Controlling the Er content of porous silicon using the doping current intensity

The results of an investigation on the Er doping of porous silicon are presented. Electrochemical impedance spectroscopy, optical reflectivity, and spatially resolved energy dispersive spectroscopy (EDS) coupled to scanning electron microscopy measurements were used to investigate on the transient during the first stages of constant current Er doping. Depending on the applied current intensity, the voltage transient displays two very different behaviors, signature of two different chemical processes. The measurements show that, for equal transferred charge and identical porous silicon (PSi) layers, the applied current intensity also influences the final Er content. An interpretative model is proposed in order to describe the two distinct chemical processes. The results can be useful for a better control over the doping process.

PACS

81.05.Rm; 82.45.Rr     

Structural and color tunable properties in Sm3+/Eu3+-doped Ca3Bi(PO4)3 phosphor for solar cell and w-LED applications

Journal of Materials Science: Materials in Electronics - Crystalline eulytite-type Ca3Bi(PO4)3 (CBP) phosphors activated with Sm3+ and combination of Sm3+ & Eu3+ ions have been prepared by...     

Structural and emission properties of Eu3+‐doped alkaline earth zinc‐phosphate glasses for white LED applications

Quaternary alkaline earth zinc‐phosphate glasses in molar composition (40 ? x)ZnO – 35P₂O₅ – 20RO – 5TiO₂ – xEu₂O₃ (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (T_g) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT‐IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (⁵D₀→⁷F₂) under excitation of 392 nm, which matches well with excitation of commercial n‐UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 ? x)ZnO – 35P₂O₅ – 20BaO – 5TiO₂ – xEu₂O₃ (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu₂O₃. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu₂O₃. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid‐state lighting devices.     

Metallurgical Approach Towards Explaining Optimized EDM Process Parameters for Better Surface Integrity of AISI D2 Tool Steel

Many attempts have been made to model and optimize performance parameters of Electrical Discharge Machining (EDM) process. In this investigation, the experimental design includes L9 orthogonal array based on the Taguchi methodology. The corresponding effect of input current, duty cycle and spark on time, on surface integrity, has been studied on AISI D2 tool steel. The residual stress measurement is done using X-ray diffraction method. The obtained output results regarding material removal rate, surface roughness, crack density, and residual stress have been modeled and optimized by regression equation and Genetic algorithm respectively. In this investigation, a metallurgical approach has been introduced towards the explanation of the resulted optimized response parameters.     

A system dynamics model for the supply chain procurement transport problem: comparing spreadsheets,fuzzy programming and simulation approaches

This article proposes a simulation approach based on system dynamics for operational procurement and transport planning in a two-level, multi-product and multi-period supply chain. This work uses the Vensim^® simulation tool to highlight the potential of system dynamics for supply chain simulation. A real continuous simulation application is presented in an automobile supply chain. The effectiveness of the proposed model is validated through the comparison of the results provided by spreadsheet-based simulation, fuzzy multi-objective programming and system dynamics-based simulation models. The fundamental point of this paper is that the simulation model is the most effective approach in quantifying the trade-off between number of truck shipments and average inventory level. In this case, the number of truck shipments is to be minimised, resulting in a higher inventory level. If the average inventory level were minimised, then there would be more truck shipments. Here, it is shown the benefit of this type of simulation model in reducing inventory by about 10%.     

White light emitting thermally stable bismuth phosphate phosphor Ca3Bi(PO4)3:Dy3+ for solid-state lighting applications

White light emitting dysprosium-doped Ca₃Bi(PO₄)₃ phosphor was successfully synthesized via co-precipitation method for the first time and the structural, vibrational, morphological, and luminescent properties have been investigated for solid-state lighting applications. X-ray diffraction (XRD) and structural refinement studies reveal that the synthesized phosphors consist of single phase with cubic structure. The field emission scanning electron microscopy (FE-SEM) images reveal that the as-synthesized phosphor has micron size particle with an irregular shape. Under near-ultraviolet (n-UV) and blue excitation, the phosphor exhibits white light emission via a combination of blue (~484 nm) and yellow (~575 nm) emission bands. The optimized concentration of Dy³⁺ ions is 6.0 mol % after which the concentration quenching takes place. The process of energy transfer between Dy³⁺ ions is due to dipole-dipole interaction, which was confirmed by applying Dexter's theory. The CIE chromaticity coordinates for the optimized phosphor were (0.329, 0.377), and they lie in the white light region. The emission intensity remains to be 83.41% at 373 K to that of at room temperature, which indicates good thermal stability. The above mentioned results demonstrate that Ca₃Bi(PO₄)₃ is a potential phosphor for solid-state lighting applications.     

Inhibitory property of Piper betel extract against photosensitization-induced damages to lipids and proteins

The protective activity of Piper betel ethanolic extract (PE) against the photosensitization-induced damage to lipids and proteins of rat liver mitochondria has been studied. PE could effectively prevent lipid peroxidation, as assessed by measuring thiobarbituric acid reactive substances, lipid hydroperoxide and conjugated diene. In addition, it prevented photo-induced oxidation of proteins in a concentration-dependent manner. Furthermore, its preventive capacity against iron-mediated lipid peroxidation was also confirmed. The protective activity of PE could be attributed to its free radical and singlet oxygen scavenging properties. The activity of PE was primarily due to its phenolic constituents, which were identified as chavibetol and 4-allylpyrocatechol.     

Effects of irrigation water quantities and seasonal variation on oil content and fatty acid composition of sunflower (Helianthus annuus L.)

A field experiment was conducted in the North Western Group of the Gezira Scheme (longitude 32°48′ and latitude 15°14′) for four successive seasons, two winter and two summer seasons, during the years 1999–2002, to study the effect of different irrigation water quantities (300, 400, 500, 600 and 700 mm per season) on oil content and oleic acid and linoleic acid percentages in two sunflower cultivars [Rodeo, an open‐pollinated variety, and Hysun33, a hybrid). The experiment was designed in a split plot design, with four replicates. The cultivars were allotted to the sub‐plots while the irrigation treatments were assigned to main plots. The results showed that different irrigation water quantities had significant effects on all parameters studied and the cultivar Hysun33 gave a higher oil content (36.6%) at 700 mm whereas the open‐pollinated variety Rodeo gave 34.1% oil at that level of irrigation. The overall percentages of oleic and linoleic acids were 29.7 and 58.1 in winter and 47.6 and 43.1 in summer, respectively. Copyright © 2007 Society of Chemical Industry     

Tensile Deformation Modeling of a Homogenized Cast Alloy 625: Effects of Large Grain Size

Metallurgical and Materials Transactions A - In the present study, tensile deformation behavior of a coarse-grained (> 1 mm) cast alloy 625 has been investigated by applying empirical and...     

On structure and mechanical properties of ultrasonically cast Al-2% Al2O3 nanocomposite

An investigation on the structure of an ultrasonically cast nanocomposite of Al with 2 wt.% nano-sized Al₂O₃ (average size ∼10 nm) dispersoids showed that the nanocomposite was consisting of nearly continuous nano-alumina dispersed zones (NDZs) in the vicinity of the grain boundaries encapsulating Al₂O₃ depleted zones (ADZs). The mechanical properties were investigated by nanoindentation and tensile tests. The nano-sized dispersoids caused a marginal increase in the elastic modulus, and a significant increase in the hardness (∼92%), and tensile strength (∼48%). Subsequent cold rolling to achieve a reduction ratio of 2 resulted in an appreciable increase in the hardness due to change in morphology of the microstructure. Estimation of the strength on the basis of inter-particle spacing, which was measured by transmission electron microscopy, could not be accounted for on the basis of Orowan mechanism, and therefore, strengthening mechanisms like local climb and/or cross slip might have a role in this room temperature (0.32T_M) deformation process.