In this paper, the graphene/carbon nanotubes/copper foam (GR/CNTs/CuF) three-dimensional field emitters were prepared by electrophoretic deposition (EPD). For comparison, the graphene/copper foam (GR/CuF) and carbon nanotubes copper foam (CNTs/CuF) field emitters were also prepared by the same way and characterized by the several different methods. The turn on electrical field (Eon) of composite materials of GR/CNTs/CuF was obtained to be 0.85 V/mu m. Threshold electric field (Eth) is 1.52 V/mu m. The composite of GR/CNTs/CuF have a large contact area, a lower volume resistance and lower contact resistance, which is more easy to electron transport. The root of the CNTs or the fold tip of GR is fixed in the interlaced composite, and the tip or fold forms a stable micro tip emission structure, which enhanced the field strength factor. The field emission performances are significantly better than that of individual GR/CuF or CNTs/CuF field emitter. The GR/CNTs/CuF as 3D field emitters were prepared by EPD method with low cost and easy manipulation, which provided a good way for a large-scale preparation of composite field emitters.

Microbial electrosynthesis (MES) is a potential energy transformation technology for the reduction of the greenhouse gas carbon oxide (CO2) into commercial chemicals. The major bottlenecks in the development of highly productive MES systems are the low bacterial loading, low electron transfer rate and low production of relevant chemicals, which limit the future potential for scaling up this process. Graphene has excellent electrical conductivity, remarkably high carrier mobility, special intrinsic mechanical strength, chemical stability, outstanding specific surface area, and biocompatibility. Therefore, in this regard, graphene can overcome these challenges and provide new opportunities. Graphene is suited for use as a cathode for increasing the bacterial loading and boosting the performance of MES. Over the last decade, graphene has been extensively developed and explored in MES. Graphene incorporation in cathodes can augment the surface area, reduce the resistance, and increase the electron transfer rate; thus, high current density, high coulombic efficiency, and high chemical production can be achieved. To better understand and further explore the modification of graphene-based materials as cathodes in MES systems, it is quite necessary to review and summarize recent developments in this field. Therefore, in this report, we briefly survey and discuss the up-to-date research activities regarding graphene in cathode modification and fabrication, with particular emphasis on their fabrication strategies and characterization, highlighting their key roles in MES systems, as well as presenting the challenges and the future prospects.

Ca9Zn1.5(PO4)(7): Eu2+/Eu3+ phosphors had been synthesized via conventional high temperature solid-state reaction. Based on the different thermal quenching characteristics between 4f-5d transition of Eu2+ ions and 4f-4f transition of Eu3+ ions, the fluorescence intensity ratio (FIR) of Eu3+ to Eu2+ exhibits temperature dependence at the temperature from 293 to 473 K. The maximum absolute and relative temperature sensitivity of Ca9Zn1.5(PO4)(7): Eu phosphor can reach up to 0.0034 K-1 and 1.4% K-1 at 453 K, respectively, when used as thermometric material. These results indicated that our study opens up an effective approach for developing other high-performance self-calibrated optical thermometers.

To optimize the field emission behavior of graphene, a simple, low-cost and large-scale method was developed to introduce metallic particles onto the graphene and is described in the present report. Cu/graphene composite field emitters were fabricated by the one-step process of electrophoretic deposition. The Cu/graphene composite emitters prepared with this technique showed a lower turn-on electrode of 1.55 V/mu m, lower threshold field of 2.45 V/mu m and higher field enhancement factor of 5600 compared with those of the pristine graphene. The optimized field emission properties of the Cu/graphene composite were mainly attributed to the introduced Cu nanoparticles, which increased the density of the emission sites and decreased the series resistance. These results provide us with a new approach to optimize graphene-based emitters for vacuum devices.

The Vertically-orientated graphene (GP) sharp edges can provide a high density of individual field emission sites and a high field emission enhancement factor. In this report, we used a Si textured structure to build the vertical GP field emission edges. Relying on the periodical textured arrays of the Si surface, a large number of vertical sharp edges of GP are formed on the Si substrate during the electrophoretic deposition process. The vertical GP edges on the textured structure of Si shows a low turn-on electric field of 0.43 V-1 mu m(-1), a high enhancement factor of 9450, excellent stability behavior and a uniform luminance intensity image. The excellent field emission properties for the vertical edges are explored and discussed in detail. This investigation of the vertical GP edges on a textured Si surface suggests a potential prospect in application in future field electron emission devices.

Eu2+/Eu3+ co-doped Sr3P4O13 phosphors were prepared by high temperature solid stated method in air atmosphere and studied in detail their luminescent properties in order to investigate the possible applications in temperature sensors. The broadband emission of Eu2+ ions and the linear emission band of Eu3+ ions can be observed in the photoluminescence (PL) spectra of Sr3P4O13: Eu2+/Eu3+ phosphors due to the self-reduction effect. X-ray photoelectron spectroscopy (XPS), PL spectra, and time-resolved fluorescence lifetime confirm the formation of double emission centers of Eu2+ and Eu3+ ions in Sr3P4O13 because of the self-reduction by charge compensation. In the Eu2+/Eu3+ co-activated Sr3P4O13 thermometric phosphor, the blue emission of Eu2+ ions and red emission of Eu3+ ions, can be used as fluorescence intensity ratio (FIR) signals. In addition, the mechanism is discussed in detail based on the experimental data, and the strong temperature dependence is explained from the point of view of thermal quenching. Additionally, benefited from their diverse thermal quenching behavior, the FIR of Eu3+ to Eu2+ is fitted very well, and Sa reached a maximum 0.008 K-1 at 573 K, while Sr reached a maximum of 1.06% K-1 at 353K. As a consequence, this work indicates that Sr3P4O13: Eu2+/Eu3+ phosphors could be widely applied in optical temperature sensors. (C) 2019 Elsevier B.V. All rights reserved.

A nonstoichiometric process by modulating the W/Se atomic ratio was employed to tune the excitonic PL band of monolayer WSe2 from 810 nm to 690 nm. DFT calculations indicate that Se-rich conditions reduce the band gap, while Se-deficient conditions facilitate the increasing band gap and decreasing excitionic binding energy, which finally induces such broadband tuning of the PL band.

With admirable luminescence performance and a cheap price, non-rare-earth-based oxide red phosphors are a potential competitor of rare-earth-doped phosphors for warm white LEDs (WLEDs). Herein, a novel double-perovskite Ba2GdSbO6:Mn4+ phosphor, demonstrating strong red emission ascribed to a spin-forbidden Mn4+:2Eg → 4A2g transition in the region of 620-750 nm, has been synthesized via a solid-state reaction route. The microstructure and luminescence properties are investigated in detail. The concentration quenching mechanism and thermal stability based on thermal quenching characteristics are also discussed. Importantly, Li+, Mg2+, Zn2+, Si4+, Ti4+ and Ge4+ dopants are discovered to be beneficial for enhancing Mn4+ luminescence, and the related mechanisms are comprehensively described. In addition, by combining red-emitting Ba2GdSb0.994O6:0.003Mn4+,0.003Mg2+ with the commercial blue-emitting BaMgAl10O17:Eu2+ and green-emitting Ba3La6(SiO4)6:Eu2+ phosphors in various ratios, a series of WLED devices with a tunable correlated color temperature (CCT) evolving from 6256 to 3486 K and a color rendering index (CRI) increasing from 72.1 to 88.3 are achieved.

Graphene/zinc oxide nanowires/graphene (G/ZnO NWs/G) sandwich composites were firstly synthesized on nickel foam by electrostatic spray deposition technique and hydrothermal reaction in sequence. Microstructure and chemical analysis showed the dense and uniform ZnO NWs encapsulated by bottom and upper graphene layers. The G/ZnO NWs/G composites as cold cathodes for field emission (FE) exhibited improved performances with a lower turn-on electric field of 7.45 V/mu m, a higher field enhancement factor of 5328 and higher emission current stability over 10 h than G/ZnO NWs. The enhanced FE properties of G/ZnO NWs/G were mainly attributed to its sandwich structure, which introduced more surface defects and numerous emission sites, simultaneously decreased the work function and resistivity of emitters. This investigation paves a new way for developing high-performance cold cathode FE materials. (C) 2017 Elsevier B.V. All rights reserved.

Graphenes are beneficial to electrons field emission due to its high aspect ratio, high carrier density, the larger carrier mobility, excellent electrical and thermal conductivity, excellent mechanical strength and chemical stability. In recent years, graphene or reduced oxide graphene field emitters have been successfully constructed by various methods such as chemical vapor deposition, chemical exfoliation, electrophoretic deposition, screen-printing and chemical synthesis methods. Graphene emitters are tried to construct in distribution with some angles or vertical orientation with respect to the substrate surface. The vertical alignment of graphene sheets or edges arrays can facilitate efficient electron emission from the atomically thick sheets. Therefore they have even more a low turn-on and threshold-field electronic field, high field enhancement factor, high current stability and high luminance. In this review, we shortly survey and discuss recent research progress in graphene field emission properties with particular an emphasis on their preparing method, characterization and applications in devices especially for vertical graphene and single layer graphene, also including their challenges and future prospects. (C) 2017 Elsevier B.V. All rights reserved.

In this study, remarkably differing to reported well-defined triangular WSe2 flakes, porous WSe2 flakes with large amount of holes were deposited using graphene quantum dots(GQDs) as promoters. By employing this method, triangular or circular thorough holes can be efficiently deposited on basal plane of WSe2 flakes. The size of holes and density of edges vary with layer number of WSe2 basal plane. Highest density of edges emerges on 4-layer WSe2 flake, which is greatly enhanced by 580% compared to those well-defined triangular 4-layer flakes. Finally we propose that the growth of holes is validated by poor wetting between WSe2 and GQDs, while the final shape is determined by crystal symmetry, diffusion and thermal dynamics.

Here, we reply to comments by Valentic et al. on our paper published in Electrochimica Acta (2014, 130:279). They commented that Au nanoparticles played the dominant role on the whole cell's performances in our improved graphene/Si solar cell. We argued that our devices are Au-doped graphene/n-Si Schottky barrier devices, not Au nanoparticles (film)/n-Si Schottky barrier devices. During the doping process, most of the Au nanopatricles covered the surfaces of the graphene. Schottky barriers between doped graphene and n-Si dominate the total cells properties. Through doping, by adjusting and tailoring the Fermi level of the graphene, the Fermi level of n-Si can be shifted down in the graphene/Si Schottky barrier cell. They also argued that the instability of our devices were related to variation in series resistance reduced at the beginning due to slightly lowered Fermi level and increased at the end by the self-compensation by deep in-diffusion of Au nanoparticles. But for our fabricated devices, we know that an oxide layer covered the Si surface, which makes it difficult for the Au ions to diffuse into the Si layer, due to the continuous growth of SiO2 layer on the Si surface which resulted in series resistance decreasing at first and increasing in the end.

A novel Eu2+-activated Ba3La6(SiO4)6:Eu2+ (BLSO:Eu2+) green-emitting phosphor with strong luminescence has been successfully prepared via a solid state reaction. The crystal structure, photoluminescence (PL) as well as thermal stability properties of BLSO:Eu2+ phosphor are investigated systematically. The BLSO:Eu2+ phosphor exhibits a broad excitation band extending from 250 to 450nm, and gives an intense asymmetric green emission band centered at 507nm. Two different Eu2+ emitting centers are identified by their PL spectra and PL decay lifetimes in BLSO:Eu2+ phosphor. The optimal Eu2+ content in BLSO:Eu2+ is confirmed to be 5mol%, and the corresponding concentration quenching mechanism is determined to the electric dipole-dipole interaction. Moreover, compared to the initial one at room temperature, the PL intensity of the investigated phosphor can maintain 52% as heated up to 423K. Finally, warm white light-emitting diode with a low correlated color temperature of 4818K and a high color rendering index of 82.9 is achieved by mixing blue/green/red (BaMgAl10O17:Eu2+/BLSO:Eu2+/CaAlSiN3:Eu2+) phosphors with the commercial n-UV-GaN chip.

Microbes can reduce CO2 into multicarbon chemicals with electrons acquired from the cathode of a bioelectrochemical reactor. This bioprocess is termed microbial electrosynthesis (MES). One of the main challenges for the development of highly productive MES reactors is achieving efficient electron transfer from the cathode to microbes. Here, carbon cloth cathodes modified with reduced graphene oxide functionalized with tetraethylene pentamine (rGO-TEPA) were readily self-assembled in the cathodic chamber of a MES reactor. Electroactive biofilms with unique spatial arrangement were subsequently formed with Sporomusa ovata at the surface of rGO-TEPA-modified electrodes resulting in a more performant MES process. The acetate production rate from CO2 was increased 3.6 fold with the formation of dense biofilms when wild type S. ovata was combined with rGO-TEPA. An improvement of 11.8 fold was observed with a highly structured biofilm including multiple spherical structures possibly consisting of bioinorganic networks of rGO-TEPA and bacterial cells from a novel strain of S. ovata adapted to reduce CO2 faster. The three dimensional biofilms observed in this study enabled highly effective electric interactions between S. ovata and the cathode, demonstrating that the development of dense cathode biofilms is an effective approach to improve MES productivity.

A novel tunable red to yellow emitting phosphor, (Ca, Ba)4(PO4)2O:Eu2+ is reported that displays a broad emission from 500 to 800nm, and its emitting color can be adjusted from red to yellow by changing Ba2+ doping concentration. X-ray powder diffraction (XRD) analysis confirmed the phase formation. Excitation and emission spectra, and concentration dependence of emission intensity of the phosphor were investigated. The results showed that the emission peak wavelength take blue-shifted from 640 to 545nm and the color hue can be tuned from red to yellow with increasing Ba2+ concentration. When single-phase (Ca3.85Ba0.10)(PO4)2O:0.05Eu2+ phosphor is pumped by a blue InGaN light-emitting diode, we obtain white light with color rending index (Ra) between 84.0 and 90.6 and color temperatures between 4000 and 5500K, which suggests that this material is competitive as a color conversion material for solid state lighting.

Monoclinic phase Bi0.95Eu0.05PO4 was synthesized by polymer mediated solid-state reaction employing polyvinyl alcohol (PVA). The powder X-ray diffraction revealed the phase purity and isostructural nature of both Eu3+-doped and undoped BiPO4. The role of PVA molecules in assisting the particle growth during the phase formation and enhancing the degree of crystallinity significantly by its combustion. The synthesized materials were characterized using different spectroscopic techniques such as FT-IR, Raman and Photoluminescence (PL). The methodology discussed here is fundamentally important, which may provide an excellent platform for the phase-controlled synthesis and further optimized materials performance.

Garnet-based Li6CaLa2−2xEu2xSb2O12(x= 0.1–1.0) red phosphors and the related inorganic glass ceramics were fabricated to find potential applications in WLEDs.