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.

Os diodos emissores de luz – Light Emitting Diodes – (LEDs) são uma fonte de luz que estão sendo introduzidas comercialmente, mas com discreta base científica nesta modalidade fototerapêutica. O presente estudo comparou os efeitos angiogênicos da luz laser coerente e colimada à luz LED ausente de coerência e colimação em feridas induzidas em ratos, com fluências diferentes. O modelo experimental consistia da indução de uma ferida circular no quadríceps de 120 ratos, utilizando um “punch" com 15 mm de diâmetro. Os animais foram divididos aleatoriamente em 5 grupos: laser (660 nm) e LED (635 nm), sendo cada um ajustado a 5 J/'CM POT.2' e 20 J/'CM POT.2', além do controle. Após 6 horas da indução das feridas, os grupos tratados recebiam aplicação pontual de contato, e irradiados a cada 24 horas. A angiogênese foi analisada por meio da histomorfometria (H.E), e a contração das feridas pelo software de planimetria, sendo estudados os resultados no 3º, 7º, 14º e 21º dias pós-lesão. Os achados da análise histológica no 3º dia foram determinantes para induzir uma grande eficiência na proliferação de vasos sanguíneos dos grupos tratados em relação ao controle, demonstrando uma taxa próxima da constante no 7º dia, e com discreto aumento no 14º dia, porém com destaque para a tecnologia LED a 5 J/'CM POT.2' (p '< OU =' 0,05). No 21º dia, os grupos fototratados com fluência de 5 J/'CM POT.2' apresentavam valores estatísticos com maior eficiência na angiogênese quando comparados com o grupo laser a 20 J/'CM POT.2, sugerindo que fluências elevadas podem induzir um processo do tipo saturação. Não ocorreu diferença da neovascularização no centro e nas margens da ferida (p '< OU =' 0,05), sugerindo que ocorria uma fotobiomodulação de toda a lesão, favorecendo o crescimento homogêneo dos vasos sanguíneos. Tanto o laser quanto o LED não apresentaram resultados significativos na redução da área das feridas. As fototerapias a laser e LED de baixa intensidade sugeriram que a coerência e a colimação não eram fatores decisivos para induzir alterações nas funções celulares, e sim a banda de absorção do espectro eletromagnético. Ambas as fontes de luz vermelha ajustadas a fluências de 5 J/'CM POT.2' podem demonstrar resultados expressivos no estímulo angiogênico em pele lesada / The light emitting diodes (LEDs) are a source of light that have been commercially introduced, but still with a lack in its scientific basis in this phototherapeutic modality. The present study compared the angiogenics effects of the laser and LED illumination in induced wounds in rat, with fluencies different. The experimental model consisted of the induction of a circular wound on the quadriceps of 120 rats, using a “punch" with 15 mm diameter. Animals were divided randomyzed in 5 groups: laser and LED each device with a dosage of 5 J/'CM POT.2' and 20 J/'CM POT.2', and control. After 6 hours of the induction of the wounds, the treated groups received contact of punctual application, and irradiated every 24 hours. The angiogenesis was studied through the histomorphometric (H.E) and the wounds contraction was photographed and analyzed in the planimetrical software in the 3rd, 7th, 14th and 21st lesion induced days. The discoveries of the histological analysis in the 3rd day revealed larger efficiency in the proliferation of the blood vessels in all irradiated groups in comparison to controls, being a rate near of the constant in the 7th day, following to discreet improves in the 14th, even so with prominence for the LED with 5 J/'CM POT.2'. In the 21st day, the groups phototreatment with fluence of 5 J/'CM POT.2' showed similar statistically values in the larger efficiency in the angiogenesis, when to compare to laser with 20 J/'CM POT.2', suggesting high fluencies can induced a saturation process. The average of the area reduction of the wound didn't present similar statistician values of the treated groups in relation to the control (p '< OU =' 0,05). The phototherapeutic laser and LEDs of low intensity they suggested that the coherence and the collimation were not decisive factors to induce alterations in the cellular functions, but the band of the spectrum electromagnetic. The both red source of light agreements to fluencies of the 5 J/'CM POT.2', they can demonstrate expressive results in the incentive ulcerated skin angiogenic

Les nanofils semiconducteurs sont des nano-objets dont la longueur peut aller jusqu'à quelques microns et dont la section peut être inférieure à la dizaine de nanomètre. En particulier, les nanofils de nitrures d'éléments III (GaN, AlN, InN, leurs alliages ternaires et leurs hétérostructures) sont extrêmement prometteurs en vue du développement d’une nouvelle génération de dispositifs d’électronique et d’optoélectronique tels que photodétecteurs, nanotransistors, biocapteurs, source de lumière, cellules solaires, etc.Dans ce travail, nous présentons la fabrication et la caractérisation de deux types de dispositifs à base de nanofils de nitrures III-V : des photodétecteurs d’une part et des dispositifs émetteurs de lumière d’autre part. Tout d'abord, nous avons réalisé et caractérisé un photodétecteur UV aveugle à la lumière du jour à base de nanofils de GaN verticalement alignés sur un substrat de Si(111) contenant une jonction p-n. Nous avons montré que ces dispositifs présentent une réponse supérieure à celle de leurs homologues en couches minces. Ensuite, nous avons fait la démonstration de photodétecteurs UV à base de nanofils uniques contenant des disques quantiques GaN / AlN multi-axiales insérés dans une région non intentionnellement dopé. Les résultats obtenus par spectroscopie de photoluminescence (PL) et cathodoluminescence (CL) montrent des contributions spectrales en-dessous et au-dessus de la bande interdite du GaN attribuées a la variation de l'épaisseur des disques. Les spectres de photocourant montrent un pic sous la bande interdite lié à l'absorption inter-bande entre les états confinés dans les disques les plus larges. Enfin, nous présentons une étude de photodétecteurs et émetteurs de lumière à base de nanofils de GaN contentant une hétérostructure cœur-coquille InGaN / GaN. Les fils utilisés comme photodétecteurs ont montré une contribution en dessous de la bande interdite de GaN. D’autre part, les mesures OBIC démontrent que ce signal provient exclusivement de la région active. Les fils de type LED basés sur la même structure montrent une forte émission d'électroluminescence et un décalage vers le rouge lorsque le taux d’indium présent dans les disques quantiques augmente, en accord avec les résultats de photoluminescence et de cathodoluminescence. / 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.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / With global need to reduce energy consumption, the search for more efficient technologies has become the focus of many studies. Among these technologies, it can mention the photovoltaic solar energy and LEDs, which have shown an expansion in recent decades. Photovoltaic generation is shown as an attractive energy source because it is renewable and its raw material is practically inexhaustible. While LEDs have a promising advance in lighting and is used in several applications. To integrate these technologies, this paper proposes the study of a DC-DC step-up switched-capacitor (SC) converter for LEDs applied to photovoltaic stand-alone systems. The proposed circuit differs from other topologies SC to insert an inductor in series with the input source, which can operate in discontinuous conduction mode (DCM), reducing losses switching, or continuous conduction mode (CCM), allowing the reduction of conduction losses in the circuit. The converter is driven by the frequency modulation, which is obtained as a function of input voltage. For this reason, the current in the LEDs can be stabilized without the need for sensor or feedback. The prototype developed in the laboratory was designed for a lamp of 54 W and operating at high frequency (up to 165 kHz), allowing the reduction of the circuit volume. Experimental results of the circuit in DCM and CCM show that the converter has a high yield, validating the proposal. / Tendo em vista a tendÃncia da reduÃÃo do consumo de energia no mundo, a busca por tecnologias mais eficientes tem se tornado o foco de muitos estudos. Dentre estas tecnologias, pode-se citar a energia solar fotovoltaica e os LEDs, que vem apresentando uma expansÃo nas ultimas dÃcadas. A geraÃÃo fotovoltaica se mostra como uma atrativa fonte de energia, por ser renovÃvel e sua matÃria-prima ser praticamente inesgotÃvel. Enquanto os LEDs apresentam um avanÃo promissor na iluminaÃÃo, sendo utilizado nas mais diversas aplicaÃÃes. Visando a integraÃÃo destas tecnologias, este trabalho propÃe o estudo de um conversor CC-CC elevador com capacitor comutado (Switched Capacitor - SC) para LEDs, aplicado a sistemas fotovoltaicos autÃnomos. O circuito proposto se difere de outras topologias SC por inserir um indutor em sÃrie com a fonte de entrada, o qual pode operar no modo de conduÃÃo descontÃnua (MCD), reduzindo as perdas por comutaÃÃo, ou no modo de conduÃÃo contÃnua (MCC), possibilitando a reduÃÃo das perdas por conduÃÃo do circuito. O conversor à acionado atravÃs da modulaÃÃo por frequÃncia, a qual à obtida em funÃÃo da tensÃo de entrada. Por este motivo, a corrente nos LEDs pode ser estabilizada sem a necessidade de sensores ou de realimentaÃÃo. O protÃtipo desenvolvido em laboratÃrio foi projetado para uma luminÃria de 54 W e operando em alta frequÃncia (atà 165 kHz), possibilitando a reduÃÃo do volume do circuito. Os resultados experimentais obtidos do circuito MCD e MCC sÃo analisados e validam a proposta, mostrando que o conversor apresenta rendimento elevado

Les diodes électroluminescentes (LEDs) constituent de nouvelles solutions pour créer des luminaires plus robustes, ayant un meilleur rendement de conversion et plus respectueuses de l'environnement. Malgré les avantages indiscutables déjà obtenus aujourd'hui, ce type de luminaire présente encore quelques optimisations possibles et offre des possibilités de fonctionnalités multiples. A travers plusieurs campagnes de tests, l'auteur montre sur des LEDs du commerce, que les points d'optimisation non encore exploités dans les luminaires commerciaux. Ces LEDs ont ainsi été testés sur de larges plages de fonctionnement du point de vue photométrique, électrique mais aussi thermique pour connaitre la reproductibilité des résultats obtenus. Ainsi les influences des conditions d'utilisation notamment en température de fonctionnement et niveaux de courant d'alimentation ont été étudiées. Pour dimensionner au mieux une alimentation électrique spécifique, une recherche de modèles de LED élémentaires a été effectuée. L'objectif est que les modèles tiennent compte des principaux paramètres mais soit suffisamment simple pour être inséré dans un environnement système afin de simuler le luminaire dans son environnement complet. Ainsi, l'étude comparative de plusieurs associations de LEDs a été effectuée permettant d'en déduire des compromis pour proposer de nouvelles solutions faibles consommatrices d'énergie à coût réduit incluant de nouveaux types d'alimentation. / Light emitting diodes (LEDs) bring new possibilities to get luminaires more robust with an improved efficiency and more environmentally respectfull. Despite the benefits already achieved today, this type of luminaire still presents some possible optimizations and provides opportunities for multiple features. Through several tests, the author shows on LEDs in market that optimization points are not operated in commercial luminaires. These LEDs have been tested over a wide range of operation in photometric, electrical but also thermal to know the reproducibility of the results. Thus the influences of operating conditions including operating temperature and supply current levels were studied. To design a specific power supply for each LED type, a search of elementary LED models was performed. The objective is to take into account the main parameters of the models but also to be enough simple to be inserted into a system environment to simulate the luminaire in whole environment. Thus, the comparative study of several associations of LEDs was conducted to deduce the best compromise and propose new solutions to reduce energy consumptions and production costs, including new types of power supply.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This paper presents a study on the application of high-brightness LED (Light Emitting Diode)to health care. The LEDs are supplied by electronic converters, proposed in order to analyze the light emitted by the LEDs and their interaction with human tissues. Throughout the work, a comparative study between the LED and LASER and their actions on human tissue is presented. Also, a study on the influence of frequency, duty cycle and the radiated power on the wavelength of light emitted by LEDs was conducted. The assesment of the effects of blue and red light emitted by high-brightness LEDs in real cases made the conclusions consistent and promising. The research work also comprises a extensive revision on electronic converters that can supply the LEDs, listing their features, advantages and disadvantages. In this study, the development of four electronic converters to supply the arrangements of LEDs is developed. The implementation of these arrangements has demonstrated to be successful, with excellent results in patients who underwent the LED therapy using the proposed converters. / Este trabalho apresenta um estudo sobre a aplicação de LEDs (Light Emitting Diode) de alto brilho aplicados a tratamentos de saúde alimentados por conversores eletrônicos propostos, com o objetivo de analisar os resultados da aplicação da luz emitida pelos LEDs sobre o tecido humano. Ao longo do trabalho, é apresentado um estudo comparativo entre o LED e o LASER e suas ações sobre os tecidos humanos. Também, é realizado um estudo sobre a influência da freqüência, da razão cíclica e da potência irradiada sobre o comprimento de onda da luz emitida pelos LEDs. A abordagem dos efeitos da cor azul e vermelha emitida por LEDs de alto brilho no tecido humano é feita de forma consistente avaliando-se a interação terapêutica sob o tecido. É também apresentado um estudo sobre conversores eletrônicos que podem alimentar LEDs elencando suas características, vantagens e desvantagens. Através deste estudo é proposto o desenvolvimento de quatro conversores eletrônicos para alimentarem os arranjos de LEDs desenvolvidos. A aplicação desses arranjos obtém êxito na terapia, apresentando excelentes resultados nos pacientes que se submeteram a LEDterapia.

La stratégie la plus utilisée aujourd'hui pour la conception de nouveaux matériaux luminescents est basée sur des méthodes d'essais-erreurs. Cependant, ces méthodes peuvent souvent entraîner une consommation d'argent et de temps. En ce sens, un modèle théorique agissant comme un outil prédictif peut servir comme une stratégie alternative. De tels modèles sont également étudiés et utilisés par des scientifiques du monde entier, mais ils sont pour la plupart difficiles à utiliser. Dans ce travail, deux modèles semi-empiriques conviviaux et faciles à utiliser ont été proposés pour la conception de luminophores intégrés dans le développement de technologies importantes, en particulier dans les éclairages à base de LED et les cellules solaires. Ces modèles sont: 1) le modèle de facteur environnemental (EF) basé sur la théorie diélectrique de la liaison chimique proposée par Philips et 2) le modèle de transfert de charge métal-métal (MMCT) utilisées pour trouver des relations entre les propriétés structurelles d'un matériau et sa luminescence. Le modèle EF a été appliqué à la famille des composés AIBIIPO4 (AI = cation monovalent, BII = cation divalent) dopés à Eu2+. Il était capable d'estimer l'énergie du bord d'excitation et d'identifier les sites de dopage à ± 1000 cm-1. Il peut donc être utilisé pour la conception de nouveaux luminophores appartenant à cette famille. Dans la deuxième partie, les deux modèles ont été utilisés pour identifier la nature de la luminescence dans les oxydes dopés à Bi3+. A cet effet, une méthode combinant les modèles motionnés avec les valeurs de Stokes shift a été trouvé fiable. En outre, la a été jugée utile pour expliquer la modification des propriétés luminescentes de YVO4:Bi3+ sous haute pression. Dans la troisième partie, les deux modèles ont été utilisés pour explorer la luminescence des oxydes dopés à Sb3+ par analogie avec Bi3+. Cependant, les résultats n'étaient pas assez bons pour identifier la nature de la luminescence dans ces matériaux. La raison pourrait être liée à la position décentrée du dopant (Sb3+). / The most used strategy for the design of new luminescent materials today is based on trial-error methods. However, these methods may often result in consummation of money and time. In this sense, a theoretical model acting as a predictive tool can serve as an alternative strategy. Such models are also studied and used by scientists around the world but they are mostly difficult to use. In this work, two friendly and easy to use semi-empirical theoretical models were proposed as a criterion for designing phosphors integrated in the development of important technologies especially in LED-based lightings and solar cells. These models are: 1) the environmental factor model (EF) based on the dielectric theory of chemical bonding proposed by Philips and 2) the metal to metal charge transfer (MMCT) model by Boutinaud that were both used for the purpose of finding relationships between the structural properties of a material and its luminescence. The EF model was applied on the family of AIBIIPO4 (AI= monovalent cation, BII= divalent cation) compounds doped with Eu2+. It was able to estimate the excitation edge energy and to identify the doping sites within uncertainty of ± 1000 cm-1. It can therefore, be used for the design of new phosphors belonging to this family. In a second part, both models were used to identify the nature of luminescence in Bi3+-doped oxides. For this purpose, a method combining the mentioned models along with the values of the Stokes shift was found reliable. In addition, the method was found useful to explain the change in luminescent properties of YVO4:Bi3+ under high pressure. In the third part, the two models were used to explore the luminescence of Sb3+-doped oxides by analogy with Bi3+. However, the results were not good enough to identify the nature of luminescence in these materials. The reason could be related to the off-centered position of the dopant (Sb3+).

Le but de cette thèse a été d'étudier les propriétés structurales et optiques de puits quantiques (PQs) d’InGaN/(Al)GaN obtenus par épitaxie en phase vapeur d’organométalliques. Différentes approches ont été mises en œuvre pour atteindre une émission dans le vert-jaune: la première utilisant une concentration d'indium ≥ 20% avec un PQ d’InGaN d’épaisseur <3.0 nm et vice versa. L'effet d'une couche d’encapsulation a également été étudié. Les techniques de microscopie à force atomique, de diffraction des rayons X, de photoluminescence (PL) et surtout de microscopie électronique à transmission (MET) ont été utilisées pour caractériser ces structures. Les épaisseurs des PQs et les compositions en indium ont été déterminées par le traitement numérique des franges de réseau dans les images MET haute résolution en section transverse. Un traitement original a été développé pour analyser quantitativement les fluctuations de l’épaisseur des PQs. L'analyse structurale des PQs ayant une composition en In élevé a montré que les défauts structuraux sont créés dans les PQs. La nature et la densité de ces défauts ont été déterminées et différents mécanismes pour leur formation ont été proposés. Il a également été montré que quelques monocouches d’encapsulation de GaN ou d’AlGaN déposées à la température de croissance des PQs limitent l’évaporation et/ou la diffusion d’indium. Ce procédé permet d’étendre la longueur d'onde d'émission avec une réduction de la dégradation de l'efficacité de la PL. Mon travail propose quelques pistes afin d'obtenir un bon compromis entre les paramètres contradictoires qui régissent l'efficacité des PQs émettant dans le vert-jaune. / The goal of this thesis was to study the structural and optical properties of InGaN/(Al)GaN multiple QWs grown by metal organic chemical vapor deposition. Different approaches have been implemented to achieve green-yellow emission: high indium concentration (≥ 20%) with low InGaN QW thickness (< 3 nm) or vice versa. Moreover, the effect of a capping layer on top of the QWs has also been investigated. Atomic force microscopy, X-ray diffraction, room temperature photoluminescence (RTPL) and mainly transmission electron microscopy (TEM) techniques have been used to characterize these structures. The QW thicknesses and indium compositions have been determined by digital processing of lattice fringes in cross-sectional high resolution TEM images. An original treatment has been developed to analyze quantitatively InGaN QW thickness fluctuations. The structural analysis of multiple QWs with high indium composition has shown that structural defects are created in the QWs. The nature and the density of these defects have been determined and different mechanisms for their formation have been proposed. It has also been shown that a few monolayers of AlGaN or GaN capping layers deposited at the InGaN QW growth temperature prohibited indium evaporation and/or diffusion. It therefore helps to extend the emission wavelength with a reduced degradation of the RTPL efficiency. My work offers a few ways to obtain a good compromise between the conflicting parameters that govern the efficiency of QWs emitting in the green-yellow spectrum range.

Os diodos emissores de luz – Light Emitting Diodes – (LEDs) são uma fonte de luz que estão sendo introduzidas comercialmente, mas com discreta base científica nesta modalidade fototerapêutica. O presente estudo comparou os efeitos angiogênicos da luz laser coerente e colimada à luz LED ausente de coerência e colimação em feridas induzidas em ratos, com fluências diferentes. O modelo experimental consistia da indução de uma ferida circular no quadríceps de 120 ratos, utilizando um “punch” com 15 mm de diâmetro. Os animais foram divididos aleatoriamente em 5 grupos: laser (660 nm) e LED (635 nm), sendo cada um ajustado a 5 J/'CM POT.2' e 20 J/'CM POT.2', além do controle. Após 6 horas da indução das feridas, os grupos tratados recebiam aplicação pontual de contato, e irradiados a cada 24 horas. A angiogênese foi analisada por meio da histomorfometria (H.E), e a contração das feridas pelo software de planimetria, sendo estudados os resultados no 3º, 7º, 14º e 21º dias pós-lesão. Os achados da análise histológica no 3º dia foram determinantes para induzir uma grande eficiência na proliferação de vasos sanguíneos dos grupos tratados em relação ao controle, demonstrando uma taxa próxima da constante no 7º dia, e com discreto aumento no 14º dia, porém com destaque para a tecnologia LED a 5 J/'CM POT.2' (p '< OU =' 0,05). No 21º dia, os grupos fototratados com fluência de 5 J/'CM POT.2' apresentavam valores estatísticos com maior eficiência na angiogênese quando comparados com o grupo laser a 20 J/'CM POT.2, sugerindo que fluências elevadas podem induzir um processo do tipo saturação. Não ocorreu diferença da neovascularização no centro e nas margens da ferida (p '< OU =' 0,05), sugerindo que ocorria uma fotobiomodulação de toda a lesão, favorecendo o crescimento homogêneo dos vasos sanguíneos. Tanto o laser quanto o LED não apresentaram resultados significativos na redução da área das feridas. As fototerapias a laser e LED de baixa intensidade sugeriram que a coerência e a colimação não eram fatores decisivos para induzir alterações nas funções celulares, e sim a banda de absorção do espectro eletromagnético. Ambas as fontes de luz vermelha ajustadas a fluências de 5 J/'CM POT.2' podem demonstrar resultados expressivos no estímulo angiogênico em pele lesada / The light emitting diodes (LEDs) are a source of light that have been commercially introduced, but still with a lack in its scientific basis in this phototherapeutic modality. The present study compared the angiogenics effects of the laser and LED illumination in induced wounds in rat, with fluencies different. The experimental model consisted of the induction of a circular wound on the quadriceps of 120 rats, using a “punch” with 15 mm diameter. Animals were divided randomyzed in 5 groups: laser and LED each device with a dosage of 5 J/'CM POT.2' and 20 J/'CM POT.2', and control. After 6 hours of the induction of the wounds, the treated groups received contact of punctual application, and irradiated every 24 hours. The angiogenesis was studied through the histomorphometric (H.E) and the wounds contraction was photographed and analyzed in the planimetrical software in the 3rd, 7th, 14th and 21st lesion induced days. The discoveries of the histological analysis in the 3rd day revealed larger efficiency in the proliferation of the blood vessels in all irradiated groups in comparison to controls, being a rate near of the constant in the 7th day, following to discreet improves in the 14th, even so with prominence for the LED with 5 J/'CM POT.2'. In the 21st day, the groups phototreatment with fluence of 5 J/'CM POT.2' showed similar statistically values in the larger efficiency in the angiogenesis, when to compare to laser with 20 J/'CM POT.2', suggesting high fluencies can induced a saturation process. The average of the area reduction of the wound didn't present similar statistician values of the treated groups in relation to the control (p '< OU =' 0,05). The phototherapeutic laser and LEDs of low intensity they suggested that the coherence and the collimation were not decisive factors to induce alterations in the cellular functions, but the band of the spectrum electromagnetic. The both red source of light agreements to fluencies of the 5 J/'CM POT.2', they can demonstrate expressive results in the incentive ulcerated skin angiogenic

Ce travail concerne l'intégration, par épitaxie sous jets moléculaires (EJM), de matériaux nitrures d'éléments III (en particulier GaN) sur des substrats et couches tremplins à base d'oxyde de zinc (ZnO). L'objectif était la réalisation et l'étude d'hétérostructures nitrures de type puits quantiques (PQs) (Al,Ga)N/GaN et (In,Ga)N/GaN, en vue d'évaluer leurs potentialités pour la réalisation de diodes électroluminescentes (LEDs). En particulier, deux orientations cristallographiques ont été étudiées : le plan " polaire " (0001) (dit plan C) et le plan " non polaire " (11-20) (dit plan A). Les couches de GaN orientées suivant le plan A (11-20), " a-GaN ", ont été épitaxiées sur des tremplins de (Zn, Mg)O (11-20) / saphir (10-12) réalisés par EJM. L'anisotropie de la morphologie de surface, de la microstructure cristalline, ainsi que de l'émission optique des couches de a-GaN, a été mise en évidence. Une série d'échantillons de PQs de a-(GaN/Al0.2Ga0.8N) avec des épaisseurs de puits différentes a été fabriquée, et l'absence d'effet Stark quantique confiné dans ces hétérostructures a été établie. Des procédés de croissance de GaN sur des substrats de ZnO massifs d'orientation A, " a-ZnO ", et C, " c-ZnO ", ont également été développés. En particulier, des couches de GaN (0001), " c-GaN ", avec une polarité Ga- ou N- ont été épitaxiées sur la face O de substrats c-ZnO. Les mécanismes de détermination de la polarité ont été analysés. Des LEDs bleues contenant une zone active constituée de PQs (In, Ga)N / GaN ont été réalisées sur des substrats c-ZnO. Des puissances de sortie atteignant 40 µW à 20 mA et 0,1 mW à 60 mA ont été mesurées. Enfin, des PQs (In, Ga)N / GaN ont été fabriqués sur substrats a-ZnO et comparés à des PQs fabriqués sur c-ZnO avec des conditions de croissance équivalentes. Les résultats indiquent une concentration en In plus importante dans le cas des PQs épitaxiés sur c-ZnO et une polarisation de l'émission de PL suivant la direction <1-100> dans le cas des PQs épitaxiés sur a-ZnO.