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Raevskaya, Alexandra, Oksana Rozovik, Anastasiya Novikova, Oleksandr Selyshchev, Oleksandr Stroyuk, Volodymyr Dzhagan, Irina Goryacheva, Nikolai Gaponik, Dietrich R. T. Zahn, and Alexander Eychmüller. "Luminescence and photoelectrochemical properties of size-selected aqueous copper-doped Ag–In–S quantum dots." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-235077.
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Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.
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DEL, GOBBO SILVANO. "Cadmium sulfide quantum dots: growth and optical properties." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/873.
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Negli ultimi anni, c’è stato un rapido sviluppo delle tecniche di crescita dei materiali nanostrutturati, e un forte impulso è stato dato dall’introduzione delle tecniche di crescita colloidale. Tali tecniche consentono di crescere un ampia gamma di materiali nanostrutturati, metalli e semiconduttori, con elevata cristallinità, dimensioni ridotte (< 5 nm) e con una distribuzione delle dimensioni molto stretta. Il solfuro di cadmio (CdS) nanostrutturato ha promettenti future applicazioni tecnologiche, come ad esempio nei dispositivi optoelettronici, celle solari ad alta efficienza e come tracciante fluorescente in biologia. Tuttavia, per poter sfruttare al meglio le proprietà fisiche a favore delle citate applicazioni è di fondamentale importanza una conoscenza approfondita delle proprietà fisiche. In questa tesi, sono state studiate le proprietà optovibrazionali e optoelettroniche dei quantum dots (QDs) di solfuro di cadmio cresciuti tramite un metodo di crescita colloidale.
Tramite i metodi di crescita colloidale è possibile produrre QDs con dimensione ridotta e una distribuzione della dimensione molto stretta. La sintesi dei CdS-QDs consiste nella termolisi a circa 260 °C dello stearato di cadmio in presenza di solfuro di idrogeno in un solvente organico altobollente (1-ottadecene). La velocità della crescita e la dimensione finale dei QDs sono regolate dalla presenza di una molecola surfattante, l’ossido di triottilfosfina (TOPO). In particolare, QDs con una determinata dimensione e con una sua distribuzione molto stretta possono essere ottenuti regolando opportunamente la temperatura di crescita, la concentrazione dei precursori e principalmente la concentrazione del surfattante e del tempo di reazione (crescita arrestata).
La morfologia, la dimensione (diametro) e la distribuzione dei diametri sono state determinate tramite TEM. Tramite spettroscopia di assorbimento, si ottengono informazioni sugli stati elettronici, inoltre, sfruttando la relazione esistente tra la band gap e il diametro, si può determinare il diametro medio di un campione di QDs. Le proprietà emissive dei QDs sono state studiate tramite spettroscopia di fotoluminescenza (PL) e dall’energia della banda di PL si può ottenere una stima del diametro medio dei QDs. Dalla larghezza di banda degli spettri di assorbimento e di PL si può ottenere anche una stima sulla distribuzione del diametro dei QDs.
Un estesa parte del lavoro riguarda lo studio delle proprietà vibrazionali dei CdS-QDs, tramite spettroscopia Raman. Queste indagini sono state effettuate su campioni di CdS-QDs cresciuti appositamente con diversi diametri. Per eseguire misure micro-Raman, i campioni di CdS-QDs coordinati da molecole di TOPO che hanno una consistenza gelatinosa, sono stati trattati con acido tioglicolico (TGA). Questo trattamento è necessario per avere CdS-QDs in forma di polvere, la quale è più adatta per essere studiata tramite spettroscopia Raman. Per evitare effetti termici negli spettri o il danneggiamento del campione, le misure micro-Raman devono essere effettuate con potenze del laser molto basse. Negli spettri Raman di CdS-QDs si osserva uno spostamento del picco del fonone LO verso frequenze più basse , in particolare, tale spostamento è più marcato per i QDs più piccoli, mentre, al crescere del diametro, la frequenza si avvicina progressivamente a quella del bulk. Questa diminuzione di frequenza è causata dall’espansione del cristallo che avviene nei QDs, con il conseguente indebolimento dei legami per i quali diminuisce la frequenza di risonanza.
Oltre a questo, il confinamento quantistico dei fononi è visibile come un allargamento asimmetrico della linea dei fononi, e come l’apparizione di un nuovo picco a circa 270 cm-1. Alcune pubblicazioni assegnano questo picco ai modi di superficie, mentre altri lo descivono come la conseguenza delle nuove regole di selezione dovute dalla bassa dimensionalità. Lo studio ha anche lo scopo di comparare le previsioni teoriche basate sia sul modello “dielectric continuum” che sui fononi di superficie con i risultati sperimentali. È stata trovata una relazione tra i valori di frequenza dei fononi predetti teoricamente e i risultati sperimentali, in particolare, le frequenze dei fononi di superficie sono in accordo con i risultati sperimentali.
In conclusione, lo scopo di questo studio consiste nello sviluppo di un metodo per crescere CdS-QDs con le caratteristiche fisiche desiderate (diamtero voluto e distribuzione di diametro stretta) per poterne poi effettuare uno studio sistematico delle proprietà vibrazionali ed elettroniche.In recent years, there has been a rapid development of the growth techniques of nanostructured materials, and a particular breakthrough was given by the introduction of colloidal growth techniques. These techniques allow to grow by affordable facilities, a wide range of nanostructured materials, metals and semiconductors, with high crystallinity, reduced size, narrow size distribution. Nanostructured cadmium sulfide (CdS) has promising future applications as in the realization of optoelectronic devices, high efficiency solar cells as well as fluorescent biological probe. However, in order to fully exploit the potential technological applications, the study of the physical properties of such materials is of crucial importance. In this thesis, the optoelectronic and optovibrational properties of cadmium sulfide quantum dots (QDs) grown by colloidal chemical method are studied. By the means of colloidal growth, it is possible to grow QDs with reduced size and narrow size distribution. The synthesis of CdS-QDs consists in the thermolysis (T=260 °C) of cadmium stearate in presence of hydrogen sulfide in a high temperature boiling point solvent (1-octadecene). The growth rate and final QDs size are regulated by the presence of the surfactating molecule trioctylphosphine oxide (TOPO). QDs with a determined size and a narrow size distribution can be obtained properly adjusting the growth parameters such as temperature, precursors concentrations, and principally the surfactant concentration and reaction time (arrested growth). The QDs morphology, their size and their size distribution is determined by TEM imaging. By absorption spectroscopy, information regarding the electronic states in QDs are obtained, and exploiting the relation existing between band gap and QD diameter, the mean diameter of the QDS is determined. The emissive properties of the QDs are probed by photoluminescence spectroscopy (PL). From the energy of PL band, an estimation of the QDs diameter can be obtained. Based on the width of absorbance and PL bands, the width of QDs size distributions can be estimated. A large part of the work is concerned with the study of vibrational properties of CdS-QDs by Raman spectroscopy. These investigations are carried out on the CdS-QDs samples purposely grown with different average sizes. In order to perform micro-Raman measurements, the gel-like TOPO-coated CdS-QDs are treated to replace the TOPO layer by thioglycolic acid (TGA). This treatment is necessary in order to have powder-like CdS-QDs being more suitable to a Raman scattering study. To avoid thermal effects or damage to the sample, the micro-Raman measurements must to be performed using very low laser powers (on the sample). In the Raman spectra of CdS-QDs, a decrease of the phonon frequency (red-shift) with respect to the bulk CdS frequency is observed. In particular, the red-shift is expected to be more pronounced for the smallest QDs, while at the increasing of QDs size, the phonon frequency will approach progressively to the bulk value. This red-shift is caused by the lattice expansion and by a subsequent weakening of the bonds which causes a reduction of the resonance frequency. Beyond the red-shift, the quantum confinement is visible also as an asymmetric broadening of the phonon line and by the apparition of a new peak a circa 270 cm-1. Some reports assign this peak to surface modes, while other reports describe this mode as a consequence of new selection rules arising from the reduced dimensionality. The study has also the aim to cross check the theoretical prediction based on the dielectric continuum model and on the surface modes with the experimental results. A relation between the theory and the experiment has been found, in particular, the predicted surface frequencies are in good agreement with the experiments. In conclusion, the goal of this thesis work is to develop a method to grow CdS-QDs with the desired physical characteristics (narrow size distribution) suitable for a systematic study of optical properties (vibrational and electronic).
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Rijal, Upendra. "Suppressed Carrier Scattering in Cadmium Sulfide-Encapsulated Lead Sulfide Nanocrystal Films." Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1402409476.
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Schmall, Nicholas Edward. "Fabrication of Binary Quantum Solids From Colloidal Semiconductor Quantum Dots." Bowling Green State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1245257669.
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Bylsma, Jason Michael. "Multidimensional Spectroscopy of Semiconductor Quantum Dots." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4001.
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The coherent properties of semiconductor nanostructures are inherently difficult to measure and one-dimensional spectroscopies are often unable to separate inhomogeneous and homogeneous linewidths. We have refined and improved a method of performing multidimensional Fourier transform spectroscopy based on four-wave
mixing (FWM) experiments in the box geometry. We have modified our system with broadband beamsplitters in all interferometer arms, high-resolution translation stages and the ability to work in reflection geometry. By improving the phase-stability of our setup and scanning pulse delays with sub-optical cycle precision, we are able to
reproduce 2DFT spectra of GaAs multiple quantum wells. With the FWM signal reflected from the sample surface instead of transmitted through, we show that very low pulse powers can be used to generate coherent 2D signals from colloidal PbS quantum dots. Dephasing times are particularly difficult to measure in small colloidal quantum dots due to environmental broadening effects from the colloidal growth. We show that low-temperature pure excitonic dephasing can be measured via time-integrated measurements as well as from the cross-diagonal linewidths of 2DFT spectra. Ultrafast
sub-picosecond dephasing times are measured at 5 K in 3 nm PbS quantum dots, while excitation-density-dependence is investigated in these dots. By retrieving the global phase with an all-optical method, we are able to retrieve the real-part 2D spectra of PbS quantum dots.
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Yildiz, Ibrahim. "Luminescent Probes and Photochromic Switches Based on Semiconductor Quantum Dots." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/103.
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A new strategy was developed to switch the luminescence of semiconductor quantum dots with chemical stimulations. It is based on the photoinduced transfer of either energy from CdSe-ZnS core-shell quantum dots to [1,3]oxazine ligands or electrons from the organic to the inorganic components. Upon addition of base or acid, energy or electron transfer pathways respectively become operative, leading to changes in the luminescence of the nanoparticles. These changes are fully reversible and can be exploited to probe the pH of aqueous solutions from 3 up to 11 and this design can lead to the development of pH-sensitive luminescent probes for biomedical applications based on the semiconductor quantum dots. Secondly, an operating principle to transduce the supramolecular association of complementary receptor-substrate pairs into an enhancement in the luminescence of sensitive quantum dots was identified. This system is based on the electrostatic adsorption of cationic quenchers on the surface of anionic quantum dots. The adsorbed quenchers efficiently suppress the emission character of the associated nanoparticles on the basis of photoinduced electron transfer. In the presence of target receptors able to bind the quenchers and prevent electron transfer, however, the luminescence of the quantum dots is restored. Thus, complementary receptor-substrate pairs can be identified with luminescence measurements relying on this system and this protocol can be adapted to signal protein-ligand interactions. Thirdly, a photochromic spiropyran with dithiolane appendage to adsorb on the surface of cadmium sulfide system was designed. The properties of the resulting photochrome-nanoparticle assemblies vary significantly with the experimental conditions selected for the preparation of the inorganic component. Finally, photochromic materials based on the photoinduced transfer of electrons from CdSe-ZnS core-shell quantum dots to bipyridinium dications were developed.
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Hess, Whitney Rochelle. "Exploring the versatility of lead sulfide quantum dots in low-temperature, solution-processed solar cells." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109683.
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Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2017.Page 161 blank. Cataloged from PDF version of thesis.
Includes bibliographical references (pages 151-160).
Solution processability and optoelectronic tunability makes lead sulfide quantum dots (PbS QDs) promising candidates for low-temperature, solution-processed thin film solar cells. Central to this thesis is the crucial role of QD surface chemistry and leveraging surface modification to prepare QDs suitable for optoelectronic device applications. The work presented here explores the versatility of PbS QDs integrated into two main device architectures, where the primary role of the QD is unique in each case. In p-i-n planar perovskite solar cells, efforts to utilize PbS QDs as a hole transport material and the effects of size tuning and surface passivation with cadmium on device characteristics are discussed. A combination of QD size reduction and minimal cadmium-to-lead cation exchange is found to improve the open circuit voltage and hole extraction into the PbS QD layer. In ZnO/PbS QD heterojunction solar cells, the feasibility of preparing fully inorganic, halometallate-passivated PbS QD inks for use as the absorber layer is discussed. A modified biphasic ligand exchange strategy is presented and in order to further elucidate electronic passivation in these QD ink systems, optical properties were investigated with steady state and time-resolved photoluminescence. Significantly, PbS QDs exhibit comparable quantum yields in solution before and after ligand exchange and no significant trap state emission was observed in solution and in film. Ink devices were fabricated with one- and two-layer depositions, which significantly reduce fabrication time compared to traditional layer-by-layer deposition, and devices exhibit anomalous efficiency improvement throughout storage in air.
by Whitney Rochelle Hess.
Ph. D. in Physical Chemistry
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Hwang, Gyuweon. "Surface trap passivation and characterization of lead sulfide quantum dots for optical and electrical applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98741.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-119).
Quantum dots (QDs) are semiconductor nanocrystals having a size comparable to or smaller than its exciton Bohr radius. The small size of QDs leads to the quantum confinement effects in their electronic structures. Their unique optical properties, including a tunable emission from UV to IR, make QDs attractive in optoelectronic applications. However, further improvements in device performance are required to make them competitive. One well-known factor that presently limits the performance of QD thin film devices is sub-band-gap states, also referred to as trap states. For instance, trap states impair optical properties and device performance by providing alternative pathways for exciton quenching and carrier recombination. Chemical modification of QDs has been commonly used for passivating trap states and thereby improving QD devices. However, the influence of chemical modifications of ligands, QD surfaces, or synthetic routes on electrical properties of QD thin films is not sufficiently characterized. Suppressing the trap states in QD thin films is a key to improve the performance of QDbased optoelectronics. This requires fundamental understanding of trap state source, which is lacking in these materials. In this thesis, I pursue to find a systematic method to control density of trap states by exploring different characterization techniques to investigate trap states in QD thin films. These attempts provide insight to develop a rationale for fabricating better performing QD devices. This thesis focuses on the trap states in IR emitting lead sulfide (PbS) QD thin films, which have great potential for application in photovoltaics, light emitting diodes (LEDs), photodetectors, and bio-imaging. Previously, QD thin films are treated with different ligands to passivate trap states and thereby improve the device performance. Through my work, I pursued to unveil the electrical characteristics and chemical origin of trap states, and develop a strategy to suppress the trap states. First, I hypothesize that surface dangling bonds are a major source of trap states. An inorganic shell layer comprised of cadmium sulfide (CdS) is introduced to PbS QDs to passivate the surface states. Addition of CdS shell layers on PbS QDs yields an enhanced stability and quantum yield (QY), which indicates decreased trap-assisted exciton quenching. These PbS/CdS core/shell QDs have a potential for deep-tissue bio-imaging in shortwavelength IR windows of 1550-1900 nm. However, the shell layer acts as a transport barrier for carriers and results in a significant decrease in conductivity. This hinders the incorporation of the core/shell QDs in electrical applications. An improved reaction condition enables the synthesis of PbS/CdS QDs having a monolayer-thick CdS shell layer. These QDs exhibit QY and stability comparable to thick-shell PbS/CdS QDs. Incorporation of these thin-shell QDs improves external quantum efficiency of IR QD-LEDs by 80 times compared to PbS core-only QDs. In the second phase of my work, I explore capacitance-based measurement techniques for better understanding of the electrical properties of PbS QD thin films. For in-depth analysis, capacitance-based techniques are introduced, which give complementary information to current-based measurements that are widely used for the characterization of QD devices. Nyquist plots are used to determine the dielectric constant of QD films and impedance analyzing models to be used for further analysis. Mott-Schottky measurements are implemented to measure carrier concentration and mobility to compare PbS core-only and PbS/CdS core/shell QD thin films. Drive-level capacitance profiling is employed to characterize the density and energy level of trap states when QD films are oxidized. Lastly, I investigate the chemical origin of trap states and use this knowledge to suppress the trap states of PbS QD thin films. Photoluminescence spectroscopy and X-ray photoelectron spectroscopy show that standard ligand exchange procedures for device fabrication lead to the formation of sub-bandgap emission features and under-charged Pb atoms. Our experimental results are corroborated by density functional theory simulation, which shows that the presence of Pb atoms with a lower charge in QDs contributes to sub-bandgap states. The trap states generated after ligand exchange were significantly reduced by oxidation of under-charged Pb atoms using 1,4-benzoquinone. The density of trap states measured electrically with drive-level capacitance profiling shows that this reduces the electrical trap density by a factor of 40. In this thesis, I characterized trap states and showed that by suppressing the trap states we can modify the electrical properties of QD thin films, which influence the performance of QD devices directly. This work is a starting point to fully analyze the trap states in QD thin devices and thereby provides insight to design a rationale for fabricating better performing QD devices.
by Gyuweon Hwang.
Ph. D.
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Roland, Paul Joseph. "Charge Carrier Processes in Photovoltaic Materials and Devices: Lead Sulfide Quantum Dots and Cadmium Telluride." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1449857685.
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Diederich, Geoffrey M. "Synthesis of Zinc Telluride/Cadmium Selenide/Cadmium Sulfide Quantum Dot Heterostructures for use in Biological Applications." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1342542873.
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Bhagyaraj, Sneha. "Green synthesis, characterization and applications of cdse based core-shell quantum dots and silver nanocomposites." Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2318.
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Thesis (DTech (Chemistry))--Cape Peninsula University of Technology, 2015.Researchers around the world are now focusing on inculcating green chemistry principles in all level of research especially in nanotechnology to make these processes environmental friendly. Nanoparticles synthesized using green chemistry principles has several advantages such as simplicity, cost effectiveness, compatibility for biomedical and pharmaceutical applications and large scale production for commercial purpose. Based on this background, this thesis present the design, synthesis, characterization and applications of various CdSe based core-shell and core-multi shell quantum dots (QDs), quantum dots-polymer nanocomposites, silver nanoparticles (Ag-NPs) and silver nanocomposites via completely green methods. Various QDs like CdSe/CdS/ZnS and CdSe/ZnS, and there polymer nanocomposites were successfully synthesized and characterized. The high quality of the as-synthesized nanoparticles was confirmed using absorption and photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Detailed optical and morphological characterization showed that the CdSe/CdS/ZnS core-multi shell QDs were small, monodispersed with high fluorescent intensity and narrow emission width. The CdSe/CdS/ZnS core multi-shell QDs were dispersed in epoxy polymer matrix to obtain fluorescent epoxy nanocomposite. The brillouin spectroscopy analysis revealed that the presence of QDs inside polymer composite reduces the acoustic frequency of the polymer. Highly fluorescent CdSe/ZnS core-shell QDs was also synthesized and dispersed in PMMA polymer matrix to prepare bright yellow emitting nanocomposite film. The as-synthesized QDs also undergone surface exchange to convert the organically soluble nanomaterial to water soluble. After the ligand exchange, the morphology and above all the fluorescence property of the quantum dots remained intact. In another approach, HDA-capped CdSe nanoparticles were synthesized in the absence of an inert gas followed by dispersion in polymer polycaprolactone to produce orange light emitting electrospun polymer nanocomposite nanofibre.
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Haugen, Neale O. "Spectroscopic Studies of Doping and Charge Transfer in Single Walled Carbon Nanotubes and Lead Sulfide Quantum Dots." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438768843.
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Veinot, Jonathan G. C. "Surface functionalization and derivatization of 25 A cadmium sulfide nanoclusters : a study of potential molecular electronic components /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://wwwlib.umi.com/cr/yorku/fullcit?pNQ43453.
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Thesis (Ph.D.)--York University, 1999. Graduate Programme in Chemistry.Typescript. Includes bibliographical references (leaves 155-161). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ43453
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Marrujo, Dan Madrid. "Spectral Conversion of Light Using Cadmium Selenium Zinc Sulfide Core Shell Quantum Dots to Increase the Efficiency of Photovoltaic Cells." DigitalCommons@CalPoly, 2008. https://digitalcommons.calpoly.edu/theses/8.
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Photovoltaics harness energy emitted from the sun. When the sun's energy is absorbed by a photovoltaic cell array, photons of light are converted into current. The amount of current produced by a photovoltaic cell is calculated by the difference between the energy of the incoming photon and the energy required for an electron to travel across the band gap of the photovoltaic cell. Traditional solar cells are commonly manufactured from silicon, which have a bandgap energy of 1.1 eV. If the photon's energy is equal to or greater than the band gap of silicon, electrons are excited from the valence band to the conduction band. Electron excitation between these respective bands enables current flow within the photovoltaic cell. Increasing the number of photons energies equal to the bandgap of the photovoltaic material will increase the amount of current produced.
The objective of this research was to explore the utilization of quantum dots to increase the amount of light collected by a silicon-based photovoltaic cell. Although the electromagnetic spectrum of the sun is broadband, only a finite portion of the spectrum can be harnessed by current solar cell technology. For example, the excess energy of ultraviolet light, when compared to the bandgap of silicon, is generally lost to thermalization; which prevents current production. Therefore the range of the electromagnetic spectrum that is available to a solar cell for electric current is limited. One mechanism to increase the efficiency of solar cells is to increase the electromagnetic spectrum collected.
Quantum dots are known to down convert high-energy photons to lower energy photons; thereby expanding the useable electromagnetic spectrum. This study investigated the changes associated with dispersing quantum dots above the surface of a photovoltaic cell, as well as, measuring how the electric current of the device is affected. The quantum dots were purchased from Evident Technologies and were made from CdSe/ZnS. Once acquired, the quantum dots were suspended in microfluidic channels fabricated from polydimethylsiloxane (PDMS). Toluene and water were respectively chosen to disperse the quantum dots. The compatibility of these solvents with PDMS was explored. The change in current was investigated when the microfluidic channels filled with quantum dots were applied to the surface of the photovoltaic cell.
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Marrujo, Dan Madrid Savage Richard N. "Spectral conversion of light using cadmium selenium zinc sulfide core shell quantum dots to increase the efficiency of photovoltaic cells : a thesis /." [San Luis Obispo, Calif. : California Polytechnic State University], 2008. http://digitalcommons.calpoly.edu/theses/8/.
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Thesis (M.S.)--California Polytechnic State University, 2008."June 2nd, 2008." "In partial fulfillment of the requirements for the degree [of] Master of Science in Engineering with Specialization in Materials Engineering." "Presented to the faculty of California Polytechnic State University, San Luis Obispo." Major professor: Richard Savage, Ph.D. Includes bibliographical references (leaves 98-100). Also available online and on microfiche (2 sheets).
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Longo, Antonio Valerio. "Development of alternate-current thin-film electroluminescent devices based on manganese-doped zinc sulfide quantum-dot technology." Electronic Thesis or Diss., Université Paris Cité, 2021. http://www.theses.fr/2021UNIP7253.
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Ce travail de thèse concerne le développement d'un dispositif émetteur de lumière, basé sur des nanoparticules de sulfure de zinc dopées au manganèse,fonctionnant sous l'application d'une tension alternative. Notre dispositif est basé sur une configuration simple impliquant une seule couche de nanoparticules luminescentes, déposée par spin coating, placée entre deux films isolants. D’abord,nous avons étudié le système de nanoparticules d'un point de vue fondamental.Ces nanoparticules, synthétisées sans aucun tensioactif par une synthèse assistée par micro-ondes, sont caractérisées par une phosphorescence dans la région orange du spectre visible provenant du dopage au manganèse. Nous avons observé et étudié une augmentation de cette activité optique sous une exposition prolongée à la lumière UV. Notre analyse nous a permis d'attribuer ce phénomène à un effet de contrainte du réseau crystallin local autour des chromophores de manganèse dû à un processus d'oxydation de surface induit par la lumière UV.Dans une deuxième partie de notre travail, nous avons étudié les propriétés diélectriques des couches isolantes, constituées d'un film de oxyde d'hafnium déposé par Atomic Layer Deposition. En explorant plusieurs épaisseurs de couches et deux températures de dépôt, nous avons montré que la température plus basse fournit des résultats significativement plus fiables et robustes. De plus, nous avons également abordé la possibilité de déposer une couche d'alumine par une approche sol-gel en solution, mettant en évidence les principales limites de cette technique.Dans la troisième partie du manuscrit, nous décrivons les principales caractéristiques du dispositif complet. Nous avons observé la bande d'émission orange due au dopage au manganèse, ainsi que le comportement seuil typique de l'intensité de la lumière émise en fonction de la tension appliquée. En exploitant la caractérisation structurelle, les mesures de spectroscopie d'impédance et une comparaison avec des travaux théoriques sur des dispositifs similaires, nous avons pu affirmer que le mécanisme derrière l'émission de lumière observée est un processus de création de charge induite par le champ électrique dans la couche active, suivi par leur transport à travers la couche et d'un processus de recombinaison radiative à l'échelle de la nanoparticule individuelle. Par rapport aux travaux antérieurs basés sur le même type de nanoparticules, notre point clé a été l'utilisation de nanoparticules non enrobées qui ont permis d'obtenir un arrangement de nanoparticules très compact, favorisant le mécanisme physique mentionné ci-dessus. Notre travail constitue une avancée dans le développement de dispositifs électroluminescents plus compacts, industriellement réalisables et respectueux de l'environnementIn this work we address the development of a light-emitting device, based on manganesedoped zinc sulfide nanoparticles, working under the application of an alternate-current voltage. Our device is based on a simple capacitive configuration implying a single layer of spin-cast nanoparticles sandwiched between two insulating thin films. In the first part of our work, we studied the nanoparticle system from a fundamental point of view. These nanoparticles, synthesized without the use of any surfactant by a microwave-assisted synthesis, are characterized by a phosphorescence activity in the orange region of the visible spectrum stemming from manganese dopants. In our work, we have observed and studied an enhancement of this optical activity under prolonged UV-light exposition. Our investigation allowed us to ascribe this phenomenon to a local lattice-strain effect around manganese chromophores due to a surface oxidation process induced by UV light. In a second part of our work, we focused on the dielectric properties of the insulating layers, consisting in an hafnium oxide film deposited by atomic layer deposition. By exploring several layer thicknesses and deposition temperatures, we have optimized the dielectric properties of the film, leading to more reliable and robust results. Moreover, we have also addressed the possibility of depositing an alumina layer by an in solution sol-gel approach, highlighting the main limitations of this technique. In the third part of the manuscript, the main characteristics of the complete electroluminescent device are addressed. More specifically, we recovered the orange emission band due to manganese doping, as well as the typical threshold behavior of the intensity of the emitted light as a function of the applied voltage. By exploiting structural characterization, impedance spectroscopy measurements and a careful comparison with theoretical works on similar devices, we have been able to state that the mechanism behind the observed light emission is a fieldinduced charge-creation process within the active layer only, followed by charge transport across the layer and radiative recombination within a single nanoparticle. Compared to previous works based on manganese-doped zinc sulfide nanoparticles, our key point has been the use of uncoated nanoparticles which allowed to achieve a very compact nanoparticle arrangement, favoring the physical mechanism mentioned above. Our work constitutes a step forward in the development of more compact, industrially feasible and eco-friendly light emitting devices
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Masilela, Nkosiphile. "Low symmetry metallophthalocyanines and their nanoparticle conjugates for photodynamic antimicrobial chemotherapy." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001906.
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This thesis reports on the syntheses of novel low symmetrically substituted Zn, Sn, Ge and Ti MPc complexes containing a single carboxylic or cysteinyl group available for attachments to MNPs. The complexes were extensively characterized by various techniques to ensure their purity. Various metallic nanoparticles consisting of silver (AgNPs), gold (AuNPs) as well as quantum dots (QDs) were successfully prepared and conjugated to the low symmetry phthalocyanine complexes. The conjugates were successfully characterized using many techniques. The Q-band maxima of the MPcs were observed at completely different wavelength regions depending on the nature of the substituents and the central metal used. Blue shifting of the Q band in the absorption spectra was observed for the complexes in the presence of AuNPs, while aggregation was observed in the presence of quantum dots. The complexes were successfully electrospun into polymer fibers for the antimicrobial inhibition of bacteria. The photophysical and photochemical properties of these complexes were extensively investigated. Higher triplet and singlet oxygen quantum yields were achieved for the Ge Pc complexes, with all the complexes giving reasonable singlet oxygen quantum yields. An enhancement in triplet and singlet oxygen quantum yields was observed for all the complexes in the presence of metal nanoparticles. However, the singlet oxygen quantum yields decreased for all the complexes when incorporated into electrospun fibers. The antimicrobial behaviour of the complexes was investigated against Bacillus Subtilis and Staphylococcus Aureus in solution and in the fiber matrix. High antimicrobial inhibitions were observed for the Ge complexes followed by the ZnPc derivatives. All the low symmetry ZnPc derivatives were conjugated to AgNPs and their antimicrobial behaviour was compared to their symmetrical counterparts. The best antimicrobial inhibition behaviour was observed for the low symmetry Pcs when compared to their symmetrical counterparts. In the absence and in the presence of AgNPs, axially ligated SiPc also showed better antimicrobial activity when it was compared to the unsubstituted ZnPc complex.
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Andrade, George Ricardo Santana. "Nanocompósitos baseados em quantum dots de CdS e CdS:Cu suportados em mercaptopropilsílica : síntese, caracterização e aplicação em fotocatálise." Universidade Federal de Sergipe, 2011. http://ri.ufs.br:8080/xmlui/handle/123456789/3514.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoTextile dyes and other commercial dyestuffs have become a focus of environmental remediation efforts in the last few years. Considerable attention has been expended recently on the photocatalytic oxidative degradation of colored contaminants in waste water over semiconductor surfaces. In this work, we evaluated the photocatalytic activities of nanocomposites based on cadmium sulfide (CdS) quantum dots anchored on (mercaptopropyl)silica (MPS) monitoring the photodegradation of methylene blue and rhodamine 6G aqueous solutions under sunlight irradiation. Herein, MPS was selected as the stabilizing agent to prepare the CdS and CdS doped with Cu2+ Qdots by the chemical reaction of cadmium acetate and thiourea in dimethylformamide Abstract|viii (DMF) by a rather simple one-step method. The quantum size effect has been monitored by UV visible spectroscopy, which showed a blue shift of about 16 48 nm relative to bulk CdS in the range 442-474 nm. Particle sizes calculated from Brus s model were found to be dependent on the MPS amount. These results evidenced that as-prepared CdS nanocrystals behave as Qdots. Additionally, XRD mensurements and HRTEM images indicated CdS cubic structure for the nanocrystals, which also exhibited an increment in the fluorescence intensity with decreasing particle size. UV absorption spectra for Cu-doped CdS are essentially similar to that of the undoped Qdots, but the luminescence properties are quite different from those of the undoped samples. Moreover, these materials could effectively degrade the organic dyes under sunlight irradiation by pseudo-first-order kinetics. This suggested that the CdS Qdots prepared in this work can be used as the potential photocatalyst to effectively treat the organic pollutants under sunlight irradiation.
Indústrias têxteis produzem elevado volume de efluentes ricos em corantes tóxicos e não-biodegradáveis. A degradação fotocatalítica de poluentes aquosos usando nanocristais semicondutores é uma área emergente na remediação ambiental. Neste trabalho, a atividade fotocatalítica de quantum dots (Qdots) de sulfeto de cádmio (CdS) ancorados em (mercaptopropil)sílica (MPS) foi investigada a partir da degradação dos corantes azul de metileno (AM) e rodamina 6G (R6G). Nanocristais de CdS e CdS dopado com íons Cu2+ foram preparados pela reação química de acetato de cádmio e tiouréia em presença da matriz de sílica organofuncionalizada, por um método bastante simples e de uma única etapa. Pelos espectros eletrônicos, foi possível notar um Resumo|vi deslocamento para o azul com o aumento da quantidade de MPS e band gaps mais largos do que o bulk de CdS. Os diâmetros das nanopartículas, estimados a partir do modelo de Brus, são dependentes da quantidade da matriz. Estes resultados sugerem que as partículas se comportam como Qdots. Fases cúbicas dos nanocristais são estabelecidas de acordo com dados de DRX e HRTEM e os espectros de emissão corroboram a presença de Qdots no material formado. A dopagem do nanocompósito com íons Cu2+ propiciou mudanças na recombinação elétron-buraco das nanopartículas de CdS, o que foi observado pelos espectros de absorção no UV-vis e de emissão. Avaliação temporal no espectro de absorção no UV-vis dos corantes AM e R6G em contato com CdS/MPS e CdS:Cu/MPS durante irradiação com luz solar mostrou uma pronunciada diminuição da intensidade de absorbância e um deslocamento do máximo de absorção para menores comprimentos de onda, em resposta à formação de subprodutos de degradação.
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Nascimento, Cristiane da Cunha. "Síntese, caracterização e aplicação em fotocatálise de nanocristais semicondutores de sulfeto de cádmio suportados em argila tiolada." Universidade Federal de Sergipe, 2011. https://ri.ufs.br/handle/riufs/3512.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe challenge of nanotechnology, the science that studies the phenomena as well as the manipulation of materials at nanoscale (1-100 nm) is the control of composition, shape and size of nanoparticles, parameters that influence the physical, chemical, optical and electronic properties. In this context, the so-called quantum dots (QDs) are semiconductor nanoparticles which have attracted considerable attention due to their heavily size-dependent optical and electronic properties. Cadmium sulfide (CdS) QDs exhibit important photoluminescent properties, allowing applications in optoelectronic systems, photocatalysis, photodegradation of pollutants in the water medium etc. In this work, we present the results of the synthesis and characterization of CdS nanocrystals, in the absence and in the presence of doping Mn (II) ions, supported on Montmorillonite thiolated (MT) as well as their application as photocatalysts. The materials were characterized by UV-Vis absorption spectroscopy, X-ray diffractometry, photoluminescence spectroscopy and High-Resolution transmission electron microscopy. The effects of nanoparticle size, evaluated first by UV-visible spectroscopy, showed that the absorption maximum changed from 470 to 460 nm for different proportions of the support relative to CdS precursors. The XRD patterns showed three peaks of CdS nanocrystals related to the cubic phase of CdS. The photoluminescence spectra have shown emission bands around 470, 476, 484 and 495 viii nm, attributed to direct recombination of electron-hole pairs, and the presence of a shoulder around 578 nm, attributed to radiative recombination in trap levels from surface deffects. HRTEM images for the sample of CdS/MT 200 mg suggest the presence of monocrystalline CdS nanocrystals with approximately 4.8 nm which assemble together forming polycrystalline aggregates with a size from about 45 nm intercalated into clay layers. The photocatalytic activity of CdS/MT and CdS:Mn / MT was studied by Rhodamine 6G (R6G) photodegradation under sunlight irradiation. The results have shown a decrease in the intensity of the bands in addition to a shift from 526 to 505 nm in the absorption maximum with increasing time. According to the results of photocatalysis after 80min practically all the dye had been degraded, on the other hand, for the adsorption test, after the first 20 minutes there were no significant changes in the dye concentration. The rate of decolorization of dye showed that after 80 min the QDs have an effective induction in the degradation of R6G and the photocatalytic decolorization of R6G can be described by a pseudo first order kinetic model.
O desafio da nanotecnologia, ciência que estuda os fenômenos e manipulação de materiais em escala nanométrica (1-100 nm), é o controle de composição, forma e tamanho de nanomateriais, parâmetros que influenciam as propriedades físicas, químicas, óticas e eletrônicas. Dentro desse contexto, os quantum dots (QDs) são nanopartículas semicondutoras que têm atraído uma atenção considerável devido as suas propriedades ópticas e eletrônicas, que são fortemente dependente da sua dimensão. Os QDs de sulfeto de cádmio (CdS) apresentam importantes propriedades de fotoluminescência, que possibilitam aplicações em sistemas optoeletrônicos, nanosemicondutores, fotocatálise, fotodegradação de poluentes na água etc. Neste trabalho, apresentamos os resultados da síntese, caracterização e aplicação em fotocatálise e adsorção dos nanocristais de CdS, na presença e na ausência de dopagem com íons Mn (II), suportados em Montmorilonita Tiolada (MT). Os materiais obtidos vi foram caracterizados por Espectroscopia de Absorção no UV-vis, Difração de Raios-X, Fotoluminescência e Microscopia Eletrônica de Transmissão de Alta Resolução. Os efeitos do tamanho das nanopartículas foram estudas por espectroscopia de UV-visível que mostraram uma absorção máxima em 470 e 460 nm para diferentes proporções da MT. Os difratogramas indicaram três picos relacionados às nanopartículas do CdS que corresponde a fase cúbica do CdS, o que foi corroborado com os dados de HRTEM. Os espectros de fotoluminescência mostram bandas de emissão em torno de 470, 476, 484 e 495 nm atribuídas à recombinação direta dos pares elétron-buraco, e a presença de um ombro em torno de 578 nm, atribuída a recombinação radiativa em níveis de armadilhas provenientes de imperfeições do material. As imagens de HRTEM para a amostra de CdS/MT 200 mg sugerem a presença de nanocristais de CdS monocristalinos, com diâmetro de aproximadamente 4,8 nm, agregados na forma de partículas policristalinas com um tamanho aproximadamente entre 45 nm intercalados nas lamelas da argila. A atividade fotocatalítica do CdS/MT e do CdS:Mn/MT foi estudada através da fotodegradação da Rodamina 6G (R6G) sob irradiação solar.Os resultados evidenciaram uma diminuição da intensidade das bandas e um deslocamento de 526 para 505 nm do máximo de absorção com o aumento do tempo, indicando a formação de intermediários de degradação. De acordo com os resultados de fotocatálise, após 80min de reação praticamente, praticamente todo o corante havia sido degradado, enquanto que para o ensaio de adsorção após os 20 primeiros minutos não houve mudanças significativas na concentração do corante nas amostras. A taxa de descolorização do corante mostrou que, depois de 80 min, os QDs tiveram uma efetiva indução na degradação da R6G e que a descoloração fotocatalítica da R6G pode ser descrita por um modelo cinético de pseudo primeira ordem.
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Adikaram, Mudiyanselage Janith S. "Nanomaterial synthesis and surface treatment by atmospheric pressure cold plasmas." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232838/1/Janith_Adikaram%20Mudiyanselage_Thesis.pdf.
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The main goal of this study was to demonstrate the potential of atmospheric pressure cold plasmas to synthesize nanoparticles and surface treatments. Silver nanoparticles and carbon quantum dots were selected for this work. The use of silver nanoparticles in bactericidal applications has been tested. In addition, carbon quantum dots are used to manufacture a low-cost metal ion sensor for the detection of copper in drinking water. The second part of the study investigated the chemical reactions that occur in plasma treated mesoporous tin oxide films. These are used to increase the efficiency of dye sensitized solar cells.
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Geszke-Moritz, Malgorzata. "Synthesis of stable and non-cadmium containing quantum dots conjugated with folic acid for imaging of cancer cells." Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL066N/document.
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Les Quantum Dots (QDs) sont des particules cristallines de semi-conducteur ou du métal de forme sphérique et de dimension nanométrique. L'intérêt majeur des QDs réside dans leur grande adaptabilité à de nombreuses applications biologiques.Le but de mon travail était de développer une nouvelle classe de QDs de faible toxicité afin de les utiliser pour la bio-imagerie des cellules cancéreuses. Pour cela, il est nécessaire de préparer des sondes hydrosolubles, photostables, biocompatibles, de luminescence élevée et possédant une faible toxicité. La synthèse des cœurs de type ZnS and ZnSe dopés au manganèse ou au cuivre et stabilisés par l’acide 3-mercapropropionique ou par le 1-thioglycérol a été réalisée par la voie hydrothermale. Les techniques analytiques de caractérisation utilisées sont la spectroscopie UV-visible, la spectroscopie de fluorescence, la diffraction des rayons X (XRD), la spectroscopie photoélectronique de rayon X (XPS), la microscopie électronique à transmission (TEM), la diffusion dynamique de la lumière DLS, la spectroscopie infra-rouge (IR), et la résonance paraélectronique (RPE). La toxicité des QDs a été déterminée sur des cellules cancéreuses. Les différents test de cytotoxicité (MTT, XTT et ferrous oxidation-xylenol orange) ont été réalisés. Finalement, les QDs de type ZnS:Mn conjugués à l’acide folique ont été utilisés pour la bio-imagerie des cellules cancéreuses par le biais d’une excitation biphotoniqueSemiconductor QDs are tiny light-emitting crystals, and are emerging as a new class of fluorescent labels for medicine and biology. The aim of this work was to develop a new class of non-toxic QDs probes with essential attributes such as water dispersibility, photostability, biocompatibility, high luminescence and possible excitation with low-energy visible light, using simple processing method. Such nanoprobes could be used for bio-imaging of cancer cells. In the performed studies, I focused on ZnS and ZnSe QDs as they are cadmium-free and might be excited biphotonically.The synthesis protocols of ZnS and ZnSe QDs doped with two ions such as Mn or Cu and stabilized by 3-mercaptopropionic acid or 1-thioglycerol were established, followed by NCs characterization (diameter, surface charge, photophysical properties, …) using analytical techniques such as spectrophotometry UV-vis, fluorimetry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), dynamic light scattering (DLS), infra-red analysis (FT-IR), thin layer chromatography (TLC) and electron paramagnetic resonance (EPR). The cytotoxicity of synthesized bare and conjugated NPs was evaluated on cancer cell lines using MTT, XTT and ferrous oxidation-xylenol orange assay.Finally, chosen well fluorescent and weakly toxic types of as-prepared and characterized QDs were used for bio-imaging of cancer cells. In these experiments, FA-functionalized NCs were excited biphotonically. The performed experiments showed the potential of QDs as cancer cells fluorescent markers and that they accumulate around the cell nuclei
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Mao, Baodong. "Synthesis and Property Characterization of Novel Ternary Semiconductor Nanomaterials." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1334065821.
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Liyanage, Geethika Kaushalya. "Infrared Emitting PbS Nanocrystals through Matrix Encapsulation." Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1403953924.
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Ong, Jackson Sen Kiat. "Análise de perda e fluorescência em fibras de cristal fotônico com líquidos e polímeros." Universidade Presbiteriana Mackenzie, 2008. http://tede.mackenzie.br/jspui/handle/tede/2752.
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Previous issue date: 2008-01-29Fundação de Amparo a Pesquisa do Estado de São Paulo
Photonic Crystal Fibers (PCFs) have led to renewed attention to the fiber optics field due to the several unique properties resulting from their microstructured profile. In particular, this profile enables one to insert liquids and polymers into the fiber so that they efficiently interact with light, which can be used for chemical and biological sensing, nonlinear optics, and the development of active photonic devices. Several applications require selectively inserting the sample into the core of a hollow-core PCF, leaving cladding holes unfilled. This dissertation presents two contributions toward the development of core-filled PCFs. Loss mechanisms in liquid-core PCFs are studied and fluorescence from a quantum-dot-doped polymer-core PCF is demonstrated. Loss studies were motivated by the evaluation of the transmission of light at 633 nm in 5-7 cm long water-core PCF samples the tips of which are cleaved at left in air. It was generally found that transmission was less than 5%, while water attenuation alone would lead to ~98% transmission. Liquid evaporation was found to be an important additional loss mechanism and its rate was determined both through microscopy and optical coherence tomography (OCT) in capillary fibers and PCFs filled with deionized water, ethanol and toluene. Although the evaporation rate in ethanol was found to be higher, for all samples a few hundreds of micrometers at the fiber tips are emptied over minutes. A method to prevent evaporation consisting of sealing the fiber tips with a clear UV curable polymer (NOA 73) was successfully tested. Filling a PCF with active elements can lead to optical amplification and laser action. Researchers at NTT recently observed fluorescence at 609nm from CdSe quantum dots in the core of a 1m long PCF. In this dissertation, the fluorescence emission is described from ~2.2 nm PbS quantum dots was observed with a specified emission peak of 890 nm. The quantum dots were suspended in NOA73 and inserted in the core of 7-9 cm long PCFs of with a hollow core diameter of 10.9 5m. The fiber was pumped by a 2.5 mW He-Ne laser or a 679 nm, 390 mW diode laser and its emission was characterized. A maximum fluorescence power of 2.2 5W and a maximum efficiency of 0.03% were achieved. Varying the quantum dot concentration revealed that lower concentrations lead to higher efficiencies.
Fibras de cristal fotônico (PCFs) têm levado a uma atenção renovada ao campo das fibras ópticas devido às diversas propriedades exclusivas resultantes do seu perfil microestruturado. Em particular, este perfil permite a introdução de líquidos e polímeros na fibra de modo que estes interajam eficientemente com a luz, levando a aplicações em sensoriamento químico e biológico, óptica não-linear, e o desenvolvimento de dispositivos fotônicos ativos. Diversas aplicações requerem a inserção seletiva da amostra no núcleo de uma PCF de núcleo oco, deixando buracos da casca sem preenchimento. Esta dissertação apresenta duas contribuições para o desenvolvimento de PCFs de núcleo preenchido. Os mecanismos de perda em PCFs de núcleo líquido são estudados e a fluorescência de uma PCF de núcleo polimérico dopado com pontos quânticos é demonstrada. Os estudos da perda foram motivados pela análise da transmissão da luz em 633 nm em amostras de 5-7 cm de PCF de núcleo de água cujas pontas eram clivadas e deixadas no ar. Geralmente a transmissão encontrada era menor do que 5%, enquanto que a atenuação da água poderia levar a ~98% de transmissão. Verificou-se que a evaporação do líquido era um mecanismo de perda importante e sua taxa foi determinada através de microscopia e de tomografia por coerência óptica (OCT) em fibras capilares e PCFs preenchidas com água deionizada, etanol e o tolueno. Embora a taxa da evaporação no etanol seja maior, para todas as amostras algumas centenas de micrômetros nas pontas da fibra são esvaziadas em minutos. Um método para impedir a evaporação que consiste em selar as pontas da fibra com um polímero curável por UV (NOA 73) foi testado com sucesso. O preenchimento de uma PCF com elementos ativos pode conduzir a amplificação óptica e ação laser. Pesquisadores da NTT observaram recentemente fluorescência em 609 nm em pontos quânticos de CdSe no núcleo de uma PCF de 1 m de comprimento. Nesta dissertação, a emissão de fluorescência é observada com pontos quânticos de PbS de ~2,2 nm e pico de emissão nominal em 890 nm. Os pontos quânticos foram suspensos em NOA73 e introduzidos no núcleo de PCFs de 7-9 cm de comprimento e núcleo oco de 10,9 5m de diâmetro. A fibra foi bombeada por um laser de He-Ne de 2,5 mW ou um laser de diodo de 679 nm e 390 mW e sua emissão foi caracterizada. Uma fluorescência com potência máxima de 2,2 5W e eficiência máxima de 0,03% foi obtida. Variando a concentração de pontos quânticos observou-se que baixas concentrações levam a eficiências mais elevadas.
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Nagamine, Gabriel 1992. "Revelando a estrutura eletrônica de nanomateriais através de espectroscopia óptica avançada." [s.n.], 2017. http://repositorio.unicamp.br/jspui/handle/REPOSIP/325655.
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Orientador: Lázaro Aurélio Padilha JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Pontos quânticos coloidais (QDs) ternários de CuInS2 (CIS) surgiram como uma alternativa não tóxica, altamente promissora, aos já bem estabelecidos QDs binários de CdX e PbX (X=Se,S). Além de não possuírem metais pesados em sua composição, esses novos materiais apresentam diversas características desejáveis, o que os torna fortes candidatos a serem aplicados em novas tecnologias, tanto em biologia quanto na geração de nova fontes de energia renovável. Além disso, esses QDs apresentam diversas propriedades ópticas que os diferem radicalmente dos QDs binários já conhecidos e ainda são pouco compreendidas. Dentre elas, podemos citar um largo espectro de fotoluminescência (PL), com decaimentos longos e multi-exponenciais e um espectro de absorção pouco definido, com uma longa cauda que vai para o infravermelho. Adicionalmente, esses nanomateriais apresentam um grande Stokes shift, de até 500 meV, cuja origem ainda é desconhecida e amplamente debatida na literatura. Com o intuito de desvendar os mecanismos por trás dessas propriedades distintas, nesse trabalho, realizamos uma série de estudos da sua dinâmica ultrarrápida e de espectroscopia não-linear para revelar a estrutura eletrônica desses QDs. Das medidas de dinâmica ultrarrápida, mostramos uma maneira alternativa de medir-se o tamanho dessas nanopartículas, por meio da sua seção de choque de absorção em 3,1 eV, que seria independente da variabilidade morfológica apresentada por elas. Adicionalmente, fazendo um estudo da dependência das interações multi-éxciton desses QDs com o tamanho, reportamos que esses nanomateriais apresentam interações Coulombianas reduzidas em relação aos QDs binários já conhecidos. Das medidas de espectroscopia não-linear, mostramos a primeira comprovação experimental de que a transição óptica entre os níveis fundamentais da banda de valência e condução é proibida por paridade em partículas esféricas. Além disso, comparando o espectro de absorção de 2 fótons das amostras estudadas com imagens de microscopia eletrônica de transmissão (TEM), mostramos que quebras na simetria das funções de onda dos portadores nesses QDs alteram as suas regras de seleção para transições ópticas. Adicionalmente, verificamos que, controlando a composição e tamanho desses QDs, é possível obter seções de choque de 2PA de até 13.500 GM dentro da janela de transparência óptica do tecido do corpo humano
Abstract: Ternary CuInS2 (CIS) Colloidal Quantum Dots (QDs) have emerged as a non-toxic promising alternative to the CdX and PbX (X=Se,S) binary QDs. Besides not having heavy metals on their composition, these new materials show several desirable features, which makes them strong candidates to be applied in new technologies, from biology to the new generation of renewable energy sources. Furthermore, these QDs present various optical properties that radically differs from the already well studied binary QDs and yet are not well understood. Among them, we can cite a large photoluminescence (PL) spectra, with long and multi-exponential decays and a poorly defined absorption spectra, with a long infrared tail. Additionally, these nanomaterials present large Stokes shift, up to 500 meV, whose origin is still not well understood and largely debated on the literature. To reveal the mechanism behind these distinguished properties, here, we perform a series of ultrafast spectroscopy and non-linear spectroscopy studies to reveal the electronic band structure of these QDs. From the ultrafast dynamics measurements, we show an alternative way to measure the size of these nanoparticles, through their absorption cross section in 3,1 eV, which would be independent from the morphologic variability presented by them. Additionally, by performing studies of the size dependent multi-exciton interactions, we report that these kind of nanomaterials present reduced Coulombic interactions in relation to de already known binary QDs. From the non-linear spectroscopy measurements, we show the first experimental confirmation that the optical transition between the electron and hole ground state are parity forbidden in the spherical particles. In addition, comparing the two-photon absorption (2PA) spectra of the studied samples with their transmission electron microscopy images, we show that symmetry breaking of the electronic wave functions in these QDs change their optical transition selection rules. Additionally, we verify that, by controlling the size and composition of these QDs, it is possible to obtain 2PA cross section as high as 13,500 GM inside the transparency window of the human tissue
Mestrado
Física
Mestre em Física
1547612/2015
13/16911-2
CAPES
FAPESP
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Shiman, Dmitriy I., Vladimir Sayevich, Christian Meerbach, Pavel A. Nikishau, Irina V. Vasilenko, Nikolai Gaponik, Sergei V. Kostjuk, and Vladimir Lesnyak. "Robust Polymer Matrix Based on Isobutylene (Co)polymers for Efficient Encapsulation of Colloidal Semiconductor Nanocrystals." American Chemical Association, 2019. https://tud.qucosa.de/id/qucosa%3A74322.
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We introduce new oxygen- and moisture-proof polymer matrixes based on polyisobutylene (PIB) and its block copolymer with styrene [poly(styrene-block-isobutylene-blockstyrene), PSt-b-PIB-b-PSt] for the encapsulation of colloidal semiconductor nanocrystals. In order to prepare transparent and processable composites, we developed a special procedure of nanocrystal surface engineering including ligand exchange of parental organic ligands to inorganic species followed by the attachment of specially designed short-chain PIB functionalized with an amino group. The latter provides excellent compatibility of the particles with the polymer matrixes. As colloidal nanocrystals, we chose CdSe nanoplatelets (NPLs) because they possess a large surface and thus are very sensitive to the environment, in particular in terms of their limited photostability. The encapsulation strategy is quite general and can be applied to a wide variety of semiconductor nanocrystals, as demonstrated on the example of PbS quantum dots. All obtained composites exhibited excellent photostability, being tested in a focus of a powerful white-light source, as well as exceptional chemical stability in a strongly acidic media. We compared these properties of the new composites with those of widely used polyacrylate-based materials, demonstrating the superiority of the former. The developed composites are of particular interest for application in optoelectronic devices, such as color-conversion light-emitting diodes, laser diodes, luminescent solar concentrators, etc.
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Khan, Motiur Rahman. "Nonlinear Charge Transport and Photo-Physical Studies in Conjugated Polymers (P3meT, P3HT) and their Hybrid Composites with Silver Sulfide Quantum Dots." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4133.
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Organic semiconductors have been investigated as an emerging class of materials for their viable applications in electronics. Despite considerable improvement in device properties, a better understanding of the nature of charge transport in these devices and the physics of contacts is crucial to further development of organic devices. The main motivation of this thesis is derived from the fact that physics of disordered systems like conjugated polymer has yet not achieved as concrete understanding as ordered and crystalline systems such as inorganic semiconductors. This thesis investigates the transport properties of electropolymerized thin films by varying the synthesis conditions, carrier density and disorder. Several efforts have been made to understand the non-linear transport phenomena in conjugated polymers. We have also studied the charge transport, charge transfer and photo-physical studies in polymer nanocomposites with inorganic quantum dots. Temperature dependent current-voltage measurements, conductivity and impedance spectroscopy were used to investigate the charge transport mechanism in polymers and nanocomposites. We have investigated the barrier effect on the bulk limited transport in electrochemically doped polymer devies and have shown that deviation in conventional trap limited transport can be modeled by considering the barrier at interface. Effect of doping on disorder and transport show that dopant diffusing from thin films creates disorder traps in the system. We observed that the polymer synthesised at room temperature shows better transport in perpendicular direction than sample prepared at low temperature. This observation was further supported by variable range hopping parameters and Glazman-Matveev model. In the nanocomposite systems, a transition from direct tunneling to thermionic emission and then Poole-Frenkel emission was observed by increasing the quamtum dots weight percentage from 5 to 80.
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Lan, Li Hsuan, and 藍立璿. "Silver sulfide quantum dot syntheses by microfluidic reaction and its applications in bioimaging." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/ar9866.
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Collins, Patricia Lillian. "Detection and speciation of silver in freshwater containing triclosan and thyroid hormone T3." Thesis, 2010. http://hdl.handle.net/1828/2915.
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In freshwater, there is more opportunity for silver (Ag) to interact with organic ligands than in seawater. Triclosan is an antibiotic agent which resembles thyroid hormone T3 and is finding its way into aquatic systems. Preliminary toxicology studies for the frogSCOPE program suggest that triclosan and nanosilver (nanoAg), also used as an antibiotic agent, may be chemically interacting, as they seem to synergistically increase the endocrine-disrupting abilities already observed independently in each chemical. Ag speciation methods can be used to determine if triclosan or thyroid hormone T3 are interacting with Ag ion (Ag+), which gets released over time by nanoAg. To fully utilize Ag speciation methods, however, total Ag in the sample must also be independently analyzed. Here we investigated a new total Ag analysis using cadmium sulfide quantum dots (CdS QDs) as fluorescence probes in solution. This method promises results in a fraction of the time of the established competitive ligand equilibration-solvent extraction (CLE-SE) technique utilizing PDC- and DDC- to bind Ag and bring it out of solution. Following this investigation were a series of experiments using CLE-SE for total Ag and Ag speciation in well water used to house bullfrog tadpoles in frogSCOPE Ag exposure studies. CLE-SE for Ag speciation was also applied to well water samples containing the two levels of nanoAg or Ag+ used in frogSCOPE Ag exposures, and used in ligand competition experiments to examine the potential of triclosan or T3 to act as strong Ag-binding ligands, as compared to glutathione and EDTA, two known Ag-binding ligands. The results of the latter experiments could be used to determine if either of these could be forming complexes with Ag which increase or decrease their delivery to amphibian cells.
The fluorometric method using CdS QDs showed no ideal analytical response to nanomolar Ag+, even when commercial QDs were modified and used, so it could not be applied to our samples. Using CLE-SE for total Ag, the well water used as a base for toxicity studies in frogSCOPE contained Ag below the method detection limit of 5 pM. Using the speciation variation of the CLE-SE method, no evidence of naturally-occurring ligands which could produce extractable (hydrophobic) or non-extractable (hydrophilic) Ag complexes was found in this well water. EDTA and glutathione responded as model Ag-binding ligands to form non-extractable hydrophilic Ag complexes in fresh water. T3 behaved like these model ligands, while triclosan enhanced the extractability of Ag in the presence of certain concentrations of the added ligand, DDC-. In another set of experiments, coordination of Ag by triclosan or T3 was not detectable within that analytical window. These results suggest that ionic Ag released over time by nanoAg may be binding T3 and preventing it from reaching its receptor, but confirming the interaction of triclosan and Ag+ will require additional experiments using different analytical windows.
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Tzung-LuenLi and 利宗倫. "Sulfide Quantum Dots as Sensitizers for Photochemical Electrodes." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/79589021958138999231.
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博士國立成功大學
化學工程學系碩博士班
100
The photoelectrode is a key component determining the efficiency in quantum dot-sensitized solar cell (QDSSC). The semiconductor QD sensitizer on the photoelectrode must have sufficiently high conduction band edge for rapid electron injection into TiO2, and wide absorption characteristics in the solar spectrum. Based on these perspectives, I-III-VI type CuInS2 QDs having bulk bandgap energy of 1.5 eV and a sufficiently high conduction band edge due to quantum confinement effect is a suitable QD sensitizer for TiO2 photoelectrode. In addition, the CuInS2-QDs/CdS heterostructural co-sensitizer, first employed in sensitizing TiO2, shows high performances in photoelectrochemical cells for both water decomposition and QDSSC. This dissertation includes three parts: 1. Solution synthesis of high-quality CuInS2 quantum dots as sensitizers for TiO2 photoelectrodes; 2. CuInS2 quantum dots coated with CdS as high-performance sensitizers for TiO2 electrodes in photoelectrochemical cells; 3. High-performance quantum dot-sensitized solar cells based on sensitization with CuInS2 quantum dots/CdS heterostructure. In the first part, we synthesize colloidal CuInS2 quantum dots (QDs) by solvothermal method for use as sensitizers for photoelectrochemical cells. The synthesis is conducted in an autoclave containing CuCl, InCl3, and S at a Cu/In/S ratio of 1/1/100. This highly sulfur-excess environment leads to burst nucleation of CuInS2 at relatively low temperatures. For synthesis conducted at 110–150 ℃ for 1 h, the atomic ratio of the CuInS2 products is Cu:In:S = 1.1:1.0:2.1 and the particle size increases with the temperature from 3.5 to 4.3 nm, with a narrow size distribution within 7–11%. The as-prepared colloidal CuInS2 exhibits the quantum confinement effect in the optical absorption spectra. The photoluminescence emission of the resulting CuInS2 QDs has high energy, which may result from excited electrons falling from quantized levels to the ground states. Under illumination of simulated AM 1.5G at one sun intensity, the CuInS2-sensitized TiO2 electrodes in aqueous sulfide/sulfite electrolyte show an encouraging photocurrent of approximately 2 mA cm-2 in water decomposition. The second part reports on a high-performance photoelectrode consisting of a nanocrystalline TiO2 film co-sensitized with CuInS2 QDs and CdS layers. In this photoelectrode, solvothermally synthesized CuInS2 QDs, monodispersed at sizes of 3.5 and 4.3 nm, are attached to a TiO2 substrate by means of a bifunctional linker, and followed by an in-situ growth of CdS by successive ionic layer adsorption and reaction. The QDs has a high-level conduction band for the efficient injection of electrons into TiO2. The CdS coating provides high surface coverage to prevent interfacial recombination and releases the quantum confinement of the QDs, resulting in band gap reduction from 2.10-1.80 eV and 1.94-1.76 eV for the 3.5 and 4.3 nm QDs, respectively. With AM 1.5G illumination at 100 mW cm-2, this heterostructural electrode exhibits a saturated photocurrent as high as 16 mA cm-2 in a polysulfide solution. Systematic analysis suggests that the photocurrent resulting from the CuInS2 QDs is increased by more than 100%, thanks to the CdS coating. This coating extends the absorption spectra of the QDs and facilitates charge separation by scavenging photogenerated holes in the valence band of the QDs. The third part reports a high-performance quantum dot-sensitized solar cell (QDSSC), which consists of a TiO2/CuInS2-QDs/CdS/ZnS photoanode, a polysulfide electrolyte, and a CuS counter electrode. The sensitization process for the TiO2 substrate is identical to that in the second part except for a final ZnS passivation layer. The CuS counter electrode, prepared via successive ionic solution coating and reaction, has a small charge transfer resistance in the polysulfide electrolyte. The QDSSC exhibits a short-circuit photocurrent (Jsc) of 16.9 mA cm-2, an open-circuit photovoltage (Voc) of 0.56 V, a fill factor of 0.45, and a conversion efficiency of 4.2% under one-sun illumination. The heterojunction between the CuInS2 QDs and CdS extends both the optical absorption and incident photon conversion efficiency (IPCE) spectra of the cell to a longer wavelength of approximately 800 nm, and provides an IPCE of nearly 80% at 510 nm. The high TiO2 surface coverage of the sensitizers suppresses recombination of the photogenerated electrons. This results in a longer lifetime for the electrons, and therefore, the high Voc value. The notably high Jsc and Voc values demonstrate that this sensitization strategy, which exploits the quantum confinement reduction and other synergistic effects of the CuInS2-QDs/CdS/ZnS heterostructure, can potentially outperform those of other QDSSCs.
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Bennett, Ellie. "Synthetic and Analytical Advancements for Zinc Sulfide Containing Quantum Dots." Thesis, 2021. https://doi.org/10.7916/d8-pg23-8v73.
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Colloidal semiconductor nanocrystals exist at the interface of inorganic chemistry, solid-state physics, and materials applications. The highly tunable and size-dependent properties position them as prime candidates for advancing a range of technologies, including improving efficiency in solid-state lighting devices and high color-purity displays. To be successful in these endeavors, quantum dots require excellent optical properties, such as bright emission. Optimization of a zinc sulfide coating is widely regarded as a key requirement to achieving these necessary performances. Even so, zinc sulfide nanocrystal chemistry remains underdeveloped.
This dissertation addresses these shortcomings and provides comprehensive synthetic and analytical tools to harness the potential of zinc sulfide containing nanocrystals. Chapter 1 introduces semiconductor nanocrystals, also referred to as quantum dots, and begins with a description of the size-dependent optical properties. Factors that lead to poorer emission properties, such as undercoordinated surface atoms are discussed. Methods to alleviate these issues, including controlling the surface coordination environment, and design and growth of heterostructures are introduced. Lastly, synthetic approaches and nanocrystal formation mechanisms are described.
Chapter 2 covers the synthesis and size-dependent optical properties of zinc sulfide nanocrystals. We find that commonly used solvents in nanocrystal reactions lead to the formation of polymeric byproducts that are challenging to purify away, and thus design the zinc sulfide synthesis such that these can be avoided. Leveraging a library of rate tunable thioureas the final nanocrystal size can be carefully controlled. The reactions follow a thermally activated growth process, with larger zinc sulfide nanocrystals accessible at higher temperatures. Most relevantly for later chapters, the surface coordination environment is highly important; bulkier zinc carboxylate ligands that cannot achieve high surface coverages result in higher growth rates. These results represent the most tunable size controls reported for zinc sulfide nanocrystals.
Chapter 3 uses high resolution electron microscopy techniques to study the shape (morphology) of zinc sulfide nanocrystals, synthesized using the methods developed in the second chapter. Irregular, anisotropic growth is commonly seen in zinc sulfide shell growth and is attributed to core/shell interfacial strain. We find that this growth also occurs in the binary zinc sulfide system. Synthetic conditions favoring fast growth result in unselective, isotropic growth of spherical zinc sulfide. Conversely, slower conditions can lead to irregular, anisotropic shapes. The shape is also highly dependent on the coordination environment during growth. Small, sterically unencumbered ligands stabilize specific crystal facets, leading to selective, anisotropic growth. These findings are translated to shelling procedures in Chapter 6, and further emphasize the need to understand and characterize zinc sulfide surfaces.
Chapter 4 establishes an empirical relationship between the band gap energy of a zinc sulfide nanocrystal and its diameter. The literature reports a wide spread of diameters for a given energy, meaning zinc sulfide sizes could not previously be easily calculated from their optical properties. Leveraging the size- and shape-control discussed in Chapters 2 and 3, we assess the utility of a range of nanocrystal characterization techniques for accurately sizing quantum confined zinc sulfide. Using electron microscopy and X-ray scattering methods we present an updated energy-size (“sizing curve”) relationship for zinc sulfide. These results represent the most comprehensive zinc sulfide nanocrystal sizing study and enable the rapid size characterization of zinc sulfide from its absorbance spectrum. This provided crucial insight into the reaction progressions described in Chapter 2.
Chapter 5 covers our endeavors to characterize and quantify the zinc sulfide nanocrystal surface chemistry, which we believe is imperative to improving shelling procedures and optical properties in zinc sulfide heterostructures. With no published extinction coefficient, the surface coverages of zinc sulfide cannot be obtained. Using the size- and shape-controlled syntheses, in conjunction with optical absorption spectroscopy and elemental analysis, we calculate extinction coefficients for a range of zinc sulfide nanocrystal sizes. The size-dependence is well described by a power law, and this represents the first reported extinction coefficient for zinc sulfide. Using this, we report the first surface coverages of zinc sulfide nanocrystals and assess the binding affinity of zinc carboxylates to the surface by monitoring their displacement by L-type ligands.
Chapter 6 widens the zinc sulfide synthetic methods developed in earlier chapters to deposit zinc sulfide shells onto blue-emitting II-VI and red-emitting III-V nanocrystals. The reaction shows versatility, shelling nanocrystals over a wide range of temperatures. We demonstrate morphology control over the zinc shell by altering the deposition kinetics and coordination environment. Usually, thick, homogenous shells are desired by the nanocrystal field. However, by correlating the shell morphology to its optical properties, we see that the anisotropic shells generally achieve higher photoluminescence quantum yields (PLQYs). We also report progress towards cadmium-free quantum dot downconverters for use in solid-state lighting applications. Among other things, the photoluminescence intensity evolution throughout the shelling procedure is highly dependent on the initial surface termination of the nanocrystal core. Application of surface treatments allows brighter zinc sulfide shelled III-V heterostructures to be accessed.
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GUO, SHENG-HORNG, and 郭聖宏. "Synthesis and Properties of Monodisperse Colloidal Lead Sulfide Quantum Dots." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/w2s5sc.
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碩士國立臺南大學
材料科學系碩士班
107
Inorganic lead chalcogenide quantum dots (PbX, X = S, Se, and Te) with the unique photoluminescence in the infrared region has recently acquired much advancement in the synthesis of homogeneous nanoparticles, and these empower them with various advantages in the optoelectronics applications in infrared range. Nevertheless, the research and development of PbS QDs have lasted in the past two decades. PbS QDs still lag the mature II-VI and III-V QDs material (CdSe, InP, InAs, etc.) which have been widely used in market. Herein, we prepared PbS QDs with different S/Pb ratios, reaction temperatures, and reaction times by the hot injection method, then the results are analyzed to choose the best reaction parameters. The photoluminescence of PbS QDs with widely tunable wavelength (900~1650 nm), narrow absorption line widths (FWHM<110 nm), and narrow particle size distributions (<10%) can be obtained. In addition, the purification of the PbS QDs has been studied in details. The removal of the unreacted PbCl2 and excess solvent that are formed as soluble Pb precursors in the synthesis has been paid special attention. Furthermore, the wavelength shift, kinetics, and the long-term stability of the final products are studied for the cation exchange of colloidal PbS nanoparticles under different temperatures.
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Shrestha, Aabhash. "Lead sulfide quantum dots and their application for solar cells." Thesis, 2016. http://hdl.handle.net/2440/104743.
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Quantum dot sensitized solar cells (QDSSCs) are interesting third generation solar cells that have potential to address the current energy related issues due to their low manufacturing cost, ease of fabrication as well as good performance. Quantum dots (QDs) offer several advantages such as size tunable band gaps across a wide range of energy levels, high molar extinction coefficients and enhanced stability. Among them, colloidal near infrared (NIR) QDs of lead sulfide (PbS) are attractive due to their narrow bulk bandgap, large exciton Bohr radii and the possibility of multiple exciton generation. Utilizing these QDs in solar cells with extendable IR absorption is promising. However, the progress of PbS QDSSCs is lacking due to the limited understanding regarding the synthesis and surface chemistry of QDs. The development of QDSSCs is also hindered by lack of proper counter electrode materials for the reduction of electrolytes. Hence, further developments in the synthesis and application of new materials for QDSSCs are necessary. This PhD project focuses on the materials development for PbS QDSSCs such as PbS QD synthesis, surface ligand exchange of PbS QDs, and the development of new counter electrode materials. The following researches are included in this thesis: 1) A robust method to synthesize monodisperse lead sulfide (PbS) QDs is presented. PbS QDs with different sizes is produced by stepwise heating of the preformed seed QDs in the presence of excess oleic acid. A combination of "living" monomer addition and Ostwald ripening is identified as the mechanism for such QD growth processes. 2) The detailed synthesis mechanism of PbS QDs is investigated. Here, the various synthesis parameters influencing the nucleation and growth of PbS QDs are elucidated. In addition, the detailed understanding of the synthesis mechanism is used to guide the synthesis of PbS QDs at ultra-small regime. 3) A versatile solution phase ligand exchange of PbS QDs in the presence of Pb-thiolate as the exchanging ligands is presented. The ligand exchange procedure better preserves the optical properties of PbS QDs and is applicable to a number of ligand/solvent systems. 4) The implementation of PbS QDs in QDSSCs is presented. The treatment of PbS QD photoelectrodes with cadmium salts is necessary to maintain the stability of PbS QDs in polysulfide based electrolytes. In addition, the number of cycles of CdS and ZnS treatment is optimized to achieve a photoconversion efficiency of 1.77 %. 5) Finally, N-doped CNₓ/CNT hetero-electrocatalyst materials using polydopamine is synthesized, which are explored as counter electrode materials for dye-sensitized solar cell (DSSC). These CNₓ/CNTs material show excellent electrocatalytic activities towards the reduction of tri-iodide electrolytes with the optimized solar devices using CNₓ/CNTs showing comparable performance (7.3 %) to reference Pt based devices (7.1 %).Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2016.
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張嘉訓. "Spectroscopic study of quantum dots on silver nanoparticle arrays." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/27131110461677427438.
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碩士國立彰化師範大學
電機工程學系
100
In the thesis, we discussed the interactions between silver nanoparticles (Ag NPs) and quantum dots (QDs) on anodized aluminum oxide (AAO) substrates by using He-Ne laser (532 nm) to excite surface plasmons (SPs) on Ag NPs. Using direct deposition and immersion methods, we deposited QDs on aluminum (Al), anodized aluminum oxide (AAO) and Ag NPs decorated anodized aluminum oxide (AAO/Ag) substrates. After 8 hours of incubation, we used a He-Ne laser to excite the quantum dots on various substrates. The light-emitting efficiency of the quantum dots was affected by the surrounding silver nanoparticles and the fluorescence from QDs was quenched. In order to further explore the influence of Ag NPs on the light-emitting efficiency of quantum dot, we compared the fluorescence signal strength of different concentrations of QDs in Ag NPs solutions. The quenching ability of Ag NPs on QDs was confirmed. The fluorescence signal of QDs on AAO/Ag substrate was quenched. However, when using 532 nm laser as the excitation source, some specific spectral features were observed. In addition, the substrate or the generation methods of AgNPs do not influence the specific wavelengths of the features. Finally, AAO/Ag substrates were irradiated by different laser sources (488, 532 and 633 nm). The same Raman shifts (1357 cm-1and 1586 cm-1) were observed under different laser sources irradiation. Therefore, the spectral features were likely to be Raman signals. However, it is to be determined what the substance is the source of the Raman signal.
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"Biodistribution of Cadmium Selenide/Zinc Sulfide Quantum Dots in Aquatic Organisms." Thesis, 2011. http://hdl.handle.net/1911/70313.
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This thesis investigates the biodistribution and toxicological effects of amphiphilic polymer coated CdSe/ZnS quantum dots (QDs) in two aquatic species, Daphnia magna (daphnia) and Danio rerio (zebrafish). The use of QDs in the life sciences has become common practice over the past decade. In addition QDs are being incorporated in commercially available light emitting diodes and photovoltaic solar cells. As the widespread commercial use of QDs increases, environmental release is inevitable, and water will contain the highest environmental concentrations based on life cycle assessments. Despite increased attention to the aquatic toxicology of nanomaterials in recent years, little information exists on the biological fate of QDs in aquatic organisms. Quantitative data on the uptake and excretion of QDs from daphnia and zebrafish were collected using fluorescence imaging paired with metal analysis. First, daphnia were examined after aqueous and dietary exposure to amphiphilic polymer coated CdSe/ZnS QDs. Surface coating influenced QD acute toxicity and high particle aggregation correlated with daphnia mortality. QDs were readily ingested by daphnia and accumulated in the intestines. High body burdens of 150-200 μg/g were found in the daphnia, with intestinal QD concentrations significantly elevated above the exposure media concentration. The slow elimination observed in daphnia suggested that trophic transfer of QDs to higher organisms may occur. Using daphnia and zebrafish as a model food chain revealed that QDs can transfer to zebrafish through dietary exposure with body burdens of 8-9.5 μg/g found. However, no biomagnification between daphnia and zebrafish was observed and the biomagnification factor (BMF = 0.04) was significantly less than one. This work demonstrates that aqueous and dietary exposures to QDs can result in high total body concentrations in aquatic organisms with little to no gross toxicity. The low acute toxicity observed for some surface coated QDs encourages further design optimization to improve the biocompatibility and reduce the environmental impact of QDs.
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Maria, Ahmed. "Improving the photoluminescence quantum efficiency of size-tunable, solution-processed lead-sulfide quantum dots in film." 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=95027&T=F.
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Wang, Chih-Wei (Chih-Wei Jo). "Surface-tunable photoluminescence and nonlithographic patterning of block copolymer-stabilized cadmium sulfide quantum dots." 2005. http://hdl.handle.net/1828/822.
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Tsai, Jia-Shan, and 蔡佳珊. "Microwave synthesized metal sulfide as counter electrode for quantum dots-sensitized solar cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/84757732802883631509.
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碩士國立臺灣科技大學
化學工程系
104
In this study, microwave assisted synthetic route was applied for rapid, facial and effective synthesis of counter electrode(CE) for quantum dots-sensitized solar cells(QDSSCs) .Moreover, it is applied for in situ deposition of metal sulfides on the CE, shorten the process time and avoids post treatments. Different metal sulfide CE(CuS, NiS, CoS2, PbS) and aqueous CuInS2/In2S3 quantum dots (QDs) are synthesized by using rapid microwave assisted synthesis approach. The CuInS2/In2S3 QDs photoanode with the CuS CE exhibits champion of short circuit current density (Jsc) of 26.76 mA/cm2, open voltage (Voc) of 650 mV and power conversion efficiency(PCE) of 8.32% at one sun (AM 1.5 G, 100 mW/cm2). Electrochemical impedance spectroscopy (EIS), Tafel and cyclic voltammetry (CV) measurement was employed to understand electro dynamic behavior of metal sulfide CE. Analysis of the data shows that CuS CE performs high electrocatalytic activity towards polysulfide reduction compared with other metal sulfide CE.
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Lu, Yu-Chieh, and 盧育杰. "Solution-based Synthesis and Applications of Nanosized Silver and Semiconductor Quantum Dots." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/65679506738026947939.
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Lin, Mei-Chia, and 林美佳. "Synthesis of silver chalcogenides-Cu2-xS quantum dots for applications in solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/51546675763472857731.
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碩士中興大學
奈米科學研究所
99
We study copper sulfide (Cu2-xS), a low-cost and non-toxic light absorbing material and apply to the quantum dot-sensitized solar cells (QDDSC). The copper sulfide quantum dots (QDs) were synthesized on a nanoporous TiO2 electrode by the successive ionic layer adsorption and reaction method (SILAR). To improve efficiency, passivation treatments including a TiO2 under layer ,a ZnS coating and additional treatments including annealing, a TiO2 scattering layer and an Au counterelectrode were used. The best cell yields a short-circuit current of 22.9 mA/cm2, an open circuit voltage of 0.14 V, a fill factor of 20.2% and a power conversion efficiency of 0.65%. By replacing the platinum count erelectrode with a gold electrode, the performance improves to conversion efficiency 0.90%, open circuit voltage 0.17V, short-circuit current 28.1mA/cm2 and fill factor 18.9%. The efficiency of gold-electrode cells are ~ 38% higher than that of the Pt electrode cells. The crystallinity and morphology were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties of these Cu2-xS QDs were characterized by UV-vis spectroscopy.
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張雅欣. "Application of Silver Nanoparticles and Nanowires for Quantum Dots and Transparent Conductive Coating." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/74788334630956041872.
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El-Ballouli, Ala’a O. "Continuous-Flow Synthesis and Materials Interface Engineering of Lead Sulfide Quantum Dots for Photovoltaic Applications." Diss., 2016. http://hdl.handle.net/10754/611210.
Full textAbstract:
Harnessing the Sun’s energy via the conversion of solar photons to electricity has emerged as a sustainable energy source to fulfill our future demands. In this regard, solution-processable, size-tunable PbS quantum dots (QDs) have been identified as a promising active materials for photovoltaics (PVs). Yet, there are still serious challenges that hinder the full exploitation of QD materials in PVs. This dissertation addresses two main challenges to aid these QDs in fulfilling their tremendous potential in PV applications.
First, it is essential to establish a large-scale synthetic technique which maintains control over the reaction parameters to yield QDs with well-defined shape, size, and composition. Rigorous protocols for cost-effective production on a scale are still missing from literature. Particularly, previous reports of record-performance QD-PVs have been based on small-scale, manual, batch syntheses. One way to achieve a controlled large-scale synthesis is by reducing the reaction volume to ensure uniformity. Accordingly, we design a droplet-based continuous-flow synthesis of PbS QDs. Only upon separating the nucleation and growth phases, via a dual-temperature-stage reactor, it was possible to achieve high-quality QDs with high photoluminescence quantum yield (50%) in large-scale. The performance of these QDs in a PV device was comparable to batch-synthesized QDs, thus providing a promise in utilizing automated synthesis of QDs for PV applications.
Second, it is crucial to study and control the charge transfer (CT) dynamics at QD interfaces in order to optimize their PV performance. Yet, the CT investigations based on PbS QDs are limited in literature. Here, we investigate the CT and charge separation (CS) at size-tunable PbS QDs and organic acceptor interfaces using a combination of femtosecond broadband transient spectroscopic techniques and steady-state measurements. The results reveal that the energy band alignment, tuned by the quantum confinement, is a key element for efficient CT and CS processes. Additionally, the presence of interfacial electrostatic interaction between the QDs and the acceptors facilitates CT from large PbS QD (bandgap < 1 eV); thus enabling light-harvesting from the broad near-infrared solar spectrum range.
The advances in this work – from automated synthesis to charge transfer studies – pave new pathways towards energy harvesting from solution-processed nanomaterials.
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Pendyala, Naresh Babu. "Synthesis, Optical And Photoelectrical Investigations On PbS nano-,micro-structures." Thesis, 2009. https://etd.iisc.ac.in/handle/2005/921.
Full textAbstract:
The thesis describes the synthesis of PbS nano-, micro-structures by colloidal and hydrothermal techniques. Size and morphology dependent luminescence studies were carried out in detail. Application oriented studies like ion sensing and modulation of luminescence are carried out on colloidal PbS QDs. Photoelectrical studies are carried out on various morphologies of PbS microstructures. We observe the persistent photoconductivity, growth and quenching of photocurrent, and a few novel phenomena in flower shaped PbS microstructures. This work is presented in eight chapters inclusive of summary and directions for future work.
CHAPTER 1 provides a brief introduction to optical and photoelectrical properties of semiconductor quantum dots and hydrothermal technique in preparation of quantum structures. A review of PbS nanostructures and its technological applications are discussed.
CHAPTER 2 provides the experimental techniques used in this work. First, the synthesis of PbS nano-, micro-structures by various methods, and characterization tools used in this work are briefly presented.
CHAPTER 3 deals with the synthesis of PbS quantum dots in poly vinyl alcohol with various precursor concentrations to identify the surface states by temperature dependent photoluminescence (PL) measurements. Average bandgap value calculated from absorption measurements was 2.1 eV. We have observed that high-energy PL bands (>1.3 eV) are due to electron traps (Pb dangling bonds) and low-energy bands (<1 eV) are due to hole traps (S dangling bonds). By capping with thiol compounds (mercaptoethanol-C2 H5OSH), absence of the 1.67 eV band indicates the passivation of Pb dangling bonds. To explain above observed results, we propose a band diagram with distributed shallow to deep states and attributed them to the specific surface related defects (Pb or S).
CHAPTER 4 discusses the ion sensing applications of PbS quantum dots. We found that the sulfur related dangling bonds are quite sensitive to different metallic ions (since mercaptoethanol passivates only Pb atoms). Sulfur related PL band (~ 1 eV) have shown an order of magnitude improvement in its intensity for Hg, Ag ions and relatively low enhancement for Zn, Cd ions at 1 µmol concentrations. However Cu quenches the luminescence. An important distinction may have to be made between PbS and Cd related quantum structures. The PbS QDs can distinguish between Cu & Hg, however Cd related QDs couldn’t distinguish between these two ions. Photo-brightening and photo-darkening is an interesting phenomena indicative of photo-induced ionic migration that either helps in enhancing the emission of sulfur related defect emission or degrades the emission properties depending on the ion concentration. This report is the first of its kind in ion sensing applications using PbS QDs.
CHAPTER 5 discusses the results of duel beam excitation on trap luminescence of PbS QDs. By using different lasers simultaneously (514 nm and 670 nm), we have observed the reversible luminescence quenching of trap emission. The high-energy PL band (1.67 eV) has double the quenching effect compared to low-energy PL band (1.1 eV). The luminescence quenching mechanism is attributed to the re-emission of the charge carriers from the traps (photo-ionization) due to the simultaneous excitation with the second beam. The dependence of the temperature, the effect of two beam excitation intensities and modulation frequency dependent quenching mechanism are primarily focused in this chapter. The quenching mechanism is considered to be quite useful in the optical modulation devices.
CHAPTER 6 discusses the PL results on various morphologies of PbS nano-, microstructures. Interestingly, after protecting the surface with organic ligands such as mercaptoethanol (C2 H5OSH), dendrite structures have shown high-energy bands (~ 1.0 eV) in the PL spectra, which indicate the existence of various quantum confinement regimes in different branches of dendrites. The anomalous temperature dependent behavior of PL intensity is attributed to the size distribution.
CHAPTER 7 discusses the results of photoconductivity measurements on various morphologies of PbS nano-, micro-structures. Flower shaped structures have shown persistent photoconductivity (PPC). This observed PPC is attributed to the presence of potential barriers, which are created by the different confinement regimes or due to the lattice relaxation, which occurs due to the carrier trapping at surfaces. In PPC, the estimated time constants of both build up and decay transients using the stretched exponentials are of the order of few tens of seconds. In PPC measurements, we observe the PC quenching below 40 K and growth above this temperature. PC quenching is attributed to the transfer of photo-excited carriers to a metastable state. The presence of metastable state is supported by the dark conductivity measurements in flower shaped structures.
CHAPTER 8 presents the summary and directions for the future work.
44
Pendyala, Naresh Babu. "Synthesis, Optical And Photoelectrical Investigations On PbS nano-,micro-structures." Thesis, 2009. http://hdl.handle.net/2005/921.
Full textAbstract:
The thesis describes the synthesis of PbS nano-, micro-structures by colloidal and hydrothermal techniques. Size and morphology dependent luminescence studies were carried out in detail. Application oriented studies like ion sensing and modulation of luminescence are carried out on colloidal PbS QDs. Photoelectrical studies are carried out on various morphologies of PbS microstructures. We observe the persistent photoconductivity, growth and quenching of photocurrent, and a few novel phenomena in flower shaped PbS microstructures. This work is presented in eight chapters inclusive of summary and directions for future work.
CHAPTER 1 provides a brief introduction to optical and photoelectrical properties of semiconductor quantum dots and hydrothermal technique in preparation of quantum structures. A review of PbS nanostructures and its technological applications are discussed.
CHAPTER 2 provides the experimental techniques used in this work. First, the synthesis of PbS nano-, micro-structures by various methods, and characterization tools used in this work are briefly presented.
CHAPTER 3 deals with the synthesis of PbS quantum dots in poly vinyl alcohol with various precursor concentrations to identify the surface states by temperature dependent photoluminescence (PL) measurements. Average bandgap value calculated from absorption measurements was 2.1 eV. We have observed that high-energy PL bands (>1.3 eV) are due to electron traps (Pb dangling bonds) and low-energy bands (<1 eV) are due to hole traps (S dangling bonds). By capping with thiol compounds (mercaptoethanol-C2 H5OSH), absence of the 1.67 eV band indicates the passivation of Pb dangling bonds. To explain above observed results, we propose a band diagram with distributed shallow to deep states and attributed them to the specific surface related defects (Pb or S).
CHAPTER 4 discusses the ion sensing applications of PbS quantum dots. We found that the sulfur related dangling bonds are quite sensitive to different metallic ions (since mercaptoethanol passivates only Pb atoms). Sulfur related PL band (~ 1 eV) have shown an order of magnitude improvement in its intensity for Hg, Ag ions and relatively low enhancement for Zn, Cd ions at 1 µmol concentrations. However Cu quenches the luminescence. An important distinction may have to be made between PbS and Cd related quantum structures. The PbS QDs can distinguish between Cu & Hg, however Cd related QDs couldn’t distinguish between these two ions. Photo-brightening and photo-darkening is an interesting phenomena indicative of photo-induced ionic migration that either helps in enhancing the emission of sulfur related defect emission or degrades the emission properties depending on the ion concentration. This report is the first of its kind in ion sensing applications using PbS QDs.
CHAPTER 5 discusses the results of duel beam excitation on trap luminescence of PbS QDs. By using different lasers simultaneously (514 nm and 670 nm), we have observed the reversible luminescence quenching of trap emission. The high-energy PL band (1.67 eV) has double the quenching effect compared to low-energy PL band (1.1 eV). The luminescence quenching mechanism is attributed to the re-emission of the charge carriers from the traps (photo-ionization) due to the simultaneous excitation with the second beam. The dependence of the temperature, the effect of two beam excitation intensities and modulation frequency dependent quenching mechanism are primarily focused in this chapter. The quenching mechanism is considered to be quite useful in the optical modulation devices.
CHAPTER 6 discusses the PL results on various morphologies of PbS nano-, microstructures. Interestingly, after protecting the surface with organic ligands such as mercaptoethanol (C2 H5OSH), dendrite structures have shown high-energy bands (~ 1.0 eV) in the PL spectra, which indicate the existence of various quantum confinement regimes in different branches of dendrites. The anomalous temperature dependent behavior of PL intensity is attributed to the size distribution.
CHAPTER 7 discusses the results of photoconductivity measurements on various morphologies of PbS nano-, micro-structures. Flower shaped structures have shown persistent photoconductivity (PPC). This observed PPC is attributed to the presence of potential barriers, which are created by the different confinement regimes or due to the lattice relaxation, which occurs due to the carrier trapping at surfaces. In PPC, the estimated time constants of both build up and decay transients using the stretched exponentials are of the order of few tens of seconds. In PPC measurements, we observe the PC quenching below 40 K and growth above this temperature. PC quenching is attributed to the transfer of photo-excited carriers to a metastable state. The presence of metastable state is supported by the dark conductivity measurements in flower shaped structures.
CHAPTER 8 presents the summary and directions for the future work.
45
Tsai, Ting-Wei, and 蔡庭瑋. "All-solid-state nanocrystalline TiO2 thin-film solar cells sensitized by antimony sulfide (Sb2S3) quantum dots." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/zsp3kk.
Full textAbstract:
碩士國立交通大學
應用化學系分子科學碩博士班
103
All-solid-state nanocrystalline TiO2 thin-film solar cells sensitized by antimony sulfide (Sb2S3) quantum dots were fabricated with using different hole-transporting materials (HTMs) - Poly(3-hexylthiophene) (P3HT), new HTM (HTM797), 2,2ʹ,7,7ʹ-tetrakis(N,N-di-pmethoxyphenylamine)-9,9ʹ-spirobifluorene (spiro-OMeTAD). HTM797 has a similar molecular structure to spiro-OMeTAD and was synthesized to enhance hole mobility via spiro-structure modification. The Sb2S3/P3HT shows the higher power conversion efficiency (PCE = 4.2%) with faster charge diffusion than the other Sb2S3/HTM devices. The Sb2S3/HTM797 exhibits a device efficiency 3.9% with better fill-factor and faster charge transport than the Sb2S3/spiro-OMeTAD (PCE = 3.2%). With using HTM797, the interfacial charge losses in the Sb2S3 solar cells were reduced due to the enhanced charge transport compared with spiro-OMeTAD. At the second part, we studied the DPA (decyl-phosphonic acid) doping effect in the spiro-OMeTAD hole transporting material to increase p-type charge carriers (holes) and to reduce charge transport resistance in the Sb2S3/spiro-OMeTAD solar cells. In the preliminary experiments, DPA surface treatment on the TiO2/Sb2S3 layer was done before HTM coating, we observed somewhat variable different device results in the Sb2S3/spiro-OMeTAD solar cells via DPA post-surface treatment. Therefore to obtain reliable and reproducible device performance by using DPA, we demonstrate DPA as a dopant in the spiro-OMeTAD and then DPA-doped spiro-OMeTAD has been employed as hole transporting material for the TiO2/Sb2S3 solar cells. Herein we can provide some of the experimental data of DPA-doped spiro-OMeTAD effect and improved device performance of the Sb2S3/spiro-OMeTAD solar cells. Key words: Solar Cells, antimony sulfide, hole transport material, 1-decyl phosphonic acid.
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Mu, Zuze. "Synthesis, photostability and photocatalytic properties of water-suspended cadmium selenide and cadmium selenide/cadmium sulfide quantum dots." Thesis, 2005. http://hdl.handle.net/1911/17807.
Full textAbstract:
Photocatalysis offers exciting opportunities in the development of a renewable energy source and environmentally-friendly chemical processes. Previous studies focused on titanium dioxide and non-oxide semiconductor nanoparticles (quantum dots), such as CdS, ZnS, MoS2 for photocatalytic breakdown of organic molecules. Catalytic performance has been limited by materials issues, e.g. low quantum yields and photocorrosion. CdSe quantum dots are a model semiconductor nanoparticle material with great potential in luminescence application, but they have not been studied for photocatalysis. In this study, the synthesis of the water-suspended CdSe and CdSe/CdS quantum dots was thoroughly studied. The CdSe and CdSe/CdS core/shell quantum dots were found to photocatalyze the degradation of 4-nitrophenol in water upon the UV-vis irradiation. Quantum efficiencies were low. The pH of the suspending fluid was found to be important in controlling colloidal stability, chemical stability, and reaction during irradiation.
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Lin, Kai-Sheng, and 林凱聖. "Microplasma-assisted Synthesis of Graphene Quantum Dots-Silver Nanoparticle Nanohybrids for Improved Surface Enhanced Raman Scattering." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/8nu2fy.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
106
Recently experimental and theoretical works have reported that graphene quantum dots (GQDs), a unique form of a zero-dimensional nanostructure, and their exceptional properties make them promising in biosensing applications. Surface-enhanced Raman scattering(SERS) is an ultra-sensitive analytical technique for bio-molecules detection. While the potential of SPR metals (e.g. Au and Ag) and graphene for SERS has been demonstrated, but the work of GQDs applied as SERS substrates is still lacking. Here we reported the rational design to develop GQD-based SERS active substrate. Furthermore, modified GQD with metal nanostructures will lead to important advance for SERS-based detection. Here we demonstrate a facile synthesis of GQD-AgNP nanohybrids by using the atmospheric-pressure microplasma-assisted electrochemistry. Detailed nanomaterial characterizations including transmission electron microscopy, UV/Vis spectroscopy show that the microplasma-assisted electrochemical reaction can successfully grow Ag nanoparticles (AgNP) onto the GQD surfaces to form the GQD-AgNP nanohybrids with heterodimeric nanostructures within the minute scale. Besides, the photoluminescence (PL) optical study and lifetime analysis of GQDs and GQD-AgNP indicated that the non-radiative fluorescence resonance energy transfer involved in the GQD-AgNP nanohybrids. In the systematic Raman study, R6G is selected as the Raman probe molecules. First, we compare the SERS property of three kinds of GQDs with different photoluminescence property (e.g. different emission wavelength), Raman results show that SERS performance of GQDs is highly influenced by the molecular adsorption ability. The as-produced GQD-AgNP nanohybrids shows superior SERS performance with high enhancement factor (EF) around 1x10^8. We further studied the GQD-AgNP nanohybrids with different FRET efficiency. The results revealed that FRET of the as-produced GQD-AgNP nanohybrids is the dominant factor to SERS properties in our study.
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Chen, Hong-Syu, and 陳泓旭. "Photocatalytic Reaction by Using Zinc Sulfide Quantum Dots Embedded Porous Materials : Application for the Reduction of Carbon Dioxide." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/44430561851605264842.
Full textAbstract:
碩士國立中興大學
化學系所
98
Recently the development of industry has generated a large amount of carbon dioxide and resulted in the greenhouse effect. To make it possible to convert the redundant carbon dioxide into usable compounds, we choose the method of photocatalytic reduction. In this research, we combine absorbents and nanosemiconductor, and successfully synthesize photocatalyst. Then we use this photocatalyst to adsorb carbon dioxide and proceed to photocatalytic reduction. During this process, we pour carbon dioxide into D2O with photocatalyst in order to reduce carbon dioxide to carbohydrate. For the last step, we collect data and analyze them. Photocatalyst not only has the ability of reduction, but also has the ability of oxidization. Because it has this quality, we use it to oxidiz alcohol. Based on this reaction, we can examine the efficiency of the catalyst during the photocatalytic reaction and estimate the function of the material.
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Kirmani, Ahmad R. "Surface Traps in Colloidal Quantum Dot Solar Cells, their Mitigation and Impact on Manufacturability." Diss., 2017. http://hdl.handle.net/10754/625510.
Full textAbstract:
Colloidal quantum dots (CQDs) are potentially low-cost, solution-processable semiconductors which are endowed, through their nanoscale dimensions, with strong absorption, band gap tunability, high dielectric constants and enhanced stability. CQDs are contenders as a standalone PV technology as well as a potential back layer for augmenting established photovoltaic (PV) technologies, such as Si. However, owing to their small size (ca. few nanometers), CQDs are prone to surface trap states that inhibit charge transport and threaten their otherwise wonderful optoelectronic properties. Surface traps have also, indirectly, impeded scalable and industry-compatible fabrication of these solar cells, as all of the reports, to date, have relied on spin-coating with sophisticated and tedious ligand exchange schemes, some of which need to be performed in low humidity environments.
In this thesis, we posit that an in-depth understanding of the process-structure-property-performance relationship in CQDs can usher in fresh insights into the nature and origin of surface traps, lead to novel ways to mitigate them, and finally help achieve scalable fabrication. To this end, we probe the CQD surfaces and their interactions with process solvents, linkers, and ambient environment employing a suite of spectroscopic techniques. These fundamental insights help us develop facile chemical and physical protocols to mitigate surface traps such as solvent engineering, remote molecular doping, and oxygen doping, directly leading to better-performing solar cells. Our efforts finally culminate in the realization of >10% efficient, air-stable CQD solar cells scalably fabricated in an ambient environment of high, uncontrolled R.H. (50-65%). As-prepared solar cells fabricated in high humidity ambient conditions are found to underperform, however, an oxygen-doping recipe is devised to mitigate the moisture-induced surface traps and recover device performances. Importantly, these solar cells are fabricated at coating speeds of >15 m min-1 with roll-to-roll compatible techniques such as blade and bar coating requiring 1/25th the CQD material consumed by the standard spin-coated devices, overcoming the two major challenges of manufacturability and scalability faced by CQD PV.
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Lawless, Darren. "Photophysical studies on ultra-small semiconductor particles : CdS quantum dots, doped and undoped TiO₂2, and silver halides." Thesis, 1993. http://spectrum.library.concordia.ca/6080/1/NN84678.pdf.
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