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The estimated production of world electronic waste until 2017 is approximately 6 Gt. Despite this enormous problem, there are no clear regulations regarding the orientation for disposal or treatment of this type of residuals in many countries. There is a federal public policy in Brazil that supports a network of Computer Reconditioning Centers—CRCs. These CRCs train young people and recover or recycle electronic equipment. Through this work, CRCs produce interlocking plastic pavers for application on pavements from recycled electronic industry waste. This article presents the characterization of these interlocking paver’s mechanical properties when applied on the pavement. This characterization is a necessary step to show the effectiveness of this product. We show that the plastic pavers behave similarly to the artifacts manufactured in concrete, thus creating commercial opportunities for this initiative, and contributing to the Brazilian Solid Waste Policy.

Hyperbilirubinemia is a systemic global problem and an often diagnosed pathology in newborns. In most cases, blue-light phototherapy (410–460 nm) is the only treatment required to prevent the bilirubin neurotoxicity, but its effectiveness is dose-dependent and is highly affected by the skills, knowledge, and attention of nurses and clinicians who implement the treatment. This paper presents a novel light-sensitive colorimetric dosimeter to simulate the effect of blue-light phototherapy on the optical properties of in vitro bilirubin. The dosimeter is based on a multilayered organic structure comprising a light-stable green-light emitter (copper phthalocyanine, C 32 Cl 16 CuN 8 ), and a blue-light-sensitive red emitter (poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene]vinylene}, OC 1O C 6 -PPV). The optical and chemical properties of the dosimeter were investigated by fluorescence and FTIR spectroscopies and by color coordinates of CIE (1931) diagram chromatics, while the photochemical processing of bilirubin was evaluated by UV–vis absorption spectroscopy. The optical response of the dosimeter under conventional (10 μW/cm 2 ) and intensive (40 μW/cm 2 ) phototherapy was found to present the same photochemical kinetics as bilirubin. These findings highlight a cutting-edge solution for monitoring bilirubin elimination in neonates as a function of the dosimeter’s color evolution. This novel colorimetric dosimeter provides a standardized method of reporting and measuring phototherapy dose to promote an efficient use of available phototherapy units in health facilities.

With the aim of improving phototherapy for neonatal jaundice (hyperbilirubinemia), this study investigates the degradation of unconjugated bilirubin under irradiance by conventional light and by white, red, green, and blue LED sources in vitro. The absorption spectra of bilirubin under these different light sources are compared. The results demonstrate that white LED phototherapy promotes more efficient bilirubin degradation than conventional blue-light therapy. This study provides a basis for the design of novel phototherapy devices for the treatment of hyperbilirubinemia.

The lack of monitoring of food freshness during the cold chain has been reported in the literature as either a problem faced by meat industries enforcing stricter controls and public health security needs. This paper presents an innovative solution for real-time food freshness discrimination: a printable, easy-to-use, and non-toxic two-faced Janus color-indicator label. This sensor is based on the pink to purple variation of a multilayer pH-sensitive composite (cellulose acetate and black carrot anthocyanin) film in the turnover process of fresh to spoilage chicken. The microstructure and permeability of the composite, and also the impact of the psychrotrophic aerobic bacteria on the optical properties of the indicator label, were investigated. This sensor demonstrating a short response time (∼ 2 min), great color stability, and provides interactive information of food freshness, being capable of communicating directly with consumers via two simple images: “happy face” for fresh meat and “sad face” for spoilage. As far as we know, this is the first time that the Janus (or Emoji) principle is designed for tracking food quality to allow consumers to have easy information on food freshness.

This paper describes a variety of experiments that reveal the potential application of impedance spectroscopy (IS) measurements to enhance performance of ultrathin polyaniline (PANI)-based films on flexible substrate to control ammonia gas exposure in the 0–20 ppm range. Further, the device is mechanically robust for making electrical contact without lithography. We have employed the IS technique to proper adjust the optimal operation frequency of an easy-to-process, inexpensive and user-friendly PANI-based resistometric detectors in which drift current and delay problems related to electrode effects and dielectric absorption of PANI are insignificant. These requirements place emphasis upon the material and device configuration, and the range of frequencies from 10 to 100 Hz corresponds to the ideal working region to operate the device to unify sensibility inside 5%, reproducibility, linearity, stability and low response time (

Made available in DSpace on 2018-11-26T17:42:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) This paper describes a new statistical model to predict the frequency dependence of the conductivity of conjugated polymer-semiconductor nanoparticle composites. The model considers AC conduction in an inhomogeneous medium represented by a two-dimensional model of resistor network. The conductivity between two neighboring sites in the polymer matrix and the semiconductor particles is assumed to obey the random free energy barrier model and the Drude model, respectively. The real and imaginary parts of the AC conductivity were determined using the transfer-matrix technique, and the statistical model was applied to experimental data of thin films composed of polyaniline (PANI) and indium-tin-oxide (ITO) nanoparticles. The conductivity critical exponent (s) obtained in two dimensions for PANI/ITO films below the percolation threshold was found to be 2.7, which is greater than the universal value of s described by the classical percolation theory (s = 1.3). This non-universality is explained by the existence of a local electric field distribution in the bulk of the nanocomposite. Finally, these results are discussed in terms of the distribution of potential barriers that vary according to the concentration of ITO amount in the composite. Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP, Brazil IFMG, Campus Ouro Preto, BR-35400000 Ouro Preto, MG, Brazil Univ Fed Ouro Preto, Dept Fis, BR-35400000 Ouro Preto, MG, Brazil Univ Estadual Paulista, Dept Fis & Quim, Campus Ilha Solteira, BR-15385000 Ilha Solteira, SP, Brazil Univ Estadual Paulista, Dept Fis & Quim, Campus Ilha Solteira, BR-15385000 Ilha Solteira, SP, Brazil

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable aliphatic-aromatic copolyester. In this paper, we report the radio induction of photoluminescence (PL) properties in PBAT, after exposure to high doses of gamma radiation. After the previous high-energy irradiation, the material shows the highest photo-stimulated luminescence emission when excited with a light-emitting diode (LED) source at wavelengths ranging from 370 to 405 nm. The PL intensities obtained after excitation with an LED source of 385 nm are proportional to gamma doses ranging from 100 to 1000 kGy in the preirradiation process. FTIR data revealed that the gamma-induced aromatic amine groups may be responsible for the appearance of the postirradiation PL character in PBAT samples. The results indicate that PBAT has great potential for applications in in vitro imaging of human cancer, bioimaging devices, and radiation dosimetry.

Research in hybrid electronics has included advances in materials, devices and architectures. However, in practice, controversy still exists on some details which limit hybrid materials to high-performance applications, such as processing–structure–design–property relations. This paper describes a practical approach to enhancing the sensing performance of a prototype ammonia gas sensor based on electrical conductivity changes, percolation theory and current limitation to a semiconducting polymer-metal oxide medium. This device is based on fully-gravure printed polyaniline/indium - tin oxide nanocomposites, Pani100−xITOx [0 ≤ x≤ 100% (wt/wt)], layers on a freestanding high-density polyethylene substrate. We find that the electrical current of the device decreases and tends to saturate as the gas concentration increases, and the value of this electrical current limit (IL) depends on x: the higher the value of x, the smaller the IL, when the current that flows through the electronic device was dominated by the ITO-nanoparticle filled PAni, which increase the concentration of hopping carriers and contribute to the desired electrical response of a heterogeneous gas sensor. In this regime, we find a good linear relationship between x and ammonia concentration. These findings suggest new directions for future research on the development and investigation of organic-inorganic devices in which the electrical current variation is desired for enhanced sensitivity and stability of hybrid sensors.

Neste trabalho as propriedades ópticas do poli[2-metóxi,5-(2’etil-hexiloxi)-p-fenilenovinileno] - MEH-PPV foram estudadas sob efeito de luz azul proveniente de super LEDs utilizada no tratamento da hiperbilirrubinemia neonatal (ou icterícia). Os resultados mostraram que o MEH-PPV apresenta uma mudança de cor do vermelho-alaranjado para o incolor, passando por diversas tonalidades de amarelo, bem como uma diminuição da intensidade dos espectros de absorção e de fotoluminescência (PL) em função do tempo de exposição à radiação. Essas mudanças foram usadas para projetar um sensor de acúmulo de dose de radiação azul, tipo indicador de cores, para avaliar a dose de radiação recebida por recém-nascidos durante o tratamento da icterícia neonatal. In this work we investigated the optical behavior of poly[2-methoxy-5(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) under the effect of blue-light LED source applied in neonatal hyperbilirubinemia treatment. There is a visible response that covers the electronic absorption of bilirubin (350-500 nm), and hence this material is applicable for controlling the radiation doses in the treatment of jaundice of neonates, which is one of the most common reasons for hospital readmission of newborn infants. The results show that the material presents a gradation of color from orange-red to yellow and quenching on the absorption and photoluminescent (PL) spectra with the radiation exposure time. The rate of these changes can be altered by manipulations of organic solution concentration, suggesting these color and emission/absorption changes can be used to design an indicator-dosimeter that is readily associated with the radiation exposure time used in treating neonatal jaundice.

In this work, a new type of WO3 and V2O5 photovoltaic cell were fabricated. The oxides were obtained by sol-gel route. Both V2O5 and WO3 presented a lamellar structure with d = 1.17 nm and 0.69 nm, respectively. From SEM of V2O5 was observed ribbons and for WO3 noted a presence of platelets. For WO3, increasing the distance of lamp was observed a decreasing of light intensity: 164 mV in 44000 lux to 42 mV in 60 lux. For V2O5, in 1700 lux it was observed a voltage of 1418 mV and in 15000 lux a value of 1572 mV.

We have developed a novel programmable, low cost, spin coater to be used for applications where flat substrates are coated with an uniform thin layer of a desirable material. The equipment is built with dc brushless motor present in most of the hard disk drivers (HDDs). The system offers manual control, wide speed range (from 0 to 10,000 rpm), spin speed stability and compact size. The paper also describes the use of such equipment for the fabrication of thin poly(o-methoxyaniline) (POMA) films, which are of particular interest for design organic electronic devices, such as diodes, transistor, sensors and displays.

In this work, a plasma-enhanced chemical vapor deposition (PECVD) system was used to deposit carbon nitride at low deposition temperatures (ca. 100 °C) to improve the lifetime of polymer light-emitting diodes (PLEDs) and to decrease photo-degradation of MEH-PPV (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinilene]) in air. The characteristics of the carbon nitride and MEH-PPV films are investigated with FTIR and UV–Visible spectroscopies, with particular emphasis on the degradation process of MEH-PPV under illumination. It was shown by absorbance measurements that the coating protects the polymer film since the damage caused by photo-oxidation diminishes considerably. Current vs. voltage curves for PLEDs also indicated that the protection of a carbon nitride layer enhances the device lifetime.

In this work, the electrical properties of polymeric light-emitting diodes (LEDs) based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene), MEH-PPV, were studied by dc current–voltage (I–V) curves and impedance/admittance spectroscopy, at different temperatures. ITO/polymer/metal (Al and Au) structures were used to study the effect of the barrier height on the charge injection at the polymer/metal interfaces. For ITO/MEH-PPV/Al devices, strong temperature influence on the dc conductivity was observed in the forward direction whereas, in the reverse direction, the conductivity was almost temperature independent. On the other hand, ITO/MEH-PPV/Au devices presented temperature dependent conductivities for both polarities. This indicates that, for low barrier height at the interfaces (

We present a detailed study of the electric mechanism of a thin poly(o-methoxyaniline) (POMA) field-effect transistor. The device was prepared using Al-Si/SiO2/(interdigitated gold lines array)/POMA structure as the gate electrode, insulating layer, source-drain electrodes, and active layer, respectively. A model is presented for the electrical characteristics of such a device that encompasses the disordered properties of the POMA, the source-drain electrical-field dependence of hole mobility, and the carrier and mobility gradients in directions perpendicular to the polymer–oxide interface. The fittings of source-drain current versus source-drain voltage, having as parameters the gate voltage, is in good agreement with the experimental data, and the dependence of both the carrier saturation velocity and of the carrier mobility with the gate voltage are obtained. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 74–78, 2005

This article presents a novel radiochromic film for selective detection of low-medium (0–10 kGy) gamma radiation (60Co) doses. This dosimeter is based on a printed fluorescent multilayer structure comprising a paper substrate having layers of copper phthalocyanine (DY220) (a green emitter material) on the bottom, and layers of poly[2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) (a green-light absorber, red emitter, and radiation sensitive polymer) on the top. The effect of gamma radiation on the optical properties of DY220/MEH-PPV was described: it was observed as a strong correlation between radiation dose and fluorescent, color coordinates for CIE (1931) chromatic diagram, and Pantone color reference of the dosimeter. The rate of these changes can be altered by manipulation of top–bottom layers to represent easily the radiation dose to be determined in a wide range. This versatile dosimeter has many uses in the field of food radiation for monitoring, quality assurance, and control of the gamma radiation process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45729.

In this paper we present the photoconduction effect of the poly( p -phenylenevinylene) (PPV) and its derivative, the poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] (MH-PPV). The structures used to study photoconductivity were prepared using solutions of either PPV-precursor in methanol or MH-PPV in chloroform, both spin-coated on an interdigitated chromium-gold line array previously deposited onto glass substrate. Currents vs. voltage curves were carried out as well as of the films optical characteristics have been studied by UV-Vis, and photoluminescence and eletroluminescent spectroscopies.

Optical absorption and fluorescence measurements have been done on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]/[aluminum-tris(8-hydroxyquinoline)] solutions. The authors show that there is a visible response that covers the electronic absorption of bilirubin ( 350 – 500 nm ) , and hence, this material is applicable for managing the radiation doses planning before treatment of jaundice of neonates, which is one of the most common reasons of hospital readmission of newborns infants. The results show that the material presents a gradation of color from orange to yellow clearly, while its peak position emission shifts from orange-red ( λ max = 571 nm ) to green ( λ max = 540 nm ) with the radiation exposure time. The rate of these changes can be altered by manipulations of organic solution concentration and they are usually slow (from 2 to 8 h ), suggesting these color and emission changes can be used to design an easy to make, easy to read, easy to operate, low cost ( US $0.50) and accuracy for individual monitoring indicator dosimeter in order to represent easily the radiation exposure time usually used in management of neonatal jaundice.

This paper presents a methodology for the preparation of a-HgI2 by Physical Vapor Transport and of PbI2 crystals using the Bridgman technique. The results of the growth of HgI2 diluted in PbI2 by the Bridgman technique are shown for the first time, its limit of solubility having been determined at 600 ppm of HgI2 in the PbI2 matrix. Optical absorption, photoluminescence and electrical conductivity measurements show that the crystals prepared are of good crystalline quality.

In this paper, we report our experimental design in searching a smart and easy-to-read dosimeter used to detect 6MV X-rays for improving patient safety in radiation oncology. The device was based on an organic emissive solutions of poly(2-methoxy-5(2′-ethylhexyloxy)- p -phenylenevinylene) (MEH-PPV), aluminum-tris-(8-hydroxyquinoline) (Alq 3 ) and additive components which were characterized by UV–Vis absorption, photoluminescence and CIE color coordinate diagram. The optical properties of MEH-PPV/Alq 3 solutions have been examined as function of radiation dose over the range of 0–100Gy. It has shown that MEH-PPV/Alq 3 solutions are specifically sensitive to X-rays, since the effect of radiation on this organic system is strongly correlated with the efficient spectral overlap between Alq 3 emission and the absorption of degraded MEH-PPV, which alters the color and photoemission of MEH-PPV/Alq 3 mixtures from red to yellow, and then to green. The rate of this change is more sensitive when MEH-PPV/Alq 3 is irradiated in the presence of benzoyl peroxide than when in the presence of hindered phenolic stabilizers, respectively, an accelerator and an inhibitor to activate or inhibit free radical formation. This gives rise to optimize the response curve of the dosimeter. It is clear from the experimental results that organic emissive semiconductors have potential to be used as dedicated and low-cost dosimeters to provide an independent check of beam output of a linear accelerator and therefore to give patients the opportunity to have information on the dose prescription or equipment-related problems a few minutes before being exposed to radiation.

A novel approach for studying the thermal conversion of poly-p-xylylidene tetrahydrothiophenium chloride (PTHT) into poly(p-phenylenevinylene) (PPV) films has been proposed on the basis of calculated optical parameters. Spin-cast PTHT films were thermally converted into partially conjugated PPV films over conversion temperatures ranging from 22 °C to 200 °C. A strong correlation between refractive index (n) and damping constant extinction coefficient (k) was verified by spectroscopic ellipsometry (SE) for the films studied in the visible range of energy. The conversion temperature has a strong influence on the values of n and k, which were theoretically modeled using a Lorentz harmonic oscillator analysis. The films were also studied by spectroscopic techniques (photoluminescence, FTIR, and UV–VIS), and it was verified that the values of n decrease with increasing the amount of C C groups present along the polymer chains, as a strong evidence that both structure and optical properties of thermally converted PPV films can be directly compared. The optical properties of the PPV films were also compared with those of two electroluminescent derivatives in which side chains are introduced into the phenyl ring of PPV, poly(2-methoxy-5-hexyloxy)-p-phenylenevinylene) (MH-PPV) and poly(3-methoxy-5-dodecyloxy-p-phenylene–vinylene) (MD-PPV).

We report on the design, fabrication and performance of a poly (2-methoxy-5(2_-ethylhexyloxy)- p-phenylenevinylene)/tris-(8-hydroxyquinoline)aluminum (MEH-PPV/Alq3) X-ray dose detector for improving safety for cancer patients shortly before radiation therapy. The detector consists of an inexpen-sive (

We report on the investigations about the modification of optical properties induced by X-rays onto film detectors of cadmium tungstate (CdWO4), poly[2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and polystyrene (PS) This device takes advantage of reduction of spectral overlap between the radioluminescence (RL) of CdWO4 and the absorption of MEH-PPV as it is exposed to radiation, forming the basis of a new dosimeter that is capable of converting the orange-red radioluminescence of PS:MEH-PPV:CdWO4 into green. We propose an explanation of the optical processes occurring in MEH-PPV:CdWO4 in terms of the radiation hardness of CdWO4 combined to the RL-induced degradation of MEH-PPV.

A fototerapia com luz azul (460 nm - 490 nm) é o procedimento mais utilizado para o tratamento da icterícia em recém-nascidos. Contudo, dois fatores alteraram drasticamente a eficiência desse tratamento: (1) o espectro da fonte luminosa e (2) a dose de radiação absorvida pelos neonatos. Este trabalho apresenta o desenvolvimento de detectores de radiação orgânicos e flexíveis, de baixo custo, de bom desempenho e de fácil operação para monitoramento da radiação incidente em neonatos ictéricos sob tratamento fototerápico. O princípio de funcionamento dos dispositivos baseia-se na resposta óptica de filmes finos à base de dois materiais orgânicos luminescentes: o tris (8-hidroxiquinolinato de alumínio) - Alq3 e o poli[2-metóxi-5-(2’-etilóxi)-p-fenilenovinileno] - MEH-PPV, dispersos em matriz de poliestireno – PS sob efeito de luz azul. Os resultados obtidos mostram que a radiação atua no sentido de alterar a intensidade de máxima emissão do vermelho ao verde, passando pelo amarelo, dos filmes de PS/MEH-PPV/Alq3. Esse resultado é atribuído à fotodegradação do MEH-PPV e, consequentemente, as mudanças na sobreposição entre os espectros de emissão do Alq3 e de absorção desse polímero. A resposta óptica dos filmes com a radiação foi usada para fabricar um sensor orgânico flexível, inédito e de custo inferior a R$ 0,50, para controle das condições de exposição de neonatos ictéricos à fototerapia com luz azul. Blue-light therapy (460 nm - 490 nm) is the most common treatment of jaundice in newborns. However, the efficiency of this treatment is dependent of two factors: (1) the spectrum of light source and (2) the delivered dose to the neonates. This work presents the development of a low-cost, flexible, good performance and an easy detector operation based on organic materials for evaluation of radiation dose delivered by the phototherapy units to jaundice newborns. The operation principles of the device is based on the optical response of poly [2-methoxy-5-(2’-ethylhexyloxy)-p-phenylene - MEH-PPV, tris (8-hydroxyquinolinato aluminum)-Alq3 and polystyrene-PS thin films under the effects of blue-light. It is observed that the optical response of the PS/MEH-PPV/Alq3 films changes from red to yellow, and then to green with the radiation exposure. It is attributed to the photodegradation process of MEH-PPV and also to the spectral overlap between the photoemission of Alq3 and the absorption of MEH-PPV. The optical response of PS/MEH-PPV/Alq3 films was used to develop a novel organic flexible and low cost (

Neste trabalho, é apresentado o desenvolvimento de um novo equipamento para fabricação de filmes finos orgânicos, baseado na tecnologia automotiva de injeção eletrônica. Tal sistema apresenta, dentre as vantagens de disponibilidade comercial e baixo custo, baixas taxas de corrosão química e de problemas de entupimento dos bicos injetores, bem como o controle de taxas de temperatura de deposição. Portanto, apresenta versatilidade para utilização de diversas soluções orgânicas usadas em microeletrônica e eletrônica orgânica, tais como Fotoresistes e polímeros semicondutivos, como o poli(etileno-dioxitiofeno) - PEDOT. Ensaios obtidos com esses materiais mostram que o desempenho do sistema proposto depende de parâmetros como frequência da válvula injetora, diâmetro do orifício ejetor, pressão aplicada na solução impressa e das características da superfície dos substratos, que influenciam diretamente na qualidade dos filmes obtidos. This paper presents the development of a new equipment for manufacturing organic thin-films based on the technology of electronic fuel injection. This system presents, among the advantages of commercial availability and low cost, low rates of chemical corrosion and problems of nozzle clogging, as well as a temperature rate control system for material deposition. Thus, the developed equipment presents the versatility of using several organic solutions, such as Photoresistes and semiconducting polymers, for microelectronic and organic electronics, such as polyethylenedioxythiophene - PEDOT. Tests obtained with these materials show that system performance depends of parameters such as frequency of the injector valve, ejector orifice diameter, pressure applied in the printed solution and the substrates surface characteristics that influence directly in the quality of films obtained.

The present work details, to our knowledge, the first examination of the influence of blue-light radiation on the optical properties of organic luminescent films in attempting to develop an indicator dosimeter for phototherapy of neonatal jaundice. Jaundice is the most common problem encountered in newborns due to immature functioning in the liver. The operating principle of the device is based on the optical response of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene (MEH-PPV) and tris(8-hydroxyquinolinato) aluminum (Alq3) materials dispersed in polystyrene (PS) matrix (denoted as PS/MEH-PPV/Alq3). It is observed a blue-shift on the photoluminescence of PS/MEH-PPV/Alq3 system from red to orange-yellow, and then to green as function of the blue-light radiation exposure time. The result is attributed to the spectral overlap between emission of Alq3 and absorption of MEH-PPV. The optical response of PS/MEH-PPV/Alq3 to radiation was investigated to design a low-cost (< US$ 0.05) “smart” sensor to represent easily the radiation dosage normally used in blue-light phototherapy. The basic idea behind this concept considers the sensor as a traffic light device, where red represents underdose and green the prescription dose or overdose, while orange-yellow suggests that radiation therapy is an ongoing process. This personal real-time radiation dosimeter appears here as a key requirement for successful development of innovations in effective management of the radiation dose planning before treatment of neonatal where control of dose absorption of infants is extremely important.

Luminescent polymers are commonly employed in light-emitting displays because of their good processability and higher luminance with low power consumption. However, even though they are candidates for lighting applications, they are susceptible to photoxidation processes which dramatically change their colour with light exposure. In this work we use the light instability of luminescent polymers in order to design a blue-light dosimeter which indicates dose accumulation by multicoloured changes of photodegraded poly(2-methoxy-5(2′-ethylhexyloxy)- p -phenylenevinylene) (MEH-PPV). Photoluminescence and absorbance spectra measurements were carried out on MEH-PPV solutions under the effect of blue-light provided by phototherapy systems. All measurements were done maintaining chief conditions of jaundice treatments. It is observed that changes from orange-red to yellow clearly on colour solutions, while its peak position emission shifts from orange-red to blue and decreases in intensity with increasing radiation exposure time. Experiments performed with oxygen enriched solutions were shown to improve these effects, which is mainly caused by the competition between two possible mechanisms: a light induced polymerization of MEH-PPV and replacement of C C by C O bonds on the polymer backbone. Analyses of the relation between the irradiance produced by phototherapy systems and CIE (1931) chromatic diagram of MEH-PPV reveal this polymer as an easy to operate blue-light dosimeter, and the results reported here clearly demonstrated the possibility to produce self-adhesive patch of luminescent polymers in order to attach such organic dosimeter safety and placed closer to the skin of jaundiced infants.

In this work we investigated the effect of visible radiation on the electrical properties of poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene]- MH-PPV films and light emitting diodes. Complex impedance measurements of (Au or ITO)/MH-PPV/(Au or Al) samples were carried out at room temperature and exposed to white light. Over the frequency range from 100 mHz to 2 MHz, the electrical results of Au/MH-PPV/Au was dominated by the Cole-Cole approach, where the electrode influence is negligible. However, some additional influence of the interface was observed to occur when Al was used as electrode. These effects were observed under both dark and visible-light illumination conditions. A simple model based on resistor-capacitor parallel circuits was developed to represent the complex impedance of the samples, thereby separating bulk and interface contributions. We observed that the polymer electrical resistivity decreased while the dielectric constant of the polymer and the thickness of the Al/MH-PPV layer were almost constant with increasing light intensity. The decrease of the polymer layer resistance comes from a better charge injection due to a light induced dissociation of positive charge carriers at the electrode.

Neste trabalho foram observadas mudanças nas propriedades de emissão e de absorção de soluções de poli[2-metoxi-5-(2’etil-hexiloxi)-p-fenilenovinileno] – MEH-PPV com a exposição à radiação na região espectral do visível na faixa de 425 a 500 nm. Os resultados demonstram a possibilidade do uso de sistemas luminescentes como elemento ativo de detectores de radiação não ionizante, sobretudo na região empregada na profilaxia e no tratamento fototerápico da hiperbilirrubinemia neonatal. In this work, we observed changes in the emission and absorption properties of poly[(2-methoxy-5-hexyloxy)-pphenylenevinylene] - MEH-PPV solutions in the visible range from 425 to 500 nm. The main results demonstrated the possibility of using luminescent polymers as active material of non-ionizing radiation dosimeter, in such a way that MEH-PPV is promising for use in a management system to monitor radiation absorbed by newborns during phototherapy treatment of neonatal hyperbilirubinemia.

Complex impedance measurements were used to analyze the influence of ultraviolet and ozone gas on the electronic behaviour of ZnO films grown by rf magnetron sputtering. The data show that UV exposure strongly increases the ac conductivity of the film at very low frequencies, and that after ozone exposure it recovers the original value. At high frequencies, however, UV-light exposure it does not change the conductivity but the ozone acts in the sense to decrease it. Two distinct mechanisms, related to two relaxation time distributions are clearly observed: they are superimposed in the virgin sample, but they split forming two semicircles in the z ″( f ) − z ′( f ) diagrams when the samples are treated with UV and/or ozone gas. A combination of the bruggeman effective medium approximation (BEMA) with the random free energy barrier model is used to fit the data and to explain the ac conductivity variation phenomena observed.

Photogenerated charge carrier profiles in poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) light-emitting diodes were determined from steady-state photocurrent spectra and transient photocurrent decay measurements. The observation that the photocurrent spectra behavior is strongly dependent on the bias polarity and amplitude suggests the existence of an intrinsic electric field, determined by the difference in the work function of the metallic electrodes, as well as a field dependence on the free charge carrier generation rates. The obtained results reveal built-in voltages of +0.2 and −0.6 V for Au and Al electrodes, respectively. The photocurrent spectra can be semi-quantitatively explained using a simple model which takes into account the internal built-in electric field of the device structure, the band gap energy and the migration/diffusion of the photogenerated charge carriers through the polymeric film. The drift mobility of carriers was investigated by the time-of-flight technique (TOF). The value for the mobility of holes was obtained from the change of slopes in the double logarithmic plot of the transient current and was independent of the applied field. The TOF transients for electrons showed no change of slopes in the double logarithmic plot and the drift mobility of electrons could not be calculated.

Complex resistivity measurements in dark and under vacuum were carried out to study the electrical behavior of luminescent polymer diodes (LEDs) having ITO or gold as hole injector electrodes, aluminium as the cathode, and poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] - MH-PPV as the luminescent layer. The results obtained were analysed by a model based on resistor-capacitor circuits, which made possible to distinguish between bulk from interface effects, and the contribution of each phenomenon to the electrical current. It was also shown that bulk properties already exist in a film of 0.4 /spl mu/m thick, and from the theoretical fittings it was obtained the dielectric constant and resistivity of MH-PPV.

A field-effect transistor (FET) having poly(o-methoxyaniline) (POMA) as the active layer was built on a SiO 2 -Si substrate which acts as the gate. The POMA layer was deposited by spin coating on the substrate interdigitated with gold lines and which acts either as the source or drain contact. A tentative theoretical model based on the Schottky gold/polymer interface contact and on the electronic properties of the POMA film was developed to explain the characteristic behavior of the FET device.

Schottky diode structures employing chlorine doped MH-PPV (Methoxy-Hexiloxy-P-Phenylene-Vinylene) as active layers were prepared to study the electronic possibilities of this conjugated polymer. MH-PPV films were deposited by spin-coating technique on ITO (indium tin oxide) coated glass substrates. Aluminum contact was then vacuum evaporated. Dark conductivity characteristic is that of a rectifier diode. Upon illumination the device shows photovoltaic characteristics. When a voltage is applied, however, the structure shows electroluminescence with a peak at 606nm. In this sense, it is a reversible photonic device.

A new type of solar cell based on poly(o-methoxyanilinc)-POMA as active layer is proposed. A simple Schottky structure was prepared: Al/POMA/ITO/glass. The POMA layer was deposited by the casting method and doped with aqueous hydrochloric acid solutions. Light absorption in POMA produces carriers for the electrical current. The dark current vs. voltage curves show a rectification feature. Under illumination, the short circuit current increases with the light intensity, characteristic of the photovoltaic effect. Studies of the dependence on hydrochloric acid concentration, doping time and POMA layer thickness were done. The easy synthesis of POMA and the simplicity of this device arc the important aspects of this structure.