Ce manuscrit présente une étude expérimentale sur les propriétés optiques des nanorubans de graphène (acronyme anglais : GNRs) et des boites quantiques de graphène (acronyme anglais : GQDs) synthétisés par la chimie ascendante.Pour la partie sur les GNRs, les spectres d'absorption et de photoluminescence ainsi que les mesures de la durée de vie sur la dispersion impliquent la formation d'états excimères résultant de l'agrégation des GNRs. Au moyen de la microscopie confocale et de la microscopie à force atomique, nous observons l'émission de petits agrégats de GNRs confirmant leur capacité à émettre de la lumière à l'état solide. D'autre part, les caractérisations optiques des GNRs synthétisés sur une surface d’or présentent des caractéristiques de Raman remarquables, impliquant les propriétés vibrationnelles spécifiques des GNRs par rapport au graphène et aux nanotubes de carbone. La PL observée est spectralement large avec une énergie plus élevée que celle de la bande interdite des GNRs. Cela pourrait être lié aux défauts créés lors de la préparation de l'échantillon.Pour la partie sur les GQDs, les résultats de spectroscopie optique indiquent que les GQDs sont individualisées en dispersion plutôt que sous la forme d’agrégats. Ensuite, grâce à la microphotoluminescence, nous abordons directement les propriétés intrinsèques des GQDs uniques. Des mesures de corrélation de photons de second ordre révèlent que les GQDs présentent une émission de photons uniques avec une grande pureté. De plus, l'émission de GQD présente une bonne photo-stabilité avec une brillance élevée. Comme premier exemple de l'accordabilité optique des GQDs via le contrôle de la structure, nous observons que l'émission de GQDs fonctionalisés avec des atomes de chlore est décalée de près de 100 nm tout en maintenant une émission de photons uniques. / This manuscript presents an experimental study on the optical properties of graphene nanoribbons (GNRs) and graphene quantum dots (GQDs) synthesized by bottom-up chemistry.For the part on GNRs, the optical absorption and photoluminescence spectra as well as the life-time measurements on the dispersion of solution-mediated synthesized GNRs implies the formation of excimer states as a result of aggregation of GNRs. By means of confocal fluorescence microscopy and atomic force microscopy, we observe the emission of small GNR aggregates confirming the ability of GNRs to emit light in the solid state. On the other hand, the optical characterizations of on-surface synthesized GNRs shows remarkable Raman features, implying the distinct vibrational properties of GNRs compared to graphene and carbon nanotubes. The observed PL is spectrally broad with higher energy instead of a bright bandgap emission, which might be related to the defects created during the sample preparation.For the part on GQDs, the optical spectroscopy results indicate that GQDs are individualized in dispersions rather than in the form of aggregates. Then by means of microphotoluminescence, we directly address the intrinsic properties of single GQDs. Second-order photon correlation measurements reveal that GQDs exhibit single-photon emission with a high purity. Notably, the emission of GQDs has good photo-stability with high brightness. As a first example of the optical tunability of GQDs through the control of their structure, we observe that the emission of single edge-chlorinated GQDs is redshifted by almost 100 nm while maintaining the single-photon emission.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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This thesis reports the photophysical and electroluminescence studies undertaken on two types of material: polymeric and dendritic. The dendritic architecture is a recent concept adopted to develop new materials for light-emitting diodes. The dendritic structure offers a combination of properties of both polymers and small organic molecules whilst having their own interesting characteristic of optimising processibility, charge transport, and optical properties independently. The dendritic structure consists of functional surface groups, conjugated dendrons and a conjugated core. Initial optical (absorption and photoluminescence) studies revealed that the dendrimer emission originates from the core and is independent of excitation wavelength. This was investigated further in distyrylbenzene based dendrimers where the effect of dendrimer generation number on photoluminescence and electroluminescence properties was studied. All dendrimers emit blue electroluminescence with, in some cases, reasonable electroluminescence quantum efficiency in the range of 0.09 % and brightness up to 150 Cd m(^-2). Having established that the furmel effect, where excitation is successfully transferred to the dendrimer core in both PL and EL, different chromophores were incorporated in the dendrimer structure. Colour control was thus demonstrated in EL devices of the different dendrimers, showing the possibility of using a large number of chromophores in a processible form for EL applications. Conjugated polymers were also studied to investigate the nature of the emitting species (poly(p-pyridine)) and the effect of side- chains (poly(p-phenylenevinylene)). In poly(p-pyridine) the emission was found to be strongly dependent on pyridyl ring rotation affecting the emission and its quantum yield while the side-chains in the poly(p-phenylenevinylene) derivatives were found to affect polymer properties such as degree of conversion of non-conjugated to conjugated polymer. The PL quantum yield system was set-up and proved useful in assessing synthesis of new materials.

Ip Kit Man = 準一維的硒化鋅納米結構的光致發光研究 / 葉潔雯. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 68-71). / Text in English; abstracts in English and Chinese. / Ip Kit Man = Zhun yi wei de xi hua xin na mi jie gou de guang zhi fa guang yan jiu / Ye Jiewen. / ACKNOWLEDGEMENTS --- p.i / ABSTRACT --- p.ii / TABLE OF CONTENTS --- p.vi / LIST OF TABLE --- p.vii / LIST OF FIGURES --- p.viii / Chapter Chapter1 --- Introduction / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Literature review --- p.2 / Chapter 1.3 --- Our study --- p.4 / Chapter 1.4 --- Growth conditions --- p.4 / Chapter Chapter2 --- Background / Chapter 2.1 --- Basic principle of PL --- p.6 / Chapter 2.2 --- Theories of excitations in semiconductor / Chapter 2.2.1 --- Bandgap and temperature effect of ZnSe --- p.8 / Chapter 2.2.2 --- Structure of ZnSe --- p.13 / Chapter 2.3 --- Surface effects --- p.16 / Chapter 2.4 --- Gas -Surface Interaction --- p.20 / Chapter Chapter 3 --- Experimental Procedures / Chapter 3.1 --- Setup of PL Spectroscopy --- p.21 / Chapter 3.2 --- Passivation and separation of ZnSe nanostructures --- p.26 / Chapter Chapter 4 --- Results and Discussions / Chapter 4.1 --- Analysis of ZnSe/Si nanostructures / Chapter 4.1.1 --- "Morphology, structure and separation of as-grown ZnSe/Si nanostructures" --- p.30 / Chapter 4.1.2 --- Temperature dependent PL of as-grown and very low density ZnSe/Si nanostructures --- p.33 / Chapter 4.1.3 --- Temperature dependent PL of ZnSe/Al203 nanowires --- p.41 / Chapter 4.1.4 --- Growth conditions dependence on PL --- p.44 / Chapter 4.1.4a --- PL result comparison: ZnSe grown on 3 different substrate --- p.45 / Chapter 4.1.4b --- PL result comparison: Silver and gold catalyst --- p.45 / Chapter 4.2 --- Analysis of the ammonium sulfide treated samples / Chapter 4.2.1 --- XPS results of ammonium sulfide treated samples --- p.47 / Chapter 4.2.2 --- Relationship between immersion time and enhancement factors of PL intensity --- p.49 / Chapter 4.3 --- Analysis of effects in PL of ZnSe/Si nanostructures in different gas ambients --- p.53 / Chapter Chapter 5 --- Conclusions --- p.66 / References --- p.68

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