873 resultados para doped-Er3 glass microsphere
Resumo:
Dissertao para obteno do grau de mestre em Engenharia de Materiais
Resumo:
As clulas foto voltaicas orgnicas ou clulas de Gretzel (depois do seu descobridor) so aparelhos para a colecta de energia solar que utilizam um semicondutor inorgnico e uma molcula orgnica. Dita molcula orgnica capaz de excitar-se na presena de radiao electromagntica e ceder esta energia atravs da doao de electres a este semicondutor. Embora estas estruturas e o seu processo de fabrico sejam relativamente pouco onerosas, o aproveitamento da energia solar ainda muito baixo. Para alm desta deficincia, os corantes sintticos sofrem de bleaching ou ento so reduzidos ou oxidados facilmente quando no conseguem transferir a energia que foi absorvida ou quando difcil voltar ao estado original por dificuldades no completamento de circulao de electres. Neste trabalho pretende-se ento estudar o comportamento de molculas e misturas complexas de molculas com capacidade para serem excitadas pela luz solar. Como a dita xcitao promove a transferncia de um electro, este processo ser seguido pela tcnica de Voltametria cclica. Como substncias absorventes de luz utilizaremos compostos naturais (principalmente flavonides) puros, ou ento na forma de complexos naturais extrados de algumas plantas. Estas misturas de corantes sero extractos aquosos (infuses) de casca de laranja e limo assim como extractos de folhas de cerejeira, com o objectivo de proporcionar lternativas aos flavonides utilizados neste estudo. A caracterizao voltamtrica desta clula feita em diferentes formas de iluminao. Sobre a clula assim formada faz-se incidir rimeiro luz de lmpadas fluorescentes, depois luz ultra violeta e por fim sem qualquer tipo de luz incidente. Na base do fabrico da variante mais clssica destas clulas est o semicondutor xido de itnio (TiO2), por ser uma substncia muito comum e barata e com propriedades semicondutoras notveis. Uma forma comum de melhorar a eficincia deste material introduzir dopantes com o intuito de melhorar a eficincia do processo de transferncia electrnica. Um segundo objectivo deste trabalho o estudo de sistemas semicondutor/molcula foto activa. Semicondutores como ZnO, TiO2 e TiO2 dopado sero ento estudados. O gels de TiO2 ou o TiO2 dopado sero depositados sobre lminas de vidro comum, nas quais foi anteriormente depositado uma pelcula de alumnio que serve de condutor (elctrodo egativo). Uma outra variante ser a utilizao de xido de zinco, um semicondutor de baixo custo que por sua vez vai ser depositado em lminas de alumnio comercial. A nossa clula foto electroqumica ser ento formada por molculas de corante, uma lmina e um semicondutor (que funcionar como elctrodo de trabalho), com ou sem electrlito/catalizador (soluo de iodo/iodeto), e elctrodos de referncia de Ag/AgCl, e outro auxiliar de grafite. Um outro objectivo fazer um pequeno estudo sobre influencia do catalisador I2/etilenodiamina no comportamento electroqumico da clula, de forma a poder utilizar o solvente (etilenodiamina) com menor volatilidade do que a gua, que empregada no par I2/I3.m A importncia deste facto prende-se com a limitada vida destas clulas quando o electrlito/solvente evaporado pelas altas temperaturas da radiao incidente.
Resumo:
White Color tuning is an attractive feature that Organic Light Emitting Diodes (OLEDs) offer. Up until now, there hasnt been any report that mix both color tuning abilities with device stability. In this work, White OLEDs (W-OLEDs) based on a single RGB blend composed of a blue emitting N,N-Di(1-naphthyl)-N,N-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB) doped with a green emitting Coumarin-153 and a red emitting 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM1) dyes were produced. The final device structure was ITO/Blend/Bathocuproine (BCP)/ Tris(8-hydroxyquinolinato)aluminium (Alq3)/Al with an emission area of 0.25 cm2. The effects of the changing in DCM1s concentration (from 0.5% to 1% wt.) allowed a tuning in the final white color resulting in devices capable of emitting a wide range of tunes from cool to warm while also keeping a low device complexity and a high stabilitty. Moreover, an explanation on the optoelectrical behavior of the device is presented. The best electroluminescense (EL) points toward 160 cd/m2 of brightness and 1.1 cd/A of efficiency, both prompted to being enhanced. An Impedance Spectroscopy (IS) analysis allowed to study both the effects of BCP as a Hole Blocking Layer and as an aging probe of the device. Finally, as a proof of concept, the emission was increased 9 and 64 times proving this structure can be effectively applied for general lighting.
Resumo:
Transparent conducting oxides (TCOs) have been largely used in the optoelectronic industry due to their singular combination of low electrical resistivity and high optical transmittance. They are usually deposited by magnetron sputtering systems being applied in several devices, specifically thin film solar cells (TFSCs). Sputtering targets are crucial components of the sputtering process, with many of the sputtered films properties dependent on the targets characteristics. The present thesis focuses on the development of high quality conductive Al-doped ZnO (AZO) ceramic sputtering targets based on nanostructured powders produced by emulsion detonation synthesis method (EDSM), and their application as a TCO. In this sense, the influence of several processing parameters was investigated from the targets raw-materials synthesis to the application of sputtered films in optoelectronic devices. The optimized manufactured AZO targets present a final density above 99 % with controlled grain size, an homogeneous microstructure with a well dispersed ZnAl2O4 spinel phase, and electrical resistivities of ~4 10-4 cm independently on the Al-doping level among 0.5 and 2.0 wt. % Al2O3. Sintering conditions proved to have a great influence on the properties of the targets and their performance as a sputtering target. It was demonstrated that both deposition process and final properties of the films are related with the targets characteristics, which in turn depends on the initial powder properties. In parallel, the influence of several deposition parameters in the films properties sputtered from these targets was investigated. The sputtered AZO TCOs showed electrical properties at room temperature that are superior to simple oxides and comparable to a reference TCO indium tin oxide (ITO), namely low electrical resistivity of 5.45 10-4 cm, high carrier mobility (29.4 cm2V-1s-1), and high charge carrier concentration (3.97 1020 cm-3), and also average transmittance in the visible region > 80 %. These superior properties allowed their successful application in different optoelectronic devices.
Resumo:
The present work focuses on the use of the life cycle assessment (LCA) and life cycle costing (LCC)methodologies to evaluate environmental and economic impacts of polymers and polymer composites materials and products. Initially a literature review is performed in order to assess the scope and limitations of existing LCA and LCC studies on these topics. Then, a case study, based on the production of a water storage glass-fibre reinforced polymer (GFRP) composite storage tank, is presented. The storage tank was evaluated via a LCA/LCC integrated model, a novel way of analysing the life cycle (LC) environmental and economic performances of structural products. The overarching conclusion of the review is that the environmental and economic performances of polymers composites in non-mobile applications are seldom assessed and never in a combined integrated way.
Resumo:
Zn1xCoxO films with different Co concentrations (with x=0.00, 0.10, 0.15, and 0.30) were grown by pulsed laser deposition (PLD) technique. The structural and optical properties of the films were investigated by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and photoluminescence (PL). The magnetic properties were measured by conventional magnetometry using a SQUID and simulated by ab-initio calculations using KorringKhonRostoker (KKR) method combined with coherent potential approximation (CPA). The effect of Co-doping on the GIXRD and Raman peaks positions, shape and intensity is discussed. PL studies demonstrate that Co-doping induces a decrease of the bandgap energy and quenching of the UV emission. They also suggest the presence of Zn interstitials when x0.15. The 10% Co-doped ZnO film shows ferromagnetism at 390 K with a spontaneous magnetic moment 4105 emu and coercive field 0.17 kOe. The origin of ferromagnetism is explained based on the calculations using KKR method.
Resumo:
A flexible and low cost energy harvester device based on the magnetoelectric (ME) effect has been designed using Fe64Co17Si7B12 as amorphous magnetostrictive ribbons and PVDF as the piezoelectric element. Sandwich-type laminated composite of 3 cm long has been fabricated by gluing these ribbons to the PVDF with the Devcon 5 minute epoxy. Good power output and power density of 6.4 W and 1.5 mW/cm3, respectively, have been obtained through a multiplier circuit. All values have been measured at the magnetomechanical resonance of the laminate. The effect of the length of the ME laminate on the power output has been also studied, exhibiting a decay as the length of the ME laminate does. Nevertheless, good performance of such device has been obtained for a 0.5 cm long device, working already at 337 KHz, within the low radio frequency (LRF) range.
Resumo:
Companies and researchers involved in developing miniaturized electronic devices face the basic problem of the needed batteries size, finite life of time and environmental pollution caused by their final deposition. The current trends to overcome this situation point towards Energy Harvesting technology. These harvesters (or scavengers) store the energy from sources present in the ambient (as wind, solar, electromagnetic, etc) and are costless for us. Piezoelectric devices are the ones that show a higher power density, and materials as ceramic PZT or polymeric PVDF have already demonstrated their ability to act as such energy harvester elements. Combinations between piezoelectric and electromagnetic mechanism have been also extensively investigated. Nevertheless, the power generated by these combinations is limited under the application of small magnetic fields, reducing the performance of the energy harvester [1]. In the last years the appearance of magnetoelectric (ME) devices, in which the piezoelectric deformation is driven by the magnetostrictive element, enables to extract the energy of very small electromagnetic signals through the generated magnetoelectric voltage at the piezoelectric element. However, very little work has been done testing PVDF polymer as piezoelectric constituent of the ME energy harvester device, and only to be proposed as a possibility of application [2]. Among the advantages of using piezopolymers for vibrational energy harvesting we can remember that they are ductile, resilient to shock, deformable and lightweight. In this work we demonstrate the feasibility of using magnetostrictive Fe-rich magnetic amorphous alloys/piezoelectric PVDF sandwich-type laminated ME devices as energy harvesters. A very simple experimental set-up will show how these laminates can extract energy, in amounts of W, from an external AC field.
Resumo:
Biopolymer-based materials have been of particular interest as alternatives do synthetic polymers due to their low toxicity, biodegradability and biocompatibility. Among them, chitosan is one of the most studied ones and has recently been investigated for the application as solid state polymer electrolytes. Furthermore, it can serve as a host for luminescent species such as rare earth ions, giving rise to materials with increased functionality, of particular interest for electrochemical devices. In this study, we investigate chitosan based luminescent materials doped wit Eu3+ and Li+ triflate salts from the structural, photophysical and conductivity points of view. Because the host presents a broad emission band in the blue to green, while Eu3+ emits in the red, fine tuning of emission colour and/or generation of white light is possible by optimizing composition and excitation scheme. Europium lifetimes (5D0) are in the range 270 350 s and quantum yields are as high as 2%. Although Li+ does not interfere with the luminescent properties, it grants ion-conducting properties to the material suggesting that a combination of both properties could be further explored in multifunctional device.
Resumo:
Biopolymer-based materials have been of particular interest and they are alternatives to synthetic polymers based on the decreasing oil resources. The polymer electrolytes were doped with choline-based IL N,N,Ntrimethyl- N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([N1 1 1 2(OH)][NTf2]), or Er (CF3SO3)3 or both. The polymer electrolytes were employed in the production of glass/ITO/WO3/electrolyte/ CeO2TiO2/ITO/glass electrochromic devices (ECDs). The lowest onset temperature for the degradation of all the SPEs is at ~130 C for the Gellan Er (CF3SO3)3 (10:1) this temperature range of stability is wide enough for a material to be applied as an electrolyte/separator component in electrochemical devices. The three ECDs displayed fast switching speed (ca. 15 s). Gellan [N1 1 1 2(OH)][NTf2] Er (CF3SO3)3 (5:1:10) exhibited an electrochromic contrast of 4.2% in the visible region, the coloration efficiency attained at 555 nm was 3.5 and 0.90 cm-2 C-1 in the colored and bleached states, respectively, and the open circuit memorywas 48 h. Preliminary tests performed with a prototype electrochromic device (ECD) incorporating WO3 as cathodic electrochromic layer, are extremely encouraging.
Resumo:
Natural Fiber Composites based on polypropylene have gained increasing interest over the past two decades, both in the scientific and industry communities. In this study, the mechanical properties of polypropylene (PP)/natural fiber composites were studied and compared with those of polypropylene reinforced by glass fiber. Flax and jute woven fabrics have been used. PP/glass fiber composites showed better performance in terms of tensile properties.
Resumo:
A series of colloidal MxFe3-xO4 (M = Mn, Co, Ni; x = 01) nanoparticles with diameters ranging from 6.8 to 11.6 nm was synthesized by hydrothermal reaction in aqueous medium at low temperature (200 C). Energy-dispersive X-ray microa-nalysis and inductively coupled plasma spectrometry confirms that the actual elemental compositions agree well with the nominal ones. The structural properties of obtained nanoparticles were investigated by using powder X-ray diffraction, Raman scattering, Mssbauer spectroscopy, and electron microscopy. The results demonstrate that our synthesis technique leads to the formation of chemically uniform single-phase solid solution nanoparticles with cubic spinel structure, confirming the intrinsic doping. Magnetic studies showed that, in comparison to Fe3O4, the saturation magnetization of MxFe3-xO4 (M = Mn, Ni) decreases with increasing dopant concentration, while Co-doped samples showed similar saturation magnetizations. On other hand, whereas Mn- and Ni-doped nanoparticles exhibits superparamagnetic behavior at room temperature, ferromagnetism emerges for CoxFe3-xO4 nanoparticles, which can be tuned by the level of Co doping.
Resumo:
Dissertao de mestrado integrado em Engenharia Civil
Resumo:
Otto-von-Guericke-Universitt Magdeburg, Fakultt fr Maschinenbau, Univ., Dissertation, 2015
Resumo:
v.10:no.37(1960)
