The structural, electronic, energetic and optical properties of the compound Li2B4O7 containing the substitutional defects Cu or Ag were investigated by means of calculations of first principles at the Density Functional Theory level using the LAPW method implemented in the computer code Wien2k. The isolated Cu and Ag defects are considered in four charge states (q = -1, 0, +1, +2) with objective to simulate situations of the capture of an electron or a hole. In all cases, the atomic positions are computationally relaxed, Cu – O and Ag – O chemical bonds nature carefully analyzed and local structure around the defects determined. It is found that the defects vastly perturbs its neighborhood and the Cu and Ag themselves exhibit significant off-site dislocation from initial Li position in their Cu1+ and Ag1+ charge states, which becomes especially more pronounced for the Cu0 and Ag0 defects. Only the Cu2+ and Ag2+ centers stabilize at the substitutional Li site. Resulting defect formation energies demonstrate that the Cu1+, Cu0, Ag1+, and Ag0 centers are the most stable ones. Electronic structure calculations reveal that the Cu and Ag ions introduce their d- and s-states within the gap and their energies and occupation depend strongly on the charge state of the defect. Experimental optical absorption spectra are well reproduced by the Cu1+ and Ag1+ defects spectra, leading to the conclusion that in the as-grown material just Cu1+ and Ag1+ centers are formed. In the case of irradiated compound, present study predicts formation of the interstitial Cu0 defects, whose presence should significantly change the optical absorption and emission of the material, as well as demonstrates the presence of new absorption peaks associated with the interstitial Ag0 and substitutional Ag2+ centers, which reasonably describe the experimental spectrum. / As propriedades estruturais, eletrônicas, energéticas e ópticas do composto Li2B4O7 contendo os defeitos substitucionais Cu ou Ag foram investigadas por meio de cálculos de primeiros princípios ao nível da Teoria do Funcional da Densidade, utilizando-se o método LAPW implementado no código computacional Wien2k. Os efeitos de troca-correlação foram considerados usando-se o potencial modificado de Becke-Johnson (mBJ) e a aproximação do gradiente generalizado (GGA) na parametrização PBEsol. As células contendo os defeitos (Cu ou Ag) foram estudadas em quatro estados de carga diferentes (q = -1, 0, +1, +2) com o objetivo de simular situações de captura de elétrons ou de buracos. Em todos os casos, as posições atômicas foram relaxadas, a natureza das ligações Cu – O e Ag – O cuidadosamente analisada e as estruturas locais em torno dos defeitos determinadas. Verificou-se que os defeitos perturbam amplamente suas vizinhanças e que os centros Cu1+ e Ag1+ exibem um deslocamento significativo a partir da posição inicial do Li, que se torna ainda mais acentuado para os centros Cu0 e Ag0. Apenas os defeitos Cu2+ e Ag2+ se estabilizam no sítio substitucional do Li. Os resultados das energias de formação dos defeitos demonstraram que os centros Cu1+, Cu0, Ag1+ e Ag0 são os mais estáveis. Cálculos de estrutura eletrônica revelaram que as impurezas introduzem os estados d e s dentro do gap, cujas energias e ocupações dependem fortemente do estado de carga do defeito. Os espectros ópticos experimentais foram bem reproduzidos pelos espectros dos centros Cu1+ e Ag1+ calculados, levando-se à conclusão de que somente estes centros são formados no material não irradiado. Durante a irradiação do composto, o presente estudo prevê a formação dos centros intersticiais Cu0, fato que deve alterar significativamente a absorção e emissão óptica do material, bem como demonstra a presença de novos picos de absorção associados aos centros intersticiais Ag0 e substitucionais Ag2+, os quais descrevem razoavelmente bem o espectro experimental. / São Cristóvão, SE

京都大学 / 新制・課程博士 / 博士(理学) / 甲第25099号 / 理博第5006号 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 PETERSRobert, 教授 柳瀬 陽一, 教授 田中 耕一郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Neste trabalho foram projetados, fabricados e caracterizados funcionalmente dispositivos eletroluminescentes empregando complexos de Terras Raras (TR) e de Metais de Transição (MT) tanto como em filmes finos termicamente evaporados quanto formados através da técnica de spin-coating. O estudo foi iniciado com os complexos de TRs (especificamente o complexo de Európio e de Térbio) com filmes termicamente evaporados, com vistas à análise da eficiência externa dos dispositivos em função do ligante principal (CL). Desta análise observou-se que a particular estrutura química do CL resulta em diferenças perceptíveis ao nível da caracterização eletro-óptica (de 0,73x10-3 [BTA] para 1,05x10-3 [DBM]). Dando seqüência à análise de dispositivo com camada emissiva termicamente evaporada, foi realizada a análise do complexo de Térbio com dois tipos de ligante neutro (NL). Com base nos resultados obtidos, neste foco do estudo, observou-se que a configuração estrutural do NL implica em diferenças na eficiência externa (de 0,8x10-3 [PHEN] para 4,1x10- 3 [BIPY]) e no comprimento de onda dominante emitido (de 542 nm [BIPY] para 563 [PHEN]). Ainda explorando os complexos de TRs, foram estudados dispositivos empregando estes dispersos em um polímero com função de matriz, neste caso o polivinilcarbazol (PVK), em filmes formados por spin-coating, os quais apresentaram maior eficiência (de 0,72x10-3 [evaporado] para 1,24x10-3 [spincoating]) externa em comparação aos termicamente evaporados. Ainda nesta linha de estudo foi explorada uma nova estrutura de dispositivo empregando filmes automontados, cujos resultados apresentaram uma melhor eficiência externa para três bicamadas de PAni/PEDOT:PSS. Na seqüência, foram empregados os complexos de MT, especificamente de Rutênio e de Rênio, em filmes finos formados por spincoating. Com o primeiro destes, foi avaliada a conseqüência da variação do seu ligante, seus processos de transporte de portadores de carga e os fenômenos relacionados com sua luminescência. Já com o segundo, que foi disperso em PVK em diversas concentrações, foi feita a análise da eficiência externa com a mesma idéia adotada com o complexo de Európio, cujo estudo revelou uma eficiente transferência de energia, descrita pelo mecanismo de Transferência de Carga Metal- Ligante (3MLCT). / This work presents the study of the Rare Earth (RE) and Transition Metals (TM) complexes, as emissive layers of Organic Light-Emitting Devices (OLEDs) designed, built and electro-optically characterized. The thin films were thermally evaporated or spin-coated. This research started with the study of Europium complex changing its central ligand (CL), which showed that its electrical response exhibits external efficiency differences (from 0.73x10-3 [BTA] to 1.05x10-3 [DBM]). It was observed that the particular chemical structure of the CL results in significant differences as seen in the electro-optical characterization. Giving continuity to the thermally evaporated device characterization, an analysis was done with the Terbium complexes with two different neutral ligands (NL). It was noticed, in this work, that an NL change in Terbium complex imply in changes in external efficiency (from 0.8x10-3 [PHEN] to 4.1x10-3 [BIPY]) and in the emitted dominant wavelength (from 542 nm [BIPY] to 563 nm [PHEN]). Following the study using RE complex, we used it as a dye dispersed in polyvinylcarbazole (PVK) matrix, in a spin-coated deposited thin-film, which results showed a better external efficiency in comparison with thermally evaporated thin-films (from 0.72x10-3 [thermal evaporation] to 1.24x10-3 [spin-coating]). Besides, it was studied a new structure of electroluminescent device with thin-film Self-Assembled deposition, which results showed a better external efficiency for three bilayers of PAni/PEDOT:PSS. In the sequence, TM complexes, namely Ruthenium and Rhenium, were studied using spincoated thin-films. With the first of them, the implications of different ligands (bipyridyne and phenanthroline) were evaluated aiming the charge carrier transport and the luminescence related phenomena. The Rhenium complex was dispersed as a dye in the PVK, using the same approach as that used to study the Europium complex showing a very efficient energy transfer process, described in literature as the Metal-Ligand Charge Transfer (3MLCT) mechanism.

Ce manuscrit présente une étude expérimentale par spectroscopie optique de l'interaction lumière-matière dans des microcavités à base d'oxyde de zinc. Nous avons étudié plusieurs types de cavités planaires qui se démarquent des structures déjà existantes autant par leurs structures que par leurs procédés d'épitaxie. Les avantages théoriques qui ont motivé la réalisation, sont discutés puis vériés par des mesures expérimentales de réectivité et de photoluminescence en fonction de la température et de l'intensité d'excitation. Grâce aux caractéristiques optiques de ces nouvelles microcavités nous avons pu étudier l'émission cohérente de lumière basée sur la condensation des polaritons à haute température jusqu'à 300K.Des facteurs de qualité importants ainsi que des énergies de Rabi élevées permettent de mener une étude approfondie sur le lien qui existe entre la fraction photonique des polaritons et la valeur du seuil d'injection optique correspondant à l'eet laser à polaritons. Ce travailde recherche met en exergue les deux processus physiques identiés conduisant à l'eet laser à polaritons : le régime thermodynamique et le régime cinétique. De plus, l'inuence des interactions exciton-phonon est particulièrement soulignée comme un processus permettant de diminuer le seuil de condensation. / This thesis reports a spectroscopic study of the light-matter interaction in ZnO based microcavities.We have examined several planar microcavities which dier from the previous ones through their structures and their epitaxial processes. The theoretical advantages that have driven these realizations are discussed and veried through experimental measurements of reectivity and photoluminescence as a function of temperature and excitation intensity. Thanks to the optical characterics of these new cavities, we have studied the coherent light emission based on the condensation of polaritons at high temperature, up to 300K. High optical quality factor and high Rabi splitting allow to deeply analyze the relationship which exists between the photonic fraction of polaritons and the threshold excitation value corresponding to the occurrence of the polariton laser eect. This work highlights two identied physical processes which contribute to the laser eect : the thermodynamic and kinetic regimes. Moreover, it appears that the exciton-phonon interaction constitutes a specic phenomenon which allows to reduce the polariton laser threshold.

Η παρούσα εργασία περιλαμβάνει την μελέτη της μη γραμμικής οπτικής απόκρισης διμεταλλικών κραμάτων ευγενών μετάλλων και άλλων μεταλλικών συστημάτων νανοσωματιδίων, είτε περιβεβλημένα με πολυμερή, είτε εγκιβωτισμένα σε μικυλιακά συστήματα συμπολυμερών κατά συστάδες. Τα μέταλλα τα οποία επιλέχθηκαν για την παρασκευή των νανοσωματιδίων ήταν ο χρυσός (Au), ο άργυρος (Ag) και το παλλάδιο (Pd). Τα δύο πρώτα έχουν αποτελέσει τα τελευταία χρόνια αντικείμενο έρευνας σε μορφή κυρίως κολλοειδών διαλυμάτων ή μέσα σε άμορφες μήτρες (π.χ. υάλους) και πολυμερικές μήτρες, καθώς λόγω των εξαιρετικών μη γραμμικοτήτων τους βρίσκουν εφαρμογή σε πληθώρα εφαρμογών της φωτονικής και της οπτο-ηλεκτρονικής. Όσον αφορά τα νανοσωματίδια Pd, οι μη-γραμμικές οπτικές ιδιότητες τους έχουν μελετηθεί ελάχιστα (μόλις μερικές εργασίες στη διεθνή βιβλιογραφία), ενώ είναι η πρώτη φορά που μελετώνται εγκιβωτισμένα σε αμφι-φιλικά συμπολυμερή κατά συστάδες. Στα πλαίσια της παρούσας εργασίας, διερευνήθηκε ο ρόλος του επιφανειακού πλασμονίου στην γραμμική και μη-γραμμική οπτική απόκριση νανοσωματιδίων Au, Ag και Pd, όταν αυτά διεγείρονται με ακτινοβολίες λέιζερ γύρω από την συχνότητα συντονισμού του πλασμονίου, καθώς αναμένεται σημαντική ενίσχυση. Στη συνέχεια αυτής της εργασίας, παρουσιάζονται οι μη γραμμικές οπτικές ιδιότητες άλλων χαμηλοδιάστατων νανοδομών, όπως κβαντικών και ανθρακικών ψηφίδων. Στη περίπτωση αυτών, οι μη γραμμικοί μηχανισμοί που προκαλούν την ενίσχυση της απόκρισης τους είναι διαφορετικοί από αυτούς των μεταλλικών νανοδομών. Η δομή της εργασίας έχει ως ακολούθως: Στα δυο πρώτα κεφάλαια αναφέρονται οι βασικές έννοιες της μη γραμμικής οπτικής και φυσικές διεργασίες που σχετίζονται με αυτή, καθώς και οι πειραματικές τεχνικές Z-scan και Οπτικού Φαινομένου Kerr, που χρησιμοποιήθηκαν για τον χαρακτηρισμό των μη γραμμικών οπτικών ιδιοτήτων των νανοσυστημάτων. Τα επόμενα κεφάλαια είναι αφιερωμένα στα πειραματικά αποτελέσματα που προέκυψαν από την μελέτη των μεταλλικών, ημιαγώγιμων και ανθρακικών νανοϋλικών. Συγκεκριμένα, στο κεφάλαιο 3 γίνεται αναφορά στα πειραματικά αποτελέσματα των νανοσωματιδίων μεταλλικών κραμάτων, τα οποία παρασκευάσθηκαν στο Πανεπιστήμιο του Μόντρεαλ από την ερευνητική ομάδα του καθηγητή κ. Μ. Μeunier. Τα νανοσωματίδια χρυσού-αργύρου είχαν διαφορετικές περιεκτικότητες των δύο μετάλλων (δηλ. ΑuxAg(1-x)), ενώ ανάλογα με τη σύσταση τους παρουσίασαν μεταβλητές οπτικές ιδιότητες, συμπεριλαμβανομένου και της θέση του επιφανειακού πλασμονίου. Η μελέτη των διαλυμάτων πραγματοποιήθηκε για μήκος κύματος διέγερσης στην ορατή φασματική περιοχή (δηλ. 532 nm), πολύ κοντά στο επιφανειακό πλασμόνιο του χρυσού. Η επίδραση του επιφανειακού πλασμονίου στην απόκριση των δυο μετάλλων αλλά και των διαφόρων κραμάτων που μελετήθηκαν ήταν εμφανής, προκαλώντας ενίσχυση με αύξηση της περιεκτικότητας σε χρυσό, ενώ ιδιαίτερο ενδιαφέρον παρουσίασε η συμπεριφορά των κραμάτων υπό διέγερση ns παλμών, καθώς βρέθηκαν να έχουν θεμελιωδώς διαφορετικές ιδιότητες από αυτές του χρυσού και του αργύρου. Στο κεφάλαιο 4, παρουσιάζονται οι μη γραμμικές οπτικές ιδιότητες συστημάτων πολυμερών/παλλαδίου. Μελετήθηκαν δυο ειδών συστήματα, τα υβριδικά μικυλιακά CbzEMAx-b-AEMAy/Pd και τα PVP/Pd, τα οποία παρασκευάσθηκαν στο τμήμα Μηχανολικών Μηχανολογίας και Κατασκευαστικής του Πανεπιστημίου Κύπρου υπό την επίβλεψη της Επ. καθηγήτριας κ. Κρασιά-Χριστοφόρου. Όπως αποδείχθηκε από τα αποτελέσματα της μελέτης, η απόκριση των συστημάτων δεν επηρεάζεται από το πολυμερικό περιβάλλον, ενώ καθορίζεται αποκλειστικά από το μέταλλο. Τέλος, σημαντικό ρόλο φάνηκε να παίζει το μέγεθος των σωματιδίων ή του μεταλλικού πυρήνα αντίστοιχα. Έπειτα, στο κεφάλαιο 5 μελετώνται χαμηλοδιάστατα υβριδικά συστήματα ιωδιούχου μολύβδου. Η σύνθεση των δειγμάτων πραγματοποιήθηκε στο εργαστήριο του Επ. καθηγητή του τμήματος Επιστήμης των Υλικών του Πανεπιστημίου της Πάτρας, κ. Κούτσελα. Η μελέτη πραγματοποιήθηκε για διαλύματα μονοδιάστατων κβαντικών ψηφίδων των οκταεδρικών νανοδομών PbI6 και για αιωρήματα της διδιάστατης δομής (FpAH)2PbI4, η οποία απαρτίζεται από μονοστρωματικά φύλλα των δομικών μονάδων (PbI6)4-. Σε όλες τις πειραματικές συνθήκες, το διδιάστατο σύστημα παρουσίασε μια γιγαντιαία ενίσχυση της μη γραμμικότητας συγκριτικά με το μονοδιάστατο, φτάνοντας τις πέντε τάξεις μεγέθους. Τέλος, στο κεφάλαιο 6 παρουσιάζεται η μη γραμμική οπτική απόκριση και ο οπτικός περιορισμός διαφόρων συστημάτων ανθρακικών ψηφίδων, φέροντας διαφορετικές οργανικές αλυσίδες στην επιφάνεια τους. Η σύνθεση των συστημάτων πραγματοποιήθηκε στο τμήμα Φυσικής του Πανεπιστημίου Ιωαννίνων από τον Επ. Καθηγητή κ. Μπουρλίνο. Οι διαφορές που εντοπίστηκαν μεταξύ των διαφόρων νανοϋλικών ήταν ουσιώδεις, υποδηλώνοντας τη δυνατότητα προσαρμογής και ελέγχου των μη γραμμικών οπτικών ιδιοτήτων, με κατάλληλη τροποποίηση της επιφάνειας των σωματιδίων. / In the present thesis, the third-order nonlinear optical (NLO) properties of metallic nanoparticles, either encapsulated in polymers or in block copolymers, as well as bimetallic nanoparticles are investigated. Among the purposes of this work is to examine metallic nanostructures based on palladium (Pd), which is one of the least studied metals regarding their nonlinear optical response. In this view, single Pd nanoparticles are compared with another class of recently synthesized Pd-based nanomaterials, i.e., Pd micellar nanohybrids. In addition, gold-silver alloyed nanoparticles are examined and compared with their monometallic counterparts, exhibiting substantial differences and potential application in optoelectronic devices and photonic applications. In all cases, the main motivation of this work is to take advantage of the surface plasmon resonance (SPR), located in the ultraviolet or visible spectral area, to enhance/tailor the NLO properties of the metallic/hybrid nanostructures. As a continuation of the low dimensional metallic structures, the NLO response of some carbon-dots and quantum-dots are investigated, aiming to examine the correlation of their optical nonlinearities with their structure and the origin of the NLO enhancement. Therefore, the structure of this thesis is as follows: Initially the basic concepts of nonlinear optics, the physical processes related with it, as well as the physical mechanisms related to the nonlinear refractive index will be presented. Moreover the equations, which describe the nonlinear optical susceptibilities (linear and nonlinear) will be derived. Then, reference will be made to the optical parameters related to the third order optical nonlinearity and to the experimental techniques which were employed for the determination of the nonlinearity, as well as to the procedure followed to derive the nonlinear optical parameters from the acquired experimental data. Moreover, in the beginning of chapter 3 the theory of SPR in metals will be explicitly presented, followed by the experimental results obtained by the Au-Ag nanoalloys. More in detail, AuxAg(1-x) nanoparticles with varying metallic content and optical properties (i.e., SPR) were excited with resonant irradiation conditions (i.e., close to the SPR maximum) both of ps and ns pulse duration. The results demonstrate a straightforward dependence of the NLO response on the gold molar fraction of the alloys, this being attributed to the different band structures of the systems, thus suggesting a mean of tailoring the NLO properties of bimetallic nanostructures. Also, it is shown that under ns laser excitation the nano-alloys exhibit fundamentally different behavior than pure Au and Ag nanoparticles. The samples were produced by fs laser ablation in the University of Montreal by the research group of Prof. Michel Meunier. In chapter 4, the NLO properties of various polymer/Pd systems will be presented. Two different type of materials were investigated: the hybrid micellar CbzeMAx-bAEMAy/Pd and PVP/Pd, which were synthesized in University of Cyprus under the supervision of Prof. Theodora Krasia-Christoforou. As shown, the polymeric environment does not affect the total NLO response, however it can be effectively used to define the size, shape and SPR properties of the nanohybrids. On the contrary, the size of Pd nanoparticles or the micellar core size was found to be determinative for the NLO behavior of the systems. Then, in chapter 5, some low-dimensional hybrid lead-iodide systems are investigated. Specifically, the PbI6 octahedral quantum dots and the two-dimensional (FpAH)2PbI4 structure, consisting of monolayers of (PbI6)4- corner sharing structural units are synthesized in University of Patras, by Prof. Ioannis Koutselas. Under all excitation conditions, the quantum wells were found to exhibit gigantic NLO response in comparison with the quantum dots, reaching even 5 orders of magnitude. Finally, in the last chapter, the NLO response and optical limiting action of a series of carbon-dots, bearing various organic chains attached on their surfaces, will be presented. The carbon-based materials were prepared in the University of Ioannina, by Prof. Athanasios Bourlinos. By comparing the various studied systems, it is shown that the surface passivation is the key to control the NLO behavior of these nanostructures. In this case, of great importance is the sp2/sp3 ratio and consequently the modification of the band structure of carbon-dots, since it can significantly affect their NLO properties.

Ce manuscrit de thèse est une contribution à l’étude du couplage fort lumière-matière dans les microcavités planaires à base d’oxyde de zinc. Nous avons déterminé les propriétés de l’interaction entre excitons et photons au travers de mesures résolues en angle pour des hétéro-structures réalisées par épitaxie par jets moléculaires (EJM) sur silicium. Il a ainsi été possible de démontrer le régime de couplage fort aussi bien aux températures de l’hélium liquide qu’à température ambiante. Un important travail de conception des cavités et de modélisation de leur réponse optique a été effectué dans le but d’obtenir une émission cohérente de lumière basée sur la condensation des polaritons tel que prédit par les travaux théoriques. Les récentes mesures pour une cavité optimisée conduisent à un facteur de qualité voisin de 500 et à une énergie de Rabi très élevée (120 meV). / This thesis manuscript is a contribution to the study of strong light-matter coupling in zinc oxide-based planar microcavities. We have determined the properties of the exciton-photon interaction through angle resolved measurements on structures grown by molecular beam epitaxy (MBE) on silicon. Thus, we have demonstrated strong coupling at both cryogenic and room temperatures. A substantial work on the conception of cavities and on the calculation of their optical response has been realized to obtain a coherent emission of light based on the condensation of polaritons as predicted by theoretical works. The latest measurements on an optimized microcavity lead to a quality factor close to 500 and a high Rabi splitting of 120 meV.

Neste trabalho foram projetados, fabricados e caracterizados funcionalmente dispositivos eletroluminescentes empregando complexos de Terras Raras (TR) e de Metais de Transição (MT) tanto como em filmes finos termicamente evaporados quanto formados através da técnica de spin-coating. O estudo foi iniciado com os complexos de TRs (especificamente o complexo de Európio e de Térbio) com filmes termicamente evaporados, com vistas à análise da eficiência externa dos dispositivos em função do ligante principal (CL). Desta análise observou-se que a particular estrutura química do CL resulta em diferenças perceptíveis ao nível da caracterização eletro-óptica (de 0,73x10-3 [BTA] para 1,05x10-3 [DBM]). Dando seqüência à análise de dispositivo com camada emissiva termicamente evaporada, foi realizada a análise do complexo de Térbio com dois tipos de ligante neutro (NL). Com base nos resultados obtidos, neste foco do estudo, observou-se que a configuração estrutural do NL implica em diferenças na eficiência externa (de 0,8x10-3 [PHEN] para 4,1x10- 3 [BIPY]) e no comprimento de onda dominante emitido (de 542 nm [BIPY] para 563 [PHEN]). Ainda explorando os complexos de TRs, foram estudados dispositivos empregando estes dispersos em um polímero com função de matriz, neste caso o polivinilcarbazol (PVK), em filmes formados por spin-coating, os quais apresentaram maior eficiência (de 0,72x10-3 [evaporado] para 1,24x10-3 [spincoating]) externa em comparação aos termicamente evaporados. Ainda nesta linha de estudo foi explorada uma nova estrutura de dispositivo empregando filmes automontados, cujos resultados apresentaram uma melhor eficiência externa para três bicamadas de PAni/PEDOT:PSS. Na seqüência, foram empregados os complexos de MT, especificamente de Rutênio e de Rênio, em filmes finos formados por spincoating. Com o primeiro destes, foi avaliada a conseqüência da variação do seu ligante, seus processos de transporte de portadores de carga e os fenômenos relacionados com sua luminescência. Já com o segundo, que foi disperso em PVK em diversas concentrações, foi feita a análise da eficiência externa com a mesma idéia adotada com o complexo de Európio, cujo estudo revelou uma eficiente transferência de energia, descrita pelo mecanismo de Transferência de Carga Metal- Ligante (3MLCT). / This work presents the study of the Rare Earth (RE) and Transition Metals (TM) complexes, as emissive layers of Organic Light-Emitting Devices (OLEDs) designed, built and electro-optically characterized. The thin films were thermally evaporated or spin-coated. This research started with the study of Europium complex changing its central ligand (CL), which showed that its electrical response exhibits external efficiency differences (from 0.73x10-3 [BTA] to 1.05x10-3 [DBM]). It was observed that the particular chemical structure of the CL results in significant differences as seen in the electro-optical characterization. Giving continuity to the thermally evaporated device characterization, an analysis was done with the Terbium complexes with two different neutral ligands (NL). It was noticed, in this work, that an NL change in Terbium complex imply in changes in external efficiency (from 0.8x10-3 [PHEN] to 4.1x10-3 [BIPY]) and in the emitted dominant wavelength (from 542 nm [BIPY] to 563 nm [PHEN]). Following the study using RE complex, we used it as a dye dispersed in polyvinylcarbazole (PVK) matrix, in a spin-coated deposited thin-film, which results showed a better external efficiency in comparison with thermally evaporated thin-films (from 0.72x10-3 [thermal evaporation] to 1.24x10-3 [spin-coating]). Besides, it was studied a new structure of electroluminescent device with thin-film Self-Assembled deposition, which results showed a better external efficiency for three bilayers of PAni/PEDOT:PSS. In the sequence, TM complexes, namely Ruthenium and Rhenium, were studied using spincoated thin-films. With the first of them, the implications of different ligands (bipyridyne and phenanthroline) were evaluated aiming the charge carrier transport and the luminescence related phenomena. The Rhenium complex was dispersed as a dye in the PVK, using the same approach as that used to study the Europium complex showing a very efficient energy transfer process, described in literature as the Metal-Ligand Charge Transfer (3MLCT) mechanism.

Mankind has come a long way since the invention of wheel to accessing information in the quintillionth of a second. At the heart of every invention ever made, there has been only one objective, to ease the way of living. The progeny of this philosophy automatically came to be known as technology. It was technology that led to the design of the wheel for fast human transportation and the same motivation let him design more sophisticated machines. In mankind’s journey to improve technology, it began to learn efficient or correct ways to utilize and understand resources around it, creating a whole new philosophy called science. Ingeniously, it was science that let humans understand what they were made of: matter, to discovering what matter itself was composed of: atoms and what puts these together: forces. Science and technology has been of tremendous comfort for mankind and has helped it evolve throughout history. However, it is not always that science and technology go hand in hand. Technology has always helped man design devices and instruments which often bring physical comfort. Science on the other hand has made sure that loss in manual labor is compensated by increased inquisitiveness. There were times when technology was more developed than science. This was the time when machines were taking mankind by fire, resulting in the first and second industrial revolutions. During that same time, science was develop-ing slowly by increasing human curiosity to learn the way nature functioned at finer details. This led to the discovery of the electron by Joseph John Thomson, who proved the electron to be a negatively charged particle. Consequently, he was awarded the 1906 Nobel Prize in Physics for his work on electricity conduction in gases. Later, his son, George Paget Thomson, counter-proved that electrons are actually waves. He was also awarded the 1937 Nobel Prize in Physics, along with Clinton Joseph Davisson for their discovery of electron diffraction caused by crystals. Despite the ambiguity, mankind today accepts electrons to have dual properties. It is both a wave and a particle. This duality is not limited to electrons but is applicable to all matter, as proposed by Louis de Broglie and is one of the fundamental principles in science. With the help of well-developed technology, mankind can now design machines that allow controlled flow of electrons establishing the world of electronics, allowing faster human communication. The study of electronic properties and its usage in designing efficient devices is what electronics is all about. Electrons are the protagonist of mankind today. The presence of electrons is unanimously accepted by everyone. All physical and chemical processes are a result of electrons getting transported. Electron transfer processes are ubiquitous in nature, be it in photosynthesis or energy production in mitochondria . It is the fundamental process in all chemical reactions and all physical processes related to electricity. Every piece of hi-tech gadget practically uses the electron, and the whole of humanity is being serviced by it. In fact, a life without utilizing the electrons is abysmally mundane. Electronics has evolved from designing the first millimeter sized point contact transistor to silicon chip processors that contain billions of nanosized transistors. Studying electron transport has also led to the discovery of light emission during conduction popularly known as LED, an abbreviation for light emitting diode. Heating up of devices during electron transport forced mankind to study heat transport and design materials that have highly efficient electron transfer processes. Electron transfer is also the basic principle behind the Scanning Tunneling Microscope (STM), Scanning Electron Microscope (SEM) and the Transmission Electron Microscope (TEM) which replaced the conventional idea of using light (photons) as a source to observe matter at the nanolevel. However, mankind is still in the process of developing a technology which exploits both properties of the electron simultaneously. Today, science and technology work together to overcome this barrier. Indeed, science and technology today have come as far as controlling electron transport up to a single atomic level where quantum effects (discretization and interference of states that make up the system) are very pronounced. This branch can be referred to as quantum electronics or quantronics. It is one of the possible alternatives to conventional silicon based electronics, and is made of three separate fields. The first one that exploits the quantum nature of electron transport in nanoscopic systems, is usually called molecular electronics or moletronics. The second involves ex-ploiting the spin of the electron and is termed as spintronics. The third is the most challenging where neither science nor technology has been able to fully grasp the characteristics, i.e utilizing the heat quanta in designing thermal de-vices at the single atomic level. In general, for ultimate exploitation of both the wave and particle characteristics of the electron, a proper comprehension of the quantum effects during electron transport is necessary to design a quantronic device. Also, in any quantronic device, apart from quantum effects, fluctuations in temperature cause changes in the flow of electrons. Since electron flow is a random process, fluctuations need to be analyzed from a statistical point of view. Moreover, to address issues related to efficiency and power of these quantronic devices, a proper understanding of the thermodynamic aspects is required. The aim of the work in the thesis is to theoretically analyze the fluctuations, quantum effects and thermodynamics, that in principle, affect the basic physics and chemistry during electron and heat transport in a specific class of out of equilibrium quantum systems. This class of quantum systems are prototypes for designing quantronic devices, where both wave and particle nature of the electrons are pronounced. These are called molecular junctions or quantum junctions. It will in turn help the field of quantronics in the long run. However, in this thesis, it is the science that I address and not the technological aspects.

Le développement de méthodes rapides, précises et ultra-sensibles pour la détection d'analytes cibles en solution est crucial pour la recherche et les applications potentielles en médecine ou biologie moléculaire. Une approche très prometteuse consiste à développer des nano-capteurs à partir de nano-objets métalliques (NOM) qui présentent une résonance d'extinction dans leur réponse optique. Cette résonance nommée résonance de plasmon de surface localisée (RPSL) peut être ajustée spectralement en jouant sur la nature, la morphologie et l'environnement du NOM. Mesurer des modifications sur la RPSL de nano-objets individuels en présence d'analytes cibles doit permettre de s'affranchir des effets de moyennes dans les mesures d'ensemble. De plus, cela ouvre la voie vers le développement d'échantillons micrométriques pour des tests multicibles sans étiquette (« label-free »).Dans ce travail on a développé un nouveau dispositif expérimental basé sur la technique de spectroscopie à modulation spatiale (SMS) permettant de sonder la réponse optique de NOM individuels en milieu liquide. En parallèle des méthodes de synthèse ont été mises au point pour obtenir des échantillons sondes stables permettant des mesures sur NOM unique, en particulier sur des bipyramides d'or qui présentent de nombreuses qualités intrinsèques faisant d'elles de bonnes candidates pour le « bio-sensing ».Des mesures ont été réalisées dans des environnements d'indice variable et les changements détectés sont en bon accord avec les simulations théoriques. De plus, de nombreuses études ont été réalisées pour comprendre l'influence des nombreux paramètres agissant sur la réponse optique des systèmes étudiés / Advances in the development of rapid, accurate and highly sensitive methods for detecting target analytes in solution will provide crucial tools for research and applications in medicine and molecular biology. One of the currently most promising approaches is the development of nanosensors based on the localized surface plasmon resonance (LSPR) of noble metal nano-objects (MNOs), which is an optical response that depends on their size, shape, composition and local environment. The ability to measure the modification of the reponse of a single MNO in the presence of a target analyte would allow each object to act as an independent probe with increased sensitivity as the signal would be isolated from the averaging effects of ensemble measurements. Furthermore it would allow the development of micrometric, functionalized multiprobe samples for multitarget label-free assays.In this work, a novel experimental setup based on the spatial modulation spectroscopy (SMS) technique has been developed to measure the optical response of individual nano-objects in a liquid environment. In parallel, a new technique has also been developed to elaborate stable probes for measurements with the new setup, with a focus on gold bipyramids due to numerous qualities that make them excellent candidates for biosensing probes. The setup has been used to measure the response of individual objects in environments of different real refractive indices and the detected changes have been shown to be in good agreement with theoretical calculations. Numerical studies have also been performed to investigate the influence on the optical response of numerous factors encountered in the studied systems

Ο όρος μη γραμμική οπτική (nonlinear optics) αναφέρεται στον κλάδο της φυσικής που μελετά τις μεταβολές που επέρχονται στις οπτικές ιδιότητες της ύλης, όταν αυτή αλληλεπιδρά με ισχυρά ηλεκτρομαγνητικά πεδία. Οι δέσμες λέιζερ (laser) αποτελούν το κατ’ εξοχήν ηλεκτρομαγνητικό πεδίο που χρησιμοποιείται για να προκαλέσει τη μη γραμμική οπτική απόκριση της ύλης, λόγω της ισχυρής ακτινοβολίας. Με την ανακάλυψη του λέιζερ τη δεκαετία του 1960, παράλληλα αναπτύχθηκαν πολλές τεχνικές μέσω των οποίων καθίσταται εφικτός ο προσδιορισμός της μη γραμμικής οπτικής απόκρισης των υλικών. Κίνητρο για αυτή την εκτεταμένη έρευνα αποτελεί το γεγονός ότι υλικά με σημαντική μη γραμμική απόκριση βρίσκουν πολλές εφαρμογές στη φωτονική και την οπτοηλεκτρονική. Ειδικότερα, τέτοια υλικά μπορούν να χρησιμοποιηθούν ως οπτικοί περιοριστές (optical limiters) για την προστασία από υψηλές δέσμες λέιζερ, ως οπτικοί διακόπτες (optical switches), καθώς και ως οπτικές λογικές πύλες (optical logic gates) κ.α. Τα τελευταία χρόνια υπάρχει ιδιαίτερο ερευνητικό ενδιαφέρον στο πεδίο των μοριακών διακοπτών (molecular switches). Ο όρος μοριακός διακόπτης αναφέρεται στην δυνατότητα ύπαρξης ενός μορίου μεταξύ δύο διαφορετικών καταστάσεων, ικανότητα που θα αποτελέσει την αφετηρία για μια λειτουργία “on/off”, σε μοριακό επίπεδο. Υποψήφια μόρια που μπορούν να υποστηρίξουν μια διακοπτική λειτουργία είναι εκείνα που παρουσιάζουν κάτω από ορισμένες συνθήκες αλλαγή σε μια εγγενή ιδιότητά τους, όπως ο φθορισμός, η αγωγιμότητα, η μαγνήτιση, ο στερεο-ισομερισμός, η μη γραμμικότητα κ.α. Σκοπός της παρούσας ειδικής ερευνητικής εργασίας ήταν ο προσδιορισμός της τρίτης τάξης μη γραμμικής οπτικής απόκρισης μοριακών συστημάτων που περιέχουν αζοβενζόλιο, υπό μορφή διαλυμάτων. Τα μόρια αυτά είναι ενδιαφέροντα γιατί αφ’ ενός εμφανίζουν trans/cis ισομερισμό, αφ’ ετέρου παρουσιάζουν μια αλλαγή στη μη γραμμικότητά τους εξαιτίας του φωτο-ισομερισμού του διπλού δεσμού –N=N-. Η δομή της εργασίας έχει ως εξής : Στο πρώτο κεφάλαιο θα γίνει μια περιγραφή της μη γραμμικής αλληλεπίδρασης ύλης-πεδίου, η εξαγωγή της μη γραμμικής κυματικής εξίσωσης, καθώς επίσης και μερικών φυσικών διαδικασιών που περιγράφονται μέσω αυτής. Στο δεύτερο κεφάλαιο θα περιγραφεί η πειραματική τεχνική που ακολουθήθηκε, θα αναφερθούν οι οπτικές παράμετροι που σχετίζονται με τη τρίτης τάξης μη γραμμικότητα και τέλος θα περιγραφεί η διαδικασία ανάλυσης των πειραματικών αποτελεσμάτων. Στο τρίτο κεφάλαιο θα γίνει μια σύντομη περιγραφή της πειραματικής διάταξης καθώς και των κυριότερων οργάνων που την αποτελούν. Στο τέταρτο κεφάλαιο θα παρουσιασθούν τα πειραματικά αποτελέσματα που προέκυψαν από την εργασία. Αρχικά παρουσιάζεται μια σύντομη περιγραφή των μοριακών συστημάτων που μελετήθηκαν. Ακολουθεί η μη γραμμική οπτική απόκριση των συστημάτων για διέγερση με παλμούς χρονικής διάρκειας 35 ps, στα 532 και 1064 nm,και ακολουθεί ο προσδιορισμός της μη μεταβατικής μη γραμμικής απόκρισης για διέγερση με παλμούς διάρκειας 4 ns. Αναφέρονται τα συμπεράσματα από τη μελέτη των συστημάτων και ακολουθεί μια πρόταση για μελλοντική μελέτη. / Extensive research in the field of molecular switches promises a wide variety of switching mechanisms characterized by an eclectic range of intrinsic properties regarding their luminescence, conductivity, magnetic and optical outputs. Because of their controlled alternating properties and the ease of their preparation and modification, molecular switches hold the promise of becoming pivotal components of organic–integrated photonic devices. Among the many available systems, azobenzene dyes represent a particularly promising class of organic switchable materials. The advantage of azobenzene chromophores as molecular switches is based not only on the large geometrical change accompanying the cis–trans isomerization, but also on their photo–stability, and the ease of their preparation and derivatization. In addition, azobenzene chromophores, exhibiting in general large nonlinear optical response, are characterized by an important change in their third-order nonlinear optical response due to the photo-isomerization of the –N=N- double bond. The purpose of this work is hence to describe how the NLO properties of the azobenzene are influenced when surrounded by an always more electron-donating and conjugated environment. In order to do so, we are studying three azobenzene-centered molecules. In two of them, the switch is bonded to two electron-rich groups such as alkylated anilines via either one or two ethynil spacers. In the latter, a Zn-porphyrin was instead linked to the aza-core. The insertion of a porphyrin core was driven by its high polarizability and optical oscillator strength which gives the material remarkable NLO behavior, making it potentially useful for ultra-fast switching technologies. In that view, the nonlinear optical response of these novel azobenzene based molecules dissolved in dichloromethane are studied by means of Z-scan technique using 35 ps laser pulses at 532 and 1064 nm. From the measurements, the nonlinear absorption and refraction and the corresponding third-order susceptibility χ(3) and second hyperpolarizability are determined.