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This work presents a method to optimize multi-product chromatographic systems with multiple objective functions. The system studied is a neodymium, samarium, europium, gadolinium mixture separated in an ion exchange chromatography step. A homogeneous Langmuir Mobile Phase Modified model is calibrated to fit the experiments, and then used to perform the optimization task. For the optimization a multi-objective Differential Evolution algorithm was used, with weighting based on relative value of the components to find optimal operation points along the Pareto front. The objectives of the Pareto front are weighted productivity and weighted yield with purity as an equality constraint. A prioritizing scheme based on relative values is applied for determining the pooling order. A simple rule of thumb for pooling strategy selection is presented. The multi-objective optimization gives a Pareto front which shows the rule of thumb, as a gap in one of the objective functions. 相似文献
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Although aluminate phosphors have attracted great interest for applications in lamps, cathode ray tubes and plasma display panels, there still remain issues affecting operational parameters such as luminescence efficiency, stability against temperature, high color purity and perfect decay time. In addition, issues involving important aspects of the monoclinic↔hexagonal phase transition temperature still exist. In this work, SrAlxOy:Eu2+,Dy3+ phosphor powders were prepared by the sol–gel method. X-ray diffraction (XRD) has shown that both crystallinity and crystallite sizes increased as the temperature increased. Both SrAl2O4 and Sr2Al3O6 phases were observed. Photoluminescence (PL) characterization shows temperature-dependence, which indicates emission at low and high annealing temperatures originating from Eu2+ and Eu3+ ions. Thermoluminescence glow and decay measurements provided useful insight on the influence of traps on luminescence behavior. Differential scanning calorimetry (DSC) and thermogravimetric studies (TGA) on composites of the phosphor in low density polyethylene (LDPE) demonstrated the varied influence of annealing temperature on some luminescence and thermal properties. 相似文献
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J. J. Dolo O. M. Ntwaeaborwa J. J. Terblans E. Coetsee B. F. Dejene M.-M. Biggs H. C. Swart 《Applied Physics A: Materials Science & Processing》2010,101(4):655-659
Luminescent Gd2O2S:Tb3+ phosphor thin films were grown on Si (100) substrates, using the pulsed laser deposition technique. The films were grown
in 100 to 300 mTorr oxygen gas (O2) atmospheres when the substrate temperature was kept constant at 400 or 600°C. The effect of the O2 ambient on the structure and morphological properties of the films were analyzed using x-ray diffraction (XRD), scanning
electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Spherical nanoparticles deposited on the Si (100)
substrates were shown to crystallize in the hexagonal structure of Gd2O2S. The photoluminescence (PL) spectra of all the films were characterized by a stable green emission peak with a maximum at
545 nm. Improved PL intensity was observed from the films deposited at higher oxygen pressures and higher substrate temperatures.
Particles sizes of the nanoparticles deposited under the different conditions varied between 19 and 36 nm for the different
samples. Smaller and more densely packet particles were produces at the higher O2 pressures and the higher temperature. 相似文献
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Europium-doped barium aluminate (BaAl x O y :Eu2+) phosphors were obtained at low temperatures (500°C) using the solution — combustion of corresponding metal nitrate-urea solution mixtures. The particle size and morphology and the structural and luminescent properties of the synthesized phosphors were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Electron diffraction spectroscopy (EDS) and photoluminescence (PL). It was found that the change in Ba: Al molar ratios showed greatly influence not only on the particle size and morphology, but also on their PL spectra and crystalline structure. The structure of BaAl x O y nanophosphors changes from a hexagonal Ba2Al10O17 phase for samples with 6:100 molar ratios to a hexagonal BaAl2O4 one with an increase in Ba content. The peak of the emission band occurs at a longer wavelength (around 615 nm) with a decrease in Ba concentration but displays a broad blue-green emission band composed from two emissions with the maximum at 495 and 530nm coming from Eu2+ in two sites for increasing Ba content. The blue-green emission is probably due to the influence of 5d electron states of Eu2+ in the crystal field because of atomic size variation causing crystal defects while the red emission is due to f - f transitions. These findings clearly demonstrate the possibility of fine tuning the colour emission. 相似文献
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Francis B. Dejene Abdub G. Ali Hendrik C. Swart Reinhardt J. Botha Kittesa Roro Liza Coetsee Mart M. Biggs 《Central European Journal of Physics》2011,9(5):1321-1326
Material property dependence on the OH−/Zn2+ molar ratio of the precursor was investigated by varying the amount of NaOH during synthesis of ZnO. It was necessary to
control the water content and temperature of the mixture to ensure the reproducibility. It was observed that the structural
properties, particle size, photoluminescence intensity and wavelength of maximum intensity were influenced by the molar ratio
of the precursor. The XRD spectra for ZnO nanoparticles show the entire peaks corresponding to the various planes of wurtzite
ZnO, indicating a single phase. UV measurements show the absorption that comes from the ZnO nanoparticles in visible region.
The absorption edge of these ZnO nanoparticles are shifted to higher energies and the determined band gap energies are blue
shifted as the OH−/Zn2 molar ration increases, due to the quantum confinement effects. The photoluminescence characterization of the ZnO nanostructures
exhibited a broad emission band centred at green (600 nm) region for all molar ratios except for OH−/Zn2+ = 1.7 where a second blue emission around 468 nm was also observed. The photoluminescence properties of ZnO nanoparticles
were largely determined by the size and surface properties of the nanoparticles. 相似文献
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S. V. Motloung F. B. Dejene H. C. Swart O. M. Ntwaeaborwa 《Journal of Sol-Gel Science and Technology》2014,70(3):422-427
Undoped and Pb2+-doped ultrafine cubic zinc aluminate (ZnAl2O4) hosts were successfully prepared at a relatively low temperature (~80 °C) using the sol–gel method. The concentration of Pb2+ was varied from 0 to 5 mol%. The TGA showed that the minimum annealing temperature required to obtain single phase ZnAl2O4 must be above 400 °C. The XRD data revealed that all the annealed samples were single phase crystalline structures and the estimated crystallites size were in the range of 21–30 nm in diameter. The FTIR results suggest that heat-treating can destroy some of the bonds. The surface morphology of the phosphors was influenced by the Pb2+ mol%. Undoped and Pb2+-doped ZnAl2O4 nanoparticles exhibit the violet emission at slightly different positions. The slight peak shifts suggests the possibilities that the luminescence centre can either be due to the defects level in the host or Pb2+ ions. The emission peaks at 390 and 399 nm are ascribed to the typical UV transitions 3P0,1 → 1S0 in Pb2+ ion. At the higher Pb2+ mol%, the luminescence quenching behaviour occurs, which suggests that doping with Pb2+ ions is accompanied by the introduction of new defect sites that enhance non-radiative recombination of the excited electrons. 相似文献
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The aim of this work was to study the influence of selenization temperature on the morphological and structural properties of CuIn1−xGaxSe2 (CIGS) polycrystalline thin films prepared by a two-step method. The compound and metallic precursors were deposited sequentially using GaSe, InSe and Cu sources by thermal evaporation. These identical InSe/Cu/GaSe precursors are then selenized with Se vapor in a vacuum system. All the CIGS films showed chalcopyrite structure and presence of secondary phases observed at low temperatures. High temperature treatment led to better crystalline and an increase in grain size. Solar cell devices are fabricated and J–V measurements performed under AM1.5 global solar spectra conditions at 25 °C are presented. 相似文献
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