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I present photonics applications of PbS quantum-dot-doped (QD-doped) glasses. The dissertation consists of two major parts: bulk material applications (Cr:forsterite laser modelocking, bleaching dynamics, optical gain, and photoluminescence) and the fabrication of QD-doped ion-exchanged waveguides.When this work began, these PbS QD-doped glasses were the state-of-the-art in QD glasses due to their narrow size distribution. Modelocking of a Cr:forsterite laser using this glass as a saturable absorber had been demonstrated, with little understanding of the dynamics. This work began by studying the dynamics of the saturable absorber to explain the ps-pulse width.In the bulk measurements, I functioned as secondary researcher. In the laser modelocking and bleaching measurements, my contribution was laser cavity alignment, sample preparation, collecting autocorrelation traces, and aiding in the setup and data collection for the bleaching measurements. On this work, I coauthored one refereed journal article in Applied Physics Letters [1] and one refereed conference paper [2], for which I am third and second author, respectively.For the gain measurements, I aided in the setup and data collection, whereas I set-up and took most of the luminescence data. The gain measurements resulted in one second-author refereed journal article in Applied Physics Letters [3] and I presented the luminescence results at CLEO2000 [4].I took the lead role in the waveguide fabrication and characterization and authored refereed journal articles in Applied Physics Letters [5], Journal of Applied Physics [6], and Journal of the Optical Society of America B [7]. I also presented an invited talk at Photonics West [8] and presented at CLEO2004 [9]. Additionally, I have been a coauthor of presentations at the Nanotechnology Symposium (2006), American Ceramic Society [10], and Photonics Europe (2006) [11]. A book chapter in The Photonics Handbook, 2nd edition [12] also discusses this work.The next step is to focus on reducing the waveguide losses. This requires new, circular wafers with better surface quality and glass homogeneity. I suggest using silver-film ion exchange followed by a field-assisted burial to eliminate the surface interaction.

Thesis advisor: Torsten Fiebig / Thesis advisor: Mary Roberts / Understanding the electronic nature of DNA is profound and has been attempted for decades. Photoexcitation of DNA with UV light deposits electronic energy in the base stack and prepares highly reactive excited states. These states are precursors for photoinduced damage reactions which can lead to mutations and ultimately to cell death. While many DNA photo products have been isolated and characterized, the primary events immediately after photon absorption are not yet understood. Recent studies with ultrafast lasers have revealed that the majority of excess energy gained by DNA with light absorbance is dissipated on the femtosecond and picosecond time scales. In this study double-stranded oligonucleotides with different base sequences, content and lengths were systematically examined using femtosecond pump-probe spectroscopy. The results indicate that excitations in DNA are delocalized over more than two bases and the extent of the delocalization depends strongly on the structure of the investigated systems. Exciton delocalization domains in the longer duplexes are larger than in the shorter ones. Also, single-stranded oligonucleotides show smaller extent of exciton delocalization than duplexes with the same length. In addition to the fundamental studies on DNA photophysics, the properties and the structure of new molecular beacons based on thiazole orange dimers were studied. A full account of the optical and structural properties of the dimers in different base environments and orientations is presented here. Currently, the development of efficient ways to utilizing solar energy is at the forefront of the scientific community due to the ever rising demand for energy. Both, colloidal semiconductor nanocrystals and single-walled carbon nanotubes are potential alternatives to conventional inorganic and organic materials in photovoltaic devices Thorough understanding of the charge transfer and related photophysical phenomena in these systems will answer the question whether these nanomaterials can be applied in future generations of solar cells. The photoinduced electron transfer in donor-acceptor CdSe/CdTe heterostructured nanorods, in which CdTe is grown on top of CdSe in a single rod structure, was studied. The electron transfer between the two nanocrystals occurs on the subpicosecond time scale, competing with the ultrafast relaxation mechanisms in the quantum confined nanocrystals. Furthermore, investigations on how quantum confinement influences the phonon wavepackets in semiconductor nanocrystals were carried out. Quantum beats corresponding to longitudinal optical phonon modes were observed in the femtosecond pump-probe spectra of colloidal CdTe nanocrystals. Size-dependent experiments revealed that the optical phonon frequencies and the exciton-phonon coupling strength do not depend on the crystal's size. Only the wavepacket dephasing time was influenced by the diameter of the particles which was correlated with the hole relaxation to the exciton band edge. Electron donor-acceptor constructs, based on single-walled carbon nanotubes (SWNT), can be attained by noncovalent functionalization of the nanotubes with pyrene derivatives. However, charge transfer does not take place in the simplest pyrene-SWNT constructs. For the first time the pure SWNT-pyrene construct was isolated and investigated. Our results revealed that the optical properties of pyrene are drastically altered due to strong electronic interactions with the SWNT surface. In other words, aromatic molecules lose their electronic (and chemical) signature when non-covalently attached to carbon nanotubes. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The availability of laser systems capable of generating ultrashort optical pulses in the visible spectral range have made it possible to study molecular species with a temporal resolution in the order of intra-molecular dynamics which previously were not accessible. Henceforth, in this study a popular pump-probe technique called ultrafast transient absorption spectroscopy (UTAS) is employed to study the initial photochromic reaction of metal complex, dithizonatophenylmercury (II) (DPM) under various conditions. These conditions include the use of different solvents and electronically altering DPM by the addition of substituents with specific electron affinity properties. For this study the photochromic behaviour of DPM dissolved in methanol is used as standard. Using this standard, the initial photochromic reaction after ultrafast excitation within less than 100 fs caused a radiationless photoreaction with a time constant of about 2 ps, which is interpreted as C=N isomerization along the twist coordinate. It is found that during this isomerization reaction an orthogonally twisted intermediate state was formed and observed through its excited-state absorption, which funnels through a conical intersection onto the ground state potential. Once here, bifurcation along pathways towards the ground states of the reactant and product configurations occurs. This was the first observation of photochromism for DPM in a strong polar solvent such as methanol. From the results of the test compound in methanol, comparisons to the photo-behaviour of DPM dissolved in deuterated methanol and dichloromethane are made. What is established is that changing the solvent resulted in slightly different decay times as well as spectral shifts in the absorption profile which suggested that the potential energy surface of the excited state is modified. This is similar to the results found from the electronically altered DPM species. Here the entire photoreaction is found to either be sped up (1 ps) or slowed down (4 ps) depending on the sample investigated. Previous studies on the photochromicity of DPM like systems concluded that apart from the photo-activated forward reaction, a back reaction occurs in the absence of light. Therefore a detailed look at the back reaction of DPM and its derivatives are also studied. This is done by temporally monitoring the absorption change of the photo-product as it converts back to the reactant. In doing so the lifetime of the photo-product is determined and found to differ greatly depending on the solvent and substituent used. Lastly, in assuming that the back reaction follows first order kinetics, an Arrhenius type measurement on the photo-product of DPM is conducted. The result of this measurement is that a potential energy barrier of 64.8 kJ/mol is overcome in the back reaction. The measurements performed and the results obtained from the photochromicity of DPM contribute to the understanding of photo-induced cis-trans isomerization reactions about a C=N double bond. / AFRIKAANSE OPSOMMING: Die beskikbaarheid van laser sisteme in staat om ultrakort optiese pulse te genereer in die sigbare spektrale gebied, het die studie van molekulˆere spesies met ’n tydresolusie in die orde van intra-molekulˆere dinamika wat voorheen nie toeganklik was nie. Voortaan, in hierdie studie word ’n populˆere aktiveer-interogeer tegniek genaamd ultravinnige tydafhanklike absorpsie spektroskopie (UTAS) aangewend om die aanvanklike fotochromiese reaksie van die metaal kompleks, ditisoonfenielkwik (II) (DFK) onder verskillende kondisies te bestudeer. Hierdie kondisies sluit in die gebruik van verskillende oplosmiddels en die elektroniese verstelling van DFK deur die toevoeging van substituente met spesifieke elektron affiniteit eienskappe. Vir hierdie studie word die fotochromiese gedrag van DFK, opgelos in metanol, as standaard gebruik. Met hierdie standaard, word gevind dat die aanvanklike fotochroom reaksie na ultravinnige opwekking binne minder as 100 fs, ’n stralingslose fotoreaksie met ’n tydkonstante van 2 ps veroorsaak. Hierdie fotoreaksie word verklaar as die C=N isomerisasie met betrekking tot die draai ko¨ordinaat. Daar is ook gevind dat gedurende hierdie isomerisasie reaksie, ’n ortogonaal verdraaide oorgangstoestand gevorm word wat waargeneem is deur sy absorpsie in die opgewekte toestand wat tregter deur ’n koniese kruispunt na die potensiaal van die grondtoestand. By hierdie punt vurk die proses na die grondtoestande van die reaktant en die produk vorme. Di´e was die eerste waarneming van fotochromisme van DFK opgelos in ’n sterk polˆere oplosmiddel soos metanol. Vanuit die resultate vir die toets mengsel in metanol word vergelykings getrek tot die fotogedrag van DFK opgelos in gedeureriese metanol en dichlorometaan. Wat hieruit vasgestel is, is dat die verandering in oplosmiddel wel die fotoreaksie be¨ınvloed deurdat verskillende vervaltye en spekrale verskuiwings in die apsorpsie profiel waargeneem word. Hierdie verskille dui aan dat die potensie¨ele energie oppervlakte van die opgewekte toestand wel gemodifiseer word. Dit is ook soortgelyk aan die resultate vir die elektronies verstelde BFK spesies. Hier is gevind dat die tempo van die totale fotoreaksie `of toeneem (1 ps) `of afneem (4 ps) afhanklik van die spesifieke spesie wat bestudeer word. Vorige studies van die fotochromiese gedrag van sisteme soortgelyk aan DFK het gevind dat behalwe vir die fotogeaktiveerde voorwaartse reaksie, daar ook ’n keersy reaksie plaasvind in die afwesigheid van lig. Dus word die keersy reaksie vir DFK en sy derivate ook in detial bestudeer. In hierdie studie word die absorpsie verskille van die fotoproduk tydelik waargeneem soos dit terugkeer na die reaktant. Op hierdie manier word die leeftyd van die fotoproduk bepaal en gevind dat dit grootliks afhang van die tipe oplosmiddel en tipe substituent wat gebruik word. Ten slote, wanneer daar aanvaar word dat di´e keersy reaksie eerste orde kinetika volg, word ’n Arrhenius tipe meting op die fotoproduk uitgevoer. Die resultaat van hierdie meting is dat ’n potensie¨ele enrgie versperring van 64.8 kJ/mol oorkom word in die keersy reaksie. Die metings wat uitgevoer is en die resultate wat verkry is van die fotochromiese gedrag van DFK dra by tot die verstandhouding van lig-ge¨ınduseerde cis-trans isomerisasie reaksies rondom ’n C=N dubbelbinding.

<p>Bilirubin is a degradation product of haem, which is constantly formed in all</p><p>mammals. Increased levels of bilirubin in humans lead to jaundice, a condition</p><p>that is very common during the first days after birth. This neonatal</p><p>jaundice can routinely be treated by phototherapy without any serious side</p><p>effects. During this treatment, bilirubin undergoes a photoreaction to isomers</p><p>that can be excreted. The most efficient photoreaction is the isomerisation</p><p>around a double bond (Z-E-isomerisation), which results in more soluble</p><p>photoproducts.</p><p>The work presented in this thesis shows results of a femtosecond optical</p><p>spectroscopy study, combined with quantum-mechanical investigations, of</p><p>the mechanism of isomerisation of bilirubin. The spectroscopic research was</p><p>conducted with bilirubin in organic solvents, and in buffer complexed by</p><p>human serum albumin. This albumin complex is present in the blood, and</p><p>has thus medical importance. Quantum-chemical calculations (CASSCF) on</p><p>a bilirubin model were used to explain experimental results.</p><p>The fluorescence decay observed with femtosecond spectroscopy shows an</p><p>ultrafast component (~120 fs), which is explained by exciton localisation,</p><p>followed by processes with a lifetime of about 1-3 ps. These are interpreted</p><p>as the formation of a twisted intermediate, which decays with a lifetime of</p><p>10-15 ps back to the ground state, as observed by absorption spectroscopy.</p><p>CASSCF calculations, in combination with the experimental results, suggest</p><p>the ca. 1-3 ps components to be relaxation to the twisted S1 minimum, followed</p><p>by the crossing of a barrier, from where further relaxation takes place</p><p>through a conical intersection back to the ground state.</p><p>Time-dependent DFT calculations were utilised to analyse the absorption</p><p>spectrum of bilirubin. Good agreement with the measured spectrum was</p><p>achieved, and low-lying states were observed, that need further investigation.</p><p>The theoretically obtained CD spectrum provides direct evidence that</p><p>bilirubin preferentially binds to human serum albumin in the enantiomeric</p><p>P-form at neutral pH.</p> / <p>Bilirubin är en nedbrytningsprodukt av hem som ständigt bildas hos alla</p><p>däggdjur. En förhöjd bilirubinkoncentration i den mänskliga kroppen kan</p><p>leda till gulsot, något som är mycket vanligt under de första dagarna efter</p><p>födelsen (neonatal gulsot). Fototerapi används rutinmässigt som säker behandlingsmetod,</p><p>under vilken bilirubin genomgår en fotoreaktion till en</p><p>isomer som kan utsöndras. Den mest effektiva fotoreaktionen är en Z-Eisomerisation,</p><p>vilken leder till lösligare fotoprodukter.</p><p>Arbetet som presenteras i denna avhandling visar resultaten av en kombinerad</p><p>femtosekund optisk-spektroskopisk och kvantmekanisk undersökning</p><p>av mekanismen bakom bilirubins isomerisation. Den spektroskopiska</p><p>studien genomfördes med bilirubin, löst i organiska lösningsmedel och i</p><p>buffert i komplex med humant serumalbumin. Detta albuminkomplex finns i</p><p>blodet, och är därför av medicinskt intresse. Kvantmekanistiska CASSCFberäkningar</p><p>på en bilirubinmodell användes för att förklara de experimentella</p><p>resultaten.</p><p>Det uppmätta fluorescence sönderfallet visar ultrasnabba komponenter</p><p>(~120 fs). Dessa tolkas som excitonlokalisering, som följs av bildandet av</p><p>ett vridet intermediat med en hastighetskonstant på ca. 1 ps-1(beroende på</p><p>lösningsmedlet). Absorptionsmätningar visar att detta intermediat sönderfaller</p><p>tillbaka till grundtillståndet med en livstid på 10-15 ps.</p><p>CASSCF beräkningar, i kombination med de experimentella resultaten, tyder</p><p>på att sönderfallet med livslängden på ca. 1 ps är en relaxation till det</p><p>vridna S1-tillståndet. Reaktionsvägen därifrån antas passera en barriär till en</p><p>konisk genomskärning, som möjliggör snabb relaxation till grundtillståndet.</p><p>Tidsberoende DFT-beräkningar användes för att analysera bilirubins absorptionsspektrum,</p><p>vilket gav bra överensstämmelse med uppmätta data. Dessutom</p><p>hittades ett tillstånd med låg excitationsenergi, som kräver ytterligare</p><p>studier. Med hjälp av det beräknade CD-spectret kunde det visas att bilirubin</p><p>binder till albumin i P-formen vid neutralt pH.</p>