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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Controlled synthesis of α-MnO{sub 2} nanowires and their catalytic performance for toluene combustion

Highlights: • One-dimensional α-MnO{sub 2} nanowires were prepared by a facile hydrothermal route. • Shape and crystal phase of the products were controlled by tuning reaction conditions. • A possible formation mechanism of the α-MnO{sub 2} nanowires was discussed. • The α-MnO{sub 2} nanowires showed great catalytic activity for toluene combustion. - Abstract: α-MnO{sub 2} nanowires with a length about 6–10 μm and an average diameter of 20 nm were synthesized through a facile hydrothermal process without any templates or surfactants. The products were characterized by X-ray powder diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, hydrogen temperature-programmed reduction techniques, X-ray photoelectron spectroscopy and surface area analysis. The effects of the hydrothermal temperature and the concentration of CH{sub 3}COOH on the crystal phase and morphology of the final products were studied in detail. The hydrothermal temperature and the concentration of CH{sub 3}COOH play crucial roles in determining the crystal phase and morphology of the products. The possible formation mechanism of the α-MnO{sub 2} nanowires was investigated and discussed. Additionally, the as-prepared α-MnO{sub 2} nanowires showed higher catalytic activity for toluene combustion than the commercial MnO{sub 2}, suggesting their potential applications in the elimination of volatile organic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Phenoxo bridged dinuclear Zn(II) Schiff base complex as new precursor for preparation zinc oxide nanoparticles: Synthesis, characterization, crystal structures and photoluminescence studies

Highlights: • A novel nano-scale Zn(II) complex was synthesized by solvothermal method. • Chemical structure of the nanostructures was characterized as well as bulk complex. • The photoluminescence property of the complex was investigated at room temperature. • The thermogravimetry and differential thermal analysis were carried out. • Thermal decomposition of the nanostructures was prepared zinc oxide nanoparticles. - Abstract: Nanoparticles of a novel Zn(II) Schiff base complex, [Zn(HL)NO{sub 3}]{sub 2} (1), (H{sub 2}L = 2-[(2-hydroxy-propylimino) methyl] phenol), was synthesized by using solvothermal method. Shape, morphology and chemical structure of the synthesized nanoparticles were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier Transform Infrared Spectoscopy (FT-IR) and UV–vis spectroscopy. Structural determination of compound 1 was determined by single-crystal X-ray diffraction. The results were revealed that the zinc complex is a centrosymmetric dimer in which deprotonated phenolates bridge the two five-coordinate metal atoms and link the two halves of the dimer. The thermal stability of compound 1 was analyzed by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of the initial substrates concentration and reaction time on size and morphology of compound 1 nanostructure was investigated as well. Furthermore, the luminescent properties of the complex 1 were examined. ZnO nanoparticles with diameter between 15 and 20 nm were simply synthesized by solid-state transformation of compound 1 at 700 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synthesis and control the morphology of Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+}/Eu{sup 2+},Mn{sup 2+} phosphors by precipitation method

Highlights: • Use facile and mild precipitation method obtained Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+}/Eu{sup 2+},Mn{sup 2+} phosphors. • Through controlling the morphology to tune the photoluminescence properties. • The columnar structure Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+} phosphor shows better emission intensity. • Self-assembled phenomenon appears by changing the Mn{sup 2+} concentration of the Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+},Mn{sup 2+} phosphor. - Abstract: Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+}/Eu{sup 2+},Mn{sup 2+} phosphors have been synthesized by the facile and mild precipitation method and they are characterized by X-ray powder diffraction, scanning electron microscopy, photoluminescence spectra. The SEM results indicate the obtained Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+} phosphors have the columnar structure and the Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+},Mn{sup 2+} phosphors is the sphere like. The effects of the stirring and sintering temperature on the morphology of Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+}/Eu{sup 2+},Mn{sup 2+} phosphors have been investigated. The photoluminescence spectra of Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+} and Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+},Mn{sup 2+} phosphors showed that the Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+} phosphors can be excited by 345 nm and exhibit blue emission around 421 nm and the Sr{sub 2}P{sub 2}O{sub 7}:Eu{sup 2+},Mn{sup 2+} phosphors can be excited by 355 nm and exhibited the emission around 420 nm and 578 nm showing the white light.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Tb{sup 3+} induced orange persistent luminescence in Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+}: The role of the auxiliary codopant

Highlights: • The orange persistent luminescence of Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+},Tb{sup 3+} was first reported. • The role of Tb{sup 3+} was discussed. • The TL curve reveals there are two traps responsible for the persistent luminescence. - Abstract: This study reports an orange emitting persistent phosphor Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+},Tb{sup 3+}. The material was synthesized by solid state reaction method in a reducing atmosphere. The persistent phosphor was characterized in detail by X-ray powder diffraction, photoluminescence, persistent luminescence and thermoluminescence spectra. After UV irradiation, Cs{sub 2}CaP{sub 2}O{sub 7}:Eu{sup 2+},Tb{sup 3+} phosphor shows an orange persistent luminescence (∼590 nm) at room temperature, whereas only photoluminescence is observed in Eu{sup 2+} singly doped samples. Both of the photoluminescence and persistent luminescence is due to the 4f{sup 6}5d{sup 1} → 4f{sup 7} transition of Eu{sup 2+} and the emission lines of Tb{sup 3+} are totally absent. The deconvolution of the thermoluminescence curve reveals there are two kinds of traps responsible for the persistent luminescence. The depth of the dominating trap is 0.61 eV. Based on experimental results, the role of Tb{sup 3+} and the trapping/detrapping processes of charge carriers were discussed. An energy level scheme was proposed to explain the mechanisms of persistent luminescence as well as photoluminescence.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synthesis and photoluminescence properties of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) red phosphor

Highlights: • The ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) red phosphors were synthesized. • Photoluminescence (PL) properties of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) phosphors also were discussed. • ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) could be a potential red phosphor for NUV LEDs and displays. - Abstract: ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) oxyapatite phosphors have been synthesized via traditional solid-state methods X-ray powder diffraction (XRD) analysis confirmed the phase formation of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) materials. The scanning electron microscope (SEM) image exhibited the irregular morphology of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) particles. The photoluminescence excitation (PLE) and emission (PL) spectra were investigated. The results showed that the phosphor could be efficiently excited by the near ultraviolet (NUV) light, and it exhibited red light emission. The calculated color coordinates lies in the red region. All the obtained results suggest that the prepared phosphors exhibit great potential application as red emitting phosphor for near ultraviolet white light emitting diodes (NUV WLEDs).

36 MATERIALS SCIENCE↗
DOE OSTI2017

Mixed rare earth oxides derived from monazite sand as an inexpensive precursor material for room temperature magnetic refrigeration applications

Highlights: • Compound is synthesized using mixed rare earth oxide derived from monazite sand. • Rietveld refinement confirms the compound is a mixture of rare earth manganites and CeO{sub 2}. • The compound exhibits a magnetic entropy change of 3.28 J kg{sup −1} K{sup −1} under 50 kOe magnetic field at 310 K. • The compound exhibit a RCP of 120 J kg{sup −1} and ΔT{sub ad} of 2.11 K at 310 K under 50 kOe field. - Abstract: An inexpensive perovskite type (RE{sub MIX}){sub 0.67}Sr{sub 0.33}MnO{sub 3} compound is synthesized via solid state method using mixed rare earth oxide precursor derived from monazite sand. Rietveld refinement of X-ray powder diffraction patterns confirms the compound is a mixture of rare earth manganites which is the major phase and CeO{sub 2} as the secondary phase. The compound shows a second order ferromagnetic to paramagnetic transition near room temperature and exhibits a magnetic entropy change (-ΔS{sub M}) of 3.28 J kg{sup −1} K{sup −1} with a relative cooling power (RCP) of 120 J kg{sup −1} and an adiabatic temperature change (ΔT{sub ad}) of 2.11 K at 310 K under 50 kOe magnetic field. The Debye temperature of the compound is found to be 543 K and room temperature thermal conductivity is 4.26 W m{sup −1} K{sup −1}. The temperature variation of electrical resistivity shows a metal to insulator transition around 180 K, which gets shifted towards higher temperature upon the application of magnetic field. The compound shows a large value of −ΔS{sub M} and this work makes an endeavor to develop low–cost materials for the magnetic refrigeration applications near the room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electrical properties and conduction mechanism study by OLPT model of NaZnPO4 compound

Highlights: • The crystal structure was resolved using Fullproof program. • The conduction in NaZn PO{sub 4} is insured by OLPT model. • Ac conductivity of NaZn PO{sub 4} compound obeys the Joncher’s law. - Abstract: A polycrystalline sample with NaZnPO{sub 4} stoichiometry was synthesized by the conventional solid-state reaction and then identified and characterized by X-ray powder diffraction, Raman spectroscopy and impedance spectroscopy. The X-ray diffraction pattern revealed that the composite represents a single phase that crystallizes in the monoclinic system with a P2{sub 1}/n space group. All vibration modes of tetrahedral PO{sub 4} appeared in the Raman spectrum. Besides, the electrical conductivity behavior of the title compound was analysed as a function of frequency ranging from 209 Hz to 1 MHz and at a temperature interval ranging from 578 K to 728 K by means of impedance spectroscopy to elucidate the conduction mechanism in this compound. The temperature dependence of frequency exponent ′s′ showed that the conduction in NaZnPO{sub 4} is insured by the overlapping large polaron tunneling (OLPT) model. A correlation between electrical and structural properties was also depicted.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Characterisation of organic-inorganic hybrid materials of the types ZnxCd1-xSe(1,3-diaminopropane)1/2 and ZnSySe1-y(1,3-diaminopropane)1/2

Highlights: • New hybrid materials: Zn{sub x}Cd{sub 1-x}Se(1,3-DAP){sub 1/2} and ZnS{sub x}Se{sub 1-x}(1,3-DAP){sub 1/2} were obtained. • Hybrids were studied using XRD, TG/DSC, XRD vs. temperature, SEM, UV–vis spectroscopy. • The impact of the composition of the layers on optical properties were studied. - Abstract: Organic-inorganic hybrid materials of the type MeQ(diamine){sub 1/2} (where Me–Zn, Cd, Mn and Q–S, Se, Te) belong to the class of 3D nanomaterials. They are built of layers of II–VI semiconductors and amines, which act as linkers. The main goal of our work was the synthesis of compounds of the type Zn{sub x}Cd{sub 1-x}Se(1,3-diaminopropane){sub 1/2} and ZnS{sub y}Se{sub 1-y}(1,3-diaminopropane){sub 1/2} (where x, y = 0, 0.25, 0.5, 0.75, 1) and the study of properties changed by the composition of the semiconducting layers. Analysis of these materials was carried out with the use of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC) as well as temperature dependent XRPD enabled us to obtain information about the thermal stability of hybrid compounds with mixed semiconducting layers. Another important part of our work was a study, performed with the use of UV–vis spectroscopy, of the optical properties of these materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Alternating current conduction mechanisms of RbMgPO4 compound

Highlights: • Two displacive reversible phase transitions located at T{sub 1} = 442/432 K and T{sub 2} = 460/445 K (heating/cooling). • The temperature dependence of conductivity was described in terms of Arrhenius relation. • The ac conductivity of this compound is proportional to ω{sup s} where the s values are between 0 and 2. • The (CBH) model was found to be the appropriate transport mechanism in RbMgPO{sub 4} compound. - Abstract: Rubidium magnesium monophosphate (RbMgPO{sub 4}) compound was prepared from highly pure constituents by solid state reaction. It was characterized by X-ray powder diffraction, IR, Raman, differential scanning calorimetry (DSC) and impedance spectroscopy. The infrared and Raman spectra were interpreted on the basis of PO{sub 4}{sup 3−} vibrations. DSC revealed two displacive and reversible phase transitions at T{sub 1} = 442/432 K and T{sub 2} = 460/445 K (heating/cooling). The electrical conductivity was measured in the frequency and temperature range 200 Hz-5 MHz and 423 K–523 K, respectively. The obtained results were analysed by fitting the experimental data to an equivalent circuit model. The temperature dependence of alternating and direct current conductivities (σ{sub ac}, σ{sub dc}) confirms the observed transitions in the calorimetric study; they were described in terms of Arrhenius relation. The activation energy’s values were determined in each phase. The AC conductivity behavior is ensured by a single process defined as a hopping transport mechanism. The conductivity frequency dependence was interpreted using the correlated barrier-hopping model (CBH) in all phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Photoluminescence, thermoluminescence and defect centres in Y2O3 and Y2O3:Tb3+ under 100 MeV swift Ni8+ ion beam irradiation

Highlights: • XRD showed decrease of crystallite size after ion irradiated. • Electron spin resonance reveals the presence of F, F{sup +} and O{sub 2}{sup −} centres. • SHI irradiated Y{sub 2}O{sub 3}:Tb{sup 3+} exhibits purity of intense green emission and long life time. • The Tb{sup 3+} doped Y{sub 2}O{sub 3} shows a linear, greater TL efficiency, longer life time and less fading under SHI irradiation. - Abstract: Y{sub 2}O{sub 3} and Y{sub 2}O{sub 3}:Tb{sup 3+} powders, synthesized via the solution combustion method, were studied in order to determine the effect of 100 MeV swift Ni{sup 8+} ions on the photoluminescence (PL), thermoluminescence (TL) and swift ion beam induced defects. Synthesized materials were characterized by X-ray powder diffraction, electron spin resonance, PL intensity, decay measurements and TL. Cubic structures were observed in both the pristine and ion irradiated materials. The ion irradiated materials exhibited smaller crystallite sizes than that of the pristine material. PL peaks in the visible region were identified at 485, 542, 582 and 621 nm due to the {sup 5}D{sub 4}→{sup 7}F{sub 3,4,5,6} transition of Tb{sup 3+}. The PL intensity showed an increase up to 3 × 10{sup 10} ions cm{sup −2} and then a significant decrease with a further increase in the ion fluence. The recorded time resolved PL at an ion irradiated fluence of 3 × 10{sup 10} ions cm{sup −2}, exhibited an increase in the life time of the material. TL glow curves were obtained for the samples irradiated with a swift Ni{sup 8+} ion beam. These glow curves showed a peak at 518 K with a shoulder peak at 473 K and its intensity linearly increased upto a fluence of 1 × 10{sup 11} ions cm{sup −2}. Whereas, the undoped sample showed peaks at 421 and 662 K and its intensity sub-linearly increased upto a fluence of 1 × 10{sup 11} ions {sup −2}. TL efficiency values of the Y{sub 2}O{sub 3}:Tb{sup 3+} sample, irradiated by a 100 MeV Ni{sup 8+} ion beam, have been measured relative to the undoped Y{sub 2}O{sub 3} sample and were found to be 1.34. The Tb{sup 3+} doped sample exhibited a less fading effect under the swift heavy ion beam.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Biogas reforming over Ni catalysts dispersed in different mixed oxides containing Zn2+, Al3+ and Zr4+cations

Highlights: • The oxides mixture containing NiO, ZnO, Al{sub 2}O{sub 3}, NiAl{sub 2}O{sub 4} and ZnAl{sub 2}O{sub 4} was detected. • The results exhibited intermediate interactions between Ni0 and other phases. • Dry reforming of methane was applied to production of synthesis gas. • Deposition of the carbon filamentous on the catalysts surface was observed. - Abstract: The active phase plays an important role in the catalytic activity. However, its applicability is directly associated with other present phases in the mixture. In view of this, we report the performance of Ni catalysts dispersed on mixed oxides containing Zn{sup 2+}, Al{sup 3+} and Zr{sup 4+}cations in biogas reforming. For this purpose, the samples were characterized by X-ray powder diffraction, which showed the formation of a homogeneous mixture of binary (NiO, ZnO, ZrO{sub 2} and Al{sub 2}O{sub 3}) and ternary (NiAl{sub 2}O{sub 4} and ZnAl{sub 2}O{sub 4}) oxides. The temperature-programmed reduction (H{sub 2}-TPR) provided information on the catalyst reduction. The performance of the catalysts was evaluated using two reduction temperatures (650 °C and 750 °C). The reactions were carried out at 750 °C, where the Ni/ZnAlZr catalyst presented the highest CO{sub 2} conversion attributed to the basic sites, which favored the CO{sub 2} adsorption. Otherwise, the Ni/ZnZr catalyst (reduced at 650 °C) showed a high CH{sub 4} conversion. The catalysts were also reduced at 750 °C and a lower conversion of both reactants (CH{sub 4} and CO{sub 2}) was observed. We argued that the agglomeration process during the reduction condition deteriorates the performance of the catalysts reduced at 750 °C.

09 BIOMASS FUELS↗
DOE OSTI2018

Improved photo-degradation of dyes over Ag-loaded NiTiO3:V nanorods on visible-light-irradiation

Highlights: • Ag/NiTiO{sub 3}:V nanorods were prepared by electrospinning synthesis. • The crystalline crystal structure was refined. • The optical absorption and band structure were clarified. • Photocatalysis was greatly enhanced in Ag/NiTiO{sub 3}:V nanorods. • The photocatalysis activities and mechanisms were discussed. - Abstract: Pure and V-doped NiTiO{sub 3} (NiTiO{sub 3}:V) nanorods were synthesized via electrospinning synthesis using sol–gel precursors, followed by sintering the samples at 600 °C. And the subsequent Ag-loaded NiTiO{sub 3}:V nanorods were prepared by the chemical precipitation method (Ag/NiTiO{sub 3}:V). The phase formations were studied via X-ray powder diffraction (XRD) measurements. The Rietveld refinements were conducted to investigate the structural characteristics. The surface property of the nanorods was measured via morphologies and X-ray photon spectrascope (XPS) measurements. The absorption spectra of products indicate sufficient optical response in visible wavelength region. The indirect allowed band gap (2.18 eV) of NiTiO{sub 3} originates from the characteristic charge-transfer (CT) transitions of O{sup 2−} → Ti{sup 4+} (UV region) and Ni{sup 2+} → Ti{sup 4+} (visible light region). While Ag/NiTiO{sub 3}:V composites have a smaller band energy of 2.09 eV. The photocatalytic activities were investigated by photo-degradation of Rhodamine B (RhB) dye solutions under visible-light irradiation. The Ag/NiTiO{sub 3}:V nanorods were efficient for the photo-degradation of RhB dye solutions. EIS measurements were used to analyze the charge-carrier migration at the interfaces. The improved photocatalysis of Ag/NiTiO{sub 3}:V is ascribed to the narrowed band energy and enhanced efficiencies of the charge separations due to the Ag-coupling and V-doping in NiTiO{sub 3} lattices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Preparation of graphene/WO3/TiO2 composite and its photocathodic protection performance for 304 stainless steel

Highlights: • TiO{sub 2} nanoparticles and WO{sub 3} nanorods were immobilized onto graphene by the hydrothermal method. • The composite can provide an effective protection for 304 stainless steel under visible light. • The composite can offer a sufficient cathodic protection even in the dark. • Possible photocathodic protection mechanism of graphene/WO{sub 3}/TiO{sub 2} composite was proposed. - Abstract: Graphene/WO{sub 3}/TiO{sub 2} composite (RGO/WO{sub 3}/TiO{sub 2}) was successfully fabricated via a two-step hydrothermal method. The structure, morphology and optical property of the as-prepared composite were characterized by X-ray powder diffraction, fourier transform infrared spectra, Raman spectra, transmission electron microscope, scanning electron microscope and ultraviolet-visible diffuse reflectance spectra, respectively. Results showed that the composite was incorporated by graphene nanosheets, WO{sub 3} nanorods and TiO{sub 2} nanoparticles. It exhibited favorable absorption ability in both UV and visible light region. The photocathodic protection performance for 304 stainless steel (304SS) was proven by photocurrent density, open circuit potential, Tafel polarization curves and electrochemical impedance spectroscopy. It was found that the composite could provide an efficient protection for 304SS under visible light irradiation and even in the dark compared to the pure TiO{sub 2}. The electrode potentials negatively shifted to −760 mV under visible light. The possible photocathodic protection mechanism of the composite was also proposed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Pyrophosphates AMoP2O7 (A = Li and Na): Synthesis, structure and electrochemical properties

Highlights: • Carbon-coated pyrophosphate materials AMoP2O7 (A = Li and Na) were prepared via freeze- drying method. • BVEL analysis revealed the remarkable difference in the alkali diffusion behaviors of two AMoP{sub 2}O{sub 7} polymorphs. • LiMoP{sub 2}O{sub 7} shows the superior electrochemical activity towards de/intercalation of Li{sup +} and Na{sup +} ions compared with NaMoP{sub 2}O{sub 7} - Abstract: The carbon-coated single-phase samples of the pyrophosphates AMoP{sub 2}O{sub 7} (A = Li and Na) were synthesized using freeze-drying followed by annealing in a sealed silica tube with the Fe/FeO getter. The Rietveld refinement of the X-Ray powder diffraction data proved both structures are built up as a network of corner-linked MoO{sub 6} octahedra and P{sub 2}O{sub 7} groups with A-cations located in the open tunnels running along the [100] (LiMoP{sub 2}O{sub 7}) and [101] (NaMoP{sub 2}O{sub 7}) directions. The bond valence energy landscapes (BVEL) analysis revealed three-dimensional pathways of alkali-ion migration with significantly different activation energies (0.8 eV for LiMoP{sub 2}O{sub 7} and 4.5 eV for NaMoP{sub 2}O{sub 7}) anticipating LiMoP{sub 2}O{sub 7} to exhibit faster Li{sup +} diffusion and better electrochemical characteristics. Both materials displayed electrochemical activity in Li- and Na-cells with reversible capacities of ∼20 mA h g{sup −1} for NaMoP{sub 2}O{sub 7} and more than 70 mA h g{sup −1} for LiMoP{sub 2}O{sub 7}, being in a good agreement with the BVEL results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Upconversion Er-doped TiO2 nanorod arrays for perovskite solar cells and the performance improvement

Highlights: • Er-doped TiO{sub 2} nanorod absorbs IR and converts into visible light. • The introduction of Er could make a positive shift in flat-band potential. • Er-doped TiO{sub 2} solar cells show a 20% increment in the current density. - Abstract: Upconversion erbium-doped rutile TiO{sub 2} nanorod arrays were synthesized by a facile process and applied in perovskite solar cells (PSCs). The structure was characterized by X-ray powder diffraction (XRD). Energy dispersive spectrometer (EDS) and Tauc plot indicated that Er was successfully introduced and changed TiO{sub 2} band gap from 3.00 eV to 3.07 eV. The incorporation of Er shifts the flat band potential positively and enhances the electron density. The Er-doped TiO{sub 2} nanorods have a broad absorption in the infrared light and up-convert it into visible light, which provides a possibility for PSCs to use NIR light for higher performance. A higher photocurrent density (J{sub sc}) of 22.97 mA/cm{sup 2} and a power conversion efficiency (PCE) of 10.6% were obtained, showing 20% and 16.5% increment in J{sub sc} and PCE, respectively, when compared with the un-doped device. The performance improvement was ascribed to the upconversion performance, enhanced electron-injection efficiency and reduced charge recombination.

14 SOLAR ENERGY↗
DOE OSTI2018

Preparation and investigation of Dy3+-doped Ca9LiGd2/3(PO4)7 single-phase full-color phosphor

Highlights: • A novel single-phased Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:xDy{sup 3+} phosphor was firstly synthesized. • Its structure, luminescent properties are well studied and characterized. • It was promising as a single-component white-light-emitting phosphor for w-LEDs. - Abstract: Novel single-phased white-light-emitting Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:xDy{sup 3+} (x = 0.02, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) β-Ca{sub 3}(PO{sub 4}){sub 2}-type phosphate phosphors were synthesized. The phase structure, luminescence, and thermal stability of the phosphors were characterized by X-ray powder diffraction analysis, photoluminescence excitation and emission spectra, thermal quenching, and decay curves. XRD analysis confirmed the phase formation of Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:Dy{sup 3+} materials. Under the excitation of 352 nm, the emission of the Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:0.20Dy{sup 3+} sample centered at blue (488 nm) and yellow (580 nm), which corresponded to {sup 4}F{sub 9/2}–{sup 6}H{sub 15/2} transition and {sup 4}F{sub 9/2}–{sup 6}H{sub 13/2} transition. The optimum dopant concentration of Dy{sup 3+} ions was around 20 mol%, and the critical transfer distance of Dy{sup 3+} was calculated as 18 Å. The thermal-quenching temperature was above 500 K for Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:0.20Dy{sup 3+}. The developed phosphor has a great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Novel white light-emitting CdSe:Mn 2+ synthesized by photo-assisted chemical bath deposition

Nowadays, white light-emitting materials have attracted extensive research due to their potential applications in lighting devices and displaying images. Several semiconductor nanoparticles have been explored to achieve efficient white light emission. In this work, we report on novel white light-emitting CdSe:Mn 2+ thin films synthesized by photo-assisted chemical bath deposition. The effect of varying the Mn 2+ ion concentrations on the thin film structure, morphology, and optical properties was investigated. X-ray powder diffraction results indicated that all the films annealed at 250 degrees C possessed a cubic structure, with crystallite sizes in the range of 1-130 nm. Scanning electron microscopy demonstrated spherical nanoparticles with no significant changes with varying Mn 2+ doping concentrations. Energy dispersive X-ray spectroscopy confirmed the presence of the anticipated elements. The atomic force microscope revealed that the surface roughness has decreased with an increase in Mn 2+ ion concentrations but decreased for 0.7 %Mn 2+ . The UV-Vis absorption spectra showed absorption edges around 600-650 nm. Photoluminescence emission spectra excited at 3.8 eV (325 nm) showed emission bands at around 1.75 eV (709 nm), and 1.88 eV (659 nm), which were attributed to the band-to-band emission, and 4 T 1 ( 4 G)-> 6 A 1 ( 6 S) transitions of Mn 2+ ions, respectively, while emission bands at 2.35 eV (528 nm), and prominent at 3.17 eV (391 nm) were due to the glass substrate. The temperature-dependent luminescence showed a decrease in relative emission intensity with the increase in the operating temperature. The chromaticity colour coordinates showed white light-emitting thin films. These present findings open a new door to developing white light using CdSe thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2021

An investigation of the phase behaviors for quaternary U-Nb/Mo-Ti-Zr metallic fuel alloys

We report quaternary fuel alloys containing U, Nb/Mo, Ti, and Zr are proposed as fuel candidates for sodium-cooled fast reactors (SFRs). In this work, two Nb-bearing alloys, i.e., U-NT5Z (U-2.5Nb-2.5Ti-5.0Zr in wt%) and U-NT7Z (U-1.5Nb-1.5Ti-7.0Zr in wt%), and two Mo-bearing alloys, i.e., U-MT5Z (U-2.5Mo-2.5Ti-5.0Zr in wt%) and U-MT7Z (U-1.5Mo-1.5Ti-7.0Zr in wt%) were characterized and compared. The characterization techniques were differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). DSC was performed to obtain the transition behaviors, and XRD and SEM/EDS were applied for phase identification. The results were combined to obtain the solid-state phase transitions between 500 °C and 850 °C for the alloys. It is found that the Nb-bearing alloys comprise similar phase transition behaviors as the Mo-bearing alloys. The phase transitions in U-NT5Z are a →γ at 608 °C and U 2 Ti → γ at 627 °C, which are ~40 °C higher than that of U-MT5Z. The phase transition in U-NT7Z is a → γ at 645 °C, and is 23 °C higher than that of U-MT7Z.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗