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1	Investigation of the correlation between the structure and fluorescence properties of semiconductor quantum dots Lin, Wen-Bin 05 August 2005 (has links) Quantum confinement structures are attractive for their unconventional size dependence of the optical and electrical properties. There are still challenges to control the size uniformity for the application. The thesis studies the correlation between the size distribution of CdSe/ZnS quantum dots (QD), and the fluorescence properties to understand the shape and size influences of their fluorescence properties. Results from the transmission electron microscopy (TEM) provide the structure and size distribution of the samples. Excitation dependent fluorescence spectra as well as the PL excitation at various emission wavelength confirm that the inhomogeneous distribution of the samples. The results show that the samples are mostly composed of QDs with quasi-spherical structure (aspect ration between 1.1 and 1.5 ;76%) and spherical structure ( aspect ratio < 1.1; 12.8%). In addition, it exhibits a distribution of the long axis of 5.4nm¡Ó1.3nm. By measuring the fluorescence spectra of individual QDs, we construct the distribution. The peaks of the fluorescence spectra show a Gaussian distribution with center at 615.7 nm and width 13.8 nm. In addition, the spectra exhibit a width of 19.7¡Ó8.0nm. This is consistent with the ensemble measurement of the fluorescence from a solution (peak at 616 nm, and width 25 nm). Results of the fluorescence lifetime on the individual QDs indicate the lifetime distribution of 10.3¡Ó5.6ns. Further analyze the size distribution by constructing the size ¡V fluorescence spectrum relationship. By analysis the distribution of the fluorescence spectra, it results the corresponding size distribution of width 0.7 nm. This is much narrower than the size distribution of the long axis measured by TEM, but is more consistent with the corrected size distribution considering the short axis contribution. We conclude that the deviation results from the non-spherical structures in the samples. quantum dot CdSe/ZnS nanocrystal
2	Interação entre proteínas fluorescentes e nanocristais de CdSe/ZnS / Interaction between fluorescent proteins and CdSe/ZnS nanocrystals Hering, Vitor Renaux 01 June 2007 (has links) Foram utilizadas proteínas da famÌlia das GFPs e nanocristais fluorescentes de CdSe/ZnS para caracterização da interação e verificação de transferência de energia por ressonância (FRET) entre estes compostos. Formou-se dois pares doador-receptor onde ora uma proteína figurava como doadora, ora um nanocristal ocupava este papel. Verificou-se que, em ambos os casos, o doador sofre supressão da fluorescência após a formação de complexo com o receptor, complexo este motivado por interação eletrostática e dependente de pH. Foi possível comprovar, através da observação de emissão sensitizada e redução da anisotropia, que entre o par formado por nanocristal com emissão no verde e proteína HcRed1 como receptora, de fato ocorre FRET. As distâncias aparentes entre doador e receptor foram determinadas a partir da eficiência da supressão da fluorescência do doador e da distância de Förster. As distâncias assim obtidas são compatíveis com as dimensões das proteínas e dos nanocristais / Proteins belonging to the GFP family were used to characterize their interaction with fluorescent CdSe/ZnS nanocrystals and to verify the occurrence of resonance energy transfer (FRET) among these elements. Two donor-acceptor pairs were established, one having a protein as donor and the other having a nanocrystal as donor. In both cases the donor suffers quenching of its fluorescence after the formation of a complex with the acceptor. The complex formation is dependent on pH and is due to electrostatic interaction. It was possible to prove the occurrence of FRET between CdSe/ZnS nanocrystals emitting green fluorescence as donors and the protein HcRed1 as acceptor, through the detection of sensitized emission and anisotropy reduction. Apparent donor-acceptor distances were determined from efficiency measurements and Förster distances. The obtained distances agreed with the protein and nanocrystal dimensions CdSe/ZnS CdSe/ZnS Fluorescent proteins FRET FRET GFP GFP HcRed1 HcRed1 Nanocristais Nanocrystals ProteÌnas fluorescentes
3	Interação entre proteínas fluorescentes e nanocristais de CdSe/ZnS / Interaction between fluorescent proteins and CdSe/ZnS nanocrystals Vitor Renaux Hering 01 June 2007 (has links) Foram utilizadas proteínas da famÌlia das GFPs e nanocristais fluorescentes de CdSe/ZnS para caracterização da interação e verificação de transferência de energia por ressonância (FRET) entre estes compostos. Formou-se dois pares doador-receptor onde ora uma proteína figurava como doadora, ora um nanocristal ocupava este papel. Verificou-se que, em ambos os casos, o doador sofre supressão da fluorescência após a formação de complexo com o receptor, complexo este motivado por interação eletrostática e dependente de pH. Foi possível comprovar, através da observação de emissão sensitizada e redução da anisotropia, que entre o par formado por nanocristal com emissão no verde e proteína HcRed1 como receptora, de fato ocorre FRET. As distâncias aparentes entre doador e receptor foram determinadas a partir da eficiência da supressão da fluorescência do doador e da distância de Förster. As distâncias assim obtidas são compatíveis com as dimensões das proteínas e dos nanocristais / Proteins belonging to the GFP family were used to characterize their interaction with fluorescent CdSe/ZnS nanocrystals and to verify the occurrence of resonance energy transfer (FRET) among these elements. Two donor-acceptor pairs were established, one having a protein as donor and the other having a nanocrystal as donor. In both cases the donor suffers quenching of its fluorescence after the formation of a complex with the acceptor. The complex formation is dependent on pH and is due to electrostatic interaction. It was possible to prove the occurrence of FRET between CdSe/ZnS nanocrystals emitting green fluorescence as donors and the protein HcRed1 as acceptor, through the detection of sensitized emission and anisotropy reduction. Apparent donor-acceptor distances were determined from efficiency measurements and Förster distances. The obtained distances agreed with the protein and nanocrystal dimensions CdSe/ZnS FRET GFP HcRed1 Nanocristais ProteÌnas fluorescentes CdSe/ZnS Fluorescent proteins FRET GFP HcRed1 Nanocrystals
4	Síntese de nanoestruturas core/shell de Co/Au magnetoplasmônica e pontos quânticos de CdSe/ZnS / Syntheses of Core/Shell Nanostructures of Magnetoplasmonic Co/Au and CdSe/ZnS quantum dots Souza Junior, João Batista 28 April 2017 (has links) Nanomateriais apresentam propriedades ajustáveis pelo seu tamanho e forma, como o fenômeno de superparamagnetismo em nanopartículas magnéticas ou o confinamento quântico dos portadores de carga em pontos quânticos (quantum dots). Assim, a síntese de nanopartículas esféricas monodispersas torna-se um fator extremamente importante, haja visto que tais propriedades podem ser ajustáveis para diferentes aplicações na área de tecnologia e biomedicina. Nanopartículas magnéticas e quantum dots podem ser apontados como promissores materiais para diagnóstico e terapia de neoplasias (câncer), e o desenvolvimento desses sistemas busca, atualmente, intensificar a magnetização e a eficiência de emissão, respectivamente, relativo às propriedades magnéticas e ópticas, além de outros requisitos. Neste trabalho, nanopartículas esféricas de cobalto metálico foram sintetizadas com diâmetro médio de 5,3 nm e desvio padrão de 0,4 nm, distribuição de tamanhos lognormal. A equação de Langevin modificada pelo modelo de partículas interagentes foi utilizada no ajuste da curva de magnetização M(H) para obtenção do diâmetro magnético médio e desvio padrão, 4,7 nm e 1,0 nm, respectivamente. Comparando os dois diâmetros, encontra-se uma camada morta de magnetização de aproximadamente 3,0 Å a qual, praticamente, não contribui para a magnetização da amostra, sendo a magnetização de saturação de 125 emu g-1. Nanoestruturas core/shell de Co/Au apresentaram a propriedade de ressonância plamon de superfície, uma propriedade adicional também desejada para aplicações biomédicas, sendo este sistema denominado magnetoplasmônico. Quantum dots de CdSe foram sintetizados como elevado controle de tamanho e forma. Utilizando rotas de síntese diferentes dos clássicos procedimentos denominados TOP-TOPO, e dióxido de selênio como precursor, estudos mostraram que na presença de um agente redutor no meio de reação e do solvente 1-octadeceno, as amostras apresentaram melhores propriedades óticas. A estrutura cristalina das amostras de CdSe corresponde à formação da fase blenda de zinco, diferentemente das sínteses TOP-TOPO que levam à formação da fase hexagonal wurtzita. A cinética de crescimento dos quantum dots de CdSe também foram avaliadas através de alíquotas retiras com o tempo de reação mostrando um crescimento exponencial do diâmetro das partículas, como previsto pelas teorias de nucleação e crescimento. Estudos por microscopia de fluorescência mostraram que os quantum dots apresentaram o comportamento de intermitência de fluorescência relatado na literatura como um dos fatores que levam a uma diminuição do rendimento quântico de fluorescência. Nanoestruturas core/shell de CdSe/ZnS foram obtidas com elevado controle da espessura da camada de recobrimento e a intensificação das propriedades de fotoluminescência foram mostradas. Os objetivos do trabalho foram alcançados com sucesso, onde foi possível observar a estabilização e a intensificação da magnetização da fase de cobalto metálico, pouco relatado na literatura. Ainda, foi possível conferir maior estabilidade química, versatilidade de funcionalização da superfície e uma segunda propriedade de ressonância plasmônica com o recobrimento com ouro, sem grande prejuízo da propriedade magnética. Em relação aos sistemas ópticos, os semicondutores de CdSe foram obtidos por nova rota de síntese com expressivo controle de tamanho e forma, recobertos com ZnS intensificando as propriedades ópticas do sistema.  / Nanomaterials properties are size- and shape-controlled, such as the superparamagnetism phenomenon of magnetic nanoparticles or the quantum confinement of charge carriers of quantum dots. Therefore, synthesis of monodisperse spherical nanoparticles became extremely important over the past few deacades, since nanoparticles can be used for plenty of applications in technology and biomedicine. Magnetic nanoparticles and quantum dots are promising materials for diagnosis and therapy of cancer. Spherical nanoparticles of metallic cobalt were synthesized with mean diameter of 5,3 nm and standard deviation of 0,4 nm, lognormal distribution. A modified Langevin equation using the interacting superparamagnetic model was used to fit magnetization curves obtaining the mean magnetic diameter and standard deviation, 4,7 nm and 1,0 nm, respectively. The difference between these two diameters was assigned to the magnetic dead layer (∼3.0 Å), which does not contribute to the sample magnetization, being the saturation magnetization of cobalt nanoparticles around 125 emu g-1. Co/Au core/shell nanostructures were synthesized and the surface plasmon ressonance property was observed, an additional property also desired for biomedical applications, being the Co/Au core/shell system called magnetoplasmonic. CdSe quantum dots were synthesized with high size- and shape-controlled. Using different synthetic routes from the classic TOP-TOPO synthesis, and selenium dioxide as a precursor, the results show that and reducing agent is necessary and 1-octadecene solvent leads to better optical properties. CdSe samples showed a zinc blend (cubic phase) crystal structure, different from TOP-TOPO syntheses that leads to wurtzite structure (hexagonal phase). The growth kinetics of CdSe particles were also evaluated through aliquots from reaction showing exponential growth of particles diameter, as predicted on the theory of nucleation and growth. Fluorescence microscopy studies showed that quantum dots exhibited fluorescence intermittence behavior already reported in the literature as one fo the reasons for the quantum yield decrease. CdSe/ZnS core/shell nanostructures were obtained with high control of the coating layer thickness and the increase of the photoluminescence properties were shown. Co/Au Magnetoplasmonic Nanostructures Core/Shell Nanostructures Magnetic Nanoparticles Nanoestruturas Core/Shell Nanoestruturas magnetoplasmônica Co/Au Nanopartículas Magnéticas Quantum Dots CdSe/ZnS Quantum Dots CdSe/ZnS Superparamagnetism Superparamagnetismo
5	Enregistrement et analyses physico-chimiques de réseaux dans des matériaux composites polymères-points quantiques Barichard, Anne 05 July 2011 (has links) Ce travail de thèse a été consacré à la photostructuration d’une matrice polymère de type acrylate contenant des points quantiques CdSe/ZnS (QDs) par l’enregistrement de réseaux. La diffusion photoinduite des nanocristaux semi-conducteurs a tout d’abord été mise en évidence par l’utilisation d’un montage permettant d’irradier sur une seule ligne, et par l’émission de fluorescence des QDs utilisée ici comme sonde de déplacement. Ensuite, pour comprendre l’augmentation de la modulation d’indice de réfraction, et par conséquent du rendement de diffraction des réseaux enregistrés dans ces matériaux composites, nous avons mis en place une approche physico-chimique. Celle-ci nous a permis de corréler les modifications chimiques et les propriétés physiques du réseau. En effet, nous avons montré que l’ajout de points quantiques influence la cinétique de polymérisation ; la vitesse de consommation du photosensibilisateur et de conversion des monomères diminuent. Cette diminution permet une meilleure diffusion des espèces au sein de la matrice. Donc, le ralentissement de la cinétique de photopolymérisation et la répartition spatiale des QDs contribuent à un accroissement de la modulation d’indice de réfraction des réseaux enregistrés. / This work is devoted to the photostructuration of an acrylate polymer matrix with dispersed CdSe/ZnS quantum dots (QDs) upon grating exposure. The photo-induced diffusion of semiconductor nanocrystals is proved by the use of a "one line irradiation" set up and by the emission of the QDs fluorescence, used here as a probe of displacement. Then, in order to understand the increase of the refractive index modulation, and so, of the diffraction efficiency of the recorded patterns in the composite materials, we apply a physico-chemical approach. This one allows correlating the chemical modifications to the physical properties of the gratings. Indeed, we show that the addition of QDs influences the kinetics of polymerization ; the rate of the photo-initiator consumption, and that of the monomer conversion decrease. This decrease favors the diffusion ofthe species inside the matrix. Therefore, the slowing down of the kinetics of the photopolymerization and the spatial distribution of QDs contribute to the enhancement of the refractive index modulation of the recorded gratings. Holographie Points quantiques CdSe/ZnS Matériau composite Cinétique Photopolymérisation Modulation d’indice de réfraction Holography Quantum dots CdSe/ZnS Composite material Kinetics Photopolymerization Refractive index modulation
6	Síntese de nanoestruturas core/shell de Co/Au magnetoplasmônica e pontos quânticos de CdSe/ZnS / Syntheses of Core/Shell Nanostructures of Magnetoplasmonic Co/Au and CdSe/ZnS quantum dots João Batista Souza Junior 28 April 2017 (has links) Nanomateriais apresentam propriedades ajustáveis pelo seu tamanho e forma, como o fenômeno de superparamagnetismo em nanopartículas magnéticas ou o confinamento quântico dos portadores de carga em pontos quânticos (quantum dots). Assim, a síntese de nanopartículas esféricas monodispersas torna-se um fator extremamente importante, haja visto que tais propriedades podem ser ajustáveis para diferentes aplicações na área de tecnologia e biomedicina. Nanopartículas magnéticas e quantum dots podem ser apontados como promissores materiais para diagnóstico e terapia de neoplasias (câncer), e o desenvolvimento desses sistemas busca, atualmente, intensificar a magnetização e a eficiência de emissão, respectivamente, relativo às propriedades magnéticas e ópticas, além de outros requisitos. Neste trabalho, nanopartículas esféricas de cobalto metálico foram sintetizadas com diâmetro médio de 5,3 nm e desvio padrão de 0,4 nm, distribuição de tamanhos lognormal. A equação de Langevin modificada pelo modelo de partículas interagentes foi utilizada no ajuste da curva de magnetização M(H) para obtenção do diâmetro magnético médio e desvio padrão, 4,7 nm e 1,0 nm, respectivamente. Comparando os dois diâmetros, encontra-se uma camada morta de magnetização de aproximadamente 3,0 Å a qual, praticamente, não contribui para a magnetização da amostra, sendo a magnetização de saturação de 125 emu g-1. Nanoestruturas core/shell de Co/Au apresentaram a propriedade de ressonância plamon de superfície, uma propriedade adicional também desejada para aplicações biomédicas, sendo este sistema denominado magnetoplasmônico. Quantum dots de CdSe foram sintetizados como elevado controle de tamanho e forma. Utilizando rotas de síntese diferentes dos clássicos procedimentos denominados TOP-TOPO, e dióxido de selênio como precursor, estudos mostraram que na presença de um agente redutor no meio de reação e do solvente 1-octadeceno, as amostras apresentaram melhores propriedades óticas. A estrutura cristalina das amostras de CdSe corresponde à formação da fase blenda de zinco, diferentemente das sínteses TOP-TOPO que levam à formação da fase hexagonal wurtzita. A cinética de crescimento dos quantum dots de CdSe também foram avaliadas através de alíquotas retiras com o tempo de reação mostrando um crescimento exponencial do diâmetro das partículas, como previsto pelas teorias de nucleação e crescimento. Estudos por microscopia de fluorescência mostraram que os quantum dots apresentaram o comportamento de intermitência de fluorescência relatado na literatura como um dos fatores que levam a uma diminuição do rendimento quântico de fluorescência. Nanoestruturas core/shell de CdSe/ZnS foram obtidas com elevado controle da espessura da camada de recobrimento e a intensificação das propriedades de fotoluminescência foram mostradas. Os objetivos do trabalho foram alcançados com sucesso, onde foi possível observar a estabilização e a intensificação da magnetização da fase de cobalto metálico, pouco relatado na literatura. Ainda, foi possível conferir maior estabilidade química, versatilidade de funcionalização da superfície e uma segunda propriedade de ressonância plasmônica com o recobrimento com ouro, sem grande prejuízo da propriedade magnética. Em relação aos sistemas ópticos, os semicondutores de CdSe foram obtidos por nova rota de síntese com expressivo controle de tamanho e forma, recobertos com ZnS intensificando as propriedades ópticas do sistema.  / Nanomaterials properties are size- and shape-controlled, such as the superparamagnetism phenomenon of magnetic nanoparticles or the quantum confinement of charge carriers of quantum dots. Therefore, synthesis of monodisperse spherical nanoparticles became extremely important over the past few deacades, since nanoparticles can be used for plenty of applications in technology and biomedicine. Magnetic nanoparticles and quantum dots are promising materials for diagnosis and therapy of cancer. Spherical nanoparticles of metallic cobalt were synthesized with mean diameter of 5,3 nm and standard deviation of 0,4 nm, lognormal distribution. A modified Langevin equation using the interacting superparamagnetic model was used to fit magnetization curves obtaining the mean magnetic diameter and standard deviation, 4,7 nm and 1,0 nm, respectively. The difference between these two diameters was assigned to the magnetic dead layer (∼3.0 Å), which does not contribute to the sample magnetization, being the saturation magnetization of cobalt nanoparticles around 125 emu g-1. Co/Au core/shell nanostructures were synthesized and the surface plasmon ressonance property was observed, an additional property also desired for biomedical applications, being the Co/Au core/shell system called magnetoplasmonic. CdSe quantum dots were synthesized with high size- and shape-controlled. Using different synthetic routes from the classic TOP-TOPO synthesis, and selenium dioxide as a precursor, the results show that and reducing agent is necessary and 1-octadecene solvent leads to better optical properties. CdSe samples showed a zinc blend (cubic phase) crystal structure, different from TOP-TOPO syntheses that leads to wurtzite structure (hexagonal phase). The growth kinetics of CdSe particles were also evaluated through aliquots from reaction showing exponential growth of particles diameter, as predicted on the theory of nucleation and growth. Fluorescence microscopy studies showed that quantum dots exhibited fluorescence intermittence behavior already reported in the literature as one fo the reasons for the quantum yield decrease. CdSe/ZnS core/shell nanostructures were obtained with high control of the coating layer thickness and the increase of the photoluminescence properties were shown. Nanoestruturas Core/Shell Nanoestruturas magnetoplasmônica Co/Au Nanopartículas Magnéticas Quantum Dots CdSe/ZnS Superparamagnetismo Co/Au Magnetoplasmonic Nanostructures Core/Shell Nanostructures Magnetic Nanoparticles Quantum Dots CdSe/ZnS Superparamagnetism
7	Sensores fotoeletroquímicos explorando o tetracianoetileneto de lítio (LiTCNE) na determinação do antioxidante terc-butil hidroquinona (TBHQ) / Photoelectrochemical sensors exploring lithium tetracyanoethylene (LiTCNE) for determination of tert-butyl hydroquinone (TBHQ) antioxidant MONTEIRO, Thatyara Oliveira 01 September 2017 (has links) Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-10-02T19:59:47Z No. of bitstreams: 1 ThatyaraMonteiro.pdf: 3528798 bytes, checksum: 12d3da9115c45896b4f14c67dbe3d20e (MD5) / Made available in DSpace on 2017-10-02T19:59:47Z (GMT). No. of bitstreams: 1 ThatyaraMonteiro.pdf: 3528798 bytes, checksum: 12d3da9115c45896b4f14c67dbe3d20e (MD5) Previous issue date: 2017-09-01 / Two novel and pioneering photoelectrochemical sensors were developed for determination of tert-butyl hydroquinone (TBHQ) in biodiesel and edible oil samples. The former based on composite formed by TiO2 nanoparticles and lithium tetracyanethylene (LiTCNE), and the last based on the sensitization of CdSe/ZnS quantum dots with LiTCNE. In both cases, indium tin oxide (ITO) was used as the work electrode surface. The LiTCNE/TiO2/ITO sensor showed a TBHQ photocurrent about 28-fold higher than the TiO2 sensor. The same was observed for the CdSe/ZnS/LiTCNE/ITO sensor, which presented a photocurrent for TBHQ about 13-fold higher than that presented by the electrode modified with CdSe/ZnS. Both developed sensors showed lower resistance to charge transfer than their non-sensitized components. They also demonstrated high selectivity to TBHQ, with high photocurrent for this compound in comparison to photocurrent responses to other phenolic antioxidants. The experimental conditions optimized for both sensors were: 0.1 mol L-1 of phosphate buffer solution pH 7.0 and applied potential to the working electrode of 450 mV, for the LiTCNE/TiO2/ITO sensor, and 0.1 mol L-1 of phosphate buffer solution pH 6.0, and potential of 400 mV for the CdSe/ZnS/LiTCNE/ITO sensor. In these conditions, the sensors presented a linear range of TBHQ response between 0.4 and 500 μmol L-1 for LiTCNE/TiO2/ITO sensor and between 0.6 and 250 μmol L-1 for the CdSe/ZnS/LiTCNE/ITO sensor, with limits of detection of 0.10 and 0.21 μmol L-1, respectively. The LiTCNE/TiO2/ITO sensor was applied in biodiesel samples for determination of TBHQ using standard addition method, showing recovery values between 96.8 and 98.2%. The CdSe/ZnS/LiTCNE/ITO sensor was applied in edible oil samples to detect TBHQ using an external calibration method, with recovery values between 98.25 and 99.83%. The photoelectrochemical sensors were successfully used to determine the TBHQ antioxidant in real samples of biodiesel and vegetable oil. / Dois novos e pioneiros sensores fotoeletroquímicos foram desenvolvidos para determinação de tert-butil hidroquinona (TBHQ) em amostras de biodiesel e de óleo comestível. O primeiro baseado no compósito formado por nanopartículas de TiO2 e tetracianoetileneto de lítio (LiTCNE), e o segundo baseado na sensibilização de quantum dots CdSe/ZnS com o LiTCNE. Em ambos os casos utilizou-se como eletrodo de trabalho o óxido de índio e estanho (ITO) como superfície eletródica. O sensor à base de LiTCNE/TiO2/ITO apresentou uma fotocorrente para o TBHQ cerca de 28 vezes mais elevada que o sensor à base de TiO2. O mesmo foi observado para o sensor à base de CdSe/ZnS/LiTCNE/ITO, que apresentou fotocorrente para o TBHQ cerca de 13 vezes maior do que à apresentada pelo eletrodo modificado com CdSe/ZnS. Ambos os sensores desenvolvidos apresentaram baixa resistência à transferência de carga em comparação a seus componentes não sensibilizados. Também demonstraram grande seletividade ao TBHQ, com alta fotocorrente para esse composto em comparação às respostas de fotocorrente para outros antioxidantes fenólicos. As condições experimentais otimizadas para ambos os sensores desenvolvidos foram, respectivamente: 0,1 mol L-1 de solução tampão fosfato pH 7,0 e potencial aplicado ao eletrodo de trabalho de 450 mV, para o sensor LiTCNE/TiO2/ITO, e 0,1 mol L-1 de solução tampão fosfato pH 6,0, e potencial de 400 mV, para o sensor CdSe/ZnS/LiTCNE/ITO. Nessas condições, os sensores apresentaram faixa linear de resposta de TBHQ entre 0,4 a 500 µmol L-1 para sensor LiTCNE/TiO2/ITO e entre 0,6 a 250 µmol L-1 para o sensor CdSe/ZnS/LiTCNE/ITO, apresentando limites de detecção de 0,10 e 0,21 µmol L-1 , respectivamente. O sensor LiTCNE/TiO2/ITO foi aplicado em amostras de biodiesel para determinação de TBHQ usando método de adição de padrão, mostrando valores de recuperação entre 96,8 e 98,2%. Já o sensor CdSe/ZnS/LiTCNE/ITO foi aplicado em amostras de óleo comestível para detecção de TBHQ usando método de calibração externa, com valores de recuperação entre 98,25 e 99,83%. Os sensores fotoeletroquímicos foram empregados com sucesso para determinação de antioxidante TBHQ em amostras reais de biodiesel e óleo vegetal. Detecção de TBHQ Sensor fotoeletroquímico Antioxidante terc-butil hidroquinona LiTCNE TiO2 Quantum dots CdSe/ZnS Biodiesel Óleo comestível TBHQ detection Photoelectrochemical sensor Edible oil CdSe/ZnS quantum dots Química Analítica
8	Photoinduced hole trapping in single semiconductor quantum dots at specific sites at silicon oxide interfaces Krasselt, Cornelius, Schuster, Jörg, von Borczyskowski, Christian 23 September 2013 (has links) (PDF) Blinking dynamics of CdSe/ZnS semiconductor quantum dots (QD) are characterized by (truncated) power law distributions exhibiting a wide dynamic range in probability densities and time scales both for off- and on-times. QDs were immobilized on silicon oxide surfaces with varying grades of hydroxylation and silanol group densities, respectively. While the off-time distributions remain unaffected by changing the surface properties of the silicon oxide, a deviation from the power law dependence is observed in the case of on-times. This deviation can be described by a superimposed single exponential function and depends critically on the local silanol group density. Furthermore, QDs in close proximity to silanol groups exhibit both high average photoluminescence intensities and large on-time fractions. The effect is attributed to an interaction between the QDs and the silanol groups which creates new or deepens already existing hole trap states within the ZnS shell. This interpretation is consistent with the trapping model introduced by Verberk et al. (R. Verberk, A. M. van Oijen and M. Orrit, Phys. Rev. B, 2002, 66, 233202). Lumineszenz-Unterbrechung Blinking Halbleiter Quantenpunkt Nanopartikel CdSe/ZnS Einzelteilchen-Detektion Siliziumoxid trap Zustände Loch trapping Photoluminescence intermittency semiconductor quantum dots CdSe/ZnS single particle detection silicon oxide trap states hole trapping ddc:539 Halbleiter Quantenpunkt Nanopartikel
9	Bezkontaktní měření teploty pomocí luminiscenčních materiálů / Noncontact temperature measurements using luminescent materials Jedlička, Jindřich January 2020 (has links) This diploma thesis deals with noncontact temperature measurement using luminescent materials. In the theoretical part of the thesis, luminescent materials were selected on the basis of a literature review with respect to sensitivity and operating temperature range. In the experimental part of the thesis, photoluminescence of CdSe/ZnS and GaAs quantum dots for various temperatures was measured and the relative change of luminescence parameters such as emission peak position, intensity, intensity ratio of two emission peaks, and lifetime of luminescence were determined from the measurements in agreement with expectations according to the literature. Achieving high spatial resolution would be made possible by measuring cathodoluminescence, where the luminescence spectra are obtained with an order of magnitude higher spatial resolution. These measurements and the influence of electron beam on the luminescence quality of selected materials will be subject of further experimental study.
10	Synthesis and Characterization of CdSe/ZnS Core/Shell Quantum Dot Sensitized PCPDTBT-P3HT:PCBM Organic Photovoltaics Bump, Buddy J 01 July 2014 (has links) Durable, cheap, and lightweight polymer based solar cells are needed, if simply to meet the demand for decentralized electrical power production in traditionally “off-grid” areas. Using a blend of Poly(3-hexylthiophene-2,5-diyl) (P3HT), Phenyl-C61-butyric acid methyl ester (PCBM), and the low band-gap polymer Poly[2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), we have fabricated devices with a wide spectral response and 3% power conversion efficiency in AM 1.5 conditions; however, this thin film system exhibits only 0.43 optical density at 500 nm. To improve the performance of this polymer blend photovoltaic, we aim to increase absorption by adding CdSe(ZnS) core (shell) quantum dots. Four groups of devices are fabricated: a control group with an active polymer layer of 16 mg/mL P3HT, 16 mg/mL PCBM, and 4 mg/mL PCPDTBT; and three groups with dispersed quantum dots at 4 mg/ml, 1 mg/mL, and 0.25 mg/mL. The (CdSe)ZnS quantum dots are coated with octadecylamine ligands and have a peak absorbance at 560 nm and peak emission at 577 nm. The active layer was dissolved in chlorobenzene solvent and spun on glass substrates, patterned with indium tin oxide. The devices were then annealed for fifteen minutes at 110° C, 140° C, and 170° C. Current-voltage characteristic curves v and optical density data were taken before and after the anneal step. Finally, surface characterization was conducted with atomic force microscopy and electrostatic force microscopy. When compared to the control, the sensitized devices exhibited increased absorption and depressed electrical performance with increasing quantum dot loading. The surface morphology, both electrical and physical, showed deviation from the typical values and patterns shown by the control that increased with quantum dot loading. When the degrading electrical characteristics, increasing optical absorbance, and surface changes, are considered together, it becomes likely that the quantum dots interact in a significant manner with the morphology of the P3HT phase, which leads to an overall decrease in performance. P3HT PCBM OPVs PCPDTBT low band gap polymer CdSe(ZnS) quantum dots and wide spectral response Polymer and Organic Materials Semiconductor and Optical Materials

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