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The use of solar panels for the purpose of converting solar energy into electrical energy has been increasingly common in the community, where the vast majority of these panels are produced from inorganic materials, especially silicon (Si). In recent decades, many researchers have been analyzing organic and hybrid materials in order to apply them to photovoltaic devices. The use of organic and hybrid materials in devices is advantageous due to some factors, such as: low production cost, variety of materials available, production of flexible devices. A fundamental analysis for any photovoltaic device is the external quantum efficiency measure (EQE). This technique correlates the number of incident photons with the number of electrons generated, making it possible to know in which region of the electromagnetic spectrum the photovoltaic device is more efficient. This work aims to apply the external quantum efficiency characterization technique for the evaluation of different types of photovoltaic devices in terms of their stability

Abstract Understanding chemical reactions in bacterial cellulose (BC) films is important to control the insertion of biomolecules that can improve their biomedical properties. Diphenyltetrazole molecules are able to react with tiols under UV irradiation and has been useful for immobilize proteins on different materials. In this work, we show the functionalization of a BC film with diphenyltetrazole and subsequent attempts of conjugation of the bovine serum albumin (BSA) to it. Diphenyltetrazole was synthesized in two steps, and functionalization of it with BC was carried out under ultrasound irradiation. Spectroscopic analysis of the film by UV–Vis and FTIR confirmed the success of the reaction. Attempts to conjugate BSA to the modified cellulose film by photoclick reaction failed under these conditions. Although this methodology is important in the conjugation of biomolecules, we understand that its application in cellulosic materials in heterogeneous phase is disadvantaged due to the half-life of the unstable intermediate and the biomolecule's access to it.

In order to study the optical properties of TFB polymer and its blend with P3HT polymer, absorption and photoluminescence (PL) measurements were performed for both polymers, and for a blend, TFB: P3HT (95:05), deposited on glass slides using the spin coating technique. Different solvents were used to prepare the samples in order to compare the effects that they might have on the emission and energy transfer between the polymers. Decay time measurements were performed, to find out if this parameter changes in the TFB prepared with different solvents, and also in the presence of P3HT. The photoluminescence measurements of the polymers show no change in the emission of these polymers as we change the solvents used in the preparation of the solutions. However, for the blend there is a change in energy transfer between the polymers depending on the solvent, which shifts the emission color of the sample for the blue or red. On the photoluminescence spectra of the blend an emission in 575 nm, which did not appear in the TFB and P3HT samples is observed. From the decay time measurements, we observed that the 575 nm emission has a long decay time, compatible with the emission by isolated molecules.

Recent advances in the production and development of two-dimensional transition metal dichalcogenides (2D TMDs) allow applications of these materials, with a structure similar to that of graphene, in a series of devices as promising technologies for optoelectronic applications. In this work, molybdenum disulfide (MoS2) nanostructures were grown directly on paper substrates through a microwave-assisted hydrothermal synthesis. The synthesized samples were subjected to morphological, structural, and optical analysis, using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman. The variation of synthesis parameters, as temperature and synthesis time, allowed the manipulation of these nanostructures during the growth process, with alteration of the metallic (1T) and semiconductor (2H) phases. By using this synthesis method, two-dimensional MoS2 nanostructures were directly grown on paper substrates. The MoS2 nanostructures were used as the active layer, to produce low-cost near-infrared photodetectors. The set of results indicates that the interdigital MoS2 photodetector with the best characteristics (responsivity of 290 mA/W, detectivity of 1.8 × 109 Jones and external quantum efficiency of 37%) was obtained using photoactive MoS2 nanosheets synthesized at 200 °C for 120 min.

A procura de produtos ambientalmente amigáveis, com obtenção a partir de fontes facilmente renováveis e de fácil acesso, menor custo, biodegradáveis, menos agressivos à saúde humana, entre outros, levou ao desenvolvimento de tecnologias empregando corantes naturais. Neste trabalho desenvolve-se uma breve revisão sobre corantes naturais, classificação e procedência, suas propriedades químicas e estruturais e discute-se a aplicação destes corantes em dispositivos como células solares - OPVCs (Organic Photovoltaic Cells), células solares sensibilizadas por corante –DSSCs (Dye Sensitized Solar Cells) e diodos emissores de luz – OLEDs (Organic Light Emitters Diodes) entre várias outras aplicações.

In this work was synthesized electrochemically the poly(3-methylthiophene) (P3MT) on transparent conductive substrates of F-doped tin oxide (FTO), using as supporting electrolyte Et4NBF4 or LiClO4 in acetonitrile. To dedope the material, the samples were reduced electrochemically and chemically (in NH4OH solution). The films were characterized by electron paramagnetic resonance spectroscopy (EPR) and infrared spectroscopy (FTIR) and their optical properties examined by ultraviolet-visible absorption spectroscopy (UV-Vis) and photoluminescence (PL). Scanning electron microscopy (SEM) images of the first synthesized samples were performed to verify the degree of homogeneity of them. The FTIR spectra show the characteristic features of P3MT and, together with the results of EPR, allowed to evaluate the charge carriers and to identify benzoid and quinoid structures in the formation of chains. The UV-Vis absorption spectra helped to obtain the average gap energy of P3MT presenting the π-π* transition band and a bipolaron band. In the PL spectra, with variation of excitation power, studies were performed through the fit with Gaussian functions, given the strong probability of the existence of two distinct contributions in the formation of the emission spectra. These two contributions were assigned to the emission of mixed chains (Gaussian centered at higher energy) and emission of benzoid chains (Gaussian of lower energy) in the formed polymeric material.

Although nowadays light sources such as LASERs (Light Amplification by Stimulated Emission of Radiation) and LEDs (Light Emitting Diodes) are largely used in several therapeutic areas, the scientific basis of their effects on biological systems still is relatively unknown by the academic community. In this study, a brief revision about effects of light on biological systems is presented. Low power light sources such as LEDs may be used as an alternative therapeutic method or be used associated to the conventional methods, having the advantage of being a low cost method and of proven efficiency in the treatment of ulcers and other diseases.

The electrical and optical properties of non-doped and Te doped 6.5 periods AlGaAsSb/AlAsSb Bragg mirrors on InP grown by MBE with different types of interfaces between ternary and quaternary layers are reported. The techniques employed were photoluminescence, refectivity and IxV measurements. The digital alloy gradient interface seems to be the best alternative to optimize conduction without significant refectivity losses.

We present a study on the optical properties of thin flms of poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) produced at a concentration of 10 mg/ml xylene. The solution was deposited onto glass substrates by the spin-coating technique at different rotational speeds (300, 1000 and 4000 rpm). We study the effect of rotational speeds on the sample at 300 K, by analyzing the photoluminescence (PL) spectra at different points of the polymeric flm. We also analyze the effects of the excitation power on the optical behavior of MEH-PPV at 300 K. At low temperatures the PL spectra of sample A1000 (1000 rpm) show a narrow peak for the electronic transition and a series of vibronic sidebands which reveal the electron coupling with two different vibronic modes. In the temperature range of 130 K to 290 K, we analyze systematically the transition lineshapes in the optical spectra using Gaussian curves.

Light-emitting diodes (LEDs) with different wavelengths are used as photorefectance light pump sources. Photorefectance spectra of bulk semiconductors of GaAs and GaAs/InGaP and GaAsSbN/GaAs heterostructures prepared on GaAs substrates were investigated, using blue, green, orange and red LEDs, in comparison with spectra obtained with the use of Ar and He-Ne lasers, using a conventional technique. Results show the possibility of using LEDs as pump light sources in photorefectance measurements.

Photoluminescence is one of the most used spectroscopy techniques for the study of the optical properties of semiconducting materials and heterostructures. In this work the potentiality of this technique is explored through the investigation and characterization of structural imperfections originated from fluctuations in the chemical composition of ternary and quaternary alloys, from interface roughnesses, and from unintentional compounds formed by the chemical elements intermixing at the interfaces. Samples of GaAs/AlGaAs, GaAsSb/GaAs, GaAsSbN/GaAs and GaAs/GaInP quantum well structures are analyzed to verify the influence of the structural imperfections on the PL spectra

Photoluminescence (PL) measurements due to temperature and excitation power were carried out in as function of sample containing a In0,53Ga0,47. As layer, grown by Molecular Beam Epitaxy on an InP substrate. The origins of the several luminescence processes observed at low temperature were determined by studying their different behaviors with increasing temperature and excitation power and by comparing the results with the data found in the literature. The following transitions have been identified: one transition involving localized excitons and two transitions involving acceptor impurities. A review of the main works published in the literature related to the optical transitions observed at low temperature in InGaAs/InP is also presented.

The reflectivity of a Bragg mirror composed by materials of the antimony family (AlGaAsSb/AlAsSb), doped with tellurium, is analyzed in this work. The sample was prepared by molecular beam epitaxy (MBE) and the reflectivity was measured by Fourier Transform Infra-Red Spectroscopy (FTIR). In order to discuss the Bragg mirror properties, the experimental reflectivity is compared to a simulation of the reflectivity based on the matrix formalism.

Neste trabalho o poli(3-metiltiofeno) (P3MT) foi sintetizado eletroquimicamente sobre substratos condutores transparentes de óxido de estanho dopado com flúor (FTO), utilizando como eletrólito de suporte Et4NBF4 ou LiClO4 em acetonitrila. Para desdopagem do material, as amostras foram reduzidas eletroquimicamente e quimicamente (em solução de NH4OH). Os filmes foram caracterizados por ressonância paramagnética eletrônica (EPR) e espectroscopia no infravermelho (FTIR) e suas propriedades óticas analisadas pela espectroscopia de absorção por refletância no ultravioleta-visível (UV-Vis) e espectroscopia de fotoluminescência (PL). Imagens de microscopia eletrônica de varredura (MEV) das primeiras amostras sintetizadas foram realizadas para verificarmos o nível de homogeneidade das mesmas. Os espectros de FTIR apresentaram as freqüências características do P3MT e, juntamente com os resultados de EPR, possibilitaram avaliar os portadores de carga e identificar estruturas benzênicas e quinônicas na formação das cadeias. Os espectros de absorção UV-Vis possibilitaram a obtenção do “gap” de energia médio do P3MT apresentando a banda de transição ?-?* e uma banda de bipólaron. Nos espectros de PL, com variação da potência de excitação, foram obtidos ajustes com duas gaussianas, considerando duas contribuições distintas de emissão. Estas duas contribuições foram atribuídas à emissão das cadeias mistas (maior energia) e a emissão das cadeias benzênicas (menor energia) presentes no material polimérico formado

Embora haja atualmente um extenso emprego de fontes de luz como LASERs (Light Amplification by Stimulated Emission of Radiation) e LEDs (Light Emitting Diodes) em diversas técnicas terapêuticas, as bases científicas de seus efeitos sobre sistemas biológicos ainda é relativamente desconhecida da comunidade acadêmica. Neste estudo é apresentada uma breve revisão sobre os efeitos da luz em sistemas biológicos. O emprego de fontes de luz de baixa potência, como diodos emissores de luz-LEDs, pode propiciar um recurso terapêutico opcional aos convencionais ou ser utilizado em conjunto com estes, com a vantagem do baixo custo e comprovada eficiência no tratamento de úlceras e outras enfermidades.

São apresentadas as propriedades elétricas e ópticas de espelhos de Bragg com 6.5 períodos de AlGaAsSb/ AlAsSb não dopado e dopados com Te, sobre InP, crescidos por MBE com diferentes tipos de interface entre as camadas de material ternário e quaternário. As técnicas empregadas foram fotoluminescência, reflectividade e medições de IxV. A interface com liga digital em gradiente parece ser a melhor alternativa para otimizar condução elétrica sem perdas significativas da reflectividade.

Apresentamos um estudo das propriedades ópticas de filmes finos de poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), preparados em uma concentração de 10 mg/ml de xileno. A solução foi depositada sobre substrato de vidro por “spin-coating” em três rotações diferentes (300, 1000 e 4000 rpm). Estudamos os efeitos da velocidade de rotação nas amostras a 300 K, analisando os espectros de fotoluminescência (PL) em diferentes pontos do flme polimérico. Analisamos também os efeitos da intensidade de excitação no comportamento óptico do MEH-PPV a 300 K. Em baixas, temperaturas os espectros de PL da amostra A1000 (1000 rpm) mostraram um pico estreito para transição puramente eletrônica e uma série de bandas vibrônicas que revelam o acoplamento com diferentes modos vibrônicos. Na amostra com rotação intermediária (1000 rpm) fzemos uma análise da emissão em função da variação da temperatura no intervalo de 130 K a 290 K. Também analisamos de modo sistemático, a forma de linha por meio de gaussianas comparando as com a literatura.

Diodos emissores de luz (LEDs) com emissão em diferentes comprimentos de onda são empregados como fonte de bombeamento em fotorefetância – PR (“photorefectance”). São analisados espectros de fotorefetância de semicondutores volumétricos de GaAs e de heteroestruturas GaAs/InGaP e GaAsSbN/ GaAs, preparadas sobre substrato de GaAs, usando LEDs azul, verde, laranja e vermelho, em comparação com espectros obtidos com o emprego de lasers de Ar e He-Ne, em montagem convencional. Nossos resultados demonstram a possibilidade do emprego de LEDs como fonte de bombeamento em medidas de fotoreflectância.

Fotoluminescência é uma das técnicas de espectroscopia mais utilizadas no estudo das propriedades ópticas de materiais e heteroestruturas semicondutoras. Neste trabalho, é explorada a potencialidade desta técnica na investigação e caracterização de imperfeições estruturais decorrentes de flutuações na composição química de ligas ternárias e quaternárias, rugosidades de interface, e compostos estequiometricamente indesejados decorrentes da troca entre elementos químicos nas interfaces. São analisadas amostras de poços quânticos formados por teroestruturas de GaAs/AlGaAs, GaAsSb/GaAs, GaAsSbN/GaAs e GaAs/GaInP, tendo como objetivo verificar a influência das imperfeições estruturais sobre os espectros de PL.

Medidas de fotoluminescência (PL) em função da temperatura e da potência de excitação foram realizadas em uma amostra contendo uma camada de In0,53Ga0,47As crescida pela técnica de epitaxia por feixe molecular-MBE (Molecular Beam Epitaxy) sobre um substrato de InP. As origens dos vários processos de luminescência observados à baixa temperatura foram determinados estudando seus diferentes comportamentos com o aumento da temperatura e da potência de excitação e comparando os resultados com os dados encontrados na literatura. Foram identificadas: uma transição envolvendo éxcitons localizados e duas transições envolvendo impurezas aceitadoras. Uma revisão dos principais trabalhos publicados na literatura relacionados às transições ópticas observadas à baixa temperatura no InGaAs/InP também é apresentada.

Analisamos neste trabalho, a refletividade de um espelho de Bragg composto por materiais da família do antimônio (AlGaAsSb/AlAsSb) dopado com telúrio. As amostras foram preparadas através da técnica de epitaxia por feixe molecular MBE (Molecular Beam Epitaxy) e as medidas de refletividade pela técnica de espectroscopia de infravermelho por transformada de Fourier FTIR (Fourier Transform Infra- Red). Para discussão das propriedades do espelho de Bragg comparamos a refletividade obtida experimentalmente e uma simulação baseada no formalismo matricial.

The progress of the semiconductor growth techniques allows the opportunity to produce new semiconductors devices that may contribute to the development of the nanotechnology. The fabrication of semiconductor heterostructures with high quality allows the obtaining of new effects based on the quantum properties of those systems, which have stimulated great technological interest, especially on the optoelectronic and telecommunications fields. In this work some basic concepts related to one of those heterostructures are discussed: the Coupled Double Quantum Well (CDQW). The deduction of the expression for the determination of the energy levels in CDQWs is presented in details. The results obtained through this expression are compared with experimental results obtained through photoluminescence (PL) measurements, complementing the work.

O rápido progresso das técnicas de crescimento de materiais semicondutores possibilitou a fabricação de uma série de novos dispositivos que contribuíram para o desenvolvimento da nanotecnologia. A confecção de heteroestruturas semicondutoras de alta qualidade permite a obtenção de novos efeitos baseados nas propriedades quânticas desses sistemas, os quais despertam grande interesse tecnológico, especialmente nos setores opto-eletrônico e de telecomunicações. Neste trabalho são discutidos alguns conceitos básicos relacionados a uma dessas heteroestruturas: o Poço Quântico Duplo Acoplado (PQDA). A dedução da expressão para a determinação dos níveis de energia de PQDAs é apresentada em detalhes. Os resultados obtidos através desta expressão são comparados com resultados experimentais obtidos através da técnica de fotoluminescência (PL), complementando o trabalho.

Luminescence down-shifting (LDS) is used in several photovoltaic technologies aiming to improve the photon conversion efficiency (PCE) of the devices through the increase of the light harvesting in the regions of the electromagnetic spectrum where the EQE of the solar cells is poor. The aim of this work was to produce films of mixtures (blends) of two luminescent materials, dispersed in a poly-methyl methacrylate (PMMA) matrix, hoping to improve their properties both as LDS layer and as UV filter when applied on the clear, external surface of P3HT:PC61BM photovoltaic devices. The best results led to an increment of 7.4% in the PCE of the devices, and a six fold enhancement in their half-life (T50%). This study indicates that multidye LDS layers with optimized optical properties can lead to an effective improvement in the performance and operational stability of OPVs. [ABSTRACT FROM AUTHOR]