Nano-sized semiconductors, known as quantum dots (QDs), are one of the hottest research areas in recent years. The energy gaps of QDs change with their diameters, giving them size-dependent optical properties. By controlling reaction conditions, people are able to make QDs that can emit in certain wavelength ranges. So far, QDs have shown great potential in telecommunication, bio-imaging, single-photon laser source, etc. This thesis starts with Chapter 1, which first introduces the finding of QDs and why they have such special properties. The quantum confinement and energy gap are discussed, followed by the absorption and emission of QDs. Moreover, the synthesis methods and mechanism involved are reviewed in brief. Chapter 2 presents the synthesis of lead-based core, core-shell and core-shell-shell QDs and previous work by other people. A few techniques including transmission electron microscopy (TEM), UV-absorption, photoluminescence (PL) measurement, and X-ray photoelectron spectroscopy (XPS) were used and shown in this chapter. Core-shell and core-shell-shell QDs are shown to present excellent stability over 20 months. The ZnS shell was proved by energy-dependent XPS and TEM measurements. A detailed discussion on quantum yield (QY) is given in Chapter 3. Absolute and relative QY measurements and some standard dyes are discussed. After that, Chapter 4 shows systematic QY measurements on lead-based core and core-shell QDs. For each type of QDs, at least two batches are selected with their emission spectra presented as well. It is revealed by collected data that they have excitation-dependent QYs. The QY drops as the excitation light increases in energy (higher wavelength), which is due to non-radiative decays from higher excited states or the Auger effects. QY of PbS and PbSe QDs can be as high as 50%. Eventually, the conclusion and future work are included in Chapter 5. All experimental work is described in detail in the experimental section. / Graduate

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A set of three benzophenoxazine dyes, two completely soluble and one partially soluble in aqueous media, has been prepared and their spectroscopic properties examined. These dyes can be used as either donor or acceptor in synthesis of through-bond energy transfer cassettes. Structural modifications prevented aggregation in water and improved their fluorescence properties in water. Their absorption and emission were studied in both organic and aqueous media. Two of the three dyes have superior quantum yields in aqueous media as compared to other reported dyes. Improved quantum yield makes these dyes attractive candidates for biological studies in aqueous media. We have also prepared alkynes and iodo derivatives of benzophenoxazines, which can be used for synthesis of water-soluble, through-bond, energy transfer cassettes. Alkynes were prepared via Sonogashira coupling.

Photochromism is a phenomenon where two isomers with markedly different absorption spectra are interconverted by a reversible photochemical reaction. The photochromism of 1’,3’,3’-trimethyl-6-nitrospiro[2H-1]-benzopyran-2,2’-indoline (NSP) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene) (DAE) was studied in aqueous solutions containing NaCl and the bile salts sodium cholate (NaC), sodium deoxycholate (NaDC) or sodium taurocholate (NaTC). Bile salts are amphiphilic compounds that aggregate in water. These aggregates can solubilize hydrophobic organic compounds in water and affect the reactivity of the bound compounds. NSP and DAE are photochromic compounds that can be switched between a colored and a colorless isomer. The colored isomer of DAE can only be transformed into the colorless form by irradiation of light, while the colored isomer of NSP is also converted into the colorless form by a dark reaction. The dark reaction rate constant of NSP increases at high concentrations of bile salt and NaCl. The bile salt structure also affects the dark reaction rate constant, which is smaller in NaTC and approximately the same in NaC and NaDC. The activation energy for the reaction in all conditions studied is similar to the value reported for polar organic solvents. A method that employs HPLC was developed to determine the molar absorptivity coefficients of photochromic compounds. The values obtained were important to determine the quantum yields for photocoloration (ΦAB) and photodecoloration (ΦBA). Quantum yield values were determined by a photokinetic method that employs irradiation at a single wavelength and numerical analysis. The values of ΦAB and ΦBA for DAE in bile salts are the same as the values in cyclohexane. For NSP, ΦAB is dependent on the structure of the bile salt and increases in the order NaTC < NaC < NaDC. / Graduate

Photochromism is a phenomenon where two isomers with markedly different absorption spectra are interconverted by a reversible photochemical reaction. The photochromism of 1,3,3-trimethyl-6-nitrospiro[2H-1]-benzopyran-2,2-indoline (NSP) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene) (DAE) was studied in aqueous solutions containing NaCl and the bile salts sodium cholate (NaC), sodium deoxycholate (NaDC) or sodium taurocholate (NaTC). Bile salts are amphiphilic compounds that aggregate in water. These aggregates can solubilize hydrophobic organic compounds in water and affect the reactivity of the bound compounds. NSP and DAE are photochromic compounds that can be switched between a colored and a colorless isomer. The colored isomer of DAE can only be transformed into the colorless form by irradiation of light, while the colored isomer of NSP is also converted into the colorless form by a dark reaction. The dark reaction rate constant of NSP increases at high concentrations of bile salt and NaCl. The bile salt structure also affects the dark reaction rate constant, which is smaller in NaTC and approximately the same in NaC and NaDC. The activation energy for the reaction in all conditions studied is similar to the value reported for polar organic solvents. A method that employs HPLC was developed to determine the molar absorptivity coefficients of photochromic compounds. The values obtained were important to determine the quantum yields for photocoloration (AB) and photodecoloration (BA). Quantum yield values were determined by a photokinetic method that employs irradiation at a single wavelength and numerical analysis. The values of AB and BA for DAE in bile salts are the same as the values in cyclohexane. For NSP, AB is dependent on the structure of the bile salt and increases in the order NaTC < NaC < NaDC. / Graduate / 2015-03-31

Rapidly expanding research in nanotechnology has led to exciting progress in a versatile array of applications from medical diagnostics to catalysis. This success resulted from the manipulation of the desired properties of nanomaterials by controlling their size, shape, and composition. Among the most thriving areas of research about nanoparticle is the synthesis and doping of the ligand-protected atomically-precise metal nanoclusters. In this thesis, we developed three different novel metal nanoclusters, such as doped Ag29 with five gold (Au) atoms leading to enhance its quantum yield with remarkable stability. We also developed half-doped (alloyed) cluster of Ni6 nanocluster with molybdenum (Mo). This enabled enhanced stability and better catalytic activity. The third metal nanocluster that we synthesized was Au28 nanocluster by using di-thiolate as the ligand stabilizer instead of mono-thiolate. The new metal clusters obtained have been characterized by spectroscopic, electrochemical and crystallographic methods.

This thesis concerns the synthesis of cadmium based nanoparticles that emitted from 400 to the near infrared (NIR) region. Once synthesised they can be possibly used as biomarkers once encapsulated in microspheres. A brief introduction to the area of nanomaterials is also provided. The focus of this thesis is split into three main categories. Firstly core/shell nanoparticles were synthesised due to their ability to emit over a large range of wavelengths. Alloyed nanoparticles were then synthesised due to their ability of being very good photoemitters. Finally core/shell/shell nanoparticles were synthesised as they had the ability of emitting in the NIR region. This thesis is split into five main chapters. The first chapter is a brief introduction to the field of nanomaterials, analysis techniques and current and possible future applications. Chapters 2, 3, and 4 contain the main research carried out with brief synthetic methods and detailed analysis and characterization. Chapter 5 contains detailed synthetic methods with experimental conditions and specific equipment used for this research.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-08-01T14:57:13Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação com a Data.pdf: 5044606 bytes, checksum: c09a234cd8ad3e6e1590e833910723e3 (MD5) / Made available in DSpace on 2017-08-01T14:57:13Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação com a Data.pdf: 5044606 bytes, checksum: c09a234cd8ad3e6e1590e833910723e3 (MD5) Previous issue date: 2017-03-28 / CNPQ / Inicialmente confirmamos a intensificação da luminescência em complexos de európio com ligantes não-iônicos mistos do tipo Eu(DBM)3(L, L’), onde DBM (1,3-difenilpropano-1,3diona) é o ligante iônico do tipo β-dicetonato e L são ligantes não-iônicos (DBSO (dibenzil sulfóxido), PTSO (ρ-toluil sulfóxido) e TPPO (óxido de trifenilfosfina)), quando comparados com complexos muito conhecidos do tipo Eu(DBM)3(L)2. A rota empregada no laboratório foi a partir da mesma metodologia de outros exemplos semelhantes de complexos mistos. Os rendimentos obtidos de cada etapa ficaram na faixa de 51-70%. Também, comprovamos experimentalmente que existe uma ordem ligantoquímica para os ligantes não-iônicos: TPPO>PTSO>DBSO>H2O. Esses dados foram corroborados a partir de cálculos teóricos do software MOPAC utilizando o modelo RM1 orbitais. As medidas de Arad obtidas para estes complexos fizeram a previsão da mesma conjectura usada anteriormente pelo nosso grupo de pesquisa: que o aumento da luminescência está relacionado com o aumento da assimetria dos complexos mistos sintetizados. Além disso, desenvolvemos uma nova metodologia de síntese, que denominamos síntese rápida (SR), para complexos do tipo Eu(β-dic)3(L)2 com diminuição no tempo de obtenção dos complexos puros (diminuição em 50% na média global) e aumento nos rendimentos globais de reação (aumento de 27% na média global). Este procedimento baseia-se na ordem de adição invertida dos ligantes (primeiramente não-iônicos e em seguida os iônicos) em relação à rota usualmente empregada na literatura. Sintetizamos também complexos de európio com ligantes iônicos mistos do tipo Eu(β’, β’’, β’’’)(TPPO)2 para comprovar que a assimetria de complexos com a utilização de ligantes iônicos também intensifica a luminescência. Os dados da luminescência obtidos comprovaram. Aperfeiçoamos a rota sintética anterior (SR) e aplicamos esta nova rota em complexos de európio que contêm ligantes iônicos mistos, realizando-a integralmente no balão de reação via One Pot. Isso proporcionou um menor tempo de reação, melhores rendimentos globais e redução na quantidade utilizada dos reagentes de partida. Foi possível também observar o efeito da triboluminescência em complexos mistos. Os complexos intermediários e finais obtidos foram caracterizados por Espectroscopia de Infravermelho, Espectroscopia de Ressonância Magnética Nuclear (RMN) de 1H, Espectroscopia de RMN de 19F, Espectroscopia de RMN de 31P, Espectrometria de Massas MALDI-TOF e Análise Elementar. Por fim, apresentamos rotas eficientes de sintetizar e de intensificar a luminescência em complexos de európio para várias aplicações em ciência dos materiais. / Initially we confirmed that the intensification of the luminescence of mixed europium complexes of the type Eu(DBM)3(L,L’), where DBM (1,3-diphenylpropane-1,3-dione) is the ionic ligand and L or L’ are the non-ionic ligands: DBSO (dibenzyl sulphoxide), PTSO (ptolyl sulphoxide) and TPPO (triphenylphosphine oxide) when compared with known complexes of the type Eu(DBM)3(L)2. They were all synthesized by the same synthetic route mostly used in the literature. The reaction yields obtained ranged from 51% to 70%. It is important to mention that it was experimentally proved that there is a chemical bond order for the non-ionic ligand to attach to the central atom, as follows: TPPO>PTSO>DBSO>H2O. In addition, theoretical calculations performed with the MOPAC software, using the RMI orbitals model comproved this same behavior. Another interesting result that we achieved was concerning the Arad data obtained from these mixed europium complexes, they were able to predict the same conjecture used previously and it was in agreement to the quantum yield data determined for the other mixed L,L’ complexes: luminescence increasesment can be directly related to the assymmetry of the ligands in the europium mixed complex. Furthermore, we developed a new synthetic route named Fast Synthesis (FS), to obtain complexes of the type Eu(β-dic)3(L)2. The application of this methodology brought great advantages: significant decrease in reaction time to obtain the pure complexes (in average 50% decrease in reaction time); increase the global reaction yield (in average 27% of reaction yield increase). This synthetic procedure is based on the inverted order of addition of the ligands to the coordination atom or else, firstly the non-ionic ligands are added, followed by the ionic ones when compared to the synthetic route commonly employed by the inorganic chemists. Using the FS methodology we prepared assymmetric europium complexes coordinated with different ionic ligands like, Eu(β’, β’’, β’’’)(TPPO)2, envisaging to comprove that structure assymmetry enhances luminescence. The data of quantum efficiency obtained were in accodance with previous luminescence results. Another important step was introduced to improve our FS route in obtaining europium complexes with mixed ionic ligands, this time performing the experiment via One Pot procedure. The results of the synthesis One Pot was astonishing: much less reaction time, much better yields and pronounced reduction on initial reagents quantities. Unexpectedly, it was possible to observe the triboluminencence phenomenon, when crystals of the complex Eu(DBM,BTFA,TTA)TPPO2 were frictioned with a spatula and luminescent glares of light appeared. All the complex intermediates and final ones had their structures characterized by IR Spectroscopy, NMR Spectroscopy of 1H, 19F and 31P; Mass Spectrometry MALDI-TOF and Elemental Analysis. To conclude, we have developed two new synthetic routes, synthesized 23 new complexes, including a new class of luminescente europium complexes of the type Eu(β’, β’’, β’’’)(TPPO)2 , opening a new branch for application on Science of Materials.

In this report we establish cyclohexasilane (CHS) as a reliable precursor for non-thermal plasma synthesis of high quality photoluminescent silicon nanocrystals (SiNCs). We demonstrate that this synthesis approach can produce high quality, size tunable silicon quantum dots with quantum yields exceeding 60% as synthesized (subsequent work in our group has measured over 70% quantum yield after density gradient ultracentrifugation size purification).After a brief background on non-thermal plasma synthesis, the characterization methods used in this study, and an overview of CHS, we report at length on our development of the apparatus used, and our exploration of the controllable processing parameters of the synthesis method. We describe our successes and challenges with size tuning, sample collection, and passivation. Finally, we discuss preliminary studies we performed to identify promising future research areas. Novel reactor designs, blue light passivation, and magnetic confinement of plasma are described briefly to entice future researchers.