Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-24T15:04:21Z No. of bitstreams: 1 luizfernandoalvesguedes.pdf: 8533376 bytes, checksum: 1fb75359e16225fb5b36b42d374e4b7a (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-24T16:59:50Z (GMT) No. of bitstreams: 1 luizfernandoalvesguedes.pdf: 8533376 bytes, checksum: 1fb75359e16225fb5b36b42d374e4b7a (MD5) / Made available in DSpace on 2017-04-24T16:59:50Z (GMT). No. of bitstreams: 1 luizfernandoalvesguedes.pdf: 8533376 bytes, checksum: 1fb75359e16225fb5b36b42d374e4b7a (MD5) Previous issue date: 2012-12-17 / Este trabalho tem o objetivo de estudar, projetar, simular e obter resultados experimentais, a partir de um conversor flyback operando no modo descontínuo (DCM), para acionar uma luminária de diodos emissores de luz (LEDs). Além disso, deseja-se que o conversor possua elevado fator de potência, alta eficiência, baixa distorção harmônica da corrente de entrada, vida útil elevada (através da possibilidade de substituir de capacitores eletrolíticos por capacitores de filme metálico) e baixo custo. Inicialmente, o trabalho apresenta um breve estudo da iluminação a LEDs, o modelo elétrico simplificado dos LEDs, bem como uma revisão de alguns conversores aplicados ao acionamento deste tipo de fonte luminosa. Em seguida é analisada a operação do conversor flyback em modo DCM alimentado a partir da retificação (em ponte) da tensão da rede elétrica. Além do estudo teórico, a simulação do conversor é apresentada de modo a validar o projeto do conversor e servir de base de comparação com os resultados experimentais. O projeto do transformador (indutores acoplados) do conversor flyback tem destaque especial neste trabalho, pois, este elemento é fundamental para elevar a eficiência do conversor. Portanto, parte deste trabalho é dedicada ao estudo de perdas do transformador. Isto é feito através de uma adaptação de técnicas consagradas nesta área por meio de uma compilação didática visando a repetitividade do estudo. A partir do estudo teórico sobre as perdas no transformador, programas elaborados no MATLAB e no MICROSOFT EXCEL auxiliam o projeto do elemento magnético do conversor flyback. Estes dois programas, visam facilitar o exaustivo equacionamento das perdas e auxiliam no desenvolvimento de um projeto com elevada eficiência do transformador flyback elevando, consequentemente, a eficiência global do conversor. Empregando os programas elaborados, o projeto é calculado e resultados experimentais são obtidos a partir de medições realizadas em um protótipo em escala. Estes resultados são analisados e comparados com os resultados teóricos e de simulação. Ao final, é realizada uma análise simplificada do custo dos componentes do conversor e também são apresentadas as principais conclusões deste trabalho. / This work aims to study, design, simulate and obtain experimental results from a flyback converter operating in discontinuous mode (DCM), to trigger a fixture of light emitting diodes (LEDs). Furthermore, it is desired that the converter has high power factor, high efficiency, low harmonic distortion of input current, high life (through the possibility of replacing the electrolytic capacitors for metal film capacitors) and low cost. Initially, the paper presents a brief study of lighting LEDs, LEDs for simplified electrical model, as well as a review of some converters used to drive this type of light source. Then it analyzed the operation of the flyback converter in DCM mode fed from the rectification (bridged) the utility voltage. Besides the theoretical study, the simulation of the converter is presented in order to validate the design of the converter as a basis for comparison with experimental results. The transformer design (coupled inductors) flyback converter has special emphasis in this work, because this element is essential to raise the efficiency of the converter. So part of this work is devoted to the study of transformer losses. This is done by an adaptation of standard techniques in this area via a teaching order to build repeatability study. From the theoretical study on the losses in the transformer, programs developed in MATLAB and MICROSOFT EXCEL aid the design of the magnetic element of the flyback converter. These two programs are designed to facilitate the comprehensive equating of losses and assist in developing a project with high efficiency flyback transformer raising therefore the overall efficiency of the converter. Employing the programs drawn up, the project is calculated and experimental results are obtained from measurements performed on a prototype scale. These results are analyzed and compared with the theoretical results and simulation. At the end we provide a simplified analysis of the cost of the converter components and also presents the main conclusions of this work.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work aims to develop a family of electronic converters with electrical isolation to supply a group of power light emitting diodes, applied to street lighting systems. The converters have high power factor and still meets the IEC61000-3-2, for lighting equipment. The integration between the power stages is realized to decrease the number of active semiconductors in the topologies. The topologies are modeled, considering the electrical model of light emitting diodes, and controllers are proposed to turns possible the reduction of the capacitances values in the analyzed topologies. This reduction aims to turns possible the replacement of the electrolytic capacitors for film capacitors, with higher lifetime. The implemented topology is a converter with 70 W of power, supplying 32 power LEDs with 700 mA. The experimental results prove the design methodology, presenting the desired characteristics, like high power factor (0.962), agreement with the standard IEC 61000-3-2 and high efficiency (88%). / Este trabalho visa o desenvolvimento de uma família de conversores eletrônicos com isolação elétrica para o acionamento de um conjunto de diodos emissores de luz de potência, aplicados à iluminação pública. Estes sistemas devem possuir elevado fator de potência e ainda estar de acordo com a norma IEC 61000-3-2, para equipamentos de iluminação. É realizada a integração entre os estágios de potência, de tal forma a reduzir o número de semicondutores ativos das topologias. As topologias são modeladas, considerando o modelo elétrico dos diodos emissores de luz, e é proposto o uso de controladores, visando possibilitar a redução dos valores de capacitâncias das topologias analisadas. Esta redução possibilita a substituição de capacitores eletrolíticos por capacitores de filme, com maior vida útil. Um protótipo para 70 W foi implementado, alimentando 32 LEDs de potência com 700 mA, foram utilizados os conversores Boost-Flyback, Buck-Flyback e Buck-Boost Flyback, além disso o conversor Flyback foi implementado visando a comparação entre conversores integrados e de estágio único. Os resultados experimentais comprovam a metodologia de projeto, apresentando as características desejadas, como elevado fator de potência (0,962), concordância com a norma IEC 6100-3-2 e rendimento de 88%.

In der vorliegenden Arbeit wurde der Einfluss von Lichtbedingungen auf den Ertrag und die nutritive Qualität der Versuchspflanze Persicaria odorata untersucht. Die Experimente wurden unter praxisnahen Bedingungen im Gewächshaus (Sonnenlicht) und Klimakammern (Dreiband-Leuchtstoffröhren) unter Berücksichtigung eines breiten Inhaltsstoffspektrums, mehreren Versuchsreihen, Lichtmodifizierungen anhand von Zusatzbestrahlungen mit LEDs und Überdeckungen mit photoselektiven Folien sowie dem Anwenden verschiedener statistischer Auswertungsverfahren durchgeführt. Die Tageslichtsumme beeinflusste das Pflanzenwachstum positiv. Beispielsweise wurde die Frischmasse bei einem Anstieg der Tageslichtsumme um 1% mit gleichbleibender spektralen Lichtzusammensetzung um 0,96% (Gewächshaus) bzw. 0,64% (Klimakammer) erhöht. Versuche mit monochromatischen LEDs zeigten, dass spektralbereichsabhängige Erhöhungen der Tageslichtsumme die Biomassesteigerungen verstärkten. Den deutlichsten Effekt im Hinblick auf die Frischmassebildung hatte das kurzwellige Blaulicht (443 nm). Bezüglich der Inhaltsstoffe zeigte insbesondere das kurzwellige Grünlicht (515 nm) einen positiven Effekt. Dieser Spektralbereich wird jedoch durch die traditionell in Gewächshäusern eingesetzten Natriumhochdrucklampen kaum emittiert. Auch sind die bisher häufig eingesetzten Bestrahlungen mit Blau- und Rotlicht in kontrollierten Anbausystemen zwar wichtig für den Aufbau von Biomasse, jedoch nicht optimal im Hinblick auf den Nährwert. Die Ergebnisse zeigen, dass die Belichtung im Gartenbau sorgfältig ausgewählt werden sollte, jedoch während strahlungsschwachen Monaten eine effektive Möglichkeit ist, den Ertrag und die nutritive Qualität von P. odorata deutlich erhöhten. Durch Modifikationen der Lichtbedingungen ist es möglich den Ertrag und Nährwert pflanzlicher Erzeugnisse zu steigern und dadurch die Versorgungslage mit gesundheitsfördernden bzw. essentiellen pflanzlichen Inhaltsstoffen zu verbessern. / This thesis examined the impact of light conditions on the nutritive quality of the test plant Persicaria odorata. Experiments took place in a greenhouse (sunlight) and climate chamber (fluorescent tube) and under consideration of a wide range of nutritive compounds, several test series, different light modifications and the use of various statistically evaluation procedures. This thesis demonstrates that varying light conditions increase nutritive value and yield under realistic conditions. Increasing the day light integral by 1% improved the fresh mass of 0,96% (greenhouse) and 0,64% (climate chamber). Experiments with monochromatic LEDs proved a high increase of biomass by spectral range dependent enhancements of the day light integral. For example, in the greenhouse, fresh mass was mostly affected by short wave blue radiation (443 nm). Additionally, the day light integral influenced the accumulation of nutrients. Higher contents of polyphenols and flavonoids in the climate chamber and the reactions on additional monochromatic LEDs proved again that it is more effective to increase day light integral by a specific enhancement of certain spectral ranges. The highest increases were achieved by supplementing spectral ranges that are not included in the emission spectrum of commonly used high pressure sodium lamps. Results also indicate that controlled agriculture’s frequently used lighting systems which emit blue and red light can improve plant growth, but it is not optimal regarding the nutritive quality. Adding short wave green light (515 nm) could increase biomass and improve the nutritive quality considerably. This thesis demonstrates that additional lighting in horticulture is an effective method to improve yield and nutritive quality of herbal vegetables in light deprived northern regions. By altering the emission spectrum of traditional artificial lighting systems, it is possible to increase yield and simultaneously improve the nutritive value of vegetables.

Colloidal semiconductor quantum dots (QDs) have gained substantial interest as adjustable, bright and spectrally tunable fluorophores in the past decades. Besides their in-depth analyses in the scientific community, first industrial applications as color conversion and color enrichment materials were implemented. However, stability and processability are essential for their successful use in these and further applications. Methods to embed QDs into oxides or polymers can only partially solve this challenge. Recently, our group introduced the embedding of QDs into ionic salts, which holds several advantages in comparison to polymer or oxide-based counterparts. Both gas permeability and environmental-related degradation processes are negligible, making these composites an almost perfect choice of material. To evaluate this new class of QD-salt mixed crystals, a thorough understanding of the formation procedure and the final composites is needed. The present work is focused on embedding both aqueous-based and oil-based metal-chalcogenide QDs into several ionic salts and the investigations of their optical and chemical properties upon incorporation into the mixed crystals. QDs with well-known, reproducible and high-quality synthetic protocols are chosen as emissive species. CdTe QDs were incorporated into NaCl as host matrix by using the straightforward "classical" method. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Besides NaCl, also borax and other salts are used as host matrices. Mercaptopropionic acid stabilized CdTe QDs can easily be co-crystallized with NaCl, while thioglycolic acid as stabilizing agent results in only weakly emitting powder-like mixed crystals. This challenge was overcome by adjusting the pH, the amount of free stabilizer and the type of salt used, demonstrating the reproducible incorporation of highest-quality CdTe QDs capped with thioglycolic acid into NaCl and KCl salt crystals. A disadvantage of the "classical" mixed crystallization procedure was its long duration which prevents a straightforward transfer of the protocol to less stable QD colloids, e.g., initially oil-based, ligand exchanged QDs. To address this challenge, the "Liquid-liquid-diffusion-assisted-crystallization" (LLDC) method is introduced. By applying the LLDC, a substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process opens the field of incorporating ligand-exchanged Cd-free QDs into NaCl matrices. To overcome the need for a ligand exchange, the LLDC can also be extended towards a two-step approach. In this modified version, the seed-mediated LLDC provides for the first time the ability to incorporate oil-based QDs directly into ionic matrices without a prior phase transfer. The ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment. As one of the main results, these matrices provide extraordinary high photo- and chemical stability. It is further demonstrated with absolute measurements of photoluminescence quantum yields (PL-QYs), that the PL-QYs of aqueous CdTe QDs can be considerably increased upon incorporation into a salt matrix by applying the "classical" crystallization procedure. The achievable PL enhancement factors depend strongly on the PL-QYs of the parent QDs and can be described by the change of the dielectric surrounding as well as the passivation of the QD surface. Studies on CdSe/ZnS in NaCl and CdTe in borax showed a crystal-induced PL-QY increase below the values expected for the respective change of the refractive index, supporting the derived hypothesis of surface defect curing by a CdClx formation as one main factor for PL-QY enhancement. The mixed crystals developed in this work show a high suitability as color conversion materials regarding both their stability and spectral tunability. First proof-of-concept devices provide promising results. However, a combination of the highest figures of merit at the same time is intended. This ambitious goal is reached by implementing a model-experimental feedback approach which ensures the desired high optical performance of the used emitters throughout all intermediate steps. Based on the approach, a white LED combining an incandescent-like warm white with an exceptional high color rendering index and a luminous efficacy of radiation is prepared. It is the first time that a combination of this highly related figures of merit could be reached using QD-based color converters. Furthermore, the idea of embedding QDs into ionic matrices gained considerable interest in the scientific community, resulting in various publications of other research groups based on the results presented here. In summary, the present work provides a profound understanding how this new class of QD-salt mixed crystal composites can be efficiently prepared. Applying the different crystallization methods and by changing the matrix material, mixed crystals emitting from blue to the near infrared region of the electromagnetic spectrum can be fabricated using both Cd-containing and Cd-free QDs. The resulting composites show extraordinary optical properties, combining the QDs spectral tunability with the rigid and tight ionic matrix of the salt. Finally, their utilization as a color conversion material resulted in a high-quality white LED that, for the first time, combines an incandescent-like hue with outstanding optical efficacy and color rendering properties. Besides that, the mixed crystals offer huge potential in other high-quality applications which apply photonic and optoelectronic components.

Tesis por compendio / [ES] La alcaparra (Capparis spinosa L.) es un arbusto característico de la región mediterránea, del que se aprovechan sus botones florales y frutos. Uno de los inconvenientes más importantes para su cultivo es la dificultad en su propagación. El fruto es una baya con muchas semillas, que presentan un porcentaje de germinación que no supera el 5%. Las semillas son de color marrón oscuro, de 2 a 3 mm y la cubierta tiene una capa lignificada con paredes radiales engrosadas. La baja germinación se relaciona con distintos tipos de latencia, que no ha sido científicamente atribuida a ningún tipo concreto. El objetivo de esta tesis es estudiar las distintas fases del proceso de germinación para determinar el tipo de latencia, cómo superarla, y establecer pautas para una propagación viable mediante semillas. Los ensayos se realizaron en el Departamento de Producción Vegetal de la Universitat Politècnica de València, utilizando semillas de producción propia y de lotes comerciales. Para determinar el tipo de latencia, se estudió el proceso de imbibición durante la germinación, la resistencia mecánica de la cubierta seminal y el endospermo frente a la protusión de la radícula, y el efecto de la aplicación de giberelinas. La absorción de agua sigue las dos primeras fases del modelo trifásico típico de absorción de agua en la germinación y la hidratación comienza por la región hilo-micropilar. La imbibición no es un factor limitante para su germinación, alcanzando un contenido de humedad del 32%, con el que se obtienen porcentajes de germinación superiores al 90%. Por tanto, no tienen una cubierta impermeable al agua, es decir, no muestran latencia física. Las semillas comerciales presentan menor viabilidad y germinación que las de producción propia, lo que se ha evidenciado con el deterioro en la cubierta seminal que se relaciona con los procesos de extracción, limpieza y almacenamiento. Para obtener altos porcentajes de germinación se requiere el uso de giberelinas, lo que indica la presencia de latencia fisiológica. Se recomienda el uso de 500 mg L-1 de ácido giberélico (AG) para humedecer el sustrato de germinación. El AG desencadena el incremento del contenido de giberelinas activas endógenas y la disminución del ácido abscísico. La germinación consta de dos eventos separados temporalmente, el agrietamiento de la cubierta, en el área hilo-micropilar y luego la perforación del endospermo micropilar, por donde emerge la radícula. Las giberelinas activas no disminuyen la fuerza de punción para perforar el endospermo, sino que aumentan el potencial de crecimiento del embrión, logrando una mayor germinación y en menor tiempo. La viabilidad y germinación de semillas recién extraídas de frutos recolectados en su dehiscencia alcanzan valores muy elevados. Si la recolección de los frutos se retrasa y la pulpa se seca, la viabilidad y la germinación disminuyen, por lo que, como regla general, se aconseja recolectar los frutos al menos una vez por semana, e inmediatamente extraer las semillas y ponerlas a germinar. En el ensayo de flotación, las semillas que flotan y que presentan buena germinación son muy pocas (0.24%), por lo que se recomienda desecharlas. La germinación no es afectada por la iluminación con diferentes longitudes de onda, por lo que puede realizarse en oscuridad, lo que puede suponer un ahorro económico para semilleros comerciales. La irradiación con láser He-Ne durante tiempos cortos de exposición mejora el porcentaje de germinación en semillas previamente humedecidas, pero no sustituye a la adición de AG al sustrato, complementando su efecto. Con la ultrasonicación se escarifica la testa sin afectar al tegmen, y se acelera la imbibición inicial, aunque la humedad alcanzada en las semillas es la misma que en el control. Existe una correlación lineal y negativa, entre la germinación y la temperatura alcanzada con estos tratamientos. / [CA] La tàpera (Capparis spinosa L.) és un arbust característic de la regió mediterrània, que s'aprofita pels seus botons florals i fruits. Un dels principals inconvenients que presenta el seu cultiu, es la dificultat que presenta la seua propagació. El fruit és una baia que té moltes llavors, que presenten una germinació que no sol superar el 5%. Les llavors són de color marró fosc, mesuren 2 - 3 mm, i la coberta té una capa lignificada amb parets radials engrossides. La baixa germinació s'ha relacionat amb diferents tipus de latència, però fins ara no ha estat científicament atribuïda a cap tipus concret. L'objectiu d'aquesta tesi és estudiar les diferents fases de la germinació per determinar el tipus de latència, com superar-la, i establir les pautes per a una propagació viable mitjançant les seves llavors. Els assajos s'han realitzat en el Dep. Producció Vegetal de la Universitat Politècnica de València, utilitzant llavors de producció pròpia, i de lots comercials. Per determinar el tipus de latència, s'ha estudiat el procés d' imbibició que es produeix durant la germinació, la resistència mecànica que exerceixen la coberta seminal i l'endosperma enfront de la protrusió de la radícula, i l' efecte de l'aplicació de gibberel·lines. L'absorció d'aigua segueix les dues primeres fases del model trifàsic típic d'absorció d'aigua en la germinació, i la hidratació comença per la regió micropilar. La imbibició no és un factor limitant per a la seua germinació, aconseguint un contingut d'humitat del 32%, permet percentatges de germinació superiors al 90%. Per tant, les llavors no tenen una coberta impermeable a l'aigua, és a dir, no mostren latència física. Les llavors comercials presenten menor viabilitat i germinació que les de producció pròpia, relacionat amb el seu deteriorament, que ha estat evident a la coberta; conseqüència dels processos d'extracció, neteja i emmagatzematge. Per obtenir alts percentatges de germinació es requereix l'ús de gibberel·lines, la qual cosa indica la presència de latència fisiològica. Es recomana l'ús d'una solució de 500 mg L-1 d'àcid gibberèl·lic (AG). L'AG desencadena l'augment del contingut de gibberel·lines actives endògenes i una disminució d'àcid abscísic. La germinació consta de dos esdeveniments separats temporalment, l'esquerdament de la coberta, que comença a l'àrea micropilar i a continuació es produeix la perforació de l'endosperma micropilar, per on emergeix la radícula. Les gibberel·lines actives no disminueixen la força de punció necessària per perforar l'endosperma, sinó que augmenten el potencial de creixement de l'embrió, aconseguint major germinació i en menor temps. La viabilitat i el percentatge de germinació de les llavors obtinguts de fruits recol·lectats en la seva dehiscència assoleixen valors molt elevats. Si la recol·lecció dels fruits es retarda i la polpa s'asseca, la viabilitat i la germinació disminueixen, per la qual cosa, com a regla general, per a la producció de llavor comercial s'aconsella recol·lectar els fruits almenys una vegada per setmana, i immediatament extreure les llavors i posar-les a germinar. En l 'assaig de flotació, les llavors que floten i que presenten capacitat germinativa són molt poques (0,24%), recomanant-se rebutjar les llavors flotants. La germinació no és afectada per la il·luminació amb llums de diferents longituds d'ona, per la qual cosa la germinació pot realitzar-se en foscor, i, pot suposar un estalvi econòmic en planters comercials. La irradiació amb làser He-Ne durant temps curts d'exposició millora el percentatge de germinació de les llavors prèviament humitejades, però no substitueix l' addició d'AG al substrat, sinó que complementa el seu efecte. Amb la ultrasonicació, s'escarifica la testa sense afectar el tegmen i s'accelera la imbibició inicial, però la humitat assolida en les llavors és la mateixa que el control. Hi ha una correlació lineal i negativa, entre la germinació i la temperatura assolida amb estos tractaments. / [EN] The caper (Capparis spinosa L.) is a shrub characteristic of the Mediterranean region. It is use for its flower buds and fruits. One of the main drawbacks of its cultivation, is the difficulty presented by its propagation, both vegetative and through seeds. The fruit is a berry containing many seeds, these have a very low germination percentage, which usually is at most 5%. The seeds are dark brown colour, measure 2 - 3 mm, and the cover has a lignified layer with thickened radial walls. Low germination power has been linked to different types of dormancies, but, it has not been scientifically attributed to any specific type. This thesis aims to study the different phases of the germination process to determine the type of dormancy, how to overcome it, and to establish guidelines for viable propagation through their seeds. The tests have been carried out in the Universitat Politècnica de València Plant Production Department, mainly using own-produced seeds, and seeds from commercial lots. To determine the type of dormancy, the imbibition process that occurs during germination has been studied, as well as the mechanical resistance exerted by the seed coat and the endosperm against the protrusion of the radicle and the effect of the external gibberellins application. Water uptake follows the first two phases of the typical three-phase water uptake pattern in seed germination, and seed hydration begins in the hilum-micropillar region. Imbibition is not a limiting factor for germination, reaching a moisture content of 32%, which allows germination percentages higher than 90%. Therefore, caper seeds do not have a waterproof coat; that is, they do not show physical dormancy. Commercial seeds showed lower viability and germination than those of own production, which has been related to seed deterioration. This deterioration, which has been evident in the seed coat, is related to their extraction, cleaning, and storage processes. Obtaining high percentages of germination requires gibberellins, which indicates the presence of physiological dormancy. The use of 500 mg L-1 of gibberellic acid (GA) is recommended to moisten the germination substrate. GA triggers an increase in endogenous active gibberellins content and a decrease in abscisic acid. The germination consists of two temporarily separated events: the cracking of the coat in the hilum-micropillar area, and then the perforation of the micropillar endosperm, where the radicle emerges. Active gibberellins do not decrease the puncture force needed to pierce the endosperm but increase the growth potential of the embryo, achieving higher germination percentages in less time. The viability and germination of seeds freshly extracted from fruits harvested in their dehiscence reach very high values. If the harvest of the fruits is delayed and the pulp dries, the viability and the percentage of germination decrease so, as a rule, for the production of commercial seed, it is advisable to collect the fruits at least once a week and immediately extract the seeds and put them to germinate. In the flotation test, floating seeds with germination capacity are very few (0.24%), so it is recommended to discard them. The germination is not affected by different wavelengths lights, so it can be carried out in darkness, which can mean economic savings in commercial nurseries. He-Ne laser irradiation during short exposure times improves the germination of previously moistened seeds but does not replace the addition of GA to the substrate but complements its effect. With the ultrasonication treatment, the testa is scarified without affecting the tegmen, and the initial imbibition is accelerated, although the seed moisture is the same as in the control. There is a linear and negative correlation between germination and the temperature reached with these treatments. / Foschi, ML. (2023). Mejora de la germinación para la propagación sexual de la alcaparra (Capparis spinosa L.) [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202596 / Compendio

Semiconductor nanowires are nanostructures with lengths up to few microns and small cross sections (10ths of nanometers). In the recent years the development in the field of III-N nanowire technology has been spectacular. In particular they are consider as promising building in nanoscale electronics and optoelectronics devices; such as photodetectors, transistors, biosensors, light source, solar cells, etc. In this work, we present fabrication and the characterization of photodetector and light emitter based devices on III-N nanowires. First we present a study of a visible blind photodetector based on p-i-n GaN nanowires ensembles grown on Si (111). We show that these devices exhibit a high responsivity exceeding that of thin film counterparts. We also demonstrate UV photodetectors based on single nanowires containing GaN/AlN multi-axial quantum discs in the intrinsic region of the nanowires. Photoluminescence and cathodoluminescence spectroscopy show spectral contributions above and below the GaN bandgap according to the variation of the discs thickness. The photocurrent spectra show a sub-band-gap peak related to the interband absorption between the confined states in the large Qdiscs. Finally we present a study of photodetectors and light emitters based on radial InGaN/GaN MQW embedded in GaN wires. The wires used as photodetectors showed a contribution below the GaN bandgap. OBIC measurements demonstrate that, this signal is exclusively generated in the InGaN MQW region. We showed that LEDs based on this structure show a electroluminescence emission and a red shift when the In content present in the QWs increases which is in good agreement with photoluminescence and cathodoluminescence results.

Os polímeros com propriedades luminescentes, e mais especificamente, os eletroluminescentes, tem atraído muita atenção devido a sua possível aplicação em dispositivos ópticos e eletrônicos do tipo LEDs (light-emitting diodes). Grande parte das pesquisas realizadas no campo da eletroluminescência se baseia em estudos sobre poli (arilenos-vinilenos), como o poli-(p-fenileno vinileno), PPV, e seus derivados. No processo de polimerização de tais polímeros, a influência de algumas variáveis são importantes em suas propriedades finais. Este trabalho descreve a exploração da influência de diversas variáveis no processo de polimerização do derivado do PPV, o poli-(2-metoxi-5-hexiloxi-p-fenileno-vinileno) MH-PPV. Além disso, com o intuito de verificar a influência da presença de aditivos na massa molar dos polímeros foram realizadas polimerizações utilizando-se os aditivos 4-metoxifenol, cloreto de tercbutila e cloreto de benzila durante o processo de polimerização. Também foram realizados estudos sobre o modo de adição e temperatura de polimerização utilizando o aditivo cloreto de benziIa. Todos os produtos foram caracterizados por HPSEC (Cromatografia de Exclusão por Tamanho) para determinação das massas molares dos polímeros. Observou-se que a temperatura e a velocidade de adição da base no meio reacional são variáveis que influenciam significativamente no processo de polimerização e, conseqüentemente, na distribuição na massa molar dos polímeros. Foi constatado que o uso de aditivos no processo de polimerização previne a formação de géis; fornece polímeros com baixa massa molar, aumentando a solubilidade dos polímeros em solventes orgânicos como clorofórmio e THF. A análise térmica dos polímeros revelou que além da Tg em tomo de 160oC, todos os polímeros apresentaram uma transição em tomo de 75oC. Os espectros de absorção e emissão não foram afetados de forma significativa dentro dos valores de massas molares médias obtidas. Foi possível também obter uma relação entre os valores de massa molar obtidos por HPSEC e valores de viscosidade relativa, que pode ser utilizada para estimar valores de Mw através de medidas de tempo de escoamento / Electroluminescent polymers have been widely investigated due to its potential applications in optoelectronic devices such as polymer light-emitting diodes (PLEDs). Most of the polymers suitable for application in PLEDs are related to the poly(arylenes-vinylene) polymers, including the poly(p-phenylene-vinylene) (PPV) and its derivatives, which are of special interest. Such materials can exhibit significant differences on their final properties upon changes on specific synthesis parameters. In this work it is described the influence of three different additives, viz. 4-methoxyphenol, terc-butyl chloride and benzyl chloride, on the polymerization process of the derivative poly(2-methoxy-5-hexyloxy-p-phenylenevinylene) MHPPV. Size Exclusion Chromatography analyses revealed that the type and rate of incorporation of the additives to the polymerization reaction largely affects the molecular weight of the polymers. In addition, it was observed that the use of additives leads to the synthesis of low molecular weight polymers, increasing their solubilities in common organic solvents, eg. chloroform and tetrahydrofuran. The glass transition temperature (Tg) of the polymers was determined by differential scanning calorimetry (DSC) to be ca. 160oC. Interestingly, all the polymers presented an additional transition point at ca. 75oC. Neither the electronic absorption nor the emission spectra were affected by the differences on the molecular weight of the polymers. Finally, it was possible to establish correlations between the molecular weight analyses (from HPSEC) and viscosity experiments, which can be useful for Mw determination

InGaN based blue and near-ultraviolet light emitting diodes and laser diodes have been successfully commercialized for many applications such as general lighting, display backlighting and high density optical storage devices. Despite having a comparably high defect density, these devices are known for their efficient operation, which is attributed to localization in potential fluctuations preventing carriers from reaching the centers of nonradiative recombination. Nitride research is currently headed towards improving deep ultraviolet AlGaN and green InGaN emitters with higher Al and In molar fractions. The efficiency of these devices trails behind the blue counterparts as the carrier localization does not seem to aid in supressing nonradiative losses. In addition, the operation of ternary nitride heterostructure based devices is further complicated by the presence of large built-in electric fields. Although the problem can be ameliorated by growing structures in nonpolar or semipolar directions, the step from research to production still awaits. In this thesis, carrier dynamics and localization effects have been studied in three different nitride ternary compounds: AlGaN epitaxial layers and quantum wells with high Al content, nonpolar m-plane InGaN/GaN quantum wells and lattice matched AlInN/GaN heterostructures. The experimental methods of this work mainly consist of spectroscopy techniques such as time-resolved photoluminescence and differential transmission pump-probe measurements as well as spatial photoluminescence mapping by means of scanning near-field microscopy. The comparison of luminescence and differential transmission measurements has allowed estimating the localization depth in AlGaN quantum wells. Additionally, it has been demonstrated that the polarization degree of luminescence from m-InGaN quantum wells decreases as carriers diffuse to localization centers.What is more, dual-scale localization potential has been evidenced by near-field measurements in both AlGaN and m-InGaN. Larger scale potential fluctuation have been observed directly and the depth of nanoscopic localization has been estimated theoretically from the recorded linewidth of the near-field spectra. Lastly, efficient carrier transport has been observed through AlInN layer despite large alloy inhomogeneities evidenced by broad luminescence spectra and the huge Stokes shift. Inhomogeneous luminescence from the underlying GaN layer has been linked to the fluctuations of the built-in electric field at the AlInN/GaN interface. / <p>QC 20121101</p>

The efficacy, reliability and versatility of the light emitting diode (LED) can outcompete most established light source technologies. However, they are particularly sensitive to high temperatures, which compromises their efficacy and reliability, undermining some of the technology s key benefits. Consequently, effective thermal management is essential to exploit the technology to its full potential. Thermal management is a well-established subject but its application in the relatively new LED lighting industry, with its specific constraints, is currently poorly defined. The question this thesis aims to answer is how can LED thermal management be achieved most effectively? This thesis starts with a review of the current state of the art, relevant thermal management technologies and market trends. This establishes current and future thermal management constraints in a commercial context. Methods to test and evaluate the thermal management performance of a luminaire system follow. The defined test methods, simulation benchmarks and operational constraints provide the foundation to develop effective thermal management strategies. Finally this work explores how the findings can be implemented in the development and comparison of multiple thermal management designs. These are optimised to assess the potential performance enhancement available when applied to a typical commercial system. The outcomes of this research showed that thermal management of LEDs can be expected to remain a key requirement but there are hints it is becoming less critical. The impacts of some common operating environments were studied, but appeared to have no significant effect on the thermal behaviour of a typical system. There are some active thermal management devices that warrant further attention, but passive systems are inherently well suited to LED luminaires and are readily adopted so were selected as the focus of this research. Using the techniques discussed in this thesis the performance of a commercially available component was evaluated. By optimising its geometry, a 5 % decrease in absolute thermal resistance or a 20 % increase in average heat transfer coefficient and 10 % reduction in heatsink mass can potentially be achieved . While greater lifecycle energy consumption savings were offered by minimising heatsink thermal resistance the most effective design was considered to be one optimised for maximum average heat transfer coefficient. Some more radical concepts were also considered. While these demonstrate the feasibility of passively manipulating fluid flow they had a detrimental impact on performance. Further analysis would be needed to conclusively dismiss these concepts but this work indicates there is very little potential in pursuing them further.

This project was aimed to use a purple non-sulphur bacterium, Rhodopseudomonas palustris, as a biocatalyst for hydrogen production, from the waste of biodiesel manufacturing, crude glycerol. The goal of this project was to understand the fundamentals relevant to scaling up the process and developing an off the shelf product. The first objective was to determine the ability of R. palustris to generate hydrogen by non-growing cells in comparison to that by growing cells. Similar average hydrogen production rates and energy conversion were found for both processes but a significant difference in the hydrogen yield was observed. Hydrogen production reached ~ 80 % of the theoretical maximum hydrogen yield by non-growing R. palustris, about eight-fold of that reached by growing R. palustris. The high yield suggested that it is economically appealing to use non-growing R. palustris as the biocatalyst for continuous hydrogen production. To accomplish the proposed scale-up systems, understanding its product formation kinetics is the key. It was found that the hydrogen production rate is not growth-associated and depends solely on the dry cell mass with a non-growth associated coefficient of 2.52 (Leudeking–Piret model dP/dt=2.52 X). Light is vital for hydrogen production by non-growing R. palustris, in terms of light intensity and wavelength range. It was found that excessive or insufficient light intensity may constrain the performance. Only photons of light with appropriate wavelengths can excite cytochrome bacteriochlorophyll complexes II in R. palustris to generate hydrogen. Among white LEDs, infrared LEDs, and incandescent light bulbs, at the same light intensity, infrared LEDs gave the best results in the H2 production rate and energy conversion by non-growing cells, 22.0 % ± 1.5 % higher than that with white LEDs and around 25-30 times of that by incandescent light bulbs. It was found that non-growing R. palustris can be immobilised in alginate beads to give similar H2 production rates as that by cells suspended in media. This preliminary result pointed the direction of developing an off the shelf product of immobilised non-growing R. palustris as a biocatalyst for continuous hydrogen production.