Inorganic alternating current electroluminescent devices (AC-ELs) are known for their ruggedness and extreme long-term reliability, which is why they can often been found in industrial and medical equipment as well as in applications in the military sector. In contrast to the inorganic phosphors used in AC-ELs, organic materials offer a number of advantages, in particular a significantly higher efficiency, easier processibility, and a wide selection of emitter materials spanning the entire visible spectrum. Several efforts towards alternating current driven organic light-emitting devices have recently been made, however, important operating mechanism are still not well understood. In the first part of this theses, alternating current driven, capacitively coupled, pin-based organic light-emitting devices are investigated with respect to the influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage. A three-capacitor model is employed to predict the basic behavior of the devices and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3–3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. In a second step, asymmetric driving of capacitively coupled OLEDs is investigated. It is found that different voltages and/or pulse lengths for positive and negative half-cycle lead to significant improvements in terms of brightness and device efficiency. Part two of this work demonstrates a device concept for highly efficient organic light-emitting devices whose emission color can be easily adjusted from, e.g., deep-blue through cold-white and warm-white to saturated yellow. The presented approach exploits the different polarities of the positive and negative half-cycles of an alternating current driving signal to independently address a fluorescent blue emission unit and a phosphorescent yellow emission unit vertically stacked on top of each other. The electrode design is optimized for simple fabrication and driving and allows for two-terminal operation by a single source. The presented approach for color-tunable OLEDs is versatile in terms of emitter combinations and meets application requirements by providing a high device efficiency of 36.2 lm/W, a color rendering index of 82 at application relevant brightness levels of 1000 cd/m², and warm-white emission color coordinates. The final part demonstrates an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows to efficiently generate every color that is a superposition of spectra of the individual emission units. The device is built in a top-emission geometrywhich is highly desirable for display fabrication as the pixel can be directly deposited onto the back-plane electronics. Furthermore, the presented device design requires only three independently addressable electrodes which simplifies fabrication and electrical driving. The electrical performance of each individual unit is on par with standard pin single emission unit OLEDs, showing very low leakage currents and achieving high brightness levels at moderate voltages of around 3–4 V.

Nesta dissertação, propomos um método que combina a técnica de varredura-Z e a luz branca supercontínua gerada em uma fibra fotônica para caracterizar o espectro de não-linearidades de amostras. O espectro não-linear fornece informações cruciais a respeito da característica, da origem e do potencial da não-linearidade para aplicação em dispositivos. Neste sentido, a luz branca supercontínua aliada à técnica de varredura-Z vem permitir uma rápida determinação de espectros numa banda larga. Neste trabalho, a luz branca foi gerada numa fibra fotônica comercial bombeada por pulsos de femtossegundo de um oscilador laser de Ti:safira. Tanto os lasers de femtosegundo quanto as fibras fotônicas estão se tornando cada vez mais acessíveis. Ademais, a técnica de varredura-Z é um método bastante conhecido para a determinação de não-linearidades devido à sua simplicidade e precisão. Dessa forma, aliamos essas vantagens para fazer um aparato simples, compacto e de baixo custo. Em geral, a determinação do espectro de não-linearidades necessita de sistemas lasers complexos que possam sintonizar o comprimento de onda. O método de varredura-Z de luz branca desenvolvido aqui foi usado para medir o espectro não-linear do corante disperse red 13 (DR13) em metanol. Esse corante possui um efeito não-linear absortivo (absorção saturada) bem caracterizado, sendo um bom material não apenas para calibração, mas também para testar nosso sistema experimental. Os resultados experimentais comprovaram a viabilidade do sistema para caracterização de amostras com efeitos não-lineares absortivos intensos. / In this dissertation, we proposed a method that combines the Z-scan technique and the white-light continuum generated by a photonic crystal fiber to characterize the nonlinear spectrum of materials. The nonlinear spectrum provides crucial information on the characteristic, the origin and the potential of the nonlinearity for devices application. In this sense, the white-light continuum allied to the Z-scan technique allows fast spectra determination in a broad spectral range. In this work, the white light was generated in a commercial photonic crystal fiber pumped by femtosecond pulses from a Ti:sapphire laser oscillator. Both the femtosecond lasers and the photonic crystal fibers are becoming more accessible. In addition, the Z-scan technique is a well-known method for nonlinearities determination due to its simplicity and precision. In this way, we merged these advantages to make a simple, compact and low-cost apparatus for studying nonlinear samples. In general, the nonlinear spectrum determination requires complex laser systems which are able to tune the wavelength. The white-light Z-scan method we developed here was used to measure the nonlinear spectrum of disperse red 13 (DR13) dye in methanol. This dye presents a well-characterized absorcive nonlinear effect (saturable absorption), being a good material not only to calibrate, but also to test our experimental setup. The experimental results confirmed the viability of the setup for characterizing samples with strong nonlinear absorption effect.

<p>A 6082 aluminium alloy has been characterized with regard to the influence of surface roughness on fatigue strength.</p><p>Fatigue life testing of smooth specimens was used to establish reference curves for the material in extruded and forged T6 condition. The extruded material was found to have better fatigue strength than the forged material, although the cyclic stress-strain response was similar for both. The forged material was tested in T5, T6 and T7 tempers, showing no significant difference in fatigue strength.</p><p>Surface roughness was created by circumferential grinding of cylindrical test specimens, and the surface topography was measured using a white light interferometry microscope. The measurements proved to be accurate, although errors were observed for certain surface features. Residual stresses were quantified by X-ray diffraction. Compressive residual stresses of around 150 MPa were found in both rough and smooth specimens. Load cycling did not significantly alter the surface residual stresses.</p><p>Stress solutions ahead of all major surface grooves were found using a linear elastic material model. Estimates of cyclic stresses and strains were calculated in the notch roots using different Neuber corrections of the linear solution. The results were compared to finite element analysis employing a bilinear kinematic hardening model. A generalized version of the Neuber correction was found to be within 20% of the nonlinear finite element results.</p><p>Several empirical models for the notch sensitivity factor were investigated. These were found to be unable to describe the notch influence on fatigue life and initiation life. In order to follow this approach, it was recommended that different test specimens should be used where the short fatigue crack growth could be monitored.</p><p>It was shown that microstructural fracture mechanics theories could be used to estimate the fatigue limit of rough surfaces. In some cases, initiation from material defects or weaknesses would override the influence of surface geometry. In one specimen, the initiation appeared to have started as at a de-bonded grain, while in other cases, initiation was thought to have started at larger second phase particles embedded in notch roots. Further work in this area should focus on statistical descriptions of surface roughness, inherent material defects, and their interaction.</p>

A 6082 aluminium alloy has been characterized with regard to the influence of surface roughness on fatigue strength. Fatigue life testing of smooth specimens was used to establish reference curves for the material in extruded and forged T6 condition. The extruded material was found to have better fatigue strength than the forged material, although the cyclic stress-strain response was similar for both. The forged material was tested in T5, T6 and T7 tempers, showing no significant difference in fatigue strength. Surface roughness was created by circumferential grinding of cylindrical test specimens, and the surface topography was measured using a white light interferometry microscope. The measurements proved to be accurate, although errors were observed for certain surface features. Residual stresses were quantified by X-ray diffraction. Compressive residual stresses of around 150 MPa were found in both rough and smooth specimens. Load cycling did not significantly alter the surface residual stresses. Stress solutions ahead of all major surface grooves were found using a linear elastic material model. Estimates of cyclic stresses and strains were calculated in the notch roots using different Neuber corrections of the linear solution. The results were compared to finite element analysis employing a bilinear kinematic hardening model. A generalized version of the Neuber correction was found to be within 20% of the nonlinear finite element results. Several empirical models for the notch sensitivity factor were investigated. These were found to be unable to describe the notch influence on fatigue life and initiation life. In order to follow this approach, it was recommended that different test specimens should be used where the short fatigue crack growth could be monitored. It was shown that microstructural fracture mechanics theories could be used to estimate the fatigue limit of rough surfaces. In some cases, initiation from material defects or weaknesses would override the influence of surface geometry. In one specimen, the initiation appeared to have started as at a de-bonded grain, while in other cases, initiation was thought to have started at larger second phase particles embedded in notch roots. Further work in this area should focus on statistical descriptions of surface roughness, inherent material defects, and their interaction.

Luminescent boron containing materials find numerous applications in modern technologies such as display/lighting, bio-imaging and sensing. Thus, investigations of structure-property relationships in organic luminescent compounds to understand their molecular and bulk properties are of fundamental importance. The main thrust of this thesis is the development of facile synthetic routes for boron containing novel polyads and study their structure-property correlations and to utilize this information to design functional materials with desired properties such as multiple emission, bio imaging, anion sensing and organic photo voltaic characteristics. This thesis contains seven chapters and the contents of each chapter are described below. Chapter 1 This chapter is a concise overview of the recent developments in the chemistry of boron based molecular systems such as triarylborane and BODIPYs. This chapter also highlights the basic nature of broad emissive materials. In addition, an advance in the frontier areas such as bio imaging is discussed in brief. Chapter 2 This chapter describes the structure and optical properties of a new triad (Borane-Bithiophene-BODIPY) 1. Triad 1 exhibits unprecedented tricolour emission when excited at borane centred high energy absorption band and also acts as a selective fluorescent and colorimetric sensor for fluoride ion with ratiometric response. The experimental results are supported by computational studies. Chapter 3 Two fluorescent compounds with similar absorption profiles and complementarily emissive properties can be regarded as the ideal couple for the generation of white-light. Two structurally close and complementarily fluorescent boron based molecular siblings 2 and 3 were prepared. The luminescence properties of individual triads were modulated to an extent to complement each other by controlling the intramolecular energy transfer in triads by fine-tuning the dihedral angle between fluorophores in 2 and 3. A binary mixture of 2 and 3 emitted white-light. Chapter 4 This chapter deals with a straight forward strategy for the generation of white-light emission in aqueous media. Using a blue-emissive AIE-active (aggregation-induced emission) 1, 8-naphthalimide- based sensitizer and a boron-dipyrromethene based red emitter as a dopant, water dispersible nanostructures with tunable emission features are produced. The white-light emissive (WL) nano-aggregates are stable at neutral pH and have been elegantly utilized for four-colour cell imaging (including near- infrared imaging). Chapter 5 This chapter describes the design and development of a NIR emitting triarylborane decorated styryl-BODIPY (4) via a facile synthetic route. Incorporation of TAB entities results in a significantly red shifted broad emission in 4 (compared to compound M3 which is devoid of TAB unit). The near coplanar orientation of Ar3B planes and BODIPY core results in a highly efficient (TAB to BODIPY) EET process in 4. Conjugate 4 acts as a highly selective and sensitive fluoride sensor with naked eye visual response as well as ratiometric fluorescent response. The dual emission in fluoride bound 4 possibly results from the restricted partial TAB to BODIPY energy transfer. Chapter 6 This chapter describes how the energy of transitions of the broad emissive molecular triads can be fine-tuned by judiciously changing the spacer oligothiophene length. A series of triarylborane and BODIPY conjugates (TAB-π-BODIPY) has been designed, and synthesized by a combined strategy of changing the connection mode between the two units, extending the conjugation size by introducing terthiophene, quaterthiophene, and pentathiophene units. The electrochemical and photophysical behavior of these conjugates were investigated. The experimental findings were rationalized by density functional theory calculations. Chapter 7 This chapter describes design and development of boron based novel electron acceptor BDY for the bulk-heterojunction solar cell. The electron mobility values of BDY was found to be of the order of standard PCBM. Bulk-heterojunction was fabricated using BDY as the electron acceptor layer. The power conversion efficiency of the newly developed solar cells with BDY as electron acceptor is much higher than the value obtained for standard cells with PCBM as the electron acceptor.

Les Diodes Electroluminescentes (DEL) à base de composés III-nitrures sont très efficaces pour les longueurs d’ondes correspondant à la couleur bleue. Ces DELs bleues sont très utilisées sur le marché car leur combinaison avec des phosphores produit une lumière blanche. Néanmoins, cette approche a plusieurs inconvénients tels que l’instabilité de la température de couleur ou les pertes liées à la conversion. Dans ce contexte la DEL blanche monolithique dont la lumière blanche est obtenue directement dans la zone active grâce à l’émission des puits quantiques à différentes longueurs d’ondes est envisagée.Pourtant, lorsque la longueur d’onde d’émission augmente, le rendement d’émission des puits quantiques InGaN/GaN diminue. Ceci est problématique pour l’application de la DEL blanche monolithique mais également pour l’application micro-display qui nécessite idéalement des DELs monochromatiques bleues, vertes et rouges fabriquées à partir de la même famille de matériaux. Ce problème est principalement du à la différence importante de paramètre de maille entre les puits quantiques InGaN et la couche GaN sur saphir utilisée comme substrat qui provoque une forte contrainte compressive. Cette contrainte est à l’origine d’un champ électrique interne dans les puits quantiques, préjudiciable au rendement d’émission, et d’un taux d’incorporation d’indium faible bien qu’originellement thermodynamiquement difficile.Cette thèse de doctorat propose de résoudre ce problème en réalisant la croissance de la DEL sur un pseudo-substrat InGaN appelé InGaNOS fabriqué par Soitec.Après avoir identifié les limitations des structures InGaN/GaN sur substrat GaN sur sapphire classique pour l’émission efficace à grande longueur d’onde, des structures « tout-InGaN » ont été crues par EPVOM sur substrats InGaNOS. Il a été démontré que la contrainte était partiellement relaxée et que l’incorporation d’indium était plus facile. Grâce à des caractérisations optiques et structurelles fines, les différentes étapes depuis la reprise de croissance InGaN jusqu’à la DEL complète ont été étudiées. En photoluminescence (PL), la longueur d’onde de 617 nm a été atteinte à température ambiante. Les performances optiques de ces structures de puits quantiques dans les régions spectrales correspondant au vert, jaune et ambre ont été mesurées et sont comparables aux meilleures valeurs de la littérature. Enfin, la croissance de la première DEL « tout InGaN » sur substrat InGaN a révélé les challenges restants qui nécessiteront des développements complémentaires. / Light emitting diodes (LEDs) based on nitride materials are very efficient in the blue range. These blue LEDs combined with phosphors are used to manufacture white LEDs widely used in the lighting market. Nonetheless, this converted approach presents some disadvantages , like an instability of the color temperature or conversion losses. In this context, the white monolithic LED which produces the white color thanks to different emission wavelengths produced from quantum wells (QWs) placed in the active region is one of the considered solution.However, as emission wavelength increases the quantum efficiency of the InGaN based QWs decreases. This is problematic for the white monolithic application but also for micro-display application which both ideally requires red, green and blue monochromatic LEDs grown in the same material system. This issue is mainly due to the great lattice mismatch between the InGaN QW and the GaN layer on sapphire substrate which induces an important compressive strain. This strain is responsible for a strong internal electric field in the QWs, which is detrimental for the quantum efficiency, and for low indium incorporation rate in GaN, originally thermodynamically difficult.This PhD thesis proposes to tackle this issue by growing the LED on an InGaN pseudo-substrate called InGaNOS manufactured by Soitec.After identifying the limitations of InGaN based structures grown on regular GaN on sapphire substrate for efficient long wavelength emission, full InGaN structures were grown by MOCVD on InGaNOS substrates. It was shown that the strain was partially released and the indium incorporation was made easier. Through fine structural, optical and electrical characterizations, the different steps leading from the InGaN buffer regrowth stage to the complete processed LED were studied. PL emission wavelengths up to 617 nm were reached at room temperature. The optical performances of these MQW structures in the green, yellow and amber range were measured to be comparable to the best ones achieved in the literature. Finally, the growth of the first full InGaN LED structure on InGaN substrate revealed the remaining challenges that will require some additional developments.

La mise en forme de lumière blanche incohérente à l’aide d’un nouveau composant est proposée dans cette thèse. L'objectif était de réaliser une carte d'irradiance arbitraire sur un écran à l’aide d’une structure originale contenant seulement des facettes, légèrement inclinées par rapport à la direction d'origine selon leurs axes propres. Une approche basée sur l’optique géométrique a été utilisée pour concevoir et analyser la structure proposée. Celle-ci est constituée d’une matrice de facettes jouant le rôle de déflecteur. Nous avons étudié le cas en transmission et en réflexion. L’obtention des angles d’inclinaison s’est faite avec deux approches différentes : l'optimisation sous Zemax et le calcul analytique. Plusieurs critères de qualité ont été proposés pour comparer la carte d'irradiance. Le tolérancement a démontré qu’il est plus intéressant de travailler en transmission qu’en réflexion. Une réalisation a été faite avec succès en utilisant une technologie additive innovante. / Beam shaping of incoherent white light with a large spectrum is proposed in this PhD thesis. The objective was to realize an arbitrary irradiance map on a target plane using a faceted structure. To maintain the design result within the geometrical optics domain, large facet element dimensions are required to obtain usable results. Each facet element can slightly tilt along its own axes to deflect the incident light, either by reflection, either by transmission. The calculation of the tilt angles is made by an analytical approach, and also by automatic optimization with Zemax. Several quality factors are proposed in order to qualify the illumination/irradiance chart on the screen. Because of the required tolerances on the fabrication technique, we show that it is more interesting to design a transmissive structure than a reflective one. With a new additive technology, a structure is realized successfully, showing the interest of the concept.

Nesta dissertação, propomos um método que combina a técnica de varredura-Z e a luz branca supercontínua gerada em uma fibra fotônica para caracterizar o espectro de não-linearidades de amostras. O espectro não-linear fornece informações cruciais a respeito da característica, da origem e do potencial da não-linearidade para aplicação em dispositivos. Neste sentido, a luz branca supercontínua aliada à técnica de varredura-Z vem permitir uma rápida determinação de espectros numa banda larga. Neste trabalho, a luz branca foi gerada numa fibra fotônica comercial bombeada por pulsos de femtossegundo de um oscilador laser de Ti:safira. Tanto os lasers de femtosegundo quanto as fibras fotônicas estão se tornando cada vez mais acessíveis. Ademais, a técnica de varredura-Z é um método bastante conhecido para a determinação de não-linearidades devido à sua simplicidade e precisão. Dessa forma, aliamos essas vantagens para fazer um aparato simples, compacto e de baixo custo. Em geral, a determinação do espectro de não-linearidades necessita de sistemas lasers complexos que possam sintonizar o comprimento de onda. O método de varredura-Z de luz branca desenvolvido aqui foi usado para medir o espectro não-linear do corante disperse red 13 (DR13) em metanol. Esse corante possui um efeito não-linear absortivo (absorção saturada) bem caracterizado, sendo um bom material não apenas para calibração, mas também para testar nosso sistema experimental. Os resultados experimentais comprovaram a viabilidade do sistema para caracterização de amostras com efeitos não-lineares absortivos intensos. / In this dissertation, we proposed a method that combines the Z-scan technique and the white-light continuum generated by a photonic crystal fiber to characterize the nonlinear spectrum of materials. The nonlinear spectrum provides crucial information on the characteristic, the origin and the potential of the nonlinearity for devices application. In this sense, the white-light continuum allied to the Z-scan technique allows fast spectra determination in a broad spectral range. In this work, the white light was generated in a commercial photonic crystal fiber pumped by femtosecond pulses from a Ti:sapphire laser oscillator. Both the femtosecond lasers and the photonic crystal fibers are becoming more accessible. In addition, the Z-scan technique is a well-known method for nonlinearities determination due to its simplicity and precision. In this way, we merged these advantages to make a simple, compact and low-cost apparatus for studying nonlinear samples. In general, the nonlinear spectrum determination requires complex laser systems which are able to tune the wavelength. The white-light Z-scan method we developed here was used to measure the nonlinear spectrum of disperse red 13 (DR13) dye in methanol. This dye presents a well-characterized absorcive nonlinear effect (saturable absorption), being a good material not only to calibrate, but also to test our experimental setup. The experimental results confirmed the viability of the setup for characterizing samples with strong nonlinear absorption effect.

The theoretical part of this master's thesis is focused on research of confocal microscopy and FLIM method. There are a principles and types of confocal microscopy and the use of broad-spectrum laser as a basic light source of these microscopes. It gives what the FLIM method and its use not only in cell biology. The practical part thesis includes the acquisition of three sets of fluorescence intensity images with use of applications tunable pulsed laser, function TimeGate and detection of hybrid detectors. For practical elaboration of this thesis is in the software Fiji created a plugin, which is the source code in the Java programming language. The types of plugins and their uses are described in the third chapter of the thesis. This plugin including the graphical user interface in the form of the dialog box, proceses the fluorescence intensity images and creates a graphical representation of data showing the fluorescence lifetime, so called pseudocolor map.

Supercontinuum (SC) generation, oftentimes referred to as white-light continuum (WLC), has been a subject of interest for more than 40 years. From the first observation of WLC in condensed media in the early 1970s to the first observation of WLC in gases in the mid-1980s, much work has been devoted to developing a framework for understanding the complex nature of this phenomenon as well as discovering its utility in various applications. The main effort of this dissertation is to develop a WLC for the purpose of broadband nonlinear spectroscopy and use it in spectroscopic measurements. The ability to generate a high-quality, high-spectral-irradiance source of radiation confined in a single beam that spans the visible and near-infrared spectral regimes has great utility for nonlinear measurement methods such as the Z-scan technique. Using a broadband WLC instead of conventional tunable sources of radiation such as optical parametric generators/amplifiers has been shown to increase the efficiency of such measurements by nearly an order of magnitude. Although WLC generation has many complex processes involved, and complete models of the process involve highly complex numerical modeling, simple models can still guide us in the optimization of systems for WLC generation. In this dissertation the effects of two key mechanisms behind WLC generation in gaseous media are explored: self-phase modulation (SPM) and ionization leading to plasma production. The effects of SPM are largely dependent upon the third-order nonlinear refractive index, n2, of the gaseous medium whereas the effects of plasma production are dependent upon many parameters including the initial number density, ionization potential/energy, and the rate of ionization production. It is found that in order to generate a stable WLC suitable for nonlinear spectroscopy, the phase contributions from SPM and plasma production should be nearly equal. This guided our experiments in inert gases using mJ level, 150 fs-FWHM (full-width at half-maximum) pulses at 780 nm as well as 40 fs-FWHM pulses primarily at 1800 nm to create a stable, high-spectral-irradiance WLC. The generated WLC is shown to have sufficient spectral energy and spatial quality suitable for nonlinear spectroscopic measurements. In addition to extending the WLC bandwidth by using a long wavelength (1800 nm) pump source, it is found that by using a secondary weak seed pulse with a peak irradiance three orders of magnitude less than the main pulse, the spectral energy density is enhanced by more than a factor of 3 in Krypton gas for a WLC spectrum that spans over 2 octaves. Numerical simulations are presented which qualitatively describe the experimental results. The spectral enhancement of the WLC by seeding is also demonstrated for other inert gases and condensed media. Other efforts described in this dissertation include the development of the Dual-Arm Z-scan technique and its extension to measuring thin film nonlinearities in the presence of large substrate signals as well as predicting the n2 spectra of organic molecules (where we can approximate their behavior as if they were centrosymmetric) from knowledge of the one-photon and two-photon absorption spectra using a simplified sum-over-states quantum perturbative model by utilizing a quasi 3-level and quasi 4-level system.