Die genaue Implikation natürlicher Killer(NK)-zellen und Neutrophile in Autoimmunerkrankungen des zentralen Nervensystems (ZNS) ist nach wie vor ungeklärt und wurde daher im Mausmodell der multiplen Sklerose (MS), der experimentellen Autoimmunenzephalomyelitis (EAE), sowie bei MS und Neuromyelitis optica (NMO) Patienten untersucht. Bei MS Patienten konnte eine mit der Krankheitsaktivität korrelierende, reduzierte Zahl zirkulierender CX3CR1+NK Zellen festgestellt werden. Daher wurden die NK Zell-Dynamiken und der Einfluss von CX3CR1 auf diese im EAE Mausmodell untersucht. Hierbei konnte in Wildtyp(WT) sowie auch CX3CR1-defizienten EAE Mäusen eine Rekrutierung peripherer NK Zellen in das ZNS beobachtet werden. Anders als bei WT EAE Mäusen wiesen die NK Zellen bei CX3CR1-defizienten Mäusen einen primär unreifen Phänotyp auf, der möglicherweise als ursächlich für die erhöhte Krankheitsaktivität dieser Tiere gemutmaßt werden kann. Der Transfer reifer NK Zellen vor Immunisierung CX3CR1-defizienter Tiere zeigte folglich protektive Effekte und lässt schlussfolgern, dass die CX3CR1-vermittelte Rekrutierung reifer NK Zellen die EAE Neuroinflammation limitiert. Die Diskriminierung der MS von der klinisch ähnlichen NMO stellt nach wie vor eine Herausforderung dar. Neutrophile in ZNS-Läsionen und der Cerebrospinalflüssigkeit(CSF) können bei NMO, nicht aber MS Patienten nachgewiesen werden, weshalb Neutrophile aus dem Blut von NMO und MS Patienten hier vergleichend untersucht wurden. Die Neutrophile beider Patientengruppen wiesen einen aktivierten Phänotyp im Vergleich zu gesunden Kontrollen auf. Im Gegensatz dazu zeigte sich eine von Medikation und neurologischen Defiziten der Patienten unabhängige, kompromittierte Funktionalität der NMO verglichen mit MS Neutrophilen im Hinblick auf Migration, oxidativen Burst und Degranulierung. Die Neutrophilenfunktionalität könnte entsprechend potentiell als diagnostisches Diskriminierungskriterium zwischen der MS und der NMO dienen. / The implication of natural killer (NK) cells and neutrophils in autoimmune disorders of the central nervous system (CNS) remains elusive, and therefore was investigated in a mouse model for multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE), and in patients with MS and neuromyelitis optica (NMO), respectively. In MS, a decreased frequency of circulating CX3CR1+NK cells correlating with the patient disease activity has been reported. Therefore, the pattern of NK cell mobilization and the contribution of CX3CR1 to NK cell dynamics in response to neuroinflammatory insult were investigated in the EAE model. Here, NK cells similarly mobilized from the periphery and accumulated in the CNS in both wild-type (WT) and CX3CR1-deficient mice during EAE. However, in mice lacking CX3CR1 the infiltrated NK cells displayed an immature phenotype contrasting with the mature infiltrates in the WT counterparts, apparently contributing to EAE exacerbation in those animals since transfer of mature WT NK cells prior to immunization of CX3CR1-deficient mice exerted a protective effect. Together, these data suggest that the CX3CR1-mediated recruitment of mature CX3CR1+NK cells limits EAE neuroinflammation. Due to clinical similarities, the discrimination between MS and NMO is still challenging. In contrast to MS, neutrophil accumulations were found in CNS lesions and the cerebrospinal fluid (CSF) of NMO patients wherefore a comparative analysis of peripheral blood neutrophils in NMO and MS patients was performed. The results revealed an activated neutrophil phenotype in NMO and MS when compared to healthy individuals. In contrast, analysis of neutrophil migration, oxidative burst activity and degranulation showed a compromised neutrophil functionality in NMO compared to MS, which was not influenced by the treatment regime and clinical parameters of the patients. Thus, neutrophil functionality may represent a new diagnostic tool to discriminate between NMO and MS.

Electronic and optical properties of semiconducting nanocrystals, that can be engineered and manipulated by various ways like varying size, shape, composition, structure, has been a subject of intense research for more than last two decades. The size dependency of these properties in semiconductor nanocrystals is direct manifestation of the quantum confinement effect. Study of electronic and optical properties in smaller dimensions provides a platform to understand the evolution of fundamental bulk properties in the semiconductors, often leading to realization and exploration of entirely new and novel properties. Not only of fundamental interests, the semiconductor nanocrystals are also shown to have great technological implications in diverse areas. Besides size tunable properties, introduction of impurities, like transition metal ions, gives rise to new functionalities in the semicon-ductor nanocrystals. These materials, termed as doped semiconductor nanocrystals, have been the subject of great interest, mainly due to the their interesting optical properties. Among different transition metal doped semiconductor nanocrystals, manganese doped systems have drawn a lot on attention due to their certain advantages over other dopants. One of the major advantages of Mn doped semiconductor nanocrystals is that they do not suffer from the problem of self-absorption of emission, which quite often, is consid-ered detrimental in their undoped counterparts. The doped nanocrystals are known to produce a characteristic yellow-orange emission upon photoexcitation of the host that is relatively insensitive to the surface degradation of the host. This emission, originating from an atomic d-d transition of Mn2+ ions, has been a subject of extensive research in the recent past. In spite of the spin forbidden nature of the specific d-d transition, namely 6A1 −4 T1, these doped nanocrystals yield intense phosphorescence. However, one major drawback of utilizing this system for a wide range application has been the substantial inability of the community to tune the emission color of Mn-doped systems in spite of an intense effort over the years; the relative constancy of the emission color in these systems has been attributed to the essentially atomic nature of the optical transition involving localized Mn d levels. Interestingly, however, the Mn emission has a very broad spectral line-width in spite of its atomic-like origin. While the long (∼ 1 ms) emission life-time of the de-excitation process is well-studied and understood in terms of the spin and orbitally forbidden nature of the transition, there is little known concerning the process of energy transfer to the Mn from the host in the excitation step. In this thesis, we have studied the ultrafast dynamic processes involved in Mn emission and addressed the issues related to its tunability and spectral purity. Chapter 1 provides a brief introduction to the fundamental concepts relevant to the studies carried out in the subsequent chapters of this thesis. This chapter is started with a small preview of the nanomaterials in general, followed by a discussion on semiconducting nanomaterials, evolution of their electronic structure with dimensions and size as well as the effect of quantum confinement on their optical properties. As all the semiconducting nanomaterials studied in the thesis are synthesized via colloidal synthesis routes, a separate section is devoted on colloidal semiconducting nanomaterials, describing various ways of modifying or tuning their optical properties. This is followed by an introduction to the important class of materials “doped semiconductor nanocrystals”. With a general overview and brief history of these materials, we proceed to discuss about various aspects of manganese doped semiconductor nanocrystals in great details, highlighting the origin of the manganese emission and the associated carrier dynamics as well as different reported synthetic strategies to prepare these materials. The chapter is closed with the open questions related to manganese doped semiconductor nanocrystals and the scope of the present work. Chapter 2 describes different experimental and theoretical methods that have been employed to carry out different studies presented in the thesis. It includes common experimental techniques like UV-Vis absorption spectroscopy, steady-state and time-resolved photoluminescence spectroscopy used for optical measurements, X-ray diffraction, trans-mission electron microscopy and atomic absorption spectroscopy used for structural and elemental analysis. Experimental tools to perform special studies like transient absorption and single nanocrystal spectroscopy are also discussed. Finally, theoretical fitting method used to analyse various spectral data has been discussed briefly. Chapter 3 deals with the dynamic processes involved in the photoexcitation and emission in manganese doped semiconductor nanocrystals. For this study, Mn doped ZnCdS alloyed nanocrystal has been chosen as a model system. There are various radiative and nonrdiative recombination pathways of the photogenerated carriers and they often compete with each other. We have studied the dynamics of all possible pathways of carrier relaxation, viz. excitonic recombination, surface state emission and Mn d-d transition. The main highlight of this chapter is the determination of the time-scale to populate surface states and the Mn d-states after the photoexcitation of the host. Employing femtosecond pump-probe based transient absorption study we have shown that the Mn dopant states are populated within sub-picosecond of the host excitation, while it takes a few picoseconds to populate the surface states. Keeping in mind the typical life-time of the excitonic emission (∼ a few ns), the ultra-fast process of energy transfer from the host to the Mn ions explains why the presence of Mn dopant ions quenches the excitonic as well as the surface state emissions so efficiently. Chapter 4 presents a study of manganese emission in ZnS nanocrystals of different sizes. By varying the size of the ZnS host nanocrystal, we show that one can tune the Mn emission over a limited range. In particular, with a decrease in host size, the Mn emission has been observed to red-shift. We have attributed this shift in Mn emission to the change in the ratio of surface to bulk dopant ions with the variation of the host size, noting that the strength of the ligand field at the Mn site should depend on the position of the Mn ion relative to the surface due to a systematic lattice relaxation in such nanocrystals. The ligand field affects the emission wavelength directly by controlling the splitting of the t2 and e levels of Mn2+ ions. The surface dopant ions experience a strong ligand field due to distorted tetrahedral environment which leads to larger splitting of these t2 and e states. We further corroborated these results by performing doping concentration dependent emission and life-time studies. In Chapter 5 addresses two fundamental challenges related to manganese photolumines-cence, namely the lack of a substantial emission tunability and presence of a very broad spectral width (∼ 180-270 meV). The large spectral width is incompatible with atomic-like manganese 4T1 −6 A1 transition. On the other hand, if this emission is atomic in nature, it should be relatively unaffected by the nature of the host, though it can be manipulated to some extent as discussed in Chapter 3. The lack of Mn emission tunability and spectral purity together seriously limit the usefulness of Mn doped semiconductor nanocrystals. To understand why the Mn emission tunability range is very limited (typically 565-630 nm) and to understand the true nature of this emission, we carried out single nanocrystal imaging and spectroscopy on Mn doped ZnCdS alloyed nanocrystals. This study reveals that Mn emission, in fact, can vary over a much wider range (∼ 370 meV) and exhibits widths substantially lower (∼ 60-75 meV) than reported so far. We explained the occur-rence of Mn emission in this broad spectral range in terms of the possibility of a large number of symmetry inequivalent sites resulting from random substitution of Cd and Zn ions that leads to differing extent of ligand field contributions towards the splitting of Mn d-levels. The broad Mn emission observed in ensemble-averaged measurements is the result of contribution from Mn ions at different sites of varying ligand field strengths inside the NC. Chapter 6 presents a synthetic strategy to strain-engineer a nanocrystal host lattice for a controlled tuning of the ligand field effect of the doped Mn sites. It is realized synthesizing a strained quantum dot system with the structure ZnSe/CdSe/ZnSe. A larger lattice parameter of CdSe compared to that of ZnSe causes a strain field that is maximum near the interface, gradually decreasing towards the surface. We control the positioning of Mn dopant ions at different distances from the interface, thereby doping Mn at different predetermined strain fields. With the help of this strain engineering, we are able to tune Mn emission across the entire range of the visible spectrum. This strain induced tuning of Mn emission is accompanied by life-times that is dependent on the emission energy which has been explained in terms of perturbation effect on the Mn center due to the strain generated inside the quantum dot. The spectacular emission tuning has been explained by modelling the quantum dot system as an elastic continuum containing three distinct layers under hydrostatic pressure. From this modelling, we found that the strain is max-imum at the interface and decreases continuously as one goes away from the interface. We also show that the Mn emission maximum red shifts with increasing distance of the dopants from the maximum strained region. In summary, we have performed a study on the photophysical processes in manganese doped semiconductor nanocrystals. We have emphasized in understanding of different dynamic processes associated with the manganese emission and tried to understand the true nature of manganese emission in a nanocrystal. This study has brought out some new aspects of manganese emission and opened up possibilities to tune and control manganese emission by proper design of the host material.

In dieser Arbeit wird die Abhängigkeit der Photolumineszenz (PL) von CdSe/ZnS-Nanokristallen von der Umgebung und der Einfluss der Filmdicke und -morphologie auf die optische Absorption von Farbstofffilmen untersucht sowie die Oberfläche von Hybridstrukturen durch Funktionalisierung mit Farbstoff analysiert. Untersuchungen von CdSe/ZnS-Nanokristallen in Toluol-Lösung zeigen, dass die PL-Intensität der Nanopartikel durch Zugabe des organischen Halbleiters TPD gequencht wird. Die zusätzliche Auswertung der PL-Lebensdauer verdeutlicht, dass die Abnahme (fast) vollständig durch statisches Quenchen, infolge der Abnahme der Anzahl der mittierenden Nanokristalle verursacht wird, bei einem Anstieg der langlebigsten Lebensdauerkomponente. Die Analyse der PL-Unterbrechung einzelner Nanokristalle auf PVA und Siliziumoxid sowie eingebettet in PS und TPD zeigt eine Ab- bzw. Zunahme der Häufigkeit langer An- bzw. Aus-Zeiten und somit eine deutliche Abhängigkeit der PL-Unterbrechung von den dielektrischen Eigenschaften der Umgebung. Bei Variation der Anregungsleistung zeigt sich für einzelne Nanokristalle auf Siliziumoxid und eingebettet in TPD eine lineare Zunahme der Blinkaktivität und eine Abnahme des An-Zeit-Anteils. Die Änderung der Verteilungen der An- und Aus-Zeiten zeigen eine deutliche Abhängigkeit von der Matrix. Die Untersuchung der optischen Absorption von aufgedampften MePTCDI- und Cl4MePTCDI-Filmen zeigt eine Verschiebung des energieärmsten optischen Überganges mit wachsender mittlere Filmdicke. Es wird ein (geometrisches) Schicht-Modell vorgestellt, das die energetische Verschiebung mit der mittleren Filmdicke korreliert und dabei die kristalline, nadelförmige Morphologie von MePTCDIFilmen und die amorphe Kugelkappen-Struktur von Cl4MePTCDI-Filmen berücksichtigt. Die Oberfläche von Hybridfilmen aus PMMA mit Siliziumoxid-Partikeln wird durch Anbindung von R6G an die Oxid-Partikel gezielt funktionalisiert. Die Ergebnisse von fluoreszenzmikroskopischen Untersuchungen zeigen, dass dadurch der Anteil der freien Oxid-Oberfläche bestimmt werden kann.

In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer. In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates. (i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.

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Currently conventional sources like coal, petroleum and natural gas meet the energy requirements of developing and undeveloped countries. Over a period of time there is high risk of these energy sources getting depleted. Hence an alternate source of energy i.e. renewable energy is the need of the hour. The advantages of renewable energy like higher sustainability, lesser maintenance, low cost of operation, and minimal impact on the environment make the role of renewable energy sources significant. Out of the various renewable energy sources like solar energy, wind energy, hydropower, biogas, tidal and geothermal, usage of solar energy is gradually increasing. Among various solar energy sources, Photovoltaics has dominated over the past two decades since it is free clean energy and availability of abundant sunlight on earth. Over the past few decades, thin film solar cells (TFSC) have gained considerable interest as an economically feasible alternative to conventional silicon (Si) photovoltaic devices. TFSCs have the potential to be as efficient as Si solar cells both in terms of conversion efficiency as well as cost. The advantages of TFSC are that they are easy to prepare, lesser thickness, requires lesser materials, light weight, low cost and opto-electronic properties can be tuned by varying the process parameters. The present study is focused on the fabrication of AgInS2/ZnS heterojunction thin film solar cell. AgInS2 absorber layer is deposited using both vacuum (sputtering/sulfurization) and non-vacuum (ultrasonic spray pyrolysis) techniques. ZnS window layer is prepared using thermal evaporation technique, detailed experimental investigation has been conducted and the results have been reported in this work. The thesis is divided into 6 chapters. Chapter 1 gives general introduction about solar cells and working principle of solar cell. It also discusses thin film solar cell technology and its advantages. Layers of thin film solar cell structure, Significance of each layers and possible materials to be used are emphasized. A detailed overview of the available literature on both AgInS2 absorber layer and ZnS window layer has been presented. Based on the literature review, objectives of the present work are defined. Chapter 2 explains the theory and experimental details of deposition techniques used for the growth of AgInS2 and ZnS films. Details of characterization techniques to study film properties are described in detail. Chapter 3 presents a systematic study of AgInS2 thin films deposited by sulfurization of sputtered Ag-In metallic precursors. Initially, AgInS2 films are deposited by varying the substrate temperature and properties of as-deposited films are characterized. Structural, morphological, electrical and optical properties of AgInS2 films are explained. From these studies, samples with better properties at particular substrate temperature are optimized. By fixing the substrate temperature, deposition time of silver is varied by keeping other deposition conditions same and the properties of films are discussed. It was observed that deposition time of silver doesn’t have much impact on structural properties of AgInS2 films. However, opto-electric properties of AgInS2 films are enhanced. Based on characterization studies, deposition time of silver is optimized. Deposition time of indium is varied by keeping substrate temperature and silver deposition to optimized value. The properties of as-deposited films are discussed. Based on the above studies, the optimized p type films have a band gap of 1.64 eV, carrier concentration of 1013 ions/cm3 and Resistivity of order 103 Ω-cm. Chapter 4 presents a systematic study of AgInS2 thin films deposited by ultrasonic spray pyrolysis. AgInS2 films are deposited by varying the substrate temperature and properties of as deposited films are characterized. Structural, morphological, electrical and optical properties of AgInS2 films are explained. From these studies, samples with better properties at particular substrate temperature are optimized. By fixing the substrate temperature, concentration of silver molarity in the precursor solution is varied by keeping other deposition conditions same and the properties of films are discussed. Structural, optical and electrical properties of AgInS2 films are enhanced with the increase in silver concentration. Based on characterization studies, concentration of silver is optimized. Similarly concentration of indium molarity in the precursor solution is varied and the properties of as-deposited films are discussed. Finally, sulfur molarity in the precursor solution is varied and properties of films are discussed. It was observed that increasing sulfur after certain limit does not have any effect on the properties of the films. Based on the above studies, this method resulted in the films with resistivity of 103 Ω-cm and band gap of 1.64 eV. These films showed a carrier concentration of 1013 ions/cm3. Chapter 5 describes the growth of ZnS films using thermal evaporation technique. Influence of thickness on the properties of ZnS films is explained. Samples with good crystallinity, high transmission, and wider gap are selected for device fabrication. This p type layer showed a band gap of 3.52 eV. Solar cells have been fabricated using the AgInS2 films developed by both sputtering and ultrasonic spray pyrolysis techniques. A maximum cell efficiency of 0.92 percent has been achieved for the cell with 0.950 µm thick sputtered AgInS2 layer and thermally evaporated 42 nm thick ZnS layer. In comparison, the ultrasonic spray pyrolysis deposited films gave an efficiency of 0.54 percent. These values are comparable to those mentioned in a couple of reports earlier. Chapter 6 summarizes the conclusions drawn from the present investigations and scope of future work is suggested.

The American Cancer Society predicts that 1,665,540 people will be diagnosed with cancer, and 585,720 people will die from cancer in 2014. One of the most common types of cancer in the United States is skin cancer. Melanoma alone is predicted to account for 10,000 of the cancer related deaths in 2014. As a highly mobile and aggressive form of cancer, melanoma is difficult to fight once it has metastasized through the body. Early detection in such varieties of cancer is critical in improving survival rates in afflicted patients. Present methods of detection rely on visual examination of suspicious regions of tissue via various forms of biopsies. Accurate assessment of cancerous cells via this method are subjective, and often unreliable in the early stages of cancer formation when only few cancer cells are forming. With fewer cancer cells, it is less likely that a cancer cell will appear in a biopsied tissue. This leads to a lower detection rate, even when cancer is present. This lack of detection when cancer is in fact present is referred to as a false negative. False negatives can have a highly detrimental effect on treating the cancer as soon as possible. More accurate methods of detecting cancer in early stages, in a nonsubjective form would alleviate these problems. A proposed alternative to visual examination of biopsied legions is to utilize fluorescent nanocrystalline biomarker constructs to directly attach to the abnormal markers found on cancerous tissues. Quantum dots (QDs) are hydrophobic nanoscale crystals composed of semiconducting materials which fluoresce when exposed to specific wavelengths of radiation, most commonly in the form of an ultraviolet light source. The QD constructs generated were composed of cadmium-selenium (CdSe) cores encapsulated with zinc-sulfide (ZnS) shells. These QDs were then encapsulated with phospholipids in an effort to create a hydrophilic particle which could interact with polar fluids as found within the human body. The goal of this thesis is to develop a method for the solubilization, encapsulation, and initial functionalization of CdSe/ZnS QDs. The first stage of this thesis focused on the generation of CdSe/ZnS QDs and the fluorescence differences between unshelled and shelled QDs. The second stage focused on utilizing the shelled QDs to generate hydrophilic constructs by utilizing phospholipids to bind with the QDs. Analysis via spectroscopy was performed in an effort to characterize the difference in QDs both prior to and after the encapsulation process. The method generated provides insight on fluorescence trends and the encapsulation of QDs in polar substances. Future research focusing on the repeatability of the process, introducing the QD constructs to a biological material, and eventual interaction with cancer cells are the next steps in generating a new technique to target and reveal skin cancer cells in the earliest possible stages without using a biopsy.