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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
761

Ultrarychlá laserová spektroskopie hybridních nanosystémů / Ultrafast spectroscopy of hybrid nanosystems

Galář, Pavel January 2016 (has links)
Title: Ultrafast spectroscopy of hybrid nanosystems Author: RNDr. Pavel Galář Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Malý, DrSc. Abstract: This Ph. D. thesis is focused on physical phenomena located at the interface of hybrid nanostructure composed of polycrystalline diamond and polymer polypyrrole. The main method used in our experimental study was ultrafast laser spectroscopy that allowed us to gain new findings about electron recombination processes in polycrystalline diamond layers, polypyrrole and in their hybrid structures. The research was focused on mutual influence of both components, especially through energy and charge transfer. In the first step of our research we carried out optical characterisation of different kinds of polypyrrole and complex study of recombination processes dynamics of photoexcited charge carriers in polycrystalline diamond. The measurements were realized by the methods of time-resolved photoluminescence and transmission spectroscopy in the time scale from picoseconds to milliseconds. On the basis of the obtained results the model explaining the origin of luminescence signal related to the different kinds of electron recombination processes in non- diamond phase and on surface defects of diamond grains in polycrystalline layers was...
762

Optische Eigenschaften von Versetzungen in Silizium

Allardt, Matthias 23 April 2015 (has links)
Versetzungen sind linienhafte Störungen in Kristallen und beeinflussen die mechanischen, elektrischen und optischen Eigenschaften des Halbleitermaterials. In dieser Arbeit werden die optischen Eigenschaften von Versetzungen in Silizium anhand des Studiums ihrer charakteristischen Lumineszenz, der sogenannten D-Linien, untersucht. Dabei wurden die Versetzungen in einkristallinen Siliziumproben verschiedener Orientierung in einem einstufigen Prozess mittels plastischer Verformung bei hohen Temperaturen erzeugt und ggf. in einem zweiten Schritt durch Hochlastverformung bei tieferen Temperaturen modifiziert. Als Methoden zur Untersuchung der optischen Eigenschaften der Versetzungen werden Photolumineszenz (PL)- und Kathodolumineszenz (KL)-Spektroskopie verwendet. Gleitstufen an der Probenoberfläche werden mittels Rasterelektronenmikroskopie (REM), die Versetzungsanordnungen im Probenvolumen mittels Transmissionselektronenmikroskopie (TEM) abgebildet. Die Versetzungsstruktur der auf Einfachgleitung orientierten Proben ist durch relaxierte Versetzungen (einstufige Verformung) bzw. gerade Versetzungen (zweistufige Verformung) gekennzeichnet. In der auf Vielfachgleitung orientierten Probe werden mehrere Gleitsysteme gleichartig aktiviert. Es bildet sich ein Zellmuster aus, wobei das Innere der ca. 1 µm großen Zellen im Wesentlichen versetzungsfrei ist und die Zellwände eine hohe Versetzungsdichte aufweisen. Generell sind die mittleren Versetzungsdichten aller Proben hoch. Sie betragen zwischen 5 x 10^7 und 1 x 10^9 cm-2. Die Lumineszenz der einstufig verformten Proben ist durch das Auftreten von vier Linien (D1 bis D4) im Spektrum gekennzeichnet. In den zweistufig verformten Proben dominieren die Linien D5 und D6 die Lumineszenz. Die spektralen Positionen aller D-Linien entsprechen den aus der Literatur bekannten Daten. Die integrale Lumineszenzintensität im Bereich der D-Linien nimmt mit wachsender mittlerer Versetzungsdichte zu. Zusätzlich kann in den zweistufig verformten Proben eine bisher nicht identifizierte Lumineszenzlinie bei einer Energie von 1,090 eV festgestellt werden. Für diese Linie wird in dieser Arbeit die Bezeichnung P^2SD verwendet. In den KL-Abbildungen wird für alle D-Linien und die P^2SD-Linie im Wesentlichen eine örtlich homogene Lumineszenzverteilung festgestellt. Dies wird auf eine im Maßstab des KL-Wechselwirkungsvolumens homogene Versetzungsverteilung zurückgeführt. Die lokalen Schwankungen der KL um die mittlere Intensität betragen maximal 15 %. Diese Schwankungen äußern sich in hellen und dunklen Lumineszenzstreifen, deren Breite deutlich größer als der mittlere Versetzungsabstand ist. Aus dem Vergleich von KL-Bildern mit Rückstreuelektronenbildern der Oberflächengleitstufen ergeben sich folgende Aussagen: Die KL-Intensität der D3- und D4-Linie ist auf markanten Gleitbändern im Vergleich zur Umgebung verringert, wogegen die Intensität der Linien D1 und D2 auf markanten Gleitbändern erhöht ist. Für die D5-Bande, die D6-, und die P^2SD-Linie kann kein allgemeiner Zusammenhang zwischen der Lokalisierung der Lumineszenz und der Gleitaktivität festgestellt werden. Anhand der experimentellen Ergebnisse kann die D3-Linie als TO-Phononenreplik der D4-Linie identifiziert werden. Für die D4-Lumineszenz werden zwei Rekombinationsmodelle diskutiert. Zum einen kann sie durch die exzitonische Rekombination an eindimensionalen Energiebändern erklärt werden, die durch das Verzerrungsfeld der Versetzungen von den jeweiligen Volumenenergiewerten abgespalten sind. Zum anderen kann auch die Rekombination eines tief gebundenen Elektrons mit einem schwach gebundenen Loch für die D4-Lumineszenz verantwortlich sein. In jedem Fall ist das Auftreten der D4-Linie an die Existenz von relaxierten 60 °- und Schraubenversetzungen gebunden. Die D1-Linie wird als OGamma-Phononenreplik der D2-Linie vorgeschlagen. Die D2-Linie selbst kann als ein strahlender Übergang zwischen zwei gebundenen Zuständen eines zweidimensionalen Potentialtopfs endlicher Tiefe modelliert werden. Die Abmessungen dieses Potentialtopfs sind dabei durch die Ausdehnung von Kinken und Jogs auf der Versetzungslinie gegeben. Allerdings könnte auch ein interner Übergang zwischen den Niveaus eines tiefen Defekts innerhalb der Bandlücke als Erklärung herangezogen werden. Wegen der Zunahme der Lumineszenzintensiät der D2-Linie durch thermische Behandlungen sollten Kinken, Jogs, und Punktdefekte im Verzerrungsfeld der Versetzungen als Ursache der D2-Lumineszenz in Frage kommen. Auch die P^2SD-Linie kann mithilfe von zwei unterschiedlichen Rekombinationsmodellen erklärt werden (free-to-bound-Übergang oder exzitonische Rekombination an zweidimensionalen Energiebändern). Punktdefekte, die während des zweistufigen Verformungsprozesses entstehen, könnten die P^2SD -Linie hervorrufen.
763

Cyclotron resonance and photoluminescence studies of dilute GaAsN in magnetic fields up to 62 Tesla

Eßer, Faina 15 February 2017 (has links)
In this thesis, we investigate optical and electrical properties of dilute nitride semiconductors GaAsN in pulsed magnetic fields up to 62 T. For the most part, the experiments are performed at the Dresden High Magnetic Field Laboratory (HLD). In the first part of this thesis, the electron effective mass of GaAsN is determined with a direct method for the first time. Cyclotron resonance (CR) absorption spectroscopy is performed in Si-doped GaAsN epilayers with a nitrogen content up to 0.2%. For the CR absorption study, we use the combination of the free-electron laser FELBE and pulsed magnetic fields at the HLD, both located at the Helmholtz-Zentrum Dresden-Rossendorf. A slight increase of the CR electron effective mass with N content is obtained. This result is in excellent agreement with calculations based on the band anticrossing model and the empirical tight-binding method. We also find an increase of the band nonparabolicity with increasing N concentration in agreement with our calculations of the energy dependent momentum effective mass. In the second part of this thesis, the photoluminescence (PL) characteristics of intrinsic GaAsN and n-doped GaAsN:Si is studied. The PL of intrinsic and very dilute GaAsN is characterized by both GaAs-related transitions and N-induced features. These distinct peaks merge into a broad spectral band of localized excitons (LEs) when the N content is increased. This so-called LE-band exhibits a partially delocalized character because of overlapping exciton wave functions and an efficient interexcitonic population transfer. Merged spectra dominate the PL of all Si-doped GaAsN samples. They have contributions of free and localized excitons and are consequently blue-shifted with respect to LE-bands of intrinsic GaAsN. The highly merged PL profiles of GaAsN:Si are studied systematically for the first time with temperature-dependent time-resolved PL. The PL decay is predominantly monoexponential and has a strong energy dispersion. In comparison to formerly reported values of intrinsic GaAsN epilayers, the determined decay times of GaAsN:Si are reduced by a factor of 10 because of enhanced Shockley-Read-Hall and possibly Auger recombinations. In the third part of this thesis, intrinsic and Si-doped GaAsN are investigated with magneto-PL in fields up to 62 T. A magneto-PL setup for pulsed magnetic fields of the HLD was built for this purpose. The blue-shift of LE-bands is studied in high magnetic fields in order to investigate its delocalized character. The blue-shift is diminished in intrinsic GaAsN at higher temperatures, which indicates that the interexcitonic population transfer is only active below a critical temperature 20 K < T < 50 K. A similar increase of the temperature has no significant impact on the partially delocalized character of the merged spectral band of GaAsN:Si. We conclude that the interexcitonic transfer of Si-doped GaAsN is more complex than in undoped GaAsN. In order to determine reduced masses of undoped GaAsN and GaAs:Si, the field-induced shift of the free exciton transition is studied in the high-field limit. We find an excellent agreement of GaAs:Si with a formerly published value of intrinsic GaAs which was determined with the same method. In both cases, the reduced mass values are enhanced by 20% in comparison to the accepted reduced mass values of GaAs. The determined GaAsN masses are 1.5 times larger than in GaAs:Si and match the rising trend of formerly reported electron effective masses of GaAsN.
764

Hydrogen-related defects in ZnO and TiO2

Herklotz, Frank 11 November 2011 (has links)
Hydrogen-related defects in single-crystal ZnO and rutile TiO2 are investigated by means of infrared absorption, Raman scattering, photoluminescence and photoconductivity. Four different defect centers in ZnO are considered: bond-centered hydrogen (HBC ), hydrogen bound within the oxygen vacancy (HO), hydrogen molecules, and a defect, which gives rise to a local vibrational mode at 3326 cm−1 . The measurements identify HBC as a shallow donor with an ionization energy of 53 meV. The internal 1s → 2p transition of HBC is detected at 330 cm−1 in the Raman scattering and photoconductivity spectra. The decay of an exciton bound to HBC results in the photoluminescence line at 3360.1 ± 0.2 meV. The local vibrational mode of the O–H bond for bond-centered hydrogen has a frequency of 3611 cm−1 (H-I) and an effective charge of 0.28±0.03e. It is found that bond-centered hydrogen is unstable against annealing at 190 °C due to diffusion and trapping by other defects. The dominant sink is the hydrogen molecule. It is demonstrated that the well-known I4 photoluminescence line at 3362.8 meV is due to the recombination of excitons bound to the HO donor. The ionization energy of the HO donor is determined to be 47 meV. The 1s → 2pz (2pxy) electronic transition of HO is detected at 265 cm−1 in photoconductivity spectra. The formation of HO occurs via trapping of HBC at vacancies left by out-diffusing oxygen. It is shown that sub-band gap illumination leads to an intensity reduction of the O–H local vibrational mode at 3326 cm−1 and the appearance of a previously unreported infrared absorption line at 3358 cm−1. The signals are identified as stretch modes of an O–H bond associated with the same defect in different charge states. The measurements indicate that this defect has a deep level in the band gap of ZnO at roughly Ec − 1.7 eV. Additionally, results on the thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented. Interstitial hydrogen in rutile TiO2 is studied by infrared absorption. It is shown that the defect is a shallow donor with an ionization energy of 10 meV. The absorption lines at about 3290 cm−1 consists of local vibrational modes due to the neutral and the positive charge states of the donor with relative intensities depending on the measurement conditions. In the neutral charge state, the defect reveals two modes at 3288.3 and 3292 cm−1 (10 K), whereas the positive charge state has a vibrational mode at 3287.4 cm−1. An unknown hydrogen complex was found to contribute to the 3288 cm−1 feature.
765

Molekulare Systeme im Wechselspiel von Struktur und Ladung: Optische in situ Spektroskopie an organischen Dünnschichten

Dienel, Thomas 23 February 2009 (has links)
Die optische in situ-Charakterisierung des Aufwachsens organischer Molekülschichten auf isolierenden und metallischen Substraten (Kaliumchlorid, -bromid und Glimmer, beziehungsweise Gold) ist Gegenstand dieser Arbeit. Am Beispiel der Substanzen Perylen-3,4,9,10- tetrakarbonsäuredianhydrid (PTCDA) und Titanylphthalozyanin (TiOPc), die mittels Molekularstrahlepitaxie abgeschieden werden, wird der Einfluss der Anordnung der Moleküle und der gegebenenfalls hinzugefügten Dotierung auf die messbaren Eigenschaften untersucht. Wie wichtig dabei die Feinabstimmung zwischen den Gitterkonstanten des Substrats und der Ausdehnung der Moleküle ist, äußert sich in schmalen Absorptions- und Emissionsbanden im Falle kommensurablenWachstums von PTCDA auf Kaliumchlorid. Diese Anordnung und ihre Metastabilität werden mit begleitenden Rasterkraftmikroskopie-Untersuchungen und Kraftfeldrechnungen nachgewiesen. Ausgehend von Monolagen neutraler Moleküle kann durch die schrittweise Dotierung mit Kalium die spektrale Entwicklung der Absorption von PTCDA-Anionen verfolgt und einzelnen Ladungsstufen – von Mono- bis Tetraanionen – zugeordnet werden. Durch vorherige Bestrahlung mit Elektronen konnte Glimmer so modifiziert werden, dass auch die spektrale Signatur von PTCDA-Monokationen aufgeklärt werden konnte. In Bestätigung früherer Rastertunnelmikoskopie-Ergebnisse zur Ausbildung von TiOPc- Kristallphasen erfolgt das Wachstum von Phase II auf einer Benetzungsschicht, die Phase I-Anordnung aufweist. Die Schichtdickenabhängigkeit der optischen Eigenschaften wird mit einer Genauigkeit im (Sub-)Monolagenbereich bestimmt und der Verlauf von Oszillatorstärke und Emissionslöschung durch die Orientierung der TiOPc-Moleküle zueinander beziehungsweise ihren Abstand zum Substrat erklärt. / The aim of this work is the in situ monitoring of the growth of molecular thin films on either insulating (potassium chloride, -bromide and mica) or gold substrates by optical spectroscopy. The influence of the molecular arrangement and an optionally added doping on the properties is studied on perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) and titanyl phthalocyanine (TiOPc), deposited by molecular beam epitaxy. The impact of perfect matching between the substrate’s lattice constants and the dimensions of the molecules, appears in narrow absorption and emission bands in case of commensurate growth of PTCDA on potassium chloride. This arrangement and its metastability are proven by accompanying atomic force microscopy and advanced potential energy calculations. Once potassium can be added stepwise to monolayers of neutral PTCDA molecules, the spectral development towards PTCDA anions can be followed and assigned to the reached levels of charging. The crystal growth of TiOPc molecules in phase II takes place on a wetting layer with phase I arrangement, proving earlier results by scanning tunneling microscopy. Measuring the thickness-dependent optical properties with (sub-)monolayer resolution allows a deeper understanding of the dependences of both, the oscillator strength and the efficiency of luminescence quenching, on the molecules’ orientations with respect to each other and on their distance to the substrate.
766

Optical and magnetic properties of rare earth Doped α-Fe2O3 for future bio-imaging applications

Mathevula, Langutani Eulenda 04 1900 (has links)
Imaging techniques have been developed for decades for the detection of biomolecules in biomedicine cells, in vitro or in living cells and organisms. The application however, often constrained by the available probes, whose optical properties may limit the imaging possibilities. It is very essential to improve the sensitivity of these devices by enhancing efficiency to detection. Recently, Fe3O4 has been used primarily in cancer theranostic application such as magnetic resonance imaging (MRI). However, its toxicity towards normal cells has been pointed out by scientific communities, when they are involved in in vitro (helics) cancer treatment. In this work, we have chosen to use α-Fe2O3, because it has proven to be less toxic than Fe3O4. Hematite is antiferromagnetic (AFM) at room temperature with a small canted moment lying within the crystal symmetry plane. At low temperature, hematite undergoes a magnetic phase transition from weak ferromagnetic (WFM) to a pure antiferromagnetic configuration (AF), which is known as the Morin transition. This magnetic property makes it possible for hematite to be applied in imaging technique. To enhance the optical properties, the α-Fe2O3 is doped with lanthanide ions due to their unique optical properties. Incorporation of these rare earth ions, enable the α-Fe2O3 to have enhance luminescence properties. Imaging techniques have been developed for decades for the detection of biomolecules in biomedicine cells, in vitro or in living cells and organisms. The application however, often constrained by the available probes, whose optical properties may limit the imaging possibilities. It is very essential to improve the sensitivity of these devices by enhancing efficiency to detection. Recently, Fe3O4 has been used primarily in cancer theranostic application such as magnetic resonance imaging (MRI). However, its toxicity towards normal cells has been pointed out by scientific communities, when they are involved in in vitro (helics) cancer treatment. In this work, we have chosen to use α-Fe2O3, because it has proven to be less toxic than Fe3O4. Hematite is antiferromagnetic (AFM) at room temperature with a small canted moment lying within the crystal symmetry plane. At low temperature, hematite undergoes a magnetic phase transition from weak ferromagnetic (WFM) to a pure antiferromagnetic configuration (AF), which is known as the Morin transition. This magnetic property makes it possible for hematite to be applied in imaging technique. To enhance the optical properties, the α-Fe2O3 is doped with lanthanide ions due to their unique optical properties. Incorporation of these rare earth ions, enable the α-Fe2O3 to have enhance luminescence properties. These lanthanide-doped nanoparticles (UCNPs) undergoes up-conversion process which have remarkable ability to combine two or more low energy photons to generate a singly high energy photon by an anti-stokes process and hold great promise for bio-imaging. These nanoparticles exhibit excellent photostability, continuous emission capability and sharp multi-peak line emission. With near infrared excitation, light scattering by biological tissues is substantially reduced. α-Fe2O3 have been singly and co-doped with Holmium, Thulium, and Ytterbium by both sol-gel and microwave methods. The doping of these lanthanides have shown improved luminescent properties of α-Fe2O3. The up-conversion has been observed from co-doping Thulium and Ytterbium. This work is a proof of concept to show the up-conversion in α-Fe2O3. However, the up-conversion intensity is low about 200000 CPS maximum observed, this could be due to the nature of the host structure quenching the luminescence. There is rather, a need to increase the intensity for the maximum application to be achieved. / Physics
767

Influence of the Matrix Environment on the Optical Properties of Incorporated Dye Molecules

Levichkova, Marieta 30 January 2008 (has links)
The present thesis is concerned with solid solutions of organic dyes. The organic molecules are incorporated in both optically inert or active and in rigid or flexible matrices, respectively. Exclusively thin films prepared by physical vapor deposition are studied. The optical response of the systems, in dependence on their structure and on the matrix nature, is investigated by means of absorption and luminescence spectroscopy. In the first part, perylene and 2,2-difluoro-1,3,2-dioxaborine derivatives, and Alq3 (tris(8-hydroxyquinoline) aluminium) embedded in the optically inactive SiO2 and polyimide hosts are studied. For the system dye molecules/SiO2 matrix, two sample preparation approaches, co-deposition and layer-by-layer, are compared. It is demonstrated that the luminescence properties of the mixed layers are affected by dye distribution and thin film composition. The photoluminescence quantum efficiency is strongly influenced by dye aggregation and Föster transfer. Therefore, effective separation and isolation of dye molecules in the matrix results in increased PL efficiency. Furthermore, it is established that layer-by-layer growth mode assures more homogeneous dye distribution. The spectroscopic studies also show that, since dye and matrix condense successively in time, luminescence losses due to thermal degradation of molecules are reduced. Hence, the film structure can be optimized with regard to high absorption and luminescence quantum efficiency. The experimental findings suggest that the luminescent properties of the embedded dyes are influenced by the nature of the host environment as well. In the rigid SiO2 matrix, it is possible to observe isolated facial Alq3 molecules with distinctive blue luminescence. In contrast, in the &amp;quot;soft&amp;quot; organic polyimide matrix Alq3 exhibits ordinary green luminescence. Thus, the structural properties of the host, rigidity and density, are found to be crucial for preservation of the facial Alq3 molecules. It is further demonstrated that the immobilization of molecules in the rigid SiO2 matrix in combination with layer-by-layer growth results in improved photostability. In polyimide matrix, the behavior of incorporated molecules is governed by the morphological changes of the host. These changes are defined by the curing procedure, needed for imidization, and give rise to a certain film structure. In the second part, special attention is paid on the luminescence response of dispersed DCM (4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyril)-4H-pyran) and rubrene (5,6,11,12-tetraphenyl-naphthacene) molecules in the optically active Alq3 matrix. The observed enhancement of luminescence intensity and alteration of emitted color are favorable for application of the doped Alq3 films as converter layers in combination with commercial blue light emitting diodes in luminescence conversion devices. It is demonstrated that by optimization of the conversion layer parameters white light generation can be achieved. The devices are characterized by high conversion efficiency and Lambertian distribution of the emitted light. However, they lack sufficient stability with regard to practical applications.
768

Integration of Micropore and Nanopore Features with Optofluidic Waveguides for Single Particle Sensing

Holmes, Matthew R. 28 June 2011 (has links) (PDF)
This dissertation outlines the research and development of ground-breaking nanometer sized openings (nanopores) integrated with an on-chip optofluidic platform. This platform represents a significant advancement for single nanoparticle sensing. In this work specifically, the integrated optofluidic platform has been used to electrically and optically filter and detect single nanoparticles using ionic current blockade and fluorescence experiments. The correlation of electrical and optical signal has provided the highest sensitivity single nanoparticle measurements ever taken with integrated optofluidic platforms. The particular optofluidic platform used for this work is an antiresonant reflecting optical waveguide (ARROW). ARROW hollow and solid core waveguides are interference based waveguides that are designed to guide light in low index media such as liquids and gases. Because of this unique guiding property, ARROW hollow cores can be used to sense and analyze low concentrations of single particles. Additionally, because ARROW platforms are based upon standard silicon processing techniques and materials, they are miniature sized (~1 cm2), inexpensive, highly parallelizable, provide a high degree of design flexibility, and can be integrated with many different optical and electrical components and sources. Finally, because of the miniature, integrated nature of the ARROW platform, it has the potential to be incorporated into hand held devices that could provide quick, inexpensive, user-friendly diagnostics. The ARROW platform has been through many revisions in the past several years in an attempt to improve performance and functionality. Specifically, advanced fabrication techniques that have been used to decrease the production time, increase the yield, and improve the optical quality of ARROW platforms are discussed in the first part of this work. These advancements were all developed in order to facilitate the production of high quality integrated nanopores and ARROW platforms. The second part of this work then focuses on the actual integration of micrometer sized openings (micropores) and nanopores in the hollow waveguide section of ARROW platforms for filtering, detecting, and analyzing single nanoparticles. The successes and attempts at achieving these results are the basis of this dissertation of work.
769

Feasibility of Manipulating Correlated Color Temperatures with a Phosphor Converted High-Powered Light Emitting Diode White Light Source

Little, Matthew Michael 01 June 2010 (has links) (PDF)
In this thesis we examine the feasibility of developing a white light source capable of producing colors between 2500 and 7500 Kelvin on the black-body radiator spectrum by simply adjusting amperage to a blue and ultraviolet (UV) light emitting diode (LED). The purpose of a lighting source of this nature is to better replicate daylight inside a building at a given time of day. This study analyzes the proposed light source using a 385 nm UV LED, a 457 nm blue LED, a 479 nm blue LED, a 562 nm peak cerium doped yttrium aluminum garnet (YAG:Ce) phosphor, and a 647 nm peak selenium doped zinc sulfide (ZnS:Se) phosphor. Our approach to this study initially examined optical performance of yellow-emitting phosphor (YAG:Ce) positioned at specific distances above a blue LED using polydimethylsiloxane (PDMS) as a substrate. An understanding of how phosphor concentration within the PDMS, the thickness of the PDMS, and how substrate distance from the LED die affected light intensity and color values (determined quantitatively by utilizing the 1931 CIE 2° Standard Observer) enabled equations to be developed for various lens designs to efficiently produce white light using a 457 nm peak wavelength LED. The combination of two luminescent sources (457 nm LED and YAG:Ce) provided a linear trend on the 1931 CIE diagram which required a red illumination source to obtain Kelvin values from 2500 to 7500. Red-emitting phosphor (ZnS:Se), selected to compliment the system, was dispersed with YAG:Ce throughout PDMS where they were stimulated with a blue LED thereby enabling all desired Kelvin values with differing concentration lenses. Stimulating ZnS:Se with the addition of a UV LED did not provide the ability to change the color value of the set up to the degree required. Many other factors resulted in the decision to remove the UV LED contribution from the multi-Kelvin light source design. The final design incorporated a combination of ZnS:Se and YAG:Ce stimulated with a blue LED to obtain a 2500 Kelvin value. A separate blue LED provides the means to obtain 7500 Kelvin light and the other color values in between, with a linear approximation, by adjusting the amperages of both LEDs. In addition to investigating the feasibility of obtaining the Kelvin values from 2500 to 7500, this thesis also examined the problem of ZnS:Se’s inability to cure in PDMS and a method to create a lens shape to provide equal color values at all points above a phosphor converted LED source. ZnS:Se was found to be curable in PDMS if first coated with a low viscosity silicon oil prior to dispersion within PDMS. The lens configuration consists of phosphors equally distributed in PDMS and cured in the shape of a Gaussian distribution unique to multiple factors in LED-based white light design.
770

Люминесцентный контроль радиационных полей с использованием двуокиси циркония : выпускная квалификационная работа специалиста / Radiation Fields Luminescence Control with the use of zirconium oxide

Казанцева, М. Г., Kazantseva, M. G. January 2015 (has links)
Цель работы – изучение люминесцентных свойств двуокиси циркония при различных видах облучения, и оценка возможности его использования для высокодозной дозиметрии электронных пучков. В результате исследования образцов получен комплекс параметров, характеризующих их фотолюминесцентные и термолюминесцентные свойства, проведено сравнение найденных параметров с известными литературными данными. Обнаружена сублинейная дозовая зависимость интенсивности термолюминесценции моноклинного ZrO2 от дозы облучения, что подтверждает возможность его использования для дозиметрии электронных пучков. Проведен анализ экологических рисков и соблюдения правил безопасности жизнедеятельности при экспериментальных исследованиях. / The purpose of this work is the study of luminescent properties of zirconia excited by different types of radiation, and to assess the possibility of its use for high-current electron beams dosimetry. Obtained set of parameters characterizing their photoluminescence and thermoluminescence properties was compared with the parameters found in literature. Sublinear dose dependence of thermoluminescence intensity of monoclinic ZrO2 confirms the possibility of its use for dosimetry of electron beams. Ecological risks and compliance with the rules of life safety during experimental investigations were analyzed.

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