Function Of Dopant Concentration Research Articles

Preparation and Luminescence of ZnAl<sub>2</sub>O<sub>4</sub>:Mn Phosphors

Nano-sized manganese-doped zinc aluminate spinel (Zn1−xMnxAl2O4; x = 0–6.0 mol%) powder phosphors were prepared by the sol–gel process. Zinc chloride, aluminum isopropoxide, and manganese chloride were employed as precursors. The influences of manganese concentration and heat treatment conditions on the crystallization and photoluminescence of the phosphors were investigated. The dried powders were amorphous to X-ray powder diffraction (XRD) and the single-phase ZnAl2O4 spinel crystallite started to form at temperatures as low as 600oC. The crystallization of powder did not significantly affected by various manganese concentrations. On heating at 1000oC, the resulting powder phosphors had the average crystallite and primary particle sizes of around 20–25 and 20–30 nm, respectively, depending on the dopant content and heating time. Photoluminescence spectra exhibited strong green emission bands centered at 512 nm under an excitation wavelength of 458 nm. The luminescence efficiency has been investigated as a function of dopant content, heating temperature, heating time, and specific surface area of the powders.

Effect of ZrO2-doping of nanosized Fe2O3/MgO system on its structural, surface and catalytic properties

Fe2O3/MgO system was prepared by wet impregnation method followed by treatment with different amounts of Zr-dopant salt then heating at 500 and 700°C. The dopant concentrations were 0.48, 0.95 and 1.4mol% ZrO2. Pure and variously doped solids were characterized using XRD, N2-adsorption isotherms carried out at −196°C and catalytic decomposition of H2O2 in aqueous solution at 25–35°C. The results revealed that the nanosized MgO phase was only detected in the diffractograms of pure and doped solids calcined at 500°C. Heating pure and doped solids at 700°C produced nanosized MgFe2O4 phase together with MgO phase. Pure and ZrO2-doped solids calcined at 500 and 700°C are mesoporous adsorbents. The doping process brought about a measurable decrease in the SBET of Fe2O3/MgO system with subsequent increase in its catalytic activity. The catalytic activity of the investigated system toward H2O2 decomposition, expressed as reaction rate constant per unit surface area was found to increase as a function of dopant concentration. The maximum increase in the reaction rate constant per unit surface area measured for the reaction carried out at 30°C attained 125% for the heavily doped samples. This significant increase was based on the catalytic activity of pure catalyst sample measured under the same conditions.

Optical, structural, and mechanical properties of different valence‐cation‐doped bismuth vanadate oxides

AbstractThe optical, structural, and mechanical properties of Bi4V2 − xMxO11 − δ (0 ≤ x ≤ 0.4 in the steps of 0.1, M = Mn, Ga, As) oxides have been investigated. The parameters like band gap (Eg), Urbach energy (Eu), grain size, hardness (H), and fracture strength (K) have been calculated as a function of dopant concentration, i.e., 0 ≤ x ≤ 0.4. In addition to this, the infrared spectra have been obtained for all the dopant oxides with different dopant concentrations. The results are discussed in light of correlation of these optical and mechanical parameters to their electrical properties. The fractured surface is analyzed by X‐ray dot mapping to check the segregation of elements and their effect on mechanical properties.

Swelling due to fission products and additives dissolved within the uranium dioxide lattice

Simulations using empirical inter-atomic potentials have been used to predict the change in volume of the uranium dioxide lattice due to the accommodation of soluble fuel additives and fission products. The incorporation of divalent, trivalent and tetravalent cations are considered. The change in accommodation mechanism for aliovalent cations between UO2 and UO2+x gives rise to markedly different defect volumes. Experimental data is in good agreement with the predictions made in this work, particularly swelling as a function of dopant concentration under different conditions. The predicted defect volumes have been combined to predict the change in lattice volume with burnup (fission product inventory) due to incorporation of these soluble species, which agrees well with swelling data from irradiated fuel.

A blend of first-principles and kinetic lattice Monte Carlo computation to optimize samarium-doped ceria

Solid oxide fuel cells (SOFCs) have been acknowledged as a possible future source for clean and efficient electric power generation. One of the most important goals in the SOFCs research is to decrease the operating temperature, which in turn will improve the stability and decrease the cost of various components enabling its widespread utilization. For realizing the aforementioned goal, it is imperative to identify suitable electrolyte materials that show enhanced conductivity in the intermediate temperature range (773–1,073 K). Sm-doped ceria (SDC) is considered a promising candidate for use as an electrolyte material for SOFC operation in intermediate temperature range due to the high oxygen ion conductivity. In this article, we present a theoretical investigation using first-principles and kinetic lattice Monte Carlo (KLMC) computations to highlight the trends in oxygen ion conductivity as a function of dopant content and temperature in SDC. Using first-principles calculations, oxygen vacancy formation and migration were examined at first, second, and third nearest neighbor positions to a Sm ion. The activation energies for oxygen vacancy migration along various pathways in SDC computed using first-principles were used as input to the KLMC model to study vacancy mediated diffusion. SDC with 20 % mole fraction of dopant content yields the maximum conductivity, which is in very good agreement with experimentally identified compositions. Rationale for increase in conductivity as a function of increase in dopant content and subsequent decrease in conductivity at higher dopant fractions in SDC is presented. This combined methodology of first-principles and KLMC computations is a useful tool for the design and identification of various ceria-based electrolyte materials used in SOFCs.

Cation substitution in synthetic meridianiite (MgSO4·11H2O) II: variation in unit-cell parameters determined from X-ray powder diffraction data

We have prepared aqueous MgSO4 solutions doped with various divalent metal cations (Ni2+, Zn2+, Mn2+, Cu2+, Fe2+, and Co2+) in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate + ice by rapid quenching in liquid nitrogen. In a companion paper (Fortes et al., in Phys Chem Min 39) we reported the identification of various phases using X-ray powder diffraction, including meridianiite-structured undecahydrates, melanterite- and epsomite-structured heptahydrates, novel enneahydrates and a new octahydrate. In this work we report the changes in unit-cell parameters of these crystalline products where they exist over sufficient dopant concentrations. We find that there is a linear relationship between the rate of change in unit-cell volume as a function of dopant concentration and the ionic radius of the dopant cation; large ions such as Mn2+ produce a substantial inflation of the hydrates’ unit-cell volume, whereas smaller ions such as Ni2+ produce a modest reduction in unit-cell volume. Indeed, when the data for all hydrates are normalised (i.e., divided by the number of formula units per unit-cell, Z, and the hydration number, n), we find a quantitatively similar relationship for different values of n. Conversely, there is no relationship between the degree of unit-cell inflation or deflation and the limit to which a given cation will substitute into a certain hydrate structure; for example, Co2+ and Zn2+ affect the unit-cell volume of MgSO4·11H2O to a very similar degree, yet the solubility limits inferred in our companion paper are >60 mol. % Co2+ and <30 mol. % Zn2+.

Effects of thermal treatment on the characteristics of boron and tantalum-doped ZnO thin films deposited by the electrospraying method at atmospheric pressure

Metal-doped (B and Ta) ZnO thin films were deposited by the electrospraying method onto a heated glass substrate. The structural, electrical and optical properties of the films were investigated as a function of dopant concentration in the solution and also as a function of annealing temperature. The results show that all the prepared metal-doped ZnO films were polycrystalline in nature with a (0 0 2) preferred orientation. As the amounts of dopant were increased in the starting solution, the crystallinity and transmittance decreased. On the other hand, heat treatment of the films enhanced the transmittance, Hall mobility, carrier concentration and crystallinity. It was also observed that 2at.% is the optimal doping amount in order to achieve the minimum resistivity and maximum optical transmittance. As-deposited films have high resistivity and low optical transmittance. The annealing of the as-deposited thin films in air resulted in the reduction of resistivity. Depending on the characteristics of dopant, mainly ionic radius, the effects of dopant were studied on the properties of ZnO thin films. Boron and tantalum have been considered as dopants, tantalum being the superior of the two, since it showed the lower resistivity and higher carrier concentration as well as higher mobility. The minimum value of resistivity was 1.95×10−4Ωcm (15Ω/□) with an optical transmittance more than 93% in the visible region and minimum resistivity of 2.16×10−4Ωcm (18Ω/□) with an optical transmittance greater than 96% for 2at. % tantalum- and boron-doped ZnO films respectively. The present values of resistivities were closer to the indium tin oxide (ITO) resistivity and also closest to the lowest resistivity values among the ZnO films that were previously reported. The prepared films exhibit the good crystalline structure, homogenous surface, high optical transmittance and low resistivity that are preferable for optical devices.

Oxygen Vacancy Ordering and the Conductivity Maximum in Y2O3-Doped CeO2

The defect structure and ionic diffusion processes within the anion-deficient, fluorite structured system Ce1–xYxO2–x/2 have been investigated at high temperatures (873 K–1073 K) as a function of dopant concentration, x, using a combination of neutron diffraction studies, impedance spectroscopy measurements, and molecular dynamics (MD) simulations using interionic potentials developed from ab initio calculations. Particular attention is paid to the short-range ion–ion correlations, with no strong evidence that the anion vacancies prefer, at high temperature, to reside in the vicinity of either cationic species. However, the vacancy–vacancy interactions play a more important role, with preferential ordering of vacancy pairs along the ⟨111⟩ directions, driven by their strong repulsion at closer distances, becoming dominant at high values of x. This effect explains the presence of a maximum in the ionic conductivity in the intermediate temperature range as a function of increasing x. The wider implications of these conclusions for understanding the structure–property relationships within anion-deficient fluorite structured oxides are briefly discussed, with reference to complementary studies of yttria and/or scandia doped zirconia published previously.

Growth, structural and optical characterizations of LiLa(1−x)Eux(WO4)2 single-crystalline fibers by the micro-pulling-down method

Transparent and uniform LiLa(1−x)Eux(WO4)2 single-crystalline fibers where x=0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25 and 1.0, with an average of 20–40mm length were obtained by the micro-pulling-down method aiming structural and optical characterization. The optimum pulling rate was found to depend on the difference between alkali and rare earth ionic radii. Rietveld analysis from X-ray diffraction data and excitation spectroscopy at room temperature were applied to investigate the lattice changes due to the Eu3+ incorporation in the host. LiLa(1−x)Eux(WO4)2 crystal fibers present red emission due to the electric dipole 5D0→7F2 transition under 395nm excitation showing a concentration quenching around 20mol% of doping. The excitation spectra of the 7F0→5D0 transition show small changes in the Eu3+ surroundings as function of dopant concentration.

Effect of doping on performance of organic solar cells

Conventional models of planar and bulk heterojunction organic solar cells have been extended by introducing doping in the active layer. We have studied the performance of organic solar cells as a function of dopant concentration. For bulk heterojunction cells, the modeling shows that for the most studied material pair (poly-3-hexylthiophene, P3HT, and phenyl-C61-butyric acid methyl ester, PCBM) doping decreases the short-circuit current density (JSC), fill factor (FF) and efficiency. However, if bulk heterojunction cells are not optimized, namely, at low charge carrier mobilities, unbalanced mobilities or non-ohmic contacts, the efficiency can be increased by doping. For planar heterojunction cells, the modeling shows that if the acceptor layer is n doped, and the donor layer is p doped, the open-circuit voltage, JSC, FF and hence the efficiency can be increased by doping. Inversely, when the acceptor is p doped, and the donor is n doped; FF decreases rapidly with increasing dopant concentrations so that the current-voltage curve becomes S shaped. We also show that the detrimental effect of nonohmic contacts on the performance of the planar heterojunction cell can be strongly weakened by doping.

Characterization of Manganese-doped Willemite Green Phosphor Gel Powders

Nanocrystalline manganese-doped zinc silicate (Zn2−xMnxSiO4; x = 0-12.0 mol%) powder phosphors were prepared by the sol-gel process. Zinc chloride, tetraethylorthosilicate, and manganese chloride were employed as precursors. The influences of water concentration on the crystallization and photoluminescence of the phosphors were investigated. Single-phase wiemite (α-Zn2SiO4) started to crystallize after calcining at 600°C for powders derived from low-water-conen so, whie β-Zn2SiO4 became the dominated phase with residual ZnO trace for high-water-content sol derived powders as calcining at below 900 °C. On firing at 800°–1200°C, the resulting phosphors had the average crystallite sizes of 15∼38 nm. With various content of water and heating the powders at 800°C, the prepared phosphors exhibited yellow and green emission peaking at 556 and 524 nm, respectively. Upon heating at 1200 °C, powder phosphors exhibited prominent photoluminescence emission bands peaked at 522∼526 nm, depending on the doping content. The luminous efficiency has been investigated as a function of dopant content and heating temperature.

BLUE EMISSION AND BANDGAP MODIFICATION IN N:ZnO NANORODS

Nanorods of nitrogen-doped ZnO (N:ZnO) are grown by hydrothermal chemical precipitation method. The average crystallite size, surface morphology, and particle size distribution are estimated and characterized from powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The characteristic vibration mode of metal-oxide is confirmed from Fourier transform infrared spectroscopy (FT-IR) study. The absorption spectra of N:ZnO in the ultraviolet visible (UV-vis) region and their variations are recorded as a function of dopant concentration. The Tauc plot elucidates that the bandgap of N:ZnO increases up to 6 atomic percent (at.%) of dopant concentration and then decreases for heavy doping. The widening and narrowing in bandgap is interpreted in terms of impurity induced absorption edge shift due to N doping. Photoluminescence (PL) spectra revealed the existence of visible band, arising from impurity related defects.

Zirconium-doped lithium niobate: photorefractive and electro-optical properties as a function of dopant concentration

Measurements of refractive indices, electro-optic coefficients and photorefractivity are performed for a set of Zirconium-doped congruent lithium niobate (Zr:LN) crystals as functions of the dopant concentration in the range 0.0-3.0 mol%. The photorefractive properties are studied by measuring the green-light induced birefringence change and by direct observation of the transmitted-beam distortion. The index of refraction data show that the threshold concentration, above which there is a change in the Zr incorporation mechanism, is about 2.0 mol%, but photorefractivity results suggest that the concentration of ZrO2 required to strongly reduce the photorefractive effect is somewhat larger than the 2.0 mol% “threshold” concentration derived from index-of-refraction data. The electro-optic coefficients are little influenced by Zr-doping. All the reported results confirm that Zr:LN is a very promising candidate for the realization of efficient electro-optic and all-optical nonlinear devices working at room temperature.

Characterization of Zirconia-India Ceramics Sintered by Spark Plasma

We present the synthesis and characterization of ZrO2:x mol %In2O3 ceramics with x = 8, 10 and 12. Sintering has been achieved with spark plasma sintering which allows for higher densification (~ 97% of theoretical density). The powders were characterized by thermal analyses, scanning electron microscopy, x-ray diffraction. The electrical properties of the sintered samples were studied by electrochemical impedance spectroscopy as a function of dopant concentration x and temperature. The spark plasma sintering is effective to sinter the ZrO2-In2O3 nanoparticles, and sample with x = 8 were found to be pure ionic conductor at temperatures above ~ 300 °C.

Structural and magnetic properties of Cr+3doped nano-structuredγ-Fe2O3synthesized by a modified solution combustion technique

Chromium doped gamma ferrite nanopowders (16.91 nm to 25.61 nm) of the composition (Fe 2- x Cr x O 3 for x = 0.00, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10) were successfully synthesized by a modified solution combustion method using citric acid as fuel at a temperature as low as 150 °C. The so prepared samples were examined by powder XRD for phase identification and crystallite size determination. The dimensions of particle size as calculated from XRD are in good agreement with those evaluated by transmission electron microscope (TEM). Fourier Transform Infrared (FTIR) analysis was carried out to identify the various chemical bonds present in the system. Magnetic examinations were performed in terms of magnetic susceptibility and hysteresis plots. A decrease in the blocking temperature with the increase of dopant concentration was observed which is explained on the basis of Neel's relaxation theory. A simple model has been suggested to explain the behaviour of hysteresis trends as the function of dopant concentration.

Resonant soft X‐ray emission and X‐ray absorption studies on Ga1‐xMnxN grown by pulsed laser deposition

AbstractIn this study thin film samples of Ga1‐xMnxN were grown by pulsed laser deposition on Al2O3 (0001) substrates. X‐ray diffraction measurements have confirmed these thin films exhibit hexagonal wurtzite structure. SQUID measurements show room temperature ferromagnetism of these dilute magnetic semiconductors (DMS). The techniques of X‐ray absorption and soft X‐ray emission spectroscopy at the N K‐edge were used to study the changes in the unoccupied and occupied N 2p partial density of states respectively as a function of dopant concentration. These element and site specific spectroscopies allow us to characterise the electronic structure of these doped materials and reveal the influence of the Mn doping on the valence band as measured through the N 2p partial density of states. X‐ray absorption measurements at the Mn L‐edge confirm significant substitutional doping of Mn into Ga‐sites. Finally, measurements of heavily Mn‐doped films using both soft X‐ray absorption and resonant soft X‐ray emission at the N K edge reveal the presence of trapped molecular nitrogen. The trapped molecular nitrogen may be due to the high instantaneous deposition rate in the PLD process for these samples (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Oxide phosphors for light upconversion; Yb3+ and Tm3+ co-doped Y2BaZnO5

The optical properties of Yb3+ and Tm3+ co-doped Y2BaZnO5, synthesized by solid-state reaction, are investigated in detail. Three main emission bands centered around 479 nm (blue), 654 nm (red), and 796 nm (near-infrared) are observed under near-infrared laser excitation via an upconversion process. Detailed studies of the upconversion properties as a function of dopant concentrations are described and upconversion efficiencies quantified precisely. Maximum efficiencies of ∼ 1.53% in the 730-870 nm near-infrared emission range and of ∼ 0.09% in the 420-530 nm blue range are obtained. The results of power dependence studies and concentration dependent lifetime measurements are presented. This in-depth spectroscopic study allows us, for the first time, to identify the dominant processes involved in the upconversion mechanism of Yb3+, Tm3+ co-doped Y2BaZnO5 oxides.

Synthesis of conducting Zn 1 − xMg xO: Al layers by spray pyrolysis for photovoltaic application

In recent years, Zn 1 − x Mg x O has attracted the attention of many researchers as its physical behavior can be suitably controlled by varying the Zn/Mg ratio. Also, it has high stability with low toxicity and the abundance of constituent elements. Further, the band offsets can be tuned to a minimum level with respect to a heterojunction partner by suitably controlling the Zn/Mg ratio. These properties make this material as a potential candidate as a buffer layer in the fabrication of Cu(In,Ga)Se 2-based solar cells. In our previous study, Zn 1 − x Mg x O films prepared by spray pyrolysis at 300 °C have shown high resistance and optical transmittance with wide energy band gap. However, it is interesting to note that if the films were conducting, then they can also be used as window layers. In the present investigation, Zn 0.76Mg 0.24O films have been prepared by spray pyrolysis at an optimized substrate temperature of 300 °C with different dopant concentrations that vary in the range, 0–6%. X-ray diffraction analysis showed that the films were polycrystalline and exhibited wurtzite crystal structure with a preferential c-axis orientation. The influence of Al doping on the electrical resistivity was found to be significant. The average transmittance of the films was found to be > 60% in the visible range with a small variation in the optical energy band gap. The changes occurred in the structure, topography, composition, electrical and optical properties of the layers as a function of dopant concentration have been studied.

Photoluminescent ZrO2:Eu3+ Nanofibers Prepared via Electrospinning

Europium-doped zirconium oxide (ZrO2:Eu3+) nanofibers were prepared via electrospinning, in which a mixture of zirconium chloride oxide octahydrate, europium nitrate hexahydrate, poly(vinyl pyrrolidone), dimethylformamide, and ethanol were electrospun at atmospheric conditions. Subsequent calcination to produce ZrO2:Eu3+ nanofibers with diameters around 300 nm. The crystal structure and photoluminescence of the ZrO2:Eu3+ nanofibers were studied as a function of dopant concentration and heating temperature. At a dopant concentration of 5 mol %, tetragonal phase crystals were observed. Photoluminescence spectra revealed several emission bands in the red region corresponding to the transition of 5D0→7FJ (J=1,2,3,4). Two most intense emission bands were observed at wavelengths of 606 and 591 nm due to the forced electric dipole (5D0→7F2) and magnetic dipole (5D0→7F1) transitions, respectively. This work demonstrates that one-dimensional photoluminescent materials can be generated by a two step electrospinning and calcination process.

Influence of Tungsten Doping on the Ferroelectric Behavior of Sr0.8Bi2.3Ta2O9 Thin Films

The substitution effect of W+6 at Ta+5 site on the structural, dielectric and ferroelectric properties of Bi-rich Sr0.8Bi2.3Ta2O9 (SBT) thin films is reported. Samples of compositions Sr0.8-x/2Bi2.3Ta2-xWxO9 (SBTW) with x ranging from 0.0 to 0.2 were synthesized by a chemical solution deposition technique using non-hydrolyzing precursors. The microstructure and ferroelectricity of SBTW films as functions of dopant concentration and annealing temperature were studied. Well-defined hysteresis loops were obtained for the doped films annealed between 650°C and 750°C. The ferroelectric properties, however, were not improved compared to those of undoped SBT films due to the appearance of a non-ferroelectric secondary phase.