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>

Recent work suggests an emerging new paradigm for the Scandinavian ice sheet (SIS); one of a dynamically fluctuating ice sheet. This doctoral research project explicitly examines the history and dynamics of the SIS at four sites within Sweden and Norway, and provides results covering different time periods of glacial history. Two relatively new dating techniques are used to constrain the ice sheet history: the optically stimulated luminescence (OSL) dating technique and the terrestrial cosmogenic nuclide (TCN) exposure dating technique. OSL dating of interstadial sediments in central Sweden and central Norway indicate ice-free conditions during times when it was previously inferred the sites were occupied by the SIS. Specifically, the SIS was absent or restricted to the mountains for at least part of Marine Isotope Stage 3 around 52 to 36 kyr ago. Inland portions of Norway were ice-free during part of the Last Glacial Maximum around 25 to 20 kyr ago. Consistent TCN exposure ages of boulders from the Vimmerby moraine in southern Sweden, and their compatibility with previous estimates for the timing of deglaciation based on radiocarbon dating and varve chronology, indicate that the southern margin of the SIS was at the Vimmerby moraine ~14 kyr ago. In central Sweden, consistent TCN ages for boulders on the summit of Mt. Åreskutan and for the earlier deglaciated highest elevation moraine related to the SIS in Sweden agree with previous estimates for the timing of deglaciation around 10 ka ago. These results indicate rapid decay of the SIS during deglaciation. Unusually old radiocarbon ages of tree remains previously studied from Mt. Åreskutan are rejected on the basis of incompatibility with consistent TCN ages for deglaciation, and incompatibility with established paleoecological and paleoglaciological reconstructions. Altogether this research conducted in different areas, covering different time periods, and using comparative geochronological methods demonstrates that the SIS was highly dynamic and sensitive to environmental change. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.

Le syndrome de Bartter de type III résulte de mutations du gène CLCNKB codant le canal chlorure CLC-KB. Un grand nombre de mutations a été répertorié, mais peu d'entre elles ont été caractérisées fonctionnellement. Devant ce manque de données, nous nous sommes fixés comme objectif de procéder à une analyse fonctionnelle des mutations de CLCNKB pour tenter d'approfondir davantage les mécanismes de régulation de CLC-KB. Ce travail a nécessité l'emploi de trois systèmes d'expression hétérologue, les ovocytes de Xenopus laevis et les lignées cellulaires rénales HEK293T et MDCK, afin de procéder à des analyses électrophysiologiques et des expériences de biologie cellulaire. Nous démontrons que toutes les mutations étudiées altèrent l'expression membranaire de la protéine et que la conductance résiduelle est proportionnée à cette expression. Ainsi, la réduction des courants provient d'une réduction du nombre de canaux et non d'une altération majeure de la conduction ou de la régulation. Nous rapportons également que certaines mutations modifient la sensibilité au pH et au calcium extracellulaires du CLC-KB. Cette altération peut avoir un impact pathologique majeur. En conclusion, cette étude fonctionnelle montre le rôle essentiel du CLC-KB dans le maintien de la balance sodée et laisse entrevoir un espoir thérapeutique à long terme de restauration des anomalies précisément identifiées. Enfin, l'analyse de mutations est un outil extrêmement puissant pour les études structure-fonction. Associée à la recherche de nouveaux partenaires, elle devrait permettre de découvrir les régulations physiologiques de ce canal, pour l'heure presqu'inconnues.

Lanthanum orthoborate (LaBO3) has aroused interest of scientists for many decades because of their remarkable properties and potential applications. They provide favorable magnetic properties for various applications. Additionally, they possess high VUV transparency and exceptional optical damage when they compose with rare earth elements. This study comprises the synthesis of pure lanthanum orthoborate, europium, dysprosium and terbium doped lanthanum orthoborate by two methods with v three fuels, citric acid, glycine and urea. LaBO3 has already been synthesized by various methods, however / in this work, two alternative roads are suggested, microwave assisted method and sol-gel microwave assisted method. The second task of the work is to find out the best luminescent product by altering the synthesis conditions, type of the doping material and the doping amount of the rare earth element. For the microwave assisted combustion method, urea was used as a fuel. After synthesis in the microwave oven, further heating up to 950&deg / C was performed. For the microwave assisted sol-gel method, citric acid and glycine were used. After obtaining the gel mixture, the product is synthesized in the microwave oven at 1200 W for ten minutes. For this route, again 950&deg / C heating for 2 hours was performed. Powder X-ray diffraction method was employed for the characterization of the material. The morphological properties of doped and un-doped materials were studied by SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscope). Besides, FT-IR (Fourier Transform Infra red) spectrometry analyses were performed to detect the differences in the bond structure and also to identify the corresponding bands. Luminescence studies were performed to detect the best emission intensities by using Fluorescence spectroscopy. The XRD patterns confirmed that lanthanum orthoborate production was successful by three precursors. The space group is Pnma, and the crystal system is orthorhombic with the unit cell dimensions / a= 5.8761(1)

Luminescent materials can be found in a broad range of everyday applications. While in the seventies and eighties, the field of luminescent materials seemed to be fairly well covered, research in nineties has been revitalized both in industry and academia. Improvements over the last three decades have led to phosphor materials that operate close to their physical limits. It cannot be expected that properties such as quantum yield and spectral energy distribution will be significantly improved or that distinctly better materials will be found in the near future. Recently, there is a considerable research activity in the field of luminescent materials for lighting and displays to improve the chemical stability and to adopt the materials to the production technology. Ongoing miniaturization, lifetime improvement and spectral stability of fluorescent lamps on the one hand and brightness and contrast improvement in imaging systems on the other hand demand luminescent materials with very high stability that is invariable to operating conditions. All of the today's efficient lighting sources are based on either direct or indirect light emission from plasma discharges. During the pioneering stage, fluorescent lamp industries predominantly used mixtures of two photo luminescent materials: (Zn,Be)2SiO4.'Mn2+ having two emission maxima at 520 and 600 nm and MgW04 with 480 nm emission. The emission from these two phosphors covers the major portion of the visible spectrum. However, the compound (Zn,Be)2Si04 is hazardous to health because of its beryllium content. In 1942, Jenkins showed that Ca5(PO4)3(F,Cl):Sb,Mn was a very efficient emitter. The halophosphates emit both in the blue (Sb3+) as well as in the orange (Mn2+) spectral region, thus in addition yield white light. By carefully adjusting the ratio of Sb3+ and Mn2+ ion concentrations, a white light emitting phosphor was obtained with color temperatures ranging between 6500 and 2700K. However, the drawback of the halophosphate lamps is that it is impossible to have simultaneously high brightness and high color rendering; if the brightness is high (efficacy -80 lm W"1), the color rendering index (CRI) is of the order of 60, the CRI value can be improved up to 90, but then brightness decreases (-50 lm W"1). In 1974, another important breakthrough came in the form of compact fluorescent lamp, based on the trichromatic phosphor blend which resulted color rending values of 80-85 (color 80 lamps) at high efficiencies of 100 lm W"1. The fluorescent lamps with very high color rendering and efficiency can be obtained if three narrow band emitters with emission maxima at 450, 540 and 610 nm are employed. A typical trichromatic lamp phosphor blend comprises of (i) Sr5(PO4)3Cl:Eu2\ BaMgAl1()O,7:Eu2' as blue component, (ii) Ce0.67Tbo.33MgAl,,0,9, LaPO4,Le3\Tb3+ as green component and (iii)Y2C>3:Eiru as the red component. The color 80 lamps employ line emitters that generated light in discrete wavelength intervals. Colored objects that absorb outside these spectral regions appear with a slightly different body color when illuminated with these lamps rather than with a black body radiator such as the light bulb. For these purposes, color 90 or Deluxe lamps have been developed. The emission maximum of the blue phosphor can be shifted towards longer Wavelength by substituting BaMgAli0Oi7:Eu2+ with Sr4Ali4025:Eu2+. The red and green line emitters can be substituted by broad band emitters covering the whole spectral range. For this concept, (Ce,Gd,Tb)MgB5Oi0:Mn has been developed as a red emitter in which energy transfer from Ce3+ via Gd3+ to Mn2+ gives rise to an additional broad band at 630 nm. On the other hand, (Ba,Sr,Ca)2Si04:Eu has been developed as an alternative green-band emitter in which depending on the exact composition, the phosphor emits between 550 and 580 nm with a high quantum yield. Unfortunately, the host lattice is not stable in water, which prevents its deposition on the lamp bulb from aqueous suspensions and for environmental reasons more and more lamps producers use water as the suspending solvent in production instead of butyl acetate. Therefore, it is necessary to develop a new full color emitting phosphors, which has both thermal and chemical stability for application in luminescent lighting. The classical cathode ray tube (CRT) invented as the brown tube more than 100 years ago has developed into a remarkably mature product considering the complexity of its manufacturing process. Cathode rays are a beam of fast electrons, the accelerating voltage in a television picture tube is high (>10 kV). Basic requirements of display phosphors are stability (2000 hr operation) and emission color purity according to the standards set by the European Broadcasting Union (EBU). The blue and green phosphors are still the very cheep ZnS based materials, essentially the same ever since color-TV was introduced in fifties. On the other hand, (Zn,Cd)S, Ag+,C1" was originally used as the red phosphor however, the broad emission centered at 650 nm due to intrinsic donor-acceptor transition leads to rather low lumen equivalent as large fraction of the emission integral lies outside the eye sensitivity curve. For this and the environmental reasons, it has been replaced by the much more expensive Y2O2S:Eu with main emission lines at 612 and 628 nm. Recently, the big electronic companies are trying to enforce flat panel displays e.g. PDPs (plasma display panels) and FEDs (field emission displays). This is because of the fact that when compared to the CRT screen pigments, FED phosphors are required to operate at lower voltages and higher current densities. Although the voltages used in FEDs are only 0.1 to < 2 kV, the high-energy surface excitation on the phosphor particles causes degradation of sulfides, leaving the oxide hosts as the only favorable choice. The phosphor blends used are mixtures of SrTiO3:Pr3+ (red), Y2Si05:Tb (green) and Y2Si05:Ce (blue). However, the white light generation efficiency is very low (-5 lm W"1) and required improvement of phosphor efficacy because of its distinct advantages such as a very wide range of operational temperatures, stability under rugged conditions and wide viewing angle of emission. Similarly, in PDPs blue emitting BaMgAlioOniEu, green emitting Z^SiO^Mn and red emitting (Y,Gd)BO3:Eu are mostly used which shows a screen efficiency of about 1.5 lm W"1, just only half that of a CRT used in today's TV sets. However, the advantages of PDPs over CRTs are that it is not sensitive towards the display manufacturing process, which includes high temperature annealing up to about 600°C and it is stable under the harsh conditions of a Ne/Xe plasma used in PDPs (ion bombardment, VUV radiation). This puts pressure on the development of phosphor for maximum brightness and high stability to replace completely the classical CRTs. On the other hand, the invention of the blue-light emitting diode (LED) based on GaN can be regarded as a triumph of materials chemistry. In principle, it is possible to vary the emission wavelength of blue GaN-based LEDs between 370 nm (band-gap of pure GaN) and 470 nm by increasing the indium (In) content in InGaN devices. Assuming a conversion from the incident light by a phosphor material emitting at 555 nm, InGaN is coated with (Yi.xGdx)3(Ali-yGay)5Oi2:Ce (YAG:Ce) which has broad yellow band varying between 510 and 580 nm. This allows the adjustment of white color temperature from 8000 down to 3000 K. Recently, S^SiCU and S^SiOs have attracted current interest due to their potential applications in developing white light-emitting-diodes (LEDs) because GaN (400 nm chip)-coated with Sr2Si04:Eu2+ or Sr3SiC>5;Eu2+ exhibits better luminous efficiency than that of the industrially available product such as InGaN (460 nm chip)-coated with YAG:Ce. However, the major drawback of this combination is the strongly decreasing overall efficiency upon lowering the color temperature. This can be solved by using a phosphor material that has sufficient absorption at the emission wavelength of the blue diode, the quantum yield should be high under UV/Vis excitation and the FWHM of the emission band should be as small as possible in order to achieve high luminous output. The search for stable inorganic rare-earths phosphors with high absoiption in the near UV/blue spectral region is therefore an attractive research work. Since luminescence materials are a key component for lighting and display concept, research in the field of rare-earths doped oxide phosphors is carried out. Although state-of-the-art materials fulfill most requirements, improvements are still necessary to further boost the efficiency of the phosphor materials. Since it is not expected that materials will be found that perform better than the already established phosphor, the present work concentrates on the improvements of the phosphor by modifying the chemical and niicrostructurai features as well as the crystal structure. Chapter I gives a brief introduction to luminescence in solids, physical aspects and applications. Chapter II describes the synthesis and various experimental techniques employed in the investigation. Chapter III deals with photoluminescence and energy transfer involving charge transfer states in Sr2-xLnxCe04+x/2 (Ln = Eu and Sm) leading to an efficient full color emitting phosphor for luminescent lighting. Chapter IV and V describe charge transfer transition involving interface states associated with transitional nanophaseprecipitates leading to photoluminescence enhancement of SrTiO3:Pr3+,Al3+ and SrAli2Oi9:Pr3+,Ti4\ The light induced charge transfer leading to changing oxidation state of Eu in Sr2Si04 involving transient crystal structure results an efficient material for optical storage is presented in Chapter VI.Photoluminescence due to efficient energy transfer from Ce3+ to Tb3+ and Mn2t in SnAlioSi02o leading to an efficient phosphor for FEDs is presented in Chapter VII. Chapter VIII describes charge transfer transition involving trap states leading to long phosphorescence in SrAl2-xBxO4 (0<x<0.2) and Sr4Al14.xBxO25 (0.1<x<0.4) co-doped with Eu2+ and Dy3+. Chapter IX presents the role of particle size on the charge transfer associated luminescence of GdVO4:Ln3+ (Ln = Eu and Sm). A summary of the important findings and the conclusions arrived on the basis of results from these investigations are presented at the end of the thesis.

En vue de la numérisation des images radiologiques, les propriétés luminescentes de l'europium divalent dans diverses familles de composés du strontium ou du baryum comportant un halogène ont été étudiées. Dans les composés riches en halogène (MCl2, M4OCl6, M5SiO4Cl6...) (M=Sr, Ba), l'extinction thermique de l' émission ne débute qu'au-dessus de 300 K. De fortes densités de centres colorés présentant des bandes d'absorption à grande longueur d'onde ont pu être obtenues après irradiation X. La conjonction de ces deux caractéristiques permet, notamment dans le cas des halogènosilicates Sr5SiO4Cl6(1-x)Br6x:Eu, l'obtention de rendements de luminescence photostimulée par laser argon particulièrement élevés.

Ce travail concerne l'étude de cristaux scintillateurs inorganiques découverts récemment : LaCl3:Ce3+ et LaBr3:Ce3+. Une réponse rapide, un rendement lumineux élevé et une excellente résolution énergétique sont quelques-unes des propriétés qui rendent les cristaux de LaCl3:Ce3+ et LaBr3:Ce3+ intéressants pour la détection de rayonnement gamma, tout particulièrement en imagerie médicale. La forte hygroscopie de ces matériaux nécessite l'adaptation des modes opératoires habituels pour la détermination des caractéristiques physico chimiques. Une fois déterminées, ces caractéristiques servent au développement de la synthèse industrielle des cristaux.<br />La bonne compréhension du mécanisme de scintillation et de l'effet des défauts présents dans le matériau permet d'envisager des pistes pour l'optimisation des performances du scintillateur. Dans ce sens, plusieurs techniques sont utilisées (RPE, radioluminescence, excitation laser, thermoluminescence,...). Au côté des ions Ce3+ , des excitons auto-piégés sont impliqués dans le mécanisme de scintillation ; leur nature et leur rôle sont précisés. La connaissance des divers processus impliqués dans le mécanisme de scintillation conduit à prévoir l'effet de la température et du taux de dopage sur les performances du scintillateur. Un mécanisme est proposé pour expliquer les processus de thermoluminescence à l'origine de l'apparition de composantes lentes dans l'émission lumineuse et d'une perte de rendement lumineux. Enfin, l'étude de la luminescence persistante permet de révéler un transfert de charge vers des pièges profonds impliqués dans la thermoluminescence à haute température.

Les microscopes en champ proche permettent d'obtenir la topographie d'un échantillon avec une résolution pouvant atteindre la résolution atomique. Ces techniques permettent également d'accéder à certaines propriétés locales de la surface telles que le potentiel, l'élasticité, la densité d'états... Ces spectroscopies locales sont de type 'contraste' et ne permettent pas de dresser la cartographie chimique de la surface sans connaissance a priori des éléments qui la composent. Les spectroscopies de rayons-X sont des méthodes de caractérisation puissantes qui permettent de déterminer la composition et la structure élémentaire de l'échantillon avec une précision inférieure à l'Ångström. La résolution latérale est essentiellement limitée par la taille du faisceau primaire, couramment de plusieurs μm². Deux voies sont possibles pour l'améliorer: - réduire l'étendue du faisceau primaire excitateur; - limiter la collecte du rayonnement émis à une portion du volume excité, tout en approchant le détecteur au maximum pour garder un rapport signal/bruit suffisant. C'est cette deuxième option que nous avons choisi de développer. Pour cela nous avons collecté localement la luminescence visible issue de l'échantillon par la pointe-sonde d'un microscope à force de cisaillement, constituée d'une fibre optique effilée de faible ouverture. Cette technique a été utilisée pour caractériser des échantillons semiconducteurs micro- et nano-structurés afin d'en obtenir simultanément la topographie et la cartographie de luminescence locale. Ces résultats ont été obtenus non seulement sur une ligne synchrotron mais également à l'aide d'une microsource de laboratoire équipée d'une lentille polycapillaire. Afin de pouvoir étendre ce concept à d'autres types de matériaux, la faisabilité de la collecte de la fluorescence X locale a été évaluée avec la microsource. Pour cela la fluorescence X émise par un échantillon de cobalt a été collectée par un capillaire cylindrique équipant un détecteur EDX. L'influence du diamètre du capillaire sur le niveau de signal a été mesurée. Une simulation numérique a été développée afin d'estimer le niveau de signal obtenu en utilisant un capillaire de 1 μm de diamètre et d'optimiser la géométrie du système. En couplant la microscopie en champ proche et l'analyse XRF, à la lumière de ces résultats, il sera possible d'atteindre 100 nm de résolution latérale en environnement synchrotron et moins de 1 μm à l'aide d'une source de laboratoire. Il serait alors possible de sélectionner un objet particulier sur une surface et d'en faire l'analyse élémentaire.

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La construction de complexes polymétalliques de lanthanides préprogrammés et sophistiqués, de taille nanométrique, pour le développement de matériaux luminescents présentant des propriétés photophysiques nouvelles ou améliorées (double émission, transfert d'énergie intermétallique, etc.) est un des sujets de la chimie supramoléculaire des lanthanides suscitant énormément d'intérêt. La compréhension, le contrôle et la programmation de l'auto-assemblage de complexes de lanthanides est un défi majeur en raison de la difficulté à contrôler l'environnement de coordination de ces ions qui se caractérise par des nombres de coordinations importants et variables et peu de préférences stéréochimiques. Ainsi, la plupart des complexes polynucléaires de lanthanides décrits dans la littérature sont formés de façon fortuite plutôt que par conception rationnelle. Afin d'inclure les ions lanthanides dans des architectures polymétalliques de haute nucléarité tout en améliorant leurs propriétés photophysiques, nous nous sommes concentrés sur des études de complexation de ligands dissymétriques (tridentates anioniques, tétradentates chiraux) permettant de promouvoir la formation des assemblages. Nous avons par ailleurs commencé à explorer le potentiel d'une méthode synthétique originale de clusters oxo par réactivité redox de complexes divalents de lanthanides. Nous présentons ici la synthèse et les propriétés photophysiques de complexes stables émettant dans le proche infrarouge basés sur des ligands anioniques hydroxyquinoléine fonctionnalisé par des groupes carboxylates ou tétrazolates. En outre, nous pouvons montrer que l'utilisation de ligands chiraux possédant un groupement oxazoline favorise l'auto-assemblage diastéréosélectif de complexes de lanthanides homo- et hétéro-polymétalliques énantiopures émettant dans le visible et le proche infrarouge. Un complexe trinucléaire d'europium énantiopure a été caractérisé par cristallographie, celui-ci présentant une forte activité en polarisation circulaire de luminescence (CPL). Le ligand chiral oxazoline a permis d'obtenir une roue heptanucléaire d'europiums, le plus important assemblage polymétallique énantiopure. Enfin, nous avons pu préparer et caractériser des complexes de lanthanides divalents hautement réactifs basés sur un ligand tripode neutre possédant des groupements pyridine (tpa). Des résultats préliminaires montrent que ces complexes peuvent être des précurseurs très utiles pour isoler des clusters oxo polymétalliques. En particulier, la réaction d'un complexe de néodyme hautement réactif a conduit à isoler un cluster oxo volumineux et très intéressant par clivage de THF en présence de tpa.