read book Coherent Optical Interactions in Semiconductors written by R.T. Phillips and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: The NATO Advanced Research Workshop on Coherent Optical Processes in Semiconductors was held in Cambridge, England on August 11-14,1993. The idea of holding this Workshop grew from the recent upsurge in activity on coherent transient effects in semiconductors. The development of this field reflects advances in both light sources and the quality of semiconductor structures, such that tunable optical pulses are now routinely available whose duration is shorter than the dephasing time for excitonic states in quantum wells. It was therefore no surprise to the organisers that as the programme developed, there emerged a heavy emphasis on time-resolved four-wave mixing, particularly in quantum wells. Nevertheless, other issues concerned with coherent effects ensured that several papers on related problems contributed some variety. The topics discussed at the workshop centred on what is a rather new field of study, and benefited enormously by having participants representing many of the principal groups working in this area. Several themes emerged through the invited contributions at the Workshop. One important development has been the careful examination of the two-level model of excitonic effects; a model which has been remarkably successful despite the expected complexities arising from the semiconductor band structure. Indeed, modest extensions to the two level model have been able to offer a useful account for some of the complicated polarisation dependence of four-wave mixing signals from GaAs quantum wells. This work clearly is leading to an improved understanding of excitons in confined systems.

Download or read book Nonlinear Optical Response of Confined Excitons in Molecular and Semiconductor Nanostructures written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The nonlinear optical response of Semiconductor Quantum Wells, Organic Superlattices and Conjugated Polyenes was calculated using collective electronic coordinates, which represent the joint dynamics of electron-hole pairs. The use of femtosecond four-wave mixing spectroscopy to probe the nature of electronic States and Exciton and free-carrier interactions in these systems was explored. The formation and dynamics of quasiparticles involving electrons dressed by nuclear deformations in conjugated polymers was studied. The Si natures of charged solitons, neutral solitons, polarons and bipolarons in the resonant and off-resonant optical susceptibilities of conjugated polymers were calculated using the Pariser-Parr-Pople (PPP) model. The optical response was obtained by solving equations of motion for the reduced single-electron density matrix, derived using the time dependent Hartree-Fock (TDHF) approximation. The approach relates the optical Signals directly to the dynamics of charges and bond orders (electronic coherences) induced by the radiation field and uses only ground-state information, thus avoiding the explicit calculation of excited states. A Density-Matrix-Electronic-Oscillator representation was employed for calculating the third order nonlinar A optical response of semiconductor quantum dots in the limits of weak and strong exciton confinement. The nonlocal electrodynamics of arrays of quantum dots was treated exactly using Green function techniques. The research program included the development of software which uses the newly developed algorithms in the design of new optical materials.

Download or read book Semiconductor Cavity Quantum Electrodynamics written by Y. Yamamoto and published by Springer. This book was released on 2003-07-01 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: This monograph is the first to give a comprehensive account of the theory of semiconductor cavity quantum electrodynamics for such systems in the weak-coupling and strong-coupling regimes. It presents the important concepts, together with relevant, recent experimental results.

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 Confined Electrons and Photons written by Elias Burstein and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 900 pages. Available in PDF, EPUB and Kindle. Book excerpt: The optical properties of semiconductors have played an important role since the identification of semiconductors as "small" bandgap materials in the thinies, due both to their fundamental interest as a class of solids baving specific optical propenies and to their many important applications. On the former aspect we can cite the fundamental edge absorption and its assignment to direct or indirect transitions, many-body effects as revealed by exciton formation and photoconductivity. On the latter aspect, large-scale applications sucb as LEDs and lasers, photovoltaic converters, photodetectors, electro-optics and non-linear optic devices, come to mind. The eighties saw a revitalization of the whole field due to the advent of heterostructures of lower-dimensionality, mainly two-dimensional quantum wells, which through their enhanced photon-matter interaction yielded new devices with unsurpassed performance. Although many of the basic phenomena were evidenced through the seventies, it was this impact on applications which in turn led to such a massive investment in fabrication tools, thanks to which many new structures and materials were studied, yielding funher advances in fundamental physics.

Download or read book Semiconductor Nanocrystals written by Alexander L. Efros and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: A physics book that covers the optical properties of quantum-confined semiconductor nanostructures from both the theoretical and experimental points of view together with technological applications. Topics to be reviewed include quantum confinement effects in semiconductors, optical adsorption and emission properties of group IV, III-V, II-VI semiconductors, deep-etched and self assembled quantum dots, nanoclusters, and laser applications in optoelectronics.