Single Phased Research Articles

Achieving White Light Emission with High Luminescence Efficiency via Combustion Produced Sr3Y(PO4)3: Dy3+ Nanophosphors for Photonic Applications.

Extensive investigations were conducted on the structural and photoluminescence characteristics of the present nanosamples, encompassing PL, TEM, PXRD, EDAX, CCT, and CIE research. PXRD studies established a single phase, and TEM instruments were used to examine the dimensions and topographical behavior. The EDAX analysis examined the magnitude of the different components that were present. Decay lifetimes, radiative and non-radiative energy transfer rates, and a number of intensity limitations have all been found using PL spectra. Two significant peaks were visible in the blue (B) and yellow (Y) regions of the photoluminescence (PL) spectra upon NUV excitation, at 486nm and 577nm. At 7mol% Dy3+ ions, the PL intensity peaked. After that, it began to decline as a result of the concentration quenching process brought on by multipolar exchanges (s = 4.1445). The values of 0.86423ms, 81%, and 226s-1 were discovered to be the decay life time, non radiative rates, and quantum efficiency of the ideal powder, respectively. Further analysis of Sr3Y0.93Dy0.07(PO4)3 nanocrystals revealed that their chromaticity coordinates (0.305, 0.321), and CCT value (6902K) matched those of NTSE and commercial LEDs, certifying their use in innovative optoelectronic appliances, particularly single phased WLEDs.

Destruction of mesoscopic chemically modulated domains in single phase high entropy alloy via plastic deformation

Chemically modulated mesoscopic domains in a fcc single phase CrMnFeCoNi equi-atomic high entropy alloy (HEA) are detected by small angle diffraction performed at a synchrotron radiation facility, whereas the mesoscopic domains cannot be detected by conventional X-ray diffraction and 2D mappings of energy dispersive X-ray spectroscopy by scanning electron microscopy and scanning transmission electron microscopy. The mesoscopic domains are deformed and shrieked, and finally destructed by plastic deformation, which is supported by the comprehensive observations/measurements, such as electrical resistivity, Vickers hardness, electron backscattering diffraction, and hard X-ray photoemission spectroscopy. The destruction of the mesoscopic domains causes the decrease in electrical resistivity via plastic deformation, so called K-effect, which is completely opposite to the normal trend of metals. We confirmed that the presence and the size of local chemical ordering or short-range order domains in the single phased HEA, and furthermore, Cr and Mn are related to form the domains.

Sintering and biocompatibility of copper-doped hydroxyapatite bioceramics

Addition of copper in biomaterials is currently investigated because it is expected to enhance the biological properties of bone graft substitutes. Copper-doped hydroxyapatite (CuHA) ceramics were prepared by high temperature solid-state reaction sintering between HA and CuO powder mixtures. The reaction occurred from 950 °C and copper-doped apatites were obtained up to 5.3 wt% of copper. For higher copper content, the presence of secondary phases of CuO and Cu2O remained in the material. Structural analyses (XRD, FTIR) showed the substitution of hydrogen by copper into the hydroxyapatite hexagonal channels in agreement with the following chemical composition Ca10(PO4)6CuIIzCuIyO2H2-2z-y with x = y + z and 0 ≤ x ≤ 0.7. Dense single phased apatitic HA ceramics containing up to 5.3 wt% of copper could be produced after natural sintering in air at 1100 °C. But, copper-substituted HA was found to be metastable leading to apatitic grains and Cu-rich grain boundaries during cooling to room temperature, which resulted in the formation of CuO grains at the material surface after annealing at 500 °C. Quenching from the sintering temperature was carried out to prevent this phenomenon and obtain ceramics made of single Cu-HA phase with a homogeneous fine grain microstructure. In vitro biological assays using MC3T3-E1 cells indicated that the sintered CuHA ceramics were biocompatible, neither cell adhesion nor proliferation being affected by copper addition. A negative effect on cell differentiation appears only from 5 wt% of copper in HA.

Generation of cold white light by using energy transfer process in single phase Ce3+/Tb3+ co-doped CaSrAl2SiO7 phosphor

Single phased CaSrAl2SiO7 phosphor singly doped with different concentrations of trivalent cerium and terbium; and co-doped with varying Tb3+ concentration were prepared by standard solid state reaction (SSR) method. The crystallinity and particle morphology of the product samples were analysed by using XRD and TEM characterizations. Photoluminescence characterizations of singly doped and co-doped samples were studied in detail. CaSrAl2SiO7:Ce3+,Tb3+ phosphor exhibit a broad blue emission band at 410 nm and some sharp emission bands in blue green and yellow regions, which originate from Ce3+ and Tb3+ ions, respectively. By increasing the concentration of Tb3+ ions while fixing Ce3+ concentration in the host lattice energy transfer takes place from Ce3+ to Tb3+ ions which create luminescence emission in white region. CaSrAl2SiO7:Ce3+,Tb3+ phosphors are proved to be promising candidates for white lighting for outdoor illumination.

Probing low temperature non-equilibrium magnetic state in Co2.75Fe0.25O4+δ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments

The low temperature lattice structure and magnetic properties of Co2.75Fe0.25O4 ferrite have been investigated using experimental results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac susceptibility, neutron diffraction and neutron depolarization techniques. The samples have been prepared by chemical co-precipitation of the Fe and Co nitrates solution in high alkaline medium and subsequent thermal annealing of the precipitates in the temperature range of 473–1173 K. Rietveld refinement of the SXRD patterns at room temperature indicated two-phased cubic spinel structure for the samples annealed at temperatures 473–873 K. The samples annealed at temperatures 973 K and 1173 K (CF90) have shown single phased lattice structure. Refinement of the neutron diffraction patterns in the measurement temperature range 5–300 K confirmed the antiferromagnetic (AFM) Co3O4 and ferrimagnetic (FIM) Co2.75Fe0.25O4 phases for the sample annealed at 873 K and single FIM phase of Co2.75Fe0.25O4 for the CF90 sample. Magnetic measurements have shown a non-equilibrium magnetic structure, consisting of high temperature FIM phase and low temperature AFM phase. The magnetic phases are sensitive to magnetic fields, where high temperature phase is suppressed at higher magnetic fields by enhancing the low temperature AFM phase, irrespective of annealing temperature of the samples.

Structural, Photoluminescence and Electron Density Distribution Analysis of Rutile Phase TiO2

In this work, the mixed anatase and rutile phases of commercial TiO2 sample was purchased and converted to single rutile phase by sintering at 1000°C. Structural and spectroscopic analysis of the single phased rutile TiO2 were analyzed by PXRD, SEM, EDS, PL analysis, respectively. Rietveld profile refinement technique was performed to fit the observed and calculated PXRD profiles. Charge density distribution studies were used to determine the chemical bonding nature of Ti-O bond by maximum entropy method (MEM). From the MEM calculations, Ti-O bond exhibited covalent nature. PL measurements showed that the emission wavelength of rutile TiO2 at around 470 nm which may be due to band to band transitions of Ti and O atoms.

A reddish-orange emitting samarium doped α-Na3Y(VO4)2 nanocrystals for single phased UV excitable white light applications

Nanocrystals of samarium doped sodium yttrium vanadate have been synthesized by citrate based solution combustion reaction method for the first time. X-ray powder diffraction analysis and transmission electron microscopic analysis revealed the highly crystalline nature and uniform spherical morphology of the sample. The strong and broad band observed in the UV–Vis absorption spectrum as well as in the photoluminescence excitation spectrum point to the efficient energy transfer from vanadate to Sm3+ ion. Under the excitation of near ultraviolet (310 nm), α-Na3Y1-xSmx(VO4)2 exhibit reddish orange emission with high purity and the optimal doping concentration of Sm3+ ion is found to be about 2 mol %. Unlike mostly reported samarium doped phosphors, red emission (4G5/2 → 6H9/2) is more intense compared to the orange emission (4G5/2 → 6H7/2) in the present system. The main reason for concentration quenching is determined to be dipole-dipole interaction leading to cross relaxation. Strong sensitization of Sm3+ ion via host, least chance for re-absorption of blue-green emission due to the weak direct f-f excitation of Sm3+ ion and high purity reddish-orange emission suggests samarium doped α-Na3Y(VO4)2 nanocrystal as a potential nanophosphor in the field of single phase white light generation.

White light emitting stannate pyrochlore based single phase phosphor CaLa1−xSnNbO7:xDy3+ for pc-WLED applications

A new series of single phase pyrochlore based white phosphors, CaLa1−xSnNbO7:xDy3+ (x = 0.01, 0.02, 0.03, 0.04) and Ca1−ySryLa0.97SnNbO7:0.03Dy3+ (y = 0.1, 0.2, 0.3) were developed by a high temperature ceramic route. The phase purity and the crystalline structure of the as-prepared samples were characterised by powder X-ray diffraction method and the phosphors were found to crystallize into the cubic pyrochlore type structure. The photoluminescence properties were investigated and the results indicated that phosphors show a strong excitation levels in near UV (388 nm) and blue (452 nm) regions and emits intense complimentary blue (487 nm and 477 nm) and yellow (589 nm) light upon UV or blue excitation which can be assigned to the characteristic 4F9/2 → 6HJ (J = 13/2 and 15/2) transitions of Dy3+ respectively. Thus the suitable combination of the above complimentary colors, yellow and blue is an approach to realize a full color emission and the Commission Internationale de I’Eclairage (CIE) color coordinates of the resultant phosphors lie in the white light region (0.38, 0.36) close to the standard chromaticity coordinates (white light) of NTSC. The substitution of bigger ion like Sr2+ for Ca2+ enhanced significantly the photoluminescence properties by way of their excitation and emission intensities due to increased polarizability and distortion of the Dy3+ environment. These results demonstrate that CaLa1−xSnNbO7:xDy3+ and Ca1−ySryLaSnNbO7:0.03Dy3+ are promising single phased white phosphor for pc-WLED applications.

Enhanced photoluminescence property and broad color emission of ZnGa2O4 phosphor due to the synergistic role of Eu3+ and carbon dots

ZnGa2O4 phosphors co-composited with nanoscale carbon dots (CDs) and Eu3+ were presented for the tunable color emission. Novel single phase CDs or/and Eu3+ composited ZnGa2O4 phosphors were synthesized by microwave hydrothermal method and their optical properties were investigated. The ZnGa2O4 phosphors composited with CDs exhibited an intense broad blue light emission at 421 nm and a more enhanced photoluminescence intensity than those without CDs. The Eu3+ composited ZnGa2O4 phosphors gave an ideal red color emission. The CDs/Eu3+ co-composited ZnGa2O4 phosphors exhibited a wide emission band peak at 450 nm and narrow emission peak at 618 nm. Furthermore, the tunable color emissions of CDs/Eu3+ co-composited ZnGa2O4 phosphors from blue to the white light region, and then to red were obtained with the increasing Eu3+ concentration, which can be a promising single phased phosphor candidate in light emitting diodes. Broadly tunable emission single phased phosphor is tuned firstly through the synergistic role of the non-metal element and the rare earth metal ions.

Single phase tunable warm white-light-emitting Sr_3La(PO_4)_3:Eu^2+, Sm^3+ phosphor for white LEDs

A novel single phased white emitting phosphor Sr3La(PO4)3:Eu2+, Sm3+ was synthesized by the solid-state method, and the crystal structure and luminescence properties of phosphors were investigated in detail by the X-ray diffraction, photoluminescence spectra and decay curves. Through the energy transfer, the warm white light can be realized with superior chromaticity coordinates of (0.3824, 0.3381), low correlated color temperature (CCT = 3598 K), and Ra of 78.4 by varying the molar ratios of Eu2+ and Sm3+ in the Sr3La(PO4)3:Eu2+, Sm3+ phosphor. The results indicate that the developed phosphor can be used as a potential warm white emitting phosphor for white light emitting diodes.

Potential single phased full colour white light Sr2−xCeO4∶xSm3+ phosphor for UV light emitting diodes

A potential single phased white Sr2CeO4∶Sm3+ phosphor was fabricated by a hydrothermal calcine method. The luminescence intensity of Sr2CeO4 host and redistribution depended on the doped Sm3+ concentration. It is also found that the photoluminescence spectrum exhibits a redshift when the Sm3+ concentration is increased from 0 to 2 mol-%. The phosphor can emit full colour white light with the Sm3+ concentration increasing from 0·5 to 1·0 mol-%. The energy transfer model is interpreted as the possible mechanisms of energy transfer from Sr2CeO4 host to Sm3+ in Sr2CeO4∶Sm3+ system. The fabrication and packaging of a white phosphor-converted light emitting diode (LED) by adopting a white Sr2CeO4∶Sm3+ phosphor with an ultraviolet (UV) LED chip with the wavelength of 350 nm is also successfully demonstrated. A white light with colour coordinates (0·3315, 0·3109) and luminescence efficiency of 56 lm W−1 could be obtained from the fabricated LEDs when keeping the Sr2−xCeO4∶xSm3+ phosphor doped with the content of Sm3+ at 1·0 mol-%, which shows that the phosphor is a promising single phase phosphor for UV LED.

Alloying of Fe3O4 and Co3O4 to develop Co3xFe3(1−x)O4 ferrite with high magnetic squareness, tunable ferromagnetic parameters, and exchange bias

Abstract Ferromagnetic (FM) Fe 3 O 4 and antiferromagnetic (AFM) Co 3 O 4 has been alloyed to form the ferrite composition Co 3 x Fe 3(1− x ) O 4 ( x = 0.1, 0.3, 0.5). Three different routes, viz., mechanical alloying at room temperature, annealing of the mechanically alloyed sample and solid state sintering, have been followed to develop the ferrite. X-ray diffraction pattern showed incomplete alloying in as milled samples. Single phased cubic spinel structure has formed after annealing of the mechanical alloyed samples at 950 °C, and also in solid state routed samples. The single phase has not formed for the samples at low Co content ( x = 0.1), but the single phased cubic spinel structure is stabilized for the higher value of Co content ( x = 0.3, 0.5). All samples showed FM loop at room temperature. The FM parameters (magnetization, squareness, coercivity) of the mechanically alloyed samples after annealing at 950 °C showed higher values in comparison with as milled and solid state routed samples with similar composition. Amongst the studied samples, the composition Co 0.9 Fe 2.1 O 4 (for x = 0.3) exhibited better FM properties in comparison with samples for the compositions x = 0.1 and 0.5. The present work highlighted few more unusual ferromagnetic features, e.g., different types of exchange bias effect, applied field controlled freezing of the ferromagnetic domains, tailoring of the Verwey transition of Fe 3 O 4 in the presence of AFM Co 3 O 4 , and field driven de-pinning of the domain wall motion at lower temperature that can be manipulated for developing next generation advanced magnetic ferrites.

Preparation and properties of sol–gel synthesized Mg-substituted Ni2Y hexagonal ferrites

A series of single phased Y-type hexagonal ferrites Sr2Ni2−xMgxFe12O22 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by the sol–gel auto combustion method. The effects on structural, magnetic and electrical properties have been investigated by substituting Mg2+ at Ni2+ sites. The X-ray diffraction (XRD) patterns confirm single phase Y-type hexaferrite and various parameters such as lattice constants, cell volume, X-ray density, bulk density and porosity have been calculated from XRD data. The Fourier transform infrared (FTIR) spectra show the characteristics absorption ferrite peaks of the sintered sample. The microstructure was studied by scanning electron microscopy (SEM). All the ferrites show a hexagonal platelet-like shape which is a most suitable shape for microwave absorption. The dielectric constant followed the Maxwell–Wagner interfacial polarization and relaxation peaks were observed in the dielectric loss properties. The room temperature dc electrical resistivity and activation energy were found to decrease for samples x=0.1, 0.2 and increase for the rest of samples hence making these materials suitable for multilayer chip inductors (MLCIs). A soft magnetic behavior was revealed by M–H loops. Saturation magnetization (Ms), retentivity (Mr), coercivity (Hc) and magnetic moment (nB) were found to decrease as the Mg2+ contents increased.

Synthesis of new brownmillerite-type systems A2(M2+,M4+,)2O5 (A = Ba, Sr, Ca; M2+ = Zn, Mg, Cd, Be; M4+, = Zr, Ce, Ti, Hf)

The A2(M,M')2O5 systems (A=Ba, Sr, Ca; M2+=Zn, Mg, Cd, Be; M4+'=Zr, Ce, Ti. Hf, Sn) having a brownmillerite-type compositions were prepared by a solid state reaction. X-ray diffraction analyses confirmed that only the combinations of (Ba-Zn-Zr), (Ba-Zr-Ce), (Ba-Zn-Hf), (Sr-Zn-Zr), (Sr-Zn-Ti) and (Sr-Zn-Hf) for the A-M2+-M4+' in the present systems showed single phases of cubic or orthorhombic perovskite-type structures at room temperature. When the average ionic radii of B site increased, the lattice constants and lattice volumes also increased. Although the samples have the brownmillerite composition, the obtained samples showed perovskite-type structure. The tolerance factor of single phased samples having the brownmillerite composition were estimated to be in the range of 0.9428 ~ 1.0061. It was found that the electrical comductivities of the new phases increased with increasing unit cell free volume.

Modified surface and bulk properties of Fe-substituted lanthanum titanates enhances catalytic activity for CO + N 2O reaction

Iron substituted lanthanum titanates with nominal composition La 2Ti 2(1− x) Fe 2 x O 7− δ (0.0 ≤ x ≤ 1.0) samples, were synthesized by gel combustion and conventional solid state reaction. The samples have been characterized by XRD, N 2-BET, SEM, FTIR, Mössbauer spectroscopy and TPR. Catalytic activity of these samples was evaluated for a decomposition reaction of N 2O using CO. Transition from La 2Ti 2O 7 (layered perovskite, A 2B 2O 7) to single phase, LaFeO 3 (perovskite, ABO 3) was observed for the samples having ≥40–60% Fe content. The microstructural analysis by SEM revealed homogeneous elongated shaped rods on single phased LTOGC surface, attributed to the layered perovskite whereas spherical grains are due to single perovskite (ABO 3) phase present in LF(0.4)GC samples. Mixed phased samples showed both elongated and spherical shape particles as observed in the SEM images. Among all samples, LF(0.6)GC have shown maximum activity of 100% conversion at 395 °C for decomposition of N 2O using CO and at 325 °C for CO oxidation. The substitution-induced anionic vacancies and asymmetric environment around Fe as suggested by Mössbauer results in partially substituted, LF(0.4)GC/SS and LF(0.6)GC/SS are responsible for considerable lowering in T max observed in their TPR profiles and enhanced activity for CO + N 2O reaction as compared to pristine samples.

Radially arrayed nanopillar formation on metallic stent wire surface via radio-frequency plasma

MP35N (Co–Ni–Cr–Mo alloy) is an important stent implant material for which many aspects, that include nanostructured surfaces, are yet to be understood. The present study provides the first creation of radially emanating metallic nanopillar structures on the surface of MP35N stent alloy wires; a novel textured surface structuring derived via controlled RF processing technique. The goal of this study was to characterize the newly found structures, identify evolution stages of nanopillar formations, as well as optimize RF process parameters for controlled surface texturing technique for stent wire materials. The exposure of a stent alloy wire, 250 μm diameter Co–Ni–Cr–Mo alloy (MP35N), to parameter-controlled RF environment resulted in dense surface nanostructures consisting of high-aspect-ratio dendritic nanopillars/nanowires. Extensive surface characterization and local compositional analyses by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) show increased values of Mo contents on the outer edges of protruding nanopillars, indicating a possibility of the higher Mo content phase contributing to the differential plasma sputter etching on the MP35N surface and resultant nanowire formation. A comparative investigation on single phase alloy versus multi-phase alloy seems to point to the importance of phase segregation for successful nanowire formation by RF plasma treatment. In addition to MP35N, some specific single phased materials, such as Fe–Ni and Fe–Cr alloys or Pt metal wire, were exposed in same RF plasma conditions and results did not form the complex structures found on MP35N samples. For the purpose of this study, metallic stent wires that have nanostructured surfaces can be considered a “polymer-less” approach to surface modification, The creation and characterization of radially arrayed nanostructured surfaces has been demonstrated on MP35N stent alloy wires using this RF plasma process; where such nanostructured surfaces contribute to design concepts that may enhance endotheliazation of stent materials via surface texturing modification.

Causes and Effects of Single-Phasing Induction Motors

It is well known that a three-phase induction motor will continue to operate when a disturbance of some sort causes the voltages supplied to the motor to become single phased. Single phasing can occur as a result of a fuse blowing or a protective device opening on one phase of the motor. Other possibilities include feeder or step-down transformer fuses blowing. Even though the motor will continue to operate in this condition, the motor will heat up very quickly, and it is essential that the motor be removed from service by the opening of a motor circuit breaker or some other type of protective device. This paper will describe three different ways in which an induction motor will operate in a single-phase condition. For purposes of this paper, "single phase" will include any condition in which the three line-to-line voltage phasors appear on the same line.

Portevin—Le Châtelier instabilities and stoichiometric effects in B2 titanium aluminides

The mechanical properties of a Ti{sub 53}Al{sub 25}Nb{sub 22} (at.%) alloy has been investigated over a large temperature range. The as-cast alloy is two-phased and contains an ordered b.c.c. (B2) phase and an ordered orthorhombic (O) phase. With appropriate heat treatments, a single phased alloy with either the B2 structure or the O structure can be obtained. The present paper reports on the observation of plastic instabilities in the B2 phase in the temperature range from 200 C to 450 C. It is shown that jerky flow in these compounds can be identified with Portevin-Le Chatelier (PLC) instabilities. The nature of the solute atom responsible for these dynamic strain aging effects is examined through the influence of alloy composition on the occurrence of unstable plastic flow. For this purpose, investigations on several TiAlMo and TiAlMoNb single phase B2 alloys, which also exhibit the PLC effect, have been performed. As a result, a new explanation is proposed for the occurrence of jerky flow in this class of intermetallic alloys.

Effect of Excess Ca/Cu on Phase Formation in Bi-2223 Superconductors

We have explored the effect of excess Ca and Cu addition on superconductivity in Bi–Pb–Sr–Ca–Cu–O system. A single phase 110 K high TC superconductor has been synthesized with Sr, Ca and Cu in the ratios of 1.6:2.4:3.6, respectively. There are two consequences, when Ca and Cu are in excess. Firstly, a single phased 110 K high TC superconductor is formed with the above mentioned ratio and secondary, the remaining Ca and Cu forms superconducting 2212 phase, non-superconducting Ca2PbO4, Ca2CuO3 and unreacted CuO. The XRD patterns and the results of the resistivity measurements are presented.

Doping effect of Sr or Ca on single phased YBa2Cu3O7−y

Abstract The relation between superconductivity and phase structure in YBa2Cu3O7−y doped with Sr and Ca has been studied systematically by the measurements of superconductivity, phase structure and thermal analysis. It is found that, for series of YBa2−xCaxCu3O7−y as 0⩽x⩽0.25, the samples are of single phase, and their Tc decrease linearly with content of Ca; for series of YBa2−xSrxCu3O7−y as 0⩽x⩽1.25, the samples are of single phase, but their Tc can change with the content of Sr either monotonously or non-monotonously, depending on the preparation conditions. A strong correlation exists between Tc and the crystal structure of the samples. The results obtained suggest strongly that the intensity of the coupling between Cu-O planes and Cu-O chains is very important to the high-Tc superconductivity of YBa2Cu3O7−y.