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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Blue photons excited highly chromatic red light emitting K3La(PO4)2:Pr3+ phosphors for white light emitting diodes

Highlights: • K{sub 3}La(PO{sub 4}){sub 2}:Pr{sup 3+} phosphors were investigated as an alternative for red light. • Highly chromatic red emission was realized upon blue excitation. • The phosphor has high color purity ∼ 97.8% and yield ∼27%. - Abstract: Highly chromatic blue photons excited red emitting K{sub 3}La(PO{sub 4}){sub 2}:Pr{sup 3+} (0–1.8 mol%) phosphors were synthesized by solution combustion method. The resulted phosphors showed peanut like morphology and had a monoclinic phase with space group P2{sub 1}/m. The photoluminescence studies disclosed that the phosphor emits red light due to the {sup 1}D{sub 2} → {sup 3}H{sub 4} and {sup 1}D{sub 2} → {sup 3}H{sub 5} transition of the Pr{sup 3+} ions under blue photons excitation. The optimal concentration for the Pr{sup 3+} ions were optimized to be 1.2 mol% after which concentration quenching occurred. Dipole-dipole interaction among the dopant ions was found to be responsible for the concentration quenching. X-ray photoelectron spectroscopy results depicted that Pr was present in the (+3) valance state in the phosphor. The photometric results suggest that the phosphor with a high color purity ∼ 97.8% and enough quantum yield ∼27% could be an eventual choice as the red component for white light emitting diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Controllable synthesis of ultra-long YCexOy:Eu3+ nanowire arrays and fluorescence activation of Ce3+

Highlights: • Ultra-long YCe{sub x}O{sub y}:Eu{sup 3+} nanowire arrays is realized by controllable synthesis. • Ce{sup 3+} ion dominates the fluorescence activation in YCe{sub x}O{sub y}:Eu{sup 3+} nanowire arrays. • Fluorescence emission in red light area is useful in medical image or cell labeling. - Abstract: Ultra-long YCe{sub x}O{sub y}:Eu{sup 3+} nanowire arrays(NWAs) have been synthesized in anodic aluminum oxide (AAO) templates by chemical co-deposition at negative pressure suction, which are amorphous, and possess precise dimension and homogeneous morphologies. The SEM, TEM, XRD and EDS were employed to investigate the morphology, structure and elemental composition of YCe{sub x}O{sub y}:Eu{sup 3+} NWAs. The fluorescence properties of the YCe{sub x}O{sub y}:Eu{sup 3+} NWAs were measured by fluorescence spectrometer (PerkinElmer LS-55) using Xenon discharge lamp as the excitation light source. There are two emission peaks at 615 nm and 702 nm with excitation wavelength of 394 nm, which corresponds to the {sup 5}D{sub 0}-{sup 2}F{sub 2} and {sup 5}D{sub 0}-{sup 7}F{sub 4} energy level transition of Eu{sup 3+}, respectively. The fluorescence intensity of YCe{sub x}O{sub y}:Eu{sup 3+} NWAs is related to the doping concentration of Eu{sup 3+} ion, which reaches a maximum with doping concentration of Eu{sup 3+} at 8%, and remarkably decreases at higher concentrations. Ce{sup 3+} ion dominates the fluorescence activation in YCe{sub x}O{sub y}:Eu{sup 3+} NWAs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Facile synthesis of the nitrogen-doped graphene quantum dots at low temperature for cellular labeling

Highlights: • The N-GQDs are prepared via a facile stirring method on a magnetic stirrer at low temperature. • The N-GQDs exhibit outstanding biocompatibility in the live HeLa cells for biological applications. • The live cells keep a 100% survival rate in the high N-GQDs concentration of 200 μg mL{sup −1} for 48 h. - Abstract: A facile one-step approach is developed for the large-scale synthesis of nitrogen doped graphene quantum dot (N-GQDs) at low temperature by using citric acid (CA) as the precursor. The emission wavelength of the N-GQDs is nearly excitation-dependent, which may mirror the effects from particles of different sizes and distribution of different emissive sites on nanoparticles. Moreover, the products are then tested with live Hela cells for the extraordinary biocompatibility. The cellular viability is remained to be 100% even after a 48 h exposure with the high N-GQDs concentration of 200 μg mL{sup −1} and this survival rate is really much higher than that have been reported previously. The as-prepared N-GQDs with negligible inherent toxicity exhibit excellent biological applications such as bio-imaging and cell tracking.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Spectroscopic studies of Dy3+ doped borate glasses for cool white light generation

Highlights: • BAZN glasses with Dy{sup 3+} ions were prepared using melt quench technique. • Under n-UV excitation the BAZN glasses show white light emission. • Energy transfer through cross-relaxation leads to concentration quenching. • Calculated CIE coordinates are close to the commercial w-LED. • 0.5 mol% of Dy{sup 3+} in these glasses are apt for cool white light generation. - Abstract: The Dy{sup 3+} ions doped Na{sub 2}O-ZnO-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3} (BAZN) glasses with variable doping concentrations were synthesized by melt-quenching technique. The XRD pattern reveals amorphous nature of the as-synthesized glass. The FT-IR spectrum reveals various stretching and bending vibration of aluminates, borate and some other groups. The emission spectra exhibit two intense bands at around 482 nm (blue) and 575 nm (yellow) corresponding to the {sup 4}F{sub 9/2} → {sup 6}H{sub 15/2} and F{sub 9/2} → {sup 6}H{sub 13/2} transitions respectively. The CIE chromaticity coordinates of the as-synthesized glasses are lying in white region and in proximity to the coordinates for white light specified by National Television Standard Committee and commercial phosphor converted white light emitting devices. The decay profile of BAZN glasses showed bi-exponential behavior due to the energy transfer mechanism from excited donor ion to unexcited acceptor ion. The above-mentioned studies show potential of the as-synthesized Dy{sup 3+} doped BAZN glasses in solid state lighting applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mn-substituted cerium oxide nanostructures and their magnetic properties

Highlights: • Mn{sub x}Ce{sub 1-x}O{sub 2} (0.1 ≤ x ≤ 0.5) nanostructures were prepared by one step microwave refluxing method. • The saturation magnetization values for the samples rose with increased Mn content. • The oxygen vacancies inherently played crucial role in increasing the magnetization values. - Abstract: In this study, we report the magnetic properties of nanostructured Mn{sub x}Ce{sub 1-x}O{sub 2} (0 0.1 ≤ x ≤ 0.5) materials, synthesized via microwave refluxing technique. Phase purity of the samples was investigated using the structural characterization techniques such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). These analyses indicated the substitution of Ce-ions with Mn-ions in the lattice. The progressive increase in the oxygen vacancies with increased dopant concentration was demonstrated by Raman, UV–vis and photoluminescence spectroscopic studies. X-ray photoelectron spectroscopy analysis further supported the presence of Mn{sup 2+}, Ce{sup 3+} and Ce{sup 4+} ions as well as oxygen vacancies in the samples. The Mn substituted CeO{sub 2} nanostructures were found to exhibit room temperature ferromagnetism (RTFM). There was a continuous improvement in the saturation magnetization (M{sub S}) values with increased Mn concentration. This might be due to the prevalence of surface oxygen vacancies and the systematic rise in their concentration with increased dopant content.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Novel red-emitting phosphor Ba3ZrNb4O15:Pr3+: The structure, characteristic photoluminescence property and thermal quenching behaviour investigation

Highlights: • Novel red emitting phosphors BZN:Pr{sup 3+} were successfully synthesized. • Phase purity, morphology and luminescent property of BZN:Pr{sup 3+} were studied. • Different concentration behavior and related mechanism were discussed. • Decay times and the fluorescence dynamics process were investigated. • Temperature sensitive thermal quenching behavior and mechanism was studied. - Abstract: Pr{sup 3+} activated niobate phosphors Ba{sub 3-x}ZrNb{sub 4}O{sub 15}:xPr{sup 3+} were firstly synthesized through high temperature solid-state method. The phase purity, crystal structure, morphology, luminescence property as well as thermal quenching behavior were carefully determined by using X-ray diffractometer, scanned electron microscope, photoluminescence and temperature dependent emission spectra, respectively. The luminescent property showed that Ba{sub 3-x}ZrNb{sub 4}O{sub 15}:xPr{sup 3+} (0.002 ≤ x ≤ 0.03) had dominate excitation around 451 nm and could exhibit red emissions peaking at 608, 618 and 651 nm, attributed to the {sup 1}D{sub 2}-{sup 3}H{sub 4}, {sup 3}P{sub 0}-{sup 3}H{sub 6} and P{sub 0}-{sup 3}F{sub 2} transitions of Pr{sup 3+} ions. The different concentration quenching behaviors were found while the related mechanism was investigated. The room temperature decay times and the related fluorescence dynamics process of Pr{sup 3+} ions in Ba{sub 3}ZrNb{sub 4}O{sub 15} were investigated. In addition, the optimal doping contents, CIE chromaticity coordinates as well as the color purity were determined. At last, the temperature sensitive emission quenching and decay behavior were discussed and the activation energy was calculated based on Arrhenius equation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The role of hydrothermal conditions in determining 1D TiO2 nanomaterials bandgap energies and crystal phases

Highlights: • Application of hydrothermal method for 1D TiO2 synthesis. • Varying hydrothermal synthesis conditions on 1D TiO2 crystal phase, size and SSA. • Effects on crystal phase, size and SSA on bandgap. - Abstract: One-dimensional TiO{sub 2} nanostructure synthesized using a hydrothermal method showed significant differences in the bandgap energies and crystal phase properties under different synthesis conditions. The objectives of this study were to evaluate the effect of the hydrothermal reaction conditions on the bandgap energy and to optimize the reaction conditions using a 3-factor 3-level Box Behnken design. The factors investigated include temperature, NaOH concentration and TiO{sub 2} concentration (BBD). A quadratic response surface model predicted optimum conditions for the maximum and minimum bandgap energy. The BBD analysis and other statistical tools provided evidence showing the temperature and NaOH concentration significantly affected the 1D TiO{sub 2} bandgap energy. Pure anatase was associated with a higher bandgap energy, whereas the biphasic anatase-rutile and anatase-TiO{sub 2}-B phases were linked with decreasing the bandgap energy. In addition, the crystal size and specific surface area (SSA) impact on the bandgap energy was due to the size quantization effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

One-pot fabrication and characterization of graphene/PMMA composite flexible films

Highlights: • Investigated the fabrication and characterization of conducting flexible films based on graphene/PMMA polymer composite. • Graphene/PMMA flexible films were fabricated by one-pot alternate stirring sonication (OPASS) process. • Electrical response of the fabricated flexible films were studied and exhibited an electrical conductivity of 44.92 S/m and 0.10 S/m with 50 wt% and 10 wt% concentrations, respectively. • Reinforcing polymers with graphite platelets will amend their surface toughness, modulus and barrier properties, suitable for commercial applications. - Abstract: The present work investigates fabrication and characterization of graphene/ poly (methyl methacrylate) (PMMA) composite flexible films. Graphene/PMMA flexible films were fabricated by one-pot alternate stirring sonication (OPASS) process. The method relies on the alternate high speed stirring and ultrasonication of graphite and its blending with PMMA without any sufactant assistance. A comparative study of the nanocomposite solution was carried out with the composite solution prepared by conventional (CL) method. The transformation of micro-sized graphite particles to nano-sized layers of graphite or few layer graphene was characterized by various analytical techniques. The electrical response of the fabricated flexible films were studied and exhibited an electrical conductivity of 44.92 S/m and 0.10 S/m with 50 wt% and 10 wt% concentrations, respectively. Thus, the fabricated flexible films could have excellent surface toughness, modulus and barrier properties, which make them a suitable candidate for commercial flexible electronic and wearable sensor applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Investigation on microstructures and phase transition characteristics of titanium/yttrium co-doped vanadium oxide thin films

Highlights: • Conjugated interaction between Ti{sup 4+} and Y{sup 3+} ions has been observed in Ti/Y codoped VO{sub 2} films. • The conjugated interaction causes the appearance of VO{sub 2} (B), even complete amorphization in Ti/Y co-doped VO{sub 2} thin film. • Ti/Y co-doping restrains the SMT feature of VO{sub 2} films. - Abstract: Co-doping with two elements has recently attracted attention as a novel approach for tailoring the semiconductor-metal transition (SMT) characteristics of vanadium dioxide (VO{sub 2}). Here, we investigate the influence of titanium/yttrium (Ti/Y) co-doping on the microstructure and SMT characteristics of VO{sub 2} thin films. At low Y concentration, Ti/Y co-doped VO{sub 2} thin films exhibit a monoclinic structure similar to VO{sub 2} but characterized by a smaller grain size, whereas, the VO{sub 2}(B) phase appears as the Y concentration is increased. Interestingly, even a complete amorphization of the film is obtained for co-doped VO{sub 2} thin films. The strong dependence of the microstructure upon the co-doping level is ascribed to the conjugated influence from the simultaneous adjustment of VV chains and VO bonds due to the existence of Ti{sup 4+} and Y{sup 3+} ions in VO{sub 2} lattice, respectively. As a result, the SMT feature of VO{sub 2} thin films is strongly limited or even fully disappears.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Highly efficient deep desulfurization of fuels by meso/macroporous H3PW12O40/TiO2 at room temperature

Highlights: • A new kind of meso/macroporous structured HPW/TiO{sub 2} catalyst was prepared by monodispersed polystyrene spheres and quaternary ammonium bromide. • Quaternary ammonium bromide with longer alkyl chains length (STAB) was found to be the best mesostructure-directing agent in the synthesis of meso/macroporous HPW/TiO{sub 2} catalyst. • The influence of dosage of macroporous templates (monodispersed polystyrene spheres) and alkyl chains length of quaternary ammonium bromide on the textural of meso/macroporous HPW/TiO{sub 2} catalyst were investigated. • With proper PS spheres and quaternary ammonium bromide usage, disordered macropores arranged periodicity and led relatively larger pore size and pore volume. • The meso/macroporous HPW/TiO{sub 2} materials exhibited enhanced excellent desulfurization performance of thiophenic sulfur in model fuel than other samples. Dibenzothiophene can be completely removed within 2 h at 30 °C. - Abstract: This paper described the synthesis of meso/macroporous phosphotungstic acid (HPW) /TiO{sub 2} catalyst with quaternary ammonium bromide and monodispersed polystyrene spheres (PS) as dual-template. The synthetic parameters, such as concentration of the templates and the alky chain length of quaternary ammonium bromide was studied carefully and optimized to generate catalyst with regulated porous features. The chemical properties of the catalyst was also investigated, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) measurements confirmed the Keggin-type HPW were highly dispersed on the TiO{sub 2} framework. The optimal meso/macroporous HPW/TiO{sub 2} catalyst exhibited excellent catalytic activity in the oxidation of refractory sulphur compounds such as benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). DBT was removed within 2 h at 30 °C under selected reaction conditions and the apparent activation energy for DBT oxidation was calculated to be 45.7 kJ/mol. The high ODS reaction rate of catalyst could be attributed to the combination of unique meso/macroporous architecture allowing for efficient mass transport of reactants and products in pore channel and its high surface area, large mesoporous size, and pore volume enabling sufficient exposure of catalytic active sites. Moreover, the meso/macroporous HPW/TiO{sub 2} catalyst also exhibited excellent reusability with no obviously degradation even after eight cycles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Highly sensitive and accurate optical thermometer through Er doped tellurite glasses

Highlights: • Upconversion mechanisms of transparent Er{sup 3+} doped tellurite glasses are discussed. • Sensitivity of the thermometer based on the FIR technique increases monotonously with the decreasing doping concentration. • Highly sensitive and accurate optical thermometer is achieved using low doping sample as the probe and high power laser as the pumping source. - Abstract: We investigate the thermal effects of Er{sup 3+} doped tellurite glasses on the upconversion properties. It is found that the sensitivity of the thermometer based on the FIR technique increases monotonously with the decreasing doping concentration. However, low doping leads to weak upconversion intensity and further decrease the sensing accuracy, which makes it difficult to achieve the high sensitivity and accuracy simultaneously. Influences of the irradiating laser power on the sensing behaviors were studied in the purpose of enhancing the signal intensity. It is found that the heating effect of incident laser (up to hundreds of mW) can be neglected, indicating the feasibility of using high laser power and low doping sample to produce both high sensitivity and high accuracy. In addition, this paper respectively discusses the mechanisms of the upconversion processes and the concentration dependent sensitivity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced piezoelectric properties in (Ba1-xCax)(Ti0.90Sn0.10)O3-0.08Dy2O3 lead-free ceramics

Highlights: • MPB exists in the BCTSD ceramics with x = 0.06–0.10. • BCTSD ceramics exhibit typical diffuse phase transition behavior, which is not sensitive to the amount of Ca{sup 2+} ions. • Remarkable improvement on piezoelectric properties (d{sub 33} = 675 pC/N, k{sub p} = 55%) were achieved at x = 0.06. - Abstract: (Ba{sub 1-x}Ca{sub x})(Ti{sub 0.90}Sn{sub 0.10})O{sub 3}-0.08Dy{sub 2}O{sub 3} ceramics (BCTSD-x, x = 0.02–0.10) were fabricated by conventional solid state sintering method. The effect of Ca{sup 2+} ions addition on the phase structure, microstructure, and electric properties of ceramics were studied. X-ray diffraction analysis reveals the replacement of Ba{sup 2+} ions in the perovskite structure by Ca{sup 2+} ions. Rhombohedral phase and tetragonal phase coexist in the composition with x = 0.06–0.10. Both d{sub 33} and K{sub p} of the ceramics increase with increasing Ca concentration, and attain maximum values of 675 pC/N and 55.0%, respectively, for x = 0.06. All the ceramics present typical diffuse phase transition behavior, and the feature is not sensitive to the amount of Ca{sup 2+} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of the role of deposition rate on optical, microstructure and ethanol sensing characteristics of nanostructured Sn doped In2O3 films

Highlights: • Deposition rate can play an important role in gas sensing of In{sub 2}O{sub 3}:Sn films. • The crystallite size and linear defects of the films is estimated by eCMWP method. • The correlation between the optical, microstructure and gas sensing properties is studied. • The size distribution behavior of samples is in agreement with the results of porosity. • Optimum deposition rate for In{sub 2}O{sub 3}:Sn films is 0.2 nm/s. - Abstract: In this paper, Sn doped In{sub 2}O{sub 3} (In{sub 2}O{sub 3}:Sn) nanostructured films as metal oxide semiconductor material which is very important in optoelectronics and gas sensing industries, were prepared by thermal evaporation technique. It is discussed how different deposition rate (0.1, 0.2, 0.3 and 0.4 nm/s) affects the optical, electrical, microstructural and ethanol gas sensing characteristics of In{sub 2}O{sub 3}:Sn films and must be precisely monitored. The gas sensing performance of the films was evaluated in terms of gas concentration and operating temperature. A correlation between the crystallite size, porosity, dislocation density, outer cut-off radius of dislocation, optical band gap, activation energy and sensitivity of the films was established. The results demonstrate that the maximum sensitivity to ethanol vapors can be obtained for the sample grown at deposition rate of 0.2 nm/s. The response and recovery times of this sensor exposed to 100 ppm of ethanol vapors were determined and found to be 9.0 s and 3.9 s, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Role of Ni concentration on structural and magnetic properties of inverse spinel Ferrite

Highlights: • Ni doped Co{sub 1-x}Mn{sub x}Fe{sub 2}O{sub 4} (0≤x≤0.1) nanoparticles have been synthesized with an average particle size in the range 15–20 nm. • Lattice parameter decreases with increase in Ni concentration in CoFe{sub 2}O{sub 4} nanoparticles. • XRD and FTIR analysis confirmed the formation of cubic spinel ferrite structure. • Room temperature and low temperature magnetic properties of described system have been measured. - Abstract: In present work, Nickel (Ni) substituted Mn-Co ferrite nanoparticles, with doping content varying from 0 to 0.1, have been synthesized. The inverse spinel structure of doped cobalt ferrite has been claimed by X-ray diffractometer with average particle size of 20 nm. The decrease in lattice parameter and increase in X-ray density has been found with increase in Ni concentration in ferrite structure. Fourier transform infrared spectroscopy analysis showed two vibrational frequency bands (υ{sub 1} and υ{sub 2}) for octahedral and tetrahedral sites depicting the formation of spinel ferrite. In addition, Transmission electron microscopy analyses were carried out to investigate particle size, which indicates that TEM and XRD analyses are in agreement. Magnetic analyses depict that coercivity value increases from 635 Oe to 841 Oe in Ni doped Mn-Co ferrite. Exchange interactions between Ni and Mn{sub 0.2}Co{sub 0.8-x}Fe{sub 2}O{sub 4} result for enlargement in coercivity and shift in hysteresis loop towards positive direction along the field axis. The increment in magnetic coercive field and exchange bias has been observed as temperature decreases. Enhanced magnetic properties at low temperature are attributed to magneto-crystalline anisotropy and surface effects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

In-situ packaging ultra-uniform 3D hematite nanotubes by polyaniline and their improved gas sensing properties

Highlights: • Ultra-uniform 3D α-Fe{sub 2}O{sub 3} nanotubes were packaged by PANI through the two-stage solution processes. • PANI/α-Fe{sub 2}O{sub 3}-based sensor could detect low concentration of acetone (1 ppm) at lower temperature of 180 °C. • The unique structure of α-Fe{sub 2}O{sub 3} support and its synergetic effect with PANI layers improved the sensor performances. - Abstract: This paper reports the PANI (polyaniline)-packaged three-dimensional (3D) α-Fe{sub 2}O{sub 3} nanotubes P/N heterojunction, which was constructed successfully though a facile hydrothermal reaction without adding any surfactant followed by in-situ chemical polymerization in the liquid phase. The structure and morphology of the products were characterized by means of FESEM, XRD, TEM & HRTEM, TGA and FT-IR. Gas sensing test results found that, the PANI/α-Fe{sub 2}O{sub 3} nanocomposite sensor exhibited obviously higher response, lower working temperature (180 °C), fast response and recovery speeds, good selectivity and excellent stability to acetone gas, indicating its promising application for high-performance acetone sensors. The enhanced gas sensing performances can be attributed to the factors like ultra-uniform 3D nanotube-like structure for α-Fe{sub 2}O{sub 3}, the noticeable advantages of PANI, as well as the construction of heterojunction barrier at their interface. The as-prepared PANI/α-Fe{sub 2}O{sub 3} nanocomposite may be also applied in other areas like photocatalysis, water purification, ion batteries, optical devices, and so on.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

SiO2-TiO2 doped with Er3+/Yb3+/Eu3+ photoluminescent material: A spectroscopy and structural study about potential application for improvement of the efficiency on solar cells

Highlights: • Intense downconversion emission of Eu{sup 3+} under Uv excitation. • Upconversion emission assigned to the Er{sup 3+}/Yb{sup 3+} under 980 laser pump. • Double excitation simultaneous providing emission in visible range. • Potential application on improvement of solar cells. - Abstract: The various synthesis conditions to obtain a material based on SiO{sub 2}-TiO{sub 2} co-doped with Er{sup 3+}/Yb{sup 3+}/Eu{sup 3+} were investigated, searching for those that present the greatest potential to improve the efficiency of solar cells. Conditions adjusted included heat-treatment temperatures, concentrations of matrix, and concentrations of dopants. Raman spectroscopy results demonstrated the effect of the annealing temperatures on the TiO{sub 2} phase transition and the crystalline phase of the materials, which interfere with the photoluminescence of the materials. The band gap of the materials was evaluated by diffuse reflectance and it decreased due to the doping. The materials were able to absorb UV and IR energy and emit in the visible region, verified by the down conversion, up conversion and the double excitation of the materials. The results showed that the materials may be used as a strategy to use a greater portion of the solar spectrum, improving solar cell efficiency.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Preparation and characterization of microwave absorbing composite materials with GSs or FeCo/GS composites

Highlights: • It is found that adding GSs or FeCo/GSs composite into the sample SiC/NR can greatly increase RL and the absorbing peak shifts to low-frequency with increasing the adding amount. • The optimum adding amount of GSs is 2%. The sample GS-200-2% possesses the lowest RL value of −31.27 dB at 7.6 GHz. • The optimum adding amount of FeCo/GSs composite is 3%. The sample AGS-450-3% possesses the lowest RL value of −20.67 dB at 7.8 GHz. - Abstract: This study mainly explored the synthesis method of graphene sheets (GSs) and FeCo/graphene sheet (FeCo/GS) composites and evaluated the microwave absorbing characteristics of composite materials containing GSs or FeCo/GS composites. First, graphite oxide (GO) was synthesized by the modified Hummers method. The synthesized GO was further used to synthesize GSs and FeCo/GS composites. Afterward, GSs or FeCo/GS composites were mixed with silicon carbide (SiC) and natural rubber (NR) to prepare microwave absorbing materials with thicknesses of 2 mm. Finally, identification and characterization of these samples were performed by XRD, FE-SEM, TEM, TGA, ESCA, RS, AFM and VNA. GSs were synthesized successfully at a low annealing temperature of 200 °C, and their thicknesses were between 0.848 nm and 2.115 nm, which corresponds to 2–6 stacked layers of graphene. FeCo/GS composites were also synthesized successfully at three different annealing temperatures. The nanoparticles of metals and metal oxides were well-dispersed on the surfaces of and the spaces between GSs. It was found that adding GSs or FeCo/GS composites into the SiC/NR sample can greatly increase reflection loss (RL) and that the absorbing peak shifts to lower frequencies as the concentration of added particles increases. The optimum concentration of added GSs was 2 wt.%. The GS-200-2% sample possessed the lowest RL value of −31.27 dB at 7.6 GHz. The optimum concentration of added FeCo/GS composites was 3 wt.%. The AGS-450-3% sample possessed the lowest RL value of −20.67 dB at 7.8 GHz.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced photocatalytic treatment of Cr(VI) and phenol by monoclinic BiVO4 with {010}-orientation growth

Highlights: • Removal of Cr(VI) and phenol in wastewater was greatly improved. • The reduction and oxidation processes were enhanced on {010} and {110} facets. • The selective transfer of charge carriers enhanced their separation. - Abstract: Photocatalytic technology has unique advantages in the purification of organic wastewater containing chromium(VI). Simultaneously photodegradation efficiency of Cr(VI) and phenol was significantly enhanced over BiVO{sub 4} with {010}-oriented growth. In this study, the effect of pH values in photoreduction of Cr(VI) and concentrations of phenol in the simultaneous photocatalytic reaction process were systematically analyzed based on characterizations about material physical properties. The results suggested that the enhanced photocatalytic activity over {010}-oriented BiVO{sub 4} was attributed to sufficient utilization of surface junction between {010} and {110}. These junctions achieved higher separation efficiency and selectively transfer of photogenerated charge carriers between two surfaces. Thus the photoreduction of Cr(VI) and photooxidation of phenol can selectively occur on the different crystal surfaces. This study demonstrates the possibility of purification of organic wastewater containing toxic heavy metals such as Cr(VI) using photocatalytic technology and provides new ideas and methods for the design of highly active photocatalytic materials.

54 ENVIRONMENTAL SCIENCES↗