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Sample records for absorbs visible light

  1. Broadband visible-light absorber via hybridization of propagating surface plasmon.

    PubMed

    Cong, Jiawei; Zhou, Zhiqiang; Yun, Binfeng; Lv, Liu; Yao, Hongbing; Fu, Yonghong; Ren, Naifei

    2016-05-01

    We demonstrate a broadband visible-light absorber based on excitation of multiple propagating surface plasmon (PSP) resonances. The simple structure is constructed of continuous gold/silica multi-layers covered by a one-dimensional gold grating. The broadening of bandwidth arises from the inter-layer hybridization and spectral superposition of PSPs, which is predicted with the analytical coupled oscillator model and validated using the RCWA simulation. The average absorption increases with the number of gold/silica pairs and exceeds 95% over the whole visible spectrum when only five pairs are included. Moreover, results show that the absorption can be further enhanced by grading the thickness of silica layers. The presented design might enable promising applications in the fields of photovoltaic cells and thermal emitters, owing to its advantages of wideband, near-unity absorption and simple fabrication simultaneously. PMID:27128050

  2. Broadband visible-light absorber via hybridization of propagating surface plasmon.

    PubMed

    Cong, Jiawei; Zhou, Zhiqiang; Yun, Binfeng; Lv, Liu; Yao, Hongbing; Fu, Yonghong; Ren, Naifei

    2016-05-01

    We demonstrate a broadband visible-light absorber based on excitation of multiple propagating surface plasmon (PSP) resonances. The simple structure is constructed of continuous gold/silica multi-layers covered by a one-dimensional gold grating. The broadening of bandwidth arises from the inter-layer hybridization and spectral superposition of PSPs, which is predicted with the analytical coupled oscillator model and validated using the RCWA simulation. The average absorption increases with the number of gold/silica pairs and exceeds 95% over the whole visible spectrum when only five pairs are included. Moreover, results show that the absorption can be further enhanced by grading the thickness of silica layers. The presented design might enable promising applications in the fields of photovoltaic cells and thermal emitters, owing to its advantages of wideband, near-unity absorption and simple fabrication simultaneously.

  3. Perovskite oxides for visible-light-absorbing ferroelectric and photovoltaic materials.

    PubMed

    Grinberg, Ilya; West, D Vincent; Torres, Maria; Gou, Gaoyang; Stein, David M; Wu, Liyan; Chen, Guannan; Gallo, Eric M; Akbashev, Andrew R; Davies, Peter K; Spanier, Jonathan E; Rappe, Andrew M

    2013-11-28

    Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties. In these materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p-n junction solar cell. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol-gel thin-film deposition and sputtering. Recent work has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and ferroelectric-electrode interfaces can greatly increase the current harvested from ferroelectric absorber materials, increasing the power conversion efficiency from about 10(-4) to about 0.5 per cent. Further improvements in photovoltaic efficiency have been inhibited by the wide bandgaps (2.7-4 electronvolts) of ferroelectric oxides, which allow the use of only 8-20 per cent of the solar spectrum. Here we describe a family of single-phase solid oxide solutions made from low-cost and non-toxic elements using conventional solid-state methods: [KNbO3]1 - x[BaNi1/2Nb1/2O3 - δ]x (KBNNO). These oxides exhibit both ferroelectricity and a wide variation of direct bandgaps in the range 1.1-3.8 electronvolts. In particular, the x = 0.1 composition is polar at room temperature, has a direct bandgap of 1.39 electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric (Pb,La)(Zr,Ti)O3 material. The ability of KBNNO to absorb three to six times more solar energy than the current ferroelectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and

  4. Bandgap Tunability in Sb-Alloyed BiVO₄ Quaternary Oxides as Visible Light Absorbers for Solar Fuel Applications.

    PubMed

    Loiudice, Anna; Ma, Jie; Drisdell, Walter S; Mattox, Tracy M; Cooper, Jason K; Thao, Timothy; Giannini, Cinzia; Yano, Junko; Wang, Lin-Wang; Sharp, Ian D; Buonsanti, Raffaella

    2015-11-01

    The challenge of fine compositional tuning and microstructure control in complex oxides is overcome by developing a general two-step synthetic approach. Antimony-alloyed bismuth vanadate, which is identified as a novel light absorber for solar fuel applications, is prepared in a wide compositional range. The bandgap of this quaternary oxide linearly decreases with the Sb content, in agreement with first-principles calculations.

  5. A metallocene molecular complex as visible-light absorber for high-voltage organic-inorganic hybrid photovoltaic cells.

    PubMed

    Ishii, Ayumi; Miyasaka, Tsutomu

    2014-04-14

    A thin solid-state dye-sensitized photovoltaic cell is fabricated by composing organic and inorganic heterojunctions in which the visible-light sensitizers are cyclopentadiene derivatives (Cp*) coordinated to a metal oxide, typically TiO2. The coordination bonds of the metallocene molecular complex (Ti-Cp*) create a new LMCT (ligand-to-metal charge transfer) absorption band and induce a rectified charge transfer from the organic ligands to TiO2, leading to photocurrent generation. Photovoltaic junctions are completed by coating crystalline organic molecules (perylene) as a hole-transport layer on the Cp*-coordinated TiO2 surface by using the vapor deposition method. The molecular plane of Cp* on the TiO2 surfaces seems to help the hole-transport layer to form ordered structures, which effectively improve carrier conductivities and minimize interfacial resistance. The organic-inorganic hybrid thin-film photocell with metallocene molecular complexes is capable of generating high open-circuit voltages exceeding 1.2 V.

  6. Synthesis of transition-metal-doped KTiOPO{sub 4} and lanthanide-doped RbTiOAsO{sub 4} isomorphs that absorb visible light

    SciTech Connect

    Anderson M.T.; Phillips, M.L.F.; Sinclair, M.B.

    1996-01-01

    The authors have substituted aliovalent transition-metal (M = Cr, Fe, Ni, Cu, Co) and lanthanide (Ln = Er) ions that absorb visible light onto the titanium sites of the nonlinear optical materials KTiOPO{sub 4} (KTP) and RbTiOAsO{sub 4} (RTA). The substitution formally creates a charge deficiency on the Ti site. To compensate for this, the authors have substituted aliovalent counterions on the titanium (Nb), phosphorus (S, Se, Cr, Mo, W, Re) oxygen (F), or potassium (Ca, Sr, Ba, Pb) sites. The resulting new materials expand the KTiOPO{sub 4} structure field for partial replacement of one or more ions. The M and Ln ions alter the optical absorption and second harmonic properties of the materials. The ions reduce the second harmonic intensities of the isomorphs and second harmonic radiation to be phase matched at slightly shorter wavelengths than in the undoped host.

  7. Broadband Visible Light Induced NO Formation

    NASA Astrophysics Data System (ADS)

    Lubart, Rachel; Eichler, Maor; Friedmann, Harry; Savion, N.; Breitbart, Haim; Ankri, Rinat

    2009-06-01

    Nitric oxide formation is a potential mechanism for photobiomodulation because it is synthesized in cells by nitric oxide synthase (NOS), which contains both flavin and heme, and thus absorbs visible light. The purpose of this work was to study broadband visible light induced NO formation in various cells. Cardiac, endothelial, sperm cells and RAW 264.7 macrophages were illuminated with broadband visible light, 40-130 mW/cm2, 2.4-39 J/cm2, and nitric oxide production was quantified by using the Griess reagent. The results showed that visible light illumination increased NO concentration both in sperm and endothelial cells, but not in cardiac cells. Activation of RAW 264.7 macrophages was very small. It thus appears that NO is involved in photobiomodulation, though different light parameters and illumination protocols are needed to induce NO in various cells.

  8. Broadband Visible Light Induced NO Formation

    SciTech Connect

    Lubart, Rachel; Eichler, Maor; Friedmann, Harry; Ankri, Rinat; Savion, N.; Breitbart, Haim

    2009-06-19

    Nitric oxide formation is a potential mechanism for photobiomodulation because it is synthesized in cells by nitric oxide synthase (NOS), which contains both flavin and heme, and thus absorbs visible light. The purpose of this work was to study broadband visible light induced NO formation in various cells. Cardiac, endothelial, sperm cells and RAW 264.7 macrophages were illuminated with broadband visible light, 40-130 mW/cm2, 2.4-39 J/cm2, and nitric oxide production was quantified by using the Griess reagent. The results showed that visible light illumination increased NO concentration both in sperm and endothelial cells, but not in cardiac cells. Activation of RAW 264.7 macrophages was very small. It thus appears that NO is involved in photobiomodulation, though different light parameters and illumination protocols are needed to induce NO in various cells.

  9. Solar synthesis: prospects in visible light photocatalysis.

    PubMed

    Schultz, Danielle M; Yoon, Tehshik P

    2014-02-28

    Chemists have long aspired to synthesize molecules the way that plants do-using sunlight to facilitate the construction of complex molecular architectures. Nevertheless, the use of visible light in photochemical synthesis is fundamentally challenging because organic molecules tend not to interact with the wavelengths of visible light that are most strongly emitted in the solar spectrum. Recent research has begun to leverage the ability of visible light-absorbing transition metal complexes to catalyze a broad range of synthetically valuable reactions. In this review, we highlight how an understanding of the mechanisms of photocatalytic activation available to these transition metal complexes, and of the general reactivity patterns of the intermediates accessible via visible light photocatalysis, has accelerated the development of this diverse suite of reactions.

  10. Damage tolerant light absorbing material

    DOEpatents

    Lauf, Robert J.; Hamby, Jr., Clyde; Akerman, M. Alfred; Seals, Roland D.

    1993-01-01

    A light absorbing article comprised of a composite of carbon-bonded carbon fibers, prepared by: blending carbon fibers with a carbonizable organic powder to form a mixture; dispersing the mixture into an aqueous slurry; vacuum molding the aqueous slurry to form a green article; drying and curing the green article to form a cured article; and, carbonizing the cured article at a temperature of at least about 1000.degree. C. to form a carbon-bonded carbon fiber light absorbing composite article having a bulk density less than 1 g/cm.sup.3.

  11. Damage tolerant light absorbing material

    DOEpatents

    Lauf, R.J.; Hamby, C. Jr.; Akerman, M.A.; Seals, R.D.

    1993-09-07

    A light absorbing article comprised of a composite of carbon-bonded carbon fibers, is prepared by: blending carbon fibers with a carbonizable organic powder to form a mixture; dispersing the mixture into an aqueous slurry; vacuum molding the aqueous slurry to form a green article; drying and curing the green article to form a cured article; and, carbonizing the cured article at a temperature of at least about 1000 C to form a carbon-bonded carbon fiber light absorbing composite article having a bulk density less than 1 g/cm[sup 3]. 9 figures.

  12. Borescope Inspects With Visible Or Ultraviolet Light

    NASA Technical Reports Server (NTRS)

    Molina, Orlando G.

    1989-01-01

    Quartz optical fibers improve performance at ultraviolet wavelengths. Borescope used to inspect interior of small-diameter tubing by visible light and ultraviolet light. Employs quartz fibers to conduct ultraviolet light and visible light with high efficiency.

  13. Visible light absorbance enhanced by nitrogen embedded in the surface layer of Mn-doped sodium niobate crystals, detected by ultra violet - visible spectroscopy, x-ray photoelectron spectroscopy, and electric conductivity tests

    NASA Astrophysics Data System (ADS)

    Molak, A.; Pilch, M.

    2016-05-01

    Sodium niobate crystals doped with manganese ions, Na(NbMn)O3, were annealed in a nitrogen N2 flow at 600, 670, and 930 K. It was verified that simultaneous doping with Mn ions and annealing in nitrogen enhanced the photocatalytic features of sodium niobate. The transmission in the ultraviolet-visible range was measured at room temperature. The absorbance edge is in the range from 3.4 to 2.3 eV. The optical band gap Egap = 1.2-1.3 eV was evaluated using the Tauc relation. Crystals annealed at 670 K and 930 K exhibited an additional shift of the absorption edge of ˜20-40 nm toward longer wavelengths. The optical energy gap narrowed as a result of the superimposed effect of Mn and N co-doping. The x-ray photoelectron spectroscopy test showed that N ions incorporated into the surface layer. The valence band consisted of O 2p states hybridized with Nb 4d, Mn 3d, and N 2s states. The disorder detected in the surroundings of Nb and O ions decreased due to annealing. The binding energy of oxygen ions situated within the surface layer was EB ≈ 531 eV. The other contributions were assigned to molecular contamination. The contribution centered at 535.5 eV vanished after annealing at 600 K and 670 K. The contribution centered at 534 eV vanished after annealing at 930 K. The N2 annealing partly removed carbonates from the surfaces of the samples. In the 480-950 K range, the electric conductivity activation energy, Ea = 0.7-1.2 eV, was comparable with the optical Egap. The electric permittivity showed dispersion in the 0.1-800 kHz range that corresponds to the occurrence of defects.

  14. Visible-Light-Induced Click Chemistry.

    PubMed

    Mueller, Jan O; Schmidt, Friedrich G; Blinco, James P; Barner-Kowollik, Christopher

    2015-08-24

    A rapid and catalyst-free cycloaddition system for visible-light-induced click chemistry is reported. A readily accessible photoreactive 2H-azirine moiety was designed to absorb light at wavelengths above 400 nm. Irradiation with low-energy light sources thus enables efficient small-molecule synthesis with a diverse range of multiple-bond-containing compounds. Moreover, in order to demonstrate the efficiency of the current approach, quantitative ligation of the photoactivatable chromophore with functional polymeric substrates was performed and full conversion with irradiation times of only 1 min at ambient conditions was achieved. The current report thus presents a highly efficient method for applications involving selective cycloaddition to electron-deficient multiple-bond-containing materials.

  15. Broadband Polarization-Independent Perfect Absorber Using a Phase-Change Metamaterial at Visible Frequencies

    PubMed Central

    Cao, Tun; Wei, Chen-wei; Simpson, Robert E.; Zhang, Lei; Cryan, Martin J.

    2014-01-01

    We report a broadband polarization-independent perfect absorber with wide-angle near unity absorbance in the visible regime. Our structure is composed of an array of thin Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) layer. It shows that the near perfect absorbance is flat and broad over a wide-angle incidence up to 80° for either transverse electric or magnetic polarization due to a high imaginary part of the dielectric permittivity of Ge2Sb2Te5. The electric field, magnetic field and current distributions in the absorber are investigated to explain the physical origin of the absorbance. Moreover, we carried out numerical simulations to investigate the temporal variation of temperature in the Ge2Sb2Te5 layer and to show that the temperature of amorphous Ge2Sb2Te5 can be raised from room temperature to > 433 K (amorphous-to-crystalline phase transition temperature) in just 0.37 ns with a low light intensity of 95 nW/μm2, owing to the enhanced broadband light absorbance through strong plasmonic resonances in the absorber. The proposed phase-change metamaterial provides a simple way to realize a broadband perfect absorber in the visible and near-infrared (NIR) regions and is important for a number of applications including thermally controlled photonic devices, solar energy conversion and optical data storage. PMID:24492415

  16. Light-absorbing impurities in Arctic snow

    NASA Astrophysics Data System (ADS)

    Doherty, S. J.; Warren, S. G.; Grenfell, T. C.; Clarke, A. D.; Brandt, R. E.

    2010-12-01

    Absorption of radiation by ice is extremely weak at visible and near-ultraviolet wavelengths, so small amounts of light-absorbing impurities in snow can dominate the absorption of solar radiation at these wavelengths, reducing the albedo relative to that of pure snow, contributing to the surface energy budget and leading to earlier snowmelt. In this study Arctic snow is surveyed for its content of light-absorbing impurities, expanding and updating the 1983-1984 survey of Clarke and Noone. Samples were collected in Alaska, Canada, Greenland, Svalbard, Norway, Russia, and the Arctic Ocean during 1998 and 2005-2009, on tundra, glaciers, ice caps, sea ice, frozen lakes, and in boreal forests. Snow was collected mostly in spring, when the entire winter snowpack is accessible for sampling. Sampling was carried out in summer on the Greenland Ice Sheet and on the Arctic Ocean, of melting glacier snow and sea ice as well as cold snow. About 1200 snow samples have been analyzed for this study. The snow is melted and filtered; the filters are analyzed in a specially designed spectrophotometer system to infer the concentration of black carbon (BC), the fraction of absorption due to non-BC light-absorbing constituents and the absorption Ångstrom exponent of all particles. This is done using BC calibration standards having a mass absorption efficiency of 6.0 m2 g-1 at 550 nm and by making an assumption that the absorption Angstrom exponent for BC is 1.0 and for non-BC light-absorbing aerosol is 5.0. The reduction of snow albedo is primarily due to BC, but other impurities, principally brown (organic) carbon, are typically responsible for ~40% of the visible and ultraviolet absorption. The meltwater from selected snow samples was saved for chemical analysis to identify sources of the impurities. Median BC amounts in surface snow are as follows (nanograms of carbon per gram of snow): Greenland 3, Arctic Ocean snow 7, melting sea ice 8, Arctic Canada 8, subarctic Canada 14

  17. Measuring scintillation light using Visible Light

    NASA Astrophysics Data System (ADS)

    Chavarria, Alvaro

    2006-11-01

    A new search for the neutron electric dipole moment (EDM) using ultra cold neutrons proposes an improvement on the neutron EDM by two orders of magnitude over the current limit (to 10-28 e*cm). Detection of scintillation light in superfluid ^4He is at the heart of this experiment. One possible scheme to detect this light is to use wavelength-shifting fibers in the superfluid ^4He to collect the scintillation light and transport it out of the measuring cell. The fiber terminates in a visible light photon counter (VLPC). VLPCs are doped, silicon based, solid state photomultipliers with high quantum efficiency (up to 80%) and high gain ( 40000 electrons per converted photon). Moreover, they are insensitive to magnetic fields and operate at temperatures of 6.5K. A test setup has been assembled at Duke University using acrylic cells wrapped in wavelength-shifting fibers that terminate on VLPCs. This setup is being used to evaluate the feasibility of this light detection scheme. The results obtained in multiple experiments done over the past summer (2006) and the current status of the project will be presented at the conference.Reference:A New Search for the Neutron Electric Dipole Moment, funding pre-proposal by the EDM collaboration; R. Golub and S. Lamoreaux, Phys. Rep. 237, 1 (1994).

  18. How visible light curing came into dentistry.

    PubMed

    Wilson, N H F

    2016-01-01

    The present paper details the history of the introduction of visible light curing into dentistry. This history provides an excellent example of 'out of the box', lateral thinking translation of innovative scientific technology into dentistry. Visible light curing is an important UK contribution to the recent history and current practice of dentistry, with several million visible light curing procedures being carried out globally on a daily basis.

  19. Effects of visible light on the skin.

    PubMed

    Mahmoud, Bassel H; Hexsel, Camile L; Hamzavi, Iltefat H; Lim, Henry W

    2008-01-01

    Electromagnetic radiation has vast and diverse effects on human skin. Although photobiologic studies of sunlight date back to Sir Isaac Newton in 1671, most available studies focus on the UV radiation part of the spectrum. The effects of visible light and infrared radiation have not been, until recently, clearly elucidated. The goal of this review is to highlight the effects of visible light on the skin. As a result of advances in the understanding of skin optics, and comprehensive studies regarding the absorption spectrum of endogenous and exogenous skin chromophores, various biologic effects have been shown to be exerted by visible light radiation including erythema, pigmentation, thermal damage and free radical production. It has also been shown that visible light can induce indirect DNA damage through the generation of reactive oxygen species. Furthermore, a number of photodermatoses have an action spectrum in the visible light range, even though most of the currently available sunscreens offer, if any, weak protection against visible light. Conversely, because of its cutaneous biologic effects, visible light is used for the treatment of a variety of skin diseases and esthetic conditions in the form of lasers, intense pulsed light and photodynamic therapy.

  20. [VISIBLE LIGHT AND HUMAN SKIN (REVIEW)].

    PubMed

    Tsibadze, A; Chikvaidze, E; Katsitadze, A; Kvachadze, I; Tskhvediani, N; Chikviladze, A

    2015-09-01

    Biological effect of a visible light depends on extend of its property to penetrate into the tissues: the greater is a wavelength the more is an effect of a radiation. An impact of a visible light on the skin is evident by wave and quantum effects. Quanta of a visible radiation carry more energy than infrared radiation, although an influence of such radiation on the skin is produced by the light spectrum on the boarder of the ultraviolet and the infrared rays and is manifested by thermal and chemical effects. It is determined that large doses of a visible light (405-436 nm) can cause skin erythema. At this time, the ratio of generation of free radicals in the skin during an exposure to the ultraviolet and the visible light range from 67-33% respectively. Visible rays of 400-500 nm length of wave cause an increase of the concentration of oxygen's active form and mutation of DNA and proteins in the skin. The urticaria in 4-18% of young people induced by photodermatosis is described. As a result of a direct exposure to sunlight photosensitive eczema is more common in elderly. Special place holds a hereditary disease - porphyria, caused by a visible light. In recent years, dermatologists widely use phototherapy. The method uses polychromatic, non-coherent (wavelength of 515-1200 nm) pulsating beam. During phototherapy/light treatment a patient is being exposed to sunlight or bright artificial light. Sources of visible light are lasers, LEDs and fluorescent lamps which have the full range of a visible light. Phototherapy is used in the treatment of acne vulgaris, seasonal affective disorders, depression, psoriasis, eczema and neurodermities. LED of the red and near infrared range also is characterized by the therapeutic effect. They have an ability to influence cromatophores and enhance ATP synthesis in mitochondria. To speed up the healing of wounds and stimulate hair growth light sources of a weak intensity are used. The light of blue-green spectrum is widely used for

  1. Damaging effects of visible light

    NASA Astrophysics Data System (ADS)

    Williams, T. P.; Baker, B. N.

    1982-02-01

    The right eyes of anesthetized, ten week old albino rats are exposed to constant photon fluxes at 6 wavelengths for 6 hours. The left eye of each animal is patched during the exposure and is used as control. Histologic examination of retinal sections disclosed a region in the superior retina which is more damaged than are other areas. Attempting to ascertain an action spectrum by measuring outer nuclear layer (ONL) lost in this sensitive region fails. However, it is shown that when ONL thickness is integrated over the entire retinal sections, a rhodopsin action-spectrum emerges. It is concluded that retinal light damage in the albina rat under these conditions is rhodopsin mediated; and assessment of the extent of damage is best made by some method which integrates over the entire retinal section. The latter methodology is not routinely incorporated into studies of retinal light-damage but probably should be.

  2. Nanosecond high-power dense microplasma switch for visible light

    SciTech Connect

    Bataller, A. Koulakis, J.; Pree, S.; Putterman, S.

    2014-12-01

    Spark discharges in high-pressure gas are known to emit a broadband spectrum during the first 10 s of nanoseconds. We present calibrated spectra of high-pressure discharges in xenon and show that the resulting plasma is optically thick. Laser transmission data show that such a body is opaque to visible light, as expected from Kirchoff's law of thermal radiation. Nanosecond framing images of the spark absorbing high-power laser light are presented. The sparks are ideal candidates for nanosecond, high-power laser switches.

  3. Nanosecond high-power dense microplasma switch for visible light

    NASA Astrophysics Data System (ADS)

    Bataller, A.; Koulakis, J.; Pree, S.; Putterman, S.

    2014-12-01

    Spark discharges in high-pressure gas are known to emit a broadband spectrum during the first 10 s of nanoseconds. We present calibrated spectra of high-pressure discharges in xenon and show that the resulting plasma is optically thick. Laser transmission data show that such a body is opaque to visible light, as expected from Kirchoff's law of thermal radiation. Nanosecond framing images of the spark absorbing high-power laser light are presented. The sparks are ideal candidates for nanosecond, high-power laser switches.

  4. Broadband polygonal invisibility cloak for visible light.

    PubMed

    Chen, Hongsheng; Zheng, Bin

    2012-01-01

    Invisibility cloaks have recently become a topic of considerable interest thanks to the theoretical works of transformation optics and conformal mapping. The design of the cloak involves extreme values of material properties and spatially dependent parameter tensors, which are very difficult to implement. The realization of an isolated invisibility cloak in the visible light, which is an important step towards achieving a fully movable invisibility cloak, has remained elusive. Here, we report the design and experimental demonstration of an isolated polygonal cloak for visible light. The cloak is made of several elements, whose electromagnetic parameters are designed by a linear homogeneous transformation method. Theoretical analysis shows the proposed cloak can be rendered invisible to the rays incident from all the directions. Using natural anisotropic materials, a simplified hexagonal cloak which works for six incident directions is fabricated for experimental demonstration. The performance is validated in a broadband visible spectrum. PMID:22355767

  5. Broadband polygonal invisibility cloak for visible light

    PubMed Central

    Chen, Hongsheng; Zheng, Bin

    2012-01-01

    Invisibility cloaks have recently become a topic of considerable interest thanks to the theoretical works of transformation optics and conformal mapping. The design of the cloak involves extreme values of material properties and spatially dependent parameter tensors, which are very difficult to implement. The realization of an isolated invisibility cloak in the visible light, which is an important step towards achieving a fully movable invisibility cloak, has remained elusive. Here, we report the design and experimental demonstration of an isolated polygonal cloak for visible light. The cloak is made of several elements, whose electromagnetic parameters are designed by a linear homogeneous transformation method. Theoretical analysis shows the proposed cloak can be rendered invisible to the rays incident from all the directions. Using natural anisotropic materials, a simplified hexagonal cloak which works for six incident directions is fabricated for experimental demonstration. The performance is validated in a broadband visible spectrum. PMID:22355767

  6. Light Absorbing Aerosols in Mexico City

    NASA Astrophysics Data System (ADS)

    Marley, N. A.; Kelley, K. L.; Kilaparty, P. S.; Gaffney, J. S.

    2008-12-01

    The direct effects of aerosol radiative forcing has been identified by the IPCC as a major uncertainty in climate modeling. The DOE Megacity Aerosol Experiment-Mexico City (MAX-Mex), as part of the MILAGRO study in March of 2006, was undertaken to reduce these uncertainties by characterization of the optical, chemical, and physical properties of atmospheric aerosols emitted from this megacity environment. Aerosol samples collected during this study using quartz filters were characterized in the uv-visible-infrared by using surface spectroscopic techniques. These included the use of an integrating sphere approach combined with the use of Kubelka-Munk theory to obtain aerosol absorption spectra. In past work black carbon has been assumed to be the only major absorbing species in atmospheric aerosols with an broad band spectral profile that follows a simple inverse wavelength dependence. Recent work has also identified a number of other absorbing species that can also add to the overall aerosol absorption. These include primary organics from biomass and trash burning and secondary organic aerosols including nitrated PAHs and humic-like substances, or HULIS. By using surface diffuse reflection spectroscopy we have also obtained spectra in the infrared that indicate significant IR absorption in the atmospheric window-region. These data will be presented and compared to spectra of model compounds that allow for evaluation of the potential importance of these species in adding strength to the direct radiative forcing of atmospheric aerosols. This work was supported by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-07ER64327 as part of the Atmospheric Science Program.

  7. Visible-Light-Activated Molecular Switches.

    PubMed

    Bléger, David; Hecht, Stefan

    2015-09-21

    The ability to influence key properties of molecular systems by using light holds much promise for the fields of materials science and life sciences. The cornerstone of such systems is molecules that are able to reversibly photoisomerize between two states, commonly referred to as photoswitches. One serious restriction to the development of functional photodynamic systems is the necessity to trigger switching in at least one direction by UV light, which is often damaging and penetrates only partially through most media. This review provides a summary of the different conceptual strategies for addressing molecular switches in the visible and near-infrared regions of the optical spectrum. Such visible-light-activated molecular switches tremendously extend the scope of photoswitchable systems for future applications and technologies.

  8. A carpet cloak for visible light.

    PubMed

    Gharghi, Majid; Gladden, Christopher; Zentgraf, Thomas; Liu, Yongmin; Yin, Xiaobo; Valentine, Jason; Zhang, Xiang

    2011-07-13

    We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n<1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies. PMID:21619019

  9. Visible light communications with compound spectra

    NASA Astrophysics Data System (ADS)

    Vitasek, Jan; Vasinek, Vladimir; Latal, Jan; Hajek, Lukas

    2016-03-01

    At present the Visible Light Communications (VLC) attract attention of academia and industry thanks to rapid progress in the development of white light emitting diodes (LED). This article deals with the VLC and proposes their new solution, which may help remove some lacks of the current VLC. The substance of the new VLC solution is purposeful suppression of a part of the spectrum by a notch filter and by subsequent reconstruction of the original spectrum. Thus, only a part of the visible spectrum will transmit the information data. This is the main difference in comparison with the current VLC. This might be the way how the crucial parameters of the VLC may be improved.

  10. Two-dimensional material-based saturable absorbers: towards compact visible-wavelength all-fiber pulsed lasers.

    PubMed

    Luo, Zhengqian; Wu, Duanduan; Xu, Bin; Xu, Huiying; Cai, Zhiping; Peng, Jian; Weng, Jian; Xu, Shuo; Zhu, Chunhui; Wang, Fengqiu; Sun, Zhipei; Zhang, Han

    2016-01-14

    Passive Q-switching or mode-locking by placing a saturable absorber inside the laser cavity is one of the most effective and popular techniques for pulse generation. However, most of the current saturable absorbers cannot work well in the visible spectral region, which seriously impedes the progress of passively Q-switched/mode-locked visible pulsed fibre lasers. Here, we report a kind of visible saturable absorber-two-dimensional transition-metal dichalcogenides (TMDs, e.g. WS2, MoS2, MoSe2), and successfully demonstrate compact red-light Q-switched praseodymium (Pr(3+))-doped all-fibre lasers. The passive Q-switching operation at 635 nm generates stable laser pulses with ∼200 ns pulse duration, 28.7 nJ pulse energy and repetition rate from 232 to 512 kHz. This achievement is attributed to the ultrafast saturable absorption of these layered TMDs in the visible region, as well as the compact and all-fibre laser-cavity design by coating a dielectric mirror on the fibre end facet. This work may open a new route for next-generation high-performance pulsed laser sources in the visible (even ultraviolet) range. PMID:26658877

  11. Photodamage to the oxygen evolving complex of photosystem II by visible light.

    PubMed

    Zavafer, Alonso; Cheah, Mun Hon; Hillier, Warwick; Chow, Wah Soon; Takahashi, Shunichi

    2015-11-12

    Light damages photosynthetic machinery, primarily photosystem II (PSII), and it results in photoinhibition. A new photodamage model, the two-step photodamage model, suggests that photodamage to PSII initially occurs at the oxygen evolving complex (OEC) by light energy absorbed by manganese and that the PSII reaction center is subsequently damaged by light energy absorbed by photosynthetic pigments due to the limitation of electrons to the PSII reaction center. However, it is still uncertain whether this model is applicable to photodamage to PSII under visible light as manganese absorbs visible light only weakly. In the present study, we identified the initial site of photodamage to PSII upon illumination of visible light using PSII membrane fragments isolated from spinach leaves. When PSII samples were exposed to visible light in the presence of an exogenous electron acceptor, both PSII total activity and the PSII reaction centre activity declined due to photodamage. The supplemental addition of an electron donor to the PSII reaction centre alleviated the decline of the reaction centre activity but not the PSII total activity upon the light exposure. Our results demonstrate that visible light damages OEC prior to photodamage to the PSII reaction center, consistent with two-step photodamage model.

  12. Bright visible light emission from graphene

    NASA Astrophysics Data System (ADS)

    Kim, Young Duck; Kim, Hakseong; Cho, Yujin; Ryoo, Ji Hoon; Park, Cheol-Hwan; Kim, Pilkwang; Kim, Yong Seung; Lee, Sunwoo; Li, Yilei; Park, Seung-Nam; Shim Yoo, Yong; Yoon, Duhee; Dorgan, Vincent E.; Pop, Eric; Heinz, Tony F.; Hone, James; Chun, Seung-Hyun; Cheong, Hyeonsik; Lee, Sang Wook; Bae, Myung-Ho; Park, Yun Daniel

    2015-08-01

    Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced. Hot electrons (˜2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.

  13. Bright visible light emission from graphene.

    PubMed

    Kim, Young Duck; Kim, Hakseong; Cho, Yujin; Ryoo, Ji Hoon; Park, Cheol-Hwan; Kim, Pilkwang; Kim, Yong Seung; Lee, Sunwoo; Li, Yilei; Park, Seung-Nam; Yoo, Yong Shim; Yoon, Duhee; Dorgan, Vincent E; Pop, Eric; Heinz, Tony F; Hone, James; Chun, Seung-Hyun; Cheong, Hyeonsik; Lee, Sang Wook; Bae, Myung-Ho; Park, Yun Daniel

    2015-08-01

    Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced. Hot electrons (∼2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.

  14. Advances and prospects in visible light communications

    NASA Astrophysics Data System (ADS)

    Hongda, Chen; Chunhui, Wu; Honglei, Li; Xiongbin, Chen; Zongyu, Gao; Shigang, Cui; Qin, Wang

    2016-01-01

    Visible light communication (VLC) is an emerging technology in optical wireless communication (OWC) that has attracted worldwide research in recent years. VLC can combine communication and illumination together, which could be applied in many application scenarios such as visible light communication local area networks (VLANs), indoor localization, and intelligent lighting. In recent years, pioneering and significant work have been made in the field of VLC. In this paper, an overview of the recent progress in VLC is presented. We also demonstrate our recent experiment results including bidirectional 100 Mbit/s VLAN or Li-Fi system based on OOK modulation without blue filter. The VLC systems that we proposed are good solutions for high-speed VLC application systems with low-cost and low-complexity. VLC technology shows a bright future due to its inherent advantages, shortage of RF spectra and ever increasing popularity of white LEDs. Project supported by the National High Technology Research and Development Program of China (Nos. 2015AA033303, 2013AA013602, 2013AA013603, 2013AA03A104), the National Natural Science Foundation of China (Nos. 61178051, 61321063, 61335010, 61178048, 61275169), and the National Basic Research Program of China (Nos. 2013CB329205, 2011CBA00608).

  15. Novel dynamic tuning of broadband visible metamaterial perfect absorber using graphene

    NASA Astrophysics Data System (ADS)

    Jia, Xiuli; Wang, Xiaoou; Yuan, Chengxun; Meng, Qingxin; Zhou, Zhongxiang

    2016-07-01

    We present a novel dynamic tuning of a broadband visible metamaterial absorber consisting of a multilayer-graphene-embedded nano-cross elliptical hole (MGENCEH) structure. It has multiple effects, including excitation of surface plasmon polaritons and extraordinary optical transmission in the first two metal layers. A numerical simulation shows that the MGENCEH structure can realize broadband perfect absorption (BPA) from 5.85 × 1014 to 6.5 × 1014 Hz over a wide incident angle range for transverse magnetic polarized light if the chemical potential of graphene (uc) is tuned to 1.0 eV. Furthermore, it has high broadband absorption (above 96%) from 4.6 × 1014 to 6.6 × 1014 Hz and three areas of narrowband perfect absorption around 4.65 × 1014, 5.1 × 1014, and 5.6 × 1014 Hz. The changes in the absorption spectra as a function of uc can be classically explained by simply considering plasmons as damped harmonic oscillators. This BPA is broader than the result of Zhou et al. [Opt. Express 23, A413-A418 (2015)] and is particularly desirable for various potential applications such as solar energy absorbers.

  16. Wavelength control of visible light laser diodes

    NASA Astrophysics Data System (ADS)

    Goto, N.; Fujii, T.; Nemoto, K.; Suzuki, H.; Nakagawa, K.; Otsu, M.

    1990-04-01

    Wavelength control of visible light laser diodes was studied. By combining an interferometer and a diffraction grating, it became possible to control the wavelength of continuous oscillation in the range of 664 to 673nm, the frequency fine control range being 2GHz. And the spectral linewidth was narrowed to about 44kHz (10 exp minus 7 nm). With the use of a collimator lens, the beam expansion was narrowed to 2mrad. It was confirmed that the pulse output of continuous oscillation visible light laser diodes can be amplified by the YAG laser excitation dye laser. In the case of pulse oscillation, oscillation of 1GHz spectral width was obtained at the wavelength of 0.8 micro m by using an injection synchronization method. In the injection synchronization method, other laser beam is injected in an oscillator and a superior laser beam of synchronized components alone is obtained. As the wavelength control method is now stabilized and satisfies the conditions of narrow band, it has the prospect to be applied to the laser uranium enrichment technology.

  17. Novel Ultraviolet Light Absorbing Polymers For Optical Applications

    NASA Astrophysics Data System (ADS)

    Doddi, Namassivaya; Yamada, Akira; Dunks, Gary B.

    1988-07-01

    Ultraviolet light absorbing monomers have been developed that can be copolymerized with acrylates. The composition of the resultant stable copolymers can be adjusted to totally block the transmission of light below about 430 nm. Fabrication of lenses from the materials is accomplished by lathe cutting and injection molding procedures. These ultraviolet light absorbing materials are non-mutagenic and non-toxic and are currently being used in intraocular lenses.

  18. Lethal effects of short-wavelength visible light on insects

    NASA Astrophysics Data System (ADS)

    Hori, Masatoshi; Shibuya, Kazuki; Sato, Mitsunari; Saito, Yoshino

    2014-12-01

    We investigated the lethal effects of visible light on insects by using light-emitting diodes (LEDs). The toxic effects of ultraviolet (UV) light, particularly shortwave (i.e., UVB and UVC) light, on organisms are well known. However, the effects of irradiation with visible light remain unclear, although shorter wavelengths are known to be more lethal. Irradiation with visible light is not thought to cause mortality in complex animals including insects. Here, however, we found that irradiation with short-wavelength visible (blue) light killed eggs, larvae, pupae, and adults of Drosophila melanogaster. Blue light was also lethal to mosquitoes and flour beetles, but the effective wavelength at which mortality occurred differed among the insect species. Our findings suggest that highly toxic wavelengths of visible light are species-specific in insects, and that shorter wavelengths are not always more toxic. For some animals, such as insects, blue light is more harmful than UV light.

  19. Lethal effects of short-wavelength visible light on insects.

    PubMed

    Hori, Masatoshi; Shibuya, Kazuki; Sato, Mitsunari; Saito, Yoshino

    2014-12-09

    We investigated the lethal effects of visible light on insects by using light-emitting diodes (LEDs). The toxic effects of ultraviolet (UV) light, particularly shortwave (i.e., UVB and UVC) light, on organisms are well known. However, the effects of irradiation with visible light remain unclear, although shorter wavelengths are known to be more lethal. Irradiation with visible light is not thought to cause mortality in complex animals including insects. Here, however, we found that irradiation with short-wavelength visible (blue) light killed eggs, larvae, pupae, and adults of Drosophila melanogaster. Blue light was also lethal to mosquitoes and flour beetles, but the effective wavelength at which mortality occurred differed among the insect species. Our findings suggest that highly toxic wavelengths of visible light are species-specific in insects, and that shorter wavelengths are not always more toxic. For some animals, such as insects, blue light is more harmful than UV light.

  20. Visible absorbance spectra: A basis for in situ and passive remote sensing of phytoplankton concentration and community composition

    NASA Technical Reports Server (NTRS)

    Farmer, F. H.; Jarrett, O., Jr.; Brown, C. A., Jr.

    1983-01-01

    The concentration and composition of phytoplankton populations are measured by an optical method which can be used either in situ or remotely. This method is based upon the in vivo light absorption characteristics of phytoplankton. To provide a data base for testing assumptions relative to the proposed method, visible absorbance spectra of pure cultures of 20 marine phytoplankton were obtained under laboratory conditions. Descriptive and analytical statistics were computed for the absorbance spectra and were used to make comparisons between members of major taxonomic groups and between groups. Spectral variation between the members of the major taxonomic groups was observed to be considerably less than the spectral variation between these groups. In several cases the differences between the mean absorbance spectra of major taxonomic groups are significant enough to be detected with passive remote sensing techniques.

  1. Macroscopic invisibility cloaking of visible light.

    PubMed

    Chen, Xianzhong; Luo, Yu; Zhang, Jingjing; Jiang, Kyle; Pendry, John B; Zhang, Shuang

    2011-01-01

    Invisibility cloaks, which used to be confined to the realm of fiction, have now been turned into a scientific reality thanks to the enabling theoretical tools of transformation optics and conformal mapping. Inspired by those theoretical works, the experimental realization of electromagnetic invisibility cloaks has been reported at various electromagnetic frequencies. All the invisibility cloaks demonstrated thus far, however, have relied on nano- or micro-fabricated artificial composite materials with spatially varying electromagnetic properties, which limit the size of the cloaked region to a few wavelengths. Here, we report the first realization of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding, for a specific light polarization, three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices.

  2. Macroscopic invisibility cloaking of visible light

    PubMed Central

    Chen, Xianzhong; Luo, Yu; Zhang, Jingjing; Jiang, Kyle; Pendry, John B.; Zhang, Shuang

    2011-01-01

    Invisibility cloaks, which used to be confined to the realm of fiction, have now been turned into a scientific reality thanks to the enabling theoretical tools of transformation optics and conformal mapping. Inspired by those theoretical works, the experimental realization of electromagnetic invisibility cloaks has been reported at various electromagnetic frequencies. All the invisibility cloaks demonstrated thus far, however, have relied on nano- or micro-fabricated artificial composite materials with spatially varying electromagnetic properties, which limit the size of the cloaked region to a few wavelengths. Here, we report the first realization of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding, for a specific light polarization, three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices. PMID:21285954

  3. Macroscopic invisibility cloak for visible light.

    PubMed

    Zhang, Baile; Luo, Yuan; Liu, Xiaogang; Barbastathis, George

    2011-01-21

    Invisibility cloaks, a subject that usually occurs in science fiction and myths, have attracted wide interest recently because of their possible realization. The biggest challenge to true invisibility is known to be the cloaking of a macroscopic object in the broad range of wavelengths visible to the human eye. Here we experimentally solve this problem by incorporating the principle of transformation optics into a conventional optical lens fabrication with low-cost materials and simple manufacturing techniques. A transparent cloak made of two pieces of calcite is created. This cloak is able to conceal a macroscopic object with a maximum height of 2 mm, larger than 3500 free-space-wavelength, inside a transparent liquid environment. Its working bandwidth encompassing red, green, and blue light is also demonstrated.

  4. Visible Light Responsive Catalyst for Air Water Purification Project

    NASA Technical Reports Server (NTRS)

    Wheeler, Raymond M.

    2014-01-01

    Investigate and develop viable approaches to render the normally UV-activated TIO2 catalyst visible light responsive (VLR) and achieve high and sustaining catalytic activity under the visible region of the solar spectrum.

  5. Visible Light Mediated Photoredox Catalytic Arylation Reactions.

    PubMed

    Ghosh, Indrajit; Marzo, Leyre; Das, Amrita; Shaikh, Rizwan; König, Burkhard

    2016-08-16

    Introducing aryl- and heteroaryl moieties into molecular scaffolds are often key steps in the syntheses of natural products, drugs, or functional materials. A variety of cross-coupling methods have been well established, mainly using transition metal mediated reactions between prefunctionalized substrates and arenes or C-H arylations with functionalization in only one coupling partner. Although highly developed, one drawback of the established sp2-sp2 arylations is the required transition metal catalyst, often in combination with specific ligands and additives. Therefore, photoredox mediated arylation methods have been developed as alternative over the past decade. We begin our survey with visible light photo-Meerwein arylation reactions, which allow C-H arylation of heteroarenes, enones, alkenes, and alkynes with organic dyes, such as eosin Y, as the photocatalyst. A good number of examples from different groups illustrate the broad application of the reaction in synthetic transformations. While initially only photo-Meerwein arylation-elimination processes were reported, the reaction was later extended to photo-Meerwein arylation-addition reactions giving access to the photoinduced three component synthesis of amides and esters from alkenes, aryl diazonium salts, nitriles or formamides, respectively. Other substrates with redox-active leaving groups have been explored in photocatalyzed arylation reactions, such as diaryliodonium and triarylsulfonium salts, and arylsulfonyl chlorides. We discus some examples with their scope and limitations. The scope of arylation reagents for photoredox reactions was extended to aryl halides. The challenge here is the extremely negative reduction potential of aryl halides in the initial electron transfer step compared to, e.g., aryl diazonium or diaryliodonium salts. In order to reach reduction potentials over -2.0 V vs SCE two consecutive photoinduced electron transfer steps were used. The intermediary formed colored radical

  6. Visible Light Mediated Photoredox Catalytic Arylation Reactions.

    PubMed

    Ghosh, Indrajit; Marzo, Leyre; Das, Amrita; Shaikh, Rizwan; König, Burkhard

    2016-08-16

    Introducing aryl- and heteroaryl moieties into molecular scaffolds are often key steps in the syntheses of natural products, drugs, or functional materials. A variety of cross-coupling methods have been well established, mainly using transition metal mediated reactions between prefunctionalized substrates and arenes or C-H arylations with functionalization in only one coupling partner. Although highly developed, one drawback of the established sp2-sp2 arylations is the required transition metal catalyst, often in combination with specific ligands and additives. Therefore, photoredox mediated arylation methods have been developed as alternative over the past decade. We begin our survey with visible light photo-Meerwein arylation reactions, which allow C-H arylation of heteroarenes, enones, alkenes, and alkynes with organic dyes, such as eosin Y, as the photocatalyst. A good number of examples from different groups illustrate the broad application of the reaction in synthetic transformations. While initially only photo-Meerwein arylation-elimination processes were reported, the reaction was later extended to photo-Meerwein arylation-addition reactions giving access to the photoinduced three component synthesis of amides and esters from alkenes, aryl diazonium salts, nitriles or formamides, respectively. Other substrates with redox-active leaving groups have been explored in photocatalyzed arylation reactions, such as diaryliodonium and triarylsulfonium salts, and arylsulfonyl chlorides. We discus some examples with their scope and limitations. The scope of arylation reagents for photoredox reactions was extended to aryl halides. The challenge here is the extremely negative reduction potential of aryl halides in the initial electron transfer step compared to, e.g., aryl diazonium or diaryliodonium salts. In order to reach reduction potentials over -2.0 V vs SCE two consecutive photoinduced electron transfer steps were used. The intermediary formed colored radical

  7. Visible light powered self-disinfecting coatings for influenza viruses

    NASA Astrophysics Data System (ADS)

    Weng, Ding; Qi, Hangfei; Wu, Ting-Ting; Yan, Ming; Sun, Ren; Lu, Yunfeng

    2012-04-01

    Influenza A viruses, the pathogens responsible for the recent swine flu outbreak and many historical pandemics, remain a threat to the public health. We report herein the fabrication of self-disinfecting surfaces from photoactive building nanocrystals, which can inactivate influenza viruses rapidly, spontaneously and continuously under visible light illumination.Influenza A viruses, the pathogens responsible for the recent swine flu outbreak and many historical pandemics, remain a threat to the public health. We report herein the fabrication of self-disinfecting surfaces from photoactive building nanocrystals, which can inactivate influenza viruses rapidly, spontaneously and continuously under visible light illumination. Electronic supplementary information (ESI) available: XRD, UV-Vis absorbance, TEM, AFM of as-prepared nanocrystals and as-fabricated self-disinfecting surfaces, disinfection of influenza A virus by TiO2 (P25) with UV irradiation as reference control, photoinactivation of influenza A virus envelope proteins and photoinactivation of trypsin. See DOI: 10.1039/c2nr30388d

  8. Light Absorbing Particle (LAP) Measurements in the Lower Stratosphere

    NASA Technical Reports Server (NTRS)

    Baumgardner, D.; Raga, G. B.; Anderson, B.; Diskin, G.; Sachse, G.; Kok, G.

    2003-01-01

    This viewgraph presentation covers the capabilities and design of the Single Particle Soot Photometer (SP-2), and reviews its role on the Sage III Ozone Loss Validation Experiment (SOLVE II) field campaign during 2003. On SOLVE II the SP-2 was carried into the Arctic onboard a DC-8 aircraft, in order to determine the size distribution of light-absorbing and non light-absorbing particles in the stratosphere. Graphs and tables relate some of the results from SOLVE II.

  9. Optical bidirectional beacon based visible light communications.

    PubMed

    Tiwari, Samrat Vikramaditya; Sewaiwar, Atul; Chung, Yeon Ho

    2015-10-01

    In an indoor bidirectional visible light communications (VLC), a line-of-sight (LOS) transmission plays a major role in obtaining adequate performance of a VLC system. Signals are often obstructed in the LOS transmission path, causing an effect called optical shadowing. In the absence of LOS, the performance of the VLC system degrades significantly and, in particular, at uplink transmission this degradation becomes severe due to design constraints and limited power at uplink devices. In this paper, a novel concept and design of an optical bidirectional beacon (OBB) is presented as an efficient model to counter the performance degradation in a non-line-of-sight (NLOS) VLC system. OBB is an independent operating bidirectional transceiver unit installed on walls, composed of red, green, and blue (RGB) light emitting diodes (LEDs), photodetectors (PDs) and color filters. OBB improves the coverage area in the form of providing additional or alternate paths for transmission and enhances the performance of the VLC system in terms of bit error rate (BER). To verify the effectiveness of the proposed system, simulations were carried out under optical shadowing conditions at various locations in an indoor environment. The simulation results and analysis show that the implementation of OBB improves the performance of the VLC system significantly, especially when the LOS bidirectional transmission paths are completely or partially obstructed.

  10. Catadioptric lenses in Visible Light Communications

    NASA Astrophysics Data System (ADS)

    Garcia-Marquez, J.; Valencia, J. C.; Perez, H.; Topsu, S.

    2015-04-01

    Since few years ago, visible light communications (VLC) have experience an accelerated interest from a research point of view. The beginning of this decade has seen many improvements in VLC at an electronic level. High rates of transmission at low bit error ratios (BER) have been reported. A few numbers of start-ups have initiated activities to offer a variety of applications ranging from indoor geo-localization to internet, but in spite of these advancements, some other problems arise. Long-range transmissions mean a high BER which reduce the number of applications. In this sense, new redesigned optical collectors or in some cases, optical reflectors must be considered to ensure a low BER at higher distance transmissions. Here we also expose a preliminary design of a catadioptric and monolithical lens for a LI-FI receiver with two rotationally symmetrical main piecewise surfaces za and zb. These surfaces are represented in a system of cylindrical coordinates with an anterior surface za with a central and refractive sector surrounded by a peripheral reflective sector and a back piecewise surface zb with a central refractive sector and a reflective sector, both characterized as ideal for capturing light within large acceptance angles.

  11. A naked eye refractive index sensor with a visible multiple peak metamaterial absorber.

    PubMed

    Ma, Heli; Song, Kun; Zhou, Liang; Zhao, Xiaopeng

    2015-01-01

    We report a naked eye refractive index sensor with a visible metamaterial absorber. The visible metamaterial absorber consisting of a silver dendritic/dielectric/metal structure shows multiple absorption peaks. By incorporating a gain material (rhodamine B) into the dielectric layer, the maximal magnitude of the absorption peak can be improved by about 30%. As the metamaterial absorber is sensitive to the refractive index of glucose solutions, it can function as a sensor that quickly responds to variations of the refractive index of the liquid. Meanwhile, since the response is presented via color changes, it can be clearly observed by the naked eyes. Further experiments have confirmed that the sensor can be used repeatedly. PMID:25822141

  12. A Naked Eye Refractive Index Sensor with a Visible Multiple Peak Metamaterial Absorber

    PubMed Central

    Ma, Heli; Song, Kun; Zhou, Liang; Zhao, Xiaopeng

    2015-01-01

    We report a naked eye refractive index sensor with a visible metamaterial absorber. The visible metamaterial absorber consisting of a silver dendritic/dielectric/metal structure shows multiple absorption peaks. By incorporating a gain material (rhodamine B) into the dielectric layer, the maximal magnitude of the absorption peak can be improved by about 30%. As the metamaterial absorber is sensitive to the refractive index of glucose solutions, it can function as a sensor that quickly responds to variations of the refractive index of the liquid. Meanwhile, since the response is presented via color changes, it can be clearly observed by the naked eyes. Further experiments have confirmed that the sensor can be used repeatedly. PMID:25822141

  13. Radiative cooling of solar absorbers using a visibly transparent photonic crystal thermal blackbody

    PubMed Central

    Zhu, Linxiao; Raman, Aaswath P.; Fan, Shanhui

    2015-01-01

    A solar absorber, under the sun, is heated up by sunlight. In many applications, including solar cells and outdoor structures, the absorption of sunlight is intrinsic for either operational or aesthetic considerations, but the resulting heating is undesirable. Because a solar absorber by necessity faces the sky, it also naturally has radiative access to the coldness of the universe. Therefore, in these applications it would be very attractive to directly use the sky as a heat sink while preserving solar absorption properties. Here we experimentally demonstrate a visibly transparent thermal blackbody, based on a silica photonic crystal. When placed on a silicon absorber under sunlight, such a blackbody preserves or even slightly enhances sunlight absorption, but reduces the temperature of the underlying silicon absorber by as much as 13 °C due to radiative cooling. Our work shows that the concept of radiative cooling can be used in combination with the utilization of sunlight, enabling new technological capabilities. PMID:26392542

  14. Radiative cooling of solar absorbers using a visibly transparent photonic crystal thermal blackbody.

    PubMed

    Zhu, Linxiao; Raman, Aaswath P; Fan, Shanhui

    2015-10-01

    A solar absorber, under the sun, is heated up by sunlight. In many applications, including solar cells and outdoor structures, the absorption of sunlight is intrinsic for either operational or aesthetic considerations, but the resulting heating is undesirable. Because a solar absorber by necessity faces the sky, it also naturally has radiative access to the coldness of the universe. Therefore, in these applications it would be very attractive to directly use the sky as a heat sink while preserving solar absorption properties. Here we experimentally demonstrate a visibly transparent thermal blackbody, based on a silica photonic crystal. When placed on a silicon absorber under sunlight, such a blackbody preserves or even slightly enhances sunlight absorption, but reduces the temperature of the underlying silicon absorber by as much as 13 °C due to radiative cooling. Our work shows that the concept of radiative cooling can be used in combination with the utilization of sunlight, enabling new technological capabilities.

  15. Radiative cooling of solar absorbers using a visibly transparent photonic crystal thermal blackbody.

    PubMed

    Zhu, Linxiao; Raman, Aaswath P; Fan, Shanhui

    2015-10-01

    A solar absorber, under the sun, is heated up by sunlight. In many applications, including solar cells and outdoor structures, the absorption of sunlight is intrinsic for either operational or aesthetic considerations, but the resulting heating is undesirable. Because a solar absorber by necessity faces the sky, it also naturally has radiative access to the coldness of the universe. Therefore, in these applications it would be very attractive to directly use the sky as a heat sink while preserving solar absorption properties. Here we experimentally demonstrate a visibly transparent thermal blackbody, based on a silica photonic crystal. When placed on a silicon absorber under sunlight, such a blackbody preserves or even slightly enhances sunlight absorption, but reduces the temperature of the underlying silicon absorber by as much as 13 °C due to radiative cooling. Our work shows that the concept of radiative cooling can be used in combination with the utilization of sunlight, enabling new technological capabilities. PMID:26392542

  16. Measuring scintillation light using Visible Light Photon Counters (VLPC)

    NASA Astrophysics Data System (ADS)

    Chavarria, Alvaro

    2006-10-01

    A new search for the neutron electric dipole moment (EDM) using ultra cold neutrons proposes an improvement on the neutron EDM by two orders of magnitude over the current limit (to 10-28 e*cm). Detection of scintillation light in superfluid ^4He is at the heart of this experiment.One possible scheme to detect this light is to use wavelength-shifting fibers in the superfluid ^4He to collect the scintillation light and transport it out of the measuring cell. The fiber terminates in a visible light photon counter (VLPC). VLPCs are doped, silicon based, solid state photomultipliers with high quantum efficiency (up to 80%) and high gain ( 40000 electrons per converted photon). Moreover, they are insensitive to magnetic fields and operate at temperatures of 6.5K.A test setup has been assembled at Duke University using acrylic cells wrapped in wavelength-shifting fibers that terminate on VLPCs. This setup is being used to evaluate the feasibility of this light detection scheme. The results obtained in multiple experiments done over the past summer (2006) and the current status of the project will be presented at the conference.Reference:A New Search for the Neutron Electric Dipole Moment, funding pre-proposal by the EDM collaboration; R. Golub and S. Lamoreaux, Phys. Rep. 237, 1 (1994).

  17. Gold nanoparticles as a saturable absorber for visible 635 nm Q-switched pulse generation.

    PubMed

    Wu, Duanduan; Peng, Jian; Cai, Zhiping; Weng, Jian; Luo, Zhengqian; Chen, Nan; Xu, Huiying

    2015-09-01

    Gold nanoparticle (GNP) possesses saturable absorption bands in the visible region induced by surface plasmon resonance (SPR). We firstly applied the GNP as a visible saturable absorber (SA) for the red Q-switched pulse generation. The GNPs were embedded in polyvinyl alcohol (PVA) for film-forming and inserted into a praseodymium (Pr(3+))-doped fiber laser cavity to achieve 635 nm passive Q-switching. The visible 635 nm Q-switched fiber laser has a wide range of pulse-repetition-rate from 285.7 to 546.4 kHz, and a narrow pulse width of 235 ns as well as the maximum output power of 11.1 mW. The results indicate that the GNPs-based SA is available for pulsed operation in the visible spectral range. PMID:26368498

  18. Indoor optical wireless communication by ultraviolet and visible light

    NASA Astrophysics Data System (ADS)

    Cui, Kaiyun; Chen, Gang; He, Qunfeng; Xu, Zhengyuan

    2009-08-01

    Visible light communication in conjunction with solid state lighting has become an emerging area of interest to achieve lighting and wireless communication simultaneously in an indoor environment. It is anticipated to be a low cost supplement to existing wireless communication technologies. Most existing work has primarily focused on a unidirectional downlink using visible light spectra. The appropriate choice of an uplink to achieve bidirectional communication is a big challenge. In this paper, candidate options of the uplink are compared in terms of device performance, light safety, background interference, and path loss. In visible light communication, white light emitting diodes as optical transmitters are also characterized in terms of impulse response and electrical spectrum. A digital preequalization idea to increase their bandwidth is proposed. Performance of the downlink visible light communication system is also experimentally studied in order to demonstrate the feasibility of the proposed design.

  19. Measurements of Light Absorbing Particles on Tropical South American Glaciers

    NASA Astrophysics Data System (ADS)

    Schmitt, C. G.; All, J.; Schwarz, J. P.; Arnott, W. P.; Warthon, J.; Andrade, M.; Celestian, A. J.; Hoffmann, D.; Cole, R. J.; Lapham, E.; Horodyskyj, U. N.; Froyd, K. D.; Liao, J.

    2014-12-01

    Glaciers in the tropical Andes have been losing mass rapidly in recent decades. In addition to the documented increase in temperature, increases in light absorbing particulates deposited on glaciers could be contributing to the observed glacier loss. Here we present results of measurements of light absorbing particles from glaciers in Peru and Bolivia. Samples have been collected by American Climber Science Program volunteers and scientists at altitudes up to 6770 meters. Collected snow samples were melted and filtered in the field. A new inexpensive technique, the Light Absorption Heating Method (LAHM) has been developed for analysis of light absorbing particles collected on filters. Results from LAHM analysis are calibrated using filters with known amounts of fullerene soot, a common industrial surrogate for black carbon (BC). For snow samples collected at the same field location LAHM analysis and measurements from the Single Particle Soot Photometer (SP2) instrument are well correlated (r2 = 0.92). Co-located SP2 and LAHM filter analysis suggest that BC could be the dominant absorbing component of the light absorbing particles in some areas.

  20. Visible Light Communication Physical Layer Design for Jist Simulation

    NASA Astrophysics Data System (ADS)

    Tomaš, Boris

    2014-12-01

    Current advances in computer networking consider using visible light spectrum to encode and decode digital data. This approach is relatively non expensive. However, designing appropriate MAC or any other upper layer protocol for Visible Light Communication (VLC) requires appropriate hardware. This paper proposes and implements such hardware simulation (physical layer) that is compatible with existing network stack.

  1. Enhancing the visibility of injuries with narrow-banded beams of light within the visible light spectrum.

    PubMed

    Limmen, Roxane M; Ceelen, Manon; Reijnders, Udo J L; Joris Stomp, S; de Keijzer, Koos C; Das, Kees

    2013-03-01

    The use of narrow-banded visible light sources in improving the visibility of injuries has been hardly investigated, and studies examining the extent of this improvement are lacking. In this study, narrow-banded beams of light within the visible light spectrum were used to explore their ability in improving the visibility of external injuries. The beams of light were induced by four crime-lites(®) providing narrow-banded beams of light between 400 and 550 nm. The visibility of the injuries was assessed through specific long-pass filters supplied with the set of crime-lites(®) . Forty-three percent of the examined injuries improved in visibility by using the narrow-banded visible light. In addition, injuries were visualized that were not visible or just barely visible to the naked eye. The improvements in visibility were particularly marked with the use of crime-lites(®) "violet" and "blue" covering the spectrum between 400-430 and 430-470 nm. The simple noninvasive method showed a great potential contribution in injury examination. PMID:23278497

  2. Enhancing the visibility of injuries with narrow-banded beams of light within the visible light spectrum.

    PubMed

    Limmen, Roxane M; Ceelen, Manon; Reijnders, Udo J L; Joris Stomp, S; de Keijzer, Koos C; Das, Kees

    2013-03-01

    The use of narrow-banded visible light sources in improving the visibility of injuries has been hardly investigated, and studies examining the extent of this improvement are lacking. In this study, narrow-banded beams of light within the visible light spectrum were used to explore their ability in improving the visibility of external injuries. The beams of light were induced by four crime-lites(®) providing narrow-banded beams of light between 400 and 550 nm. The visibility of the injuries was assessed through specific long-pass filters supplied with the set of crime-lites(®) . Forty-three percent of the examined injuries improved in visibility by using the narrow-banded visible light. In addition, injuries were visualized that were not visible or just barely visible to the naked eye. The improvements in visibility were particularly marked with the use of crime-lites(®) "violet" and "blue" covering the spectrum between 400-430 and 430-470 nm. The simple noninvasive method showed a great potential contribution in injury examination.

  3. Integrating visible light 3D scanning into the everyday world

    NASA Astrophysics Data System (ADS)

    Straub, Jeremy

    2015-05-01

    Visible light 3D scanning offers the potential to non-invasively and nearly non-perceptibly incorporate 3D imaging into the everyday world. This paper considers the various possible uses of visible light 3D scanning technology. It discusses multiple possible usage scenarios including in hospitals, security perimeter settings and retail environments. The paper presents a framework for assessing the efficacy of visible light 3D scanning for a given application (and compares this to other scanning approaches such as those using blue light or lasers). It also discusses ethical and legal considerations relevant to real-world use and concludes by presenting a decision making framework.

  4. The Development of Visible-Light Photoredox Catalysis in Flow

    PubMed Central

    Garlets, Zachary J.; Nguyen, John D.

    2014-01-01

    Visible-light photoredox catalysis has recently emerged as a viable alternative for radical reactions otherwise carried out with tin and boron reagents. It has been recognized that by merging photoredox catalysis with flow chemistry, slow reaction times, lower yields, and safety concerns may be obviated. While flow reactors have been successfully applied to reactions carried out with UV light, only recent developments have demonstrated the same potential of flow reactors for the improvement of visible-light-mediated reactions. This review examines the initial and continuing development of visible-light-mediated photoredox flow chemistry by exemplifying the benefits of flow chemistry compared with conventional batch techniques. PMID:25484447

  5. Highly Transparent, Visible-Light Photodetector Based on Oxide Semiconductors and Quantum Dots.

    PubMed

    Shin, Seung Won; Lee, Kwang-Ho; Park, Jin-Seong; Kang, Seong Jun

    2015-09-01

    Highly transparent phototransistors that can detect visible light have been fabricated by combining indium-gallium-zinc oxide (IGZO) and quantum dots (QDs). A wide-band-gap IGZO film was used as a transparent semiconducting channel, while small-band-gap QDs were adopted to absorb and convert visible light to an electrical signal. Typical IGZO thin-film transistors (TFTs) did not show a photocurrent with illumination of visible light. However, IGZO TFTs decorated with QDs showed enhanced photocurrent upon exposure to visible light. The device showed a responsivity of 1.35×10(4) A/W and an external quantum efficiency of 2.59×10(4) under illumination by a 635 nm laser. The origin of the increased photocurrent in the visible light was the small band gap of the QDs combined with the transparent IGZO films. Therefore, transparent phototransistors based on IGZO and QDs were fabricated and characterized in detail. The result is relevant for the development of highly transparent photodetectors that can detect visible light. PMID:26293387

  6. Highly Transparent, Visible-Light Photodetector Based on Oxide Semiconductors and Quantum Dots.

    PubMed

    Shin, Seung Won; Lee, Kwang-Ho; Park, Jin-Seong; Kang, Seong Jun

    2015-09-01

    Highly transparent phototransistors that can detect visible light have been fabricated by combining indium-gallium-zinc oxide (IGZO) and quantum dots (QDs). A wide-band-gap IGZO film was used as a transparent semiconducting channel, while small-band-gap QDs were adopted to absorb and convert visible light to an electrical signal. Typical IGZO thin-film transistors (TFTs) did not show a photocurrent with illumination of visible light. However, IGZO TFTs decorated with QDs showed enhanced photocurrent upon exposure to visible light. The device showed a responsivity of 1.35×10(4) A/W and an external quantum efficiency of 2.59×10(4) under illumination by a 635 nm laser. The origin of the increased photocurrent in the visible light was the small band gap of the QDs combined with the transparent IGZO films. Therefore, transparent phototransistors based on IGZO and QDs were fabricated and characterized in detail. The result is relevant for the development of highly transparent photodetectors that can detect visible light.

  7. Analysis of optical transmission by 400-500 nm visible light into aesthetic dental biomaterials.

    PubMed

    Watts, D C; Cash, A J

    1994-04-01

    The penetration of visible light into dental biomaterials is an essential factor in photoinitiation of setting reactions and in the optical aspects of dental aesthetics. Light of visible blue wavelengths, 400-500 nm, has been applied at normal angles to 0.2-5.0 mm sections of human dentine and representative ceramic, polymerceramic composites and hybrid glass-polyalkenoate materials. The integrated optical transmission has been determined for each material section. The data have been converted to absorbance values and analysed to check for mathematical conformity to the Beer-Lambert Law. It is found that conformity (typically, P < 0.01) to the linear Beer-Lambert Law is only attained by making a substantial correction for the intensity of light reflected from the surface of aesthetic biomaterials. This is otherwise expressed by distinguishing between true and apparent absorbance. From linear regression of apparent absorbance with section thickness, the intercept depends upon the logarithm of the surface-reflection ratio. This factor ranges from 30% to 90% in the materials investigated. It follows that there is a high degree of inefficiency in the transmission of visible light into and through aesthetic biomaterials for the purposes of photoactivation using existing technology. Means by which this limitation and inefficiency may be reduced are discussed. While the reflectivity of aesthetic biomaterials has been perceived by dental practitioners, the magnitude of this effect and its implications in connection with light-cured materials have not been analysed and emphasized hitherto. PMID:8195476

  8. Visible light alters yeast metabolic rhythms by inhibiting respiration.

    PubMed

    Robertson, James Brian; Davis, Chris R; Johnson, Carl Hirschie

    2013-12-24

    Exposure of cells to visible light in nature or in fluorescence microscopy often is considered to be relatively innocuous. However, using the yeast respiratory oscillation (YRO) as a sensitive measurement of metabolism, we find that non-UV visible light has a significant impact on yeast metabolism. Blue/green wavelengths of visible light shorten the period and dampen the amplitude of the YRO, which is an ultradian rhythm of cell metabolism and transcription. The wavelengths of light that have the greatest effect coincide with the peak absorption regions of cytochromes. Moreover, treating yeast with the electron transport inhibitor sodium azide has similar effects on the YRO as visible light. Because impairment of respiration by light would change several state variables believed to play vital roles in the YRO (e.g., oxygen tension and ATP levels), we tested oxygen's role in YRO stability and found that externally induced oxygen depletion can reset the phase of the oscillation, demonstrating that respiratory capacity plays a role in the oscillation's period and phase. Light-induced damage to the cytochromes also produces reactive oxygen species that up-regulate the oxidative stress response gene TRX2 that is involved in pathways that enable sustained growth in bright visible light. Therefore, visible light can modulate cellular rhythmicity and metabolism through unexpectedly photosensitive pathways.

  9. Coherence and visibility for vectorial light.

    PubMed

    Luis, Alfredo

    2010-08-01

    Two-path interference of transversal vectorial waves is embedded within a larger scheme: this is four-path interference between four scalar waves. This comprises previous approaches to coherence between vectorial waves and restores the equivalence between correlation-based coherence and visibility. PMID:20686580

  10. Laser-Modified Black Titanium Oxide Nanospheres and Their Photocatalytic Activities under Visible Light.

    PubMed

    Chen, Xing; Zhao, Dongxu; Liu, Kewei; Wang, Chunrui; Liu, Lei; Li, Binghui; Zhang, Zhenzhong; Shen, Dezhen

    2015-07-29

    A facile pulse laser ablation approach for preparing black titanium oxide nanospheres, which could be used as photocatalysts under visible light, is proposed. The black titanium oxide nanospheres are prepared by pulsed-laser irradiation of pure titanium oxide in suspended aqueous solution. The crystalline phases, morphology, and optical properties of the obtained nanospheres are characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and UV-vis-NIR diffuse reflectance spectroscopy. It is shown that high-energy laser ablation of titanium oxide suspended solution benefited the formation of Ti(3+) species and surface disorder on the surface of the titanium oxide nanospheres. The laser-modified black titanium oxide nanospheres could absorb the full spectrum of visible light, thus exhibiting good photocatalytic performance under visible light.

  11. Warming of the Arctic lower stratosphere by light absorbing particles

    NASA Astrophysics Data System (ADS)

    Baumgardner, D.; Kok, G.; Raga, G.

    2004-03-01

    Recent measurements of light absorbing particles in the Arctic lower stratosphere show significantly higher mass concentrations of black carbon than were measured in 1992. The difference is primarily a result of measurements with a more quantitative and accurate technique than was previously used. We attribute the large amount of light absorbing material to transport from lower latitude, tropospheric sources rather than increases in aircraft emissions. The calculated heating rate in this aerosol layer, as compared to an atmosphere consisting of only gases, increases by 12% during the winter. This is a result of light absorption by the particles and could perturb the altitude of the local tropopause and affect tropospheric/stratospheric exchange processes.

  12. A titanium and visible light-polymerized resin obturator.

    PubMed

    Rilo, Benito; da Silva, José Luis; Martinez-Insua, Arturo; Santana, Urbano

    2002-04-01

    Obturator prostheses are typically large, and their weight and size are often important design factors. This article describes the fabrication of an obturator prosthesis with a titanium framework and visible light-polymerized denture base resin. It is speculated that these low-density materials may produce prostheses lighter than similar ones made with conventional materials. An added advantage is that visible light-polymerizing resins facilitate relining. PMID:12011852

  13. Visible Light Sensitization of Vinyl Azides by Transition Metal Photocatalysis

    PubMed Central

    Farney, Elliot P.; Yoon, Tehshik P.

    2014-01-01

    Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of C–N bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic utility of these reactions. PMID:24281908

  14. A titanium and visible light-polymerized resin obturator.

    PubMed

    Rilo, Benito; da Silva, José Luis; Martinez-Insua, Arturo; Santana, Urbano

    2002-04-01

    Obturator prostheses are typically large, and their weight and size are often important design factors. This article describes the fabrication of an obturator prosthesis with a titanium framework and visible light-polymerized denture base resin. It is speculated that these low-density materials may produce prostheses lighter than similar ones made with conventional materials. An added advantage is that visible light-polymerizing resins facilitate relining.

  15. Making Light Rays Visible in 3-D

    ERIC Educational Resources Information Center

    Logiurato, F.; Gratton, L. M.; Oss, S.

    2007-01-01

    Students become deeply involved in physics classes when spectacular demonstrations take over from abstract and formal presentations. In this paper we propose a simple experimental setup in which the wave behavior of light can be made spectacularly evident along the whole path of the light beam in a practically unlimited number of configurations.…

  16. Damaging effects of visible light. Progress report

    SciTech Connect

    Williams, T.P.

    1980-01-01

    Research progress in studies of photodynamic damage of visual photoreceptors is presented. It was found the retina is not homogeneous in its susceptibility to light damage. Steady state rhodopsin levels have been evaluated in albino rats and in pigmented rats at several light intensities. Studies have continued of the effects of peroxidative photodynamic damage on the properties of rod outer segments. (ACR)

  17. Triple-layer Fabry-Perot/SPP aluminum absorber in the visible and near-infrared region.

    PubMed

    Shu, Shiwei; Li, Yang Yang

    2015-03-15

    We report a theoretical study on a novel type of absorber that can achieve near perfect absorption in the visible and near-infrared regions by utilizing the Fabry-Perot and the surface plasmon polariton (SPP) effects. The absorber consists of an Al/dielectric/Al triple-layered structure with the top Al layer consisting of an array of holes. The absorption features can be easily controlled by tuning the structural parameters, particularly the porous features of the top Al layer. When the porous features in the top Al layer are significantly smaller than the wavelength, light absorption is enabled through the Fabry-Perot effect. On the other hand, when the porous features in the top layer are at the subwavelength scale, new absorption peaks emerge due to the SPP effect. Furthermore, when the top Al layer consists of an array of hollow rings, the electric field at the interface between the top Al layer and the middle dielectric layer is greatly enhanced due to the plasmonic effect, indicating that the absorber reported here may be suitable for novel applications, e.g., the surface-enhanced Raman spectroscopy (SERS) substrates.

  18. Visible light metasurfaces based on gallium nitride high contrast gratings

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhai; He, Shumin; Liu, Qifa; Wang, Wei

    2016-05-01

    We propose visible-light metasurfaces (VLMs) capable of serving as lens and beam deflecting element based on gallium nitride (GaN) high contrast gratings (HCGs). By precisely manipulating the wavefront of the transmitted light, we theoretically demonstrate an HCG focusing lens with transmissivity of 86.3%, and a VLM with beam deflection angle of 6.09° and transmissivity as high as 91.4%. The proposed all-dielectric metasurfaces are promising for GaN-based visible light-emitting diodes (LEDs), which would be robust and versatile for controlling the output light propagation and polarization, as well as enhancing the extraction efficiency of the LEDs.

  19. Robotic visible-light laser adaptive optics

    NASA Astrophysics Data System (ADS)

    Baranec, Christoph; Riddle, Reed; Law, Nicholas; Ramaprakash, A. N.; Tendulkar, Shriharsh; Bui, Khanh; Burse, Mahesh; Chordia, Pravin; Das, Hillol; Dekany, Richard; Kulkarni, Shrinivas; Punnadi, Sujit

    2013-12-01

    Robo-AO is the first autonomous laser adaptive optics system and science instrument operating on sky. With minimal human oversight, the system robotically executes large scale surveys, monitors long-term astrophysical dynamics and characterizes newly discovered transients, all at the visible diffraction limit. The adaptive optics setup time, from the end of the telescope slew to the beginning of an observation, is a mere ~50-60 s, enabling over 200 observations per night. The first of many envisioned systems has finished 58 nights of science observing at the Palomar Observatory 60-inch (1.5 m) telescope, with over 6,400 robotic observations executed thus far. The system will be augmented in late 2013 with a low-noise wide field infrared camera, which doubles as a tip-tilt sensor, to widen the spectral bandwidth of observations and increase available sky coverage while also enabling deeper visible imaging using adaptive-optics sharpened infrared tip-tilt guide sources. Techniques applicable to larger telescope systems will also be tested: the infrared camera will be used to demonstrate advanced multiple region-of-interest tip-tilt guiding methods, and a visitor instrument port will be used for evaluation of other instrumentation, e.g. single-mode and photonic fibers to feed compact spectrographs.

  20. Light propagation in biological tissues containing an absorbing plate.

    PubMed

    Kim, Arnold D

    2004-01-20

    We study light propagation in biological tissue containing an absorbing obstacle. In particular, we solve the infinite-domain problem in which an absorbing plate of negligible thickness prevents a portion of the light from the source from reaching the detector plane. Inasmuch as scattering in the medium is sharply peaked in the forward direction, we replace the governing radiative transport equation with the Fokker-Planck equation. The problem is solved first by application of the Kirchhoff approximation to determine the secondary source distribution over the surface of the plate. That result is propagated to the detector plane by use of Green's function. The Green's function is given as an expansion of plane-wave modes that are calculated numerically. The radiance is shown to obey Babinet's principle. Results from numerical computations that demonstrate this theory are shown.

  1. Tailorable, Visible Light Emission From Silicon Nanocrystals

    SciTech Connect

    Samara, G.A.; Wilcoxon, J.P.

    1999-07-20

    J. P. Wilcoxon and G. A. Samara Crystalline, size-selected Si nanocrystals in the size range 1.8-10 nm grown in inverse micellar cages exhibit highly structured optical absorption and photoluminescence (PL) across the visible range of the spectrum. The most intense PL for the smallest nanocrystals produced This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. to induce a useful level of visible photoluminescence (PL) from silicon (Si). The approaches understood. Visible PL has been observed from Si nanocrystals, or quantum dots, produced by a variety of techniques including aerosols,2 colloids,3 and ion implantation.4 However, all of The optical absorption spectra of our nanocrystals are much richer in spectral features spectrum of bulk Si where the spectral features reflect the details of the band structure shown in nanocrystals estimated to have a Si core diameter of 1-2 nm. These measured quantum those in the spectrum of bulk Si in Fig. 1 are striking indicating that nanocrystals of this size 8-Room temperature PL results on an HPLC size-selected, purified 2 nm nanocrystals but blue shifted by -0.4 eV due to quantum confinement. Excitation at 245 nm yields

  2. Visible light surface emitting semiconductor laser

    DOEpatents

    Olbright, Gregory R.; Jewell, Jack L.

    1993-01-01

    A vertical-cavity surface-emitting laser is disclosed comprising a laser cavity sandwiched between two distributed Bragg reflectors. The laser cavity comprises a pair of spacer layers surrounding one or more active, optically emitting quantum-well layers having a bandgap in the visible which serve as the active optically emitting material of the device. The thickness of the laser cavity is m .lambda./2n.sub.eff where m is an integer, .lambda. is the free-space wavelength of the laser radiation and n.sub.eff is the effective index of refraction of the cavity. Electrical pumping of the laser is achieved by heavily doping the bottom mirror and substrate to one conductivity-type and heavily doping regions of the upper mirror with the opposite conductivity type to form a diode structure and applying a suitable voltage to the diode structure. Specific embodiments of the invention for generating red, green, and blue radiation are described.

  3. Damaging effects of visible light. Progress report

    SciTech Connect

    Williams, T.P.; Baker, B.N.

    1982-02-01

    The right eyes of anesthetized, ten week old albino rats are exposed to constant photon fluxes at 6 wavelengths for 6 hours. The left eye of each animal is patched during the exposure and is used as control. Histologic examination of retinal sections disclosed a region in the superior retina which is more damaged than are other areas. Attempting to ascertain an action spectrum by measuring ONL lost in this sensative region fails. However, it is shown that, when ONL thickness is integrated over the entire retinal sections, a rhodopsin action-spectrum emerges. It is concluded that (i) retinal light damage in the albino rat under these conditions is rhodopsin mediated; and (ii) assessment of the extent of damage is best made by some method which integrates over the entire retinal section. The latter methodology is not routinely incorporated into studies of retinal light-damage but probably should be.

  4. All-silicon Michelson instrument on chip: Distance and surface profile measurement and prospects for visible light spectrometry

    SciTech Connect

    Malak, M.; Marty, F.; Bourouina, T.; Nouira, H.; Vailleau, G.

    2013-04-08

    A miniature Michelson interferometer is analyzed theoretically and experimentally. The fabricated micro-interferometer is incorporated at the tip of a monolithic silicon probe to achieve contactless distance measurements and surface profilometry. For infrared operation, two approaches are studied, based on the use of monochromatic light and wavelength sweep, respectively. A theoretical model is devised to depict the system characteristics taking into account Gaussian beam divergence and light spot size. Furthermore, preliminary results using visible light demonstrate operation of the probe as a visible light spectrometer, despite silicon absorbance, thanks to the micrometer thickness involved in the beam splitter.

  5. What is light? The visible spectrum and beyond.

    PubMed

    Sliney, D H

    2016-02-01

    In this International Year of Light, it is particularly appropriate to review the historical concept of what is light and the controversies surrounding the extent of the visible spectrum. Today we recognize that light possesses both a wave and particle nature. It is also clear that the limits of visibility really extend from about 310 nm in the ultraviolet (in youth) to about 1100 nm in the near-infrared, but depend very much on the radiance, that is, 'brightness' of the light source. The spectral content of artificial lighting are undergoing very significant changes in our lifetime, and the full biological implications of the spectral content of newer lighting technologies remain to be fully explored.

  6. What is light? The visible spectrum and beyond.

    PubMed

    Sliney, D H

    2016-02-01

    In this International Year of Light, it is particularly appropriate to review the historical concept of what is light and the controversies surrounding the extent of the visible spectrum. Today we recognize that light possesses both a wave and particle nature. It is also clear that the limits of visibility really extend from about 310 nm in the ultraviolet (in youth) to about 1100 nm in the near-infrared, but depend very much on the radiance, that is, 'brightness' of the light source. The spectral content of artificial lighting are undergoing very significant changes in our lifetime, and the full biological implications of the spectral content of newer lighting technologies remain to be fully explored. PMID:26768917

  7. Improved spring model-based collaborative indoor visible light positioning

    NASA Astrophysics Data System (ADS)

    Luo, Zhijie; Zhang, WeiNan; Zhou, GuoFu

    2016-06-01

    Gaining accuracy with indoor positioning of individuals is important as many location-based services rely on the user's current position to provide them with useful services. Many researchers have studied indoor positioning techniques based on WiFi and Bluetooth. However, they have disadvantages such as low accuracy or high cost. In this paper, we propose an indoor positioning system in which visible light radiated from light-emitting diodes is used to locate the position of receivers. Compared with existing methods using light-emitting diode light, we present a high-precision and simple implementation collaborative indoor visible light positioning system based on an improved spring model. We first estimate coordinate position information using the visible light positioning system, and then use the spring model to correct positioning errors. The system can be employed easily because it does not require additional sensors and the occlusion problem of visible light would be alleviated. We also describe simulation experiments, which confirm the feasibility of our proposed method.

  8. Rhenium complexes with visible-light-induced anticancer activity.

    PubMed

    Kastl, Anja; Dieckmann, Sandra; Wähler, Kathrin; Völker, Timo; Kastl, Lena; Merkel, Anna Lena; Vultur, Adina; Shannan, Batool; Harms, Klaus; Ocker, Matthias; Parak, Wolfgang J; Herlyn, Meenhard; Meggers, Eric

    2013-06-01

    Shedding light on the matter: Rhenium(I) indolato complexes with highly potent visible-light-triggered antiproliferative activity (complex 1: EC50 light=0.1 μM vs EC50 dark=100 μM) in 2D- and 3D-organized cancer cells are reported and can be traced back to an efficient generation of singlet oxygen, causing rapid morphological changes and an induction of apoptosis.

  9. Visible-light active conducting polymer nanostructures with superior photocatalytic activity

    PubMed Central

    Ghosh, Srabanti; Kouame, Natalie Amoin; Remita, Samy; Ramos, Laurence; Goubard, Fabrice; Aubert, Pierre-Henri; Dazzi, Alexandre; Deniset-Besseau, Ariane; Remita, Hynd

    2015-01-01

    The development of visible-light responsive photocatalysts would permit more efficient use of solar energy, and thus would bring sustainable solutions to many environmental issues. Conductive polymers appear as a new class of very active photocatalysts under visible light. Among them poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most promising conjugated polymer with a wide range of applications. PEDOT nanostructures synthesized in soft templates via chemical oxidative polymerization demonstrate unprecedented photocatalytic activities for water treatment without the assistance of sacrificial reagents or noble metal co-catalysts and turn out to be better than TiO2 as benchmark catalyst. The PEDOT nanostructures exhibit a narrow band gap (E = 1.69 eV) and are characterized by excellent ability to absorb light in visible and near infrared region. The novel PEDOT-based photocatalysts are very stable with cycling and can be reused without appreciable loss of activity. Interestingly, hollow micrometric vesicular structures of PEDOT are not effective photocatalysts as compared to nanometric spindles suggesting size and shape dependent photocatalytic properties. The visible-light active photocatalytic properties of the polymer nanostructures present promising applications in solar light harvesting and broader fields. PMID:26657168

  10. Measurements of light-absorbing particles on the glaciers in the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Schmitt, C. G.; All, J. D.; Schwarz, J. P.; Arnott, W. P.; Cole, R. J.; Lapham, E.; Celestian, A.

    2015-02-01

    Glaciers in the tropical Andes have been rapidly losing mass since the 1970s. In addition to the documented increase in temperature, increases in light-absorbing particles deposited on glaciers could be contributing to the observed glacier loss. Here we report on measurements of light-absorbing particles sampled from glaciers during three surveys in the Cordillera Blanca Mountains in Peru. During three research expeditions in the dry seasons (May-August) of 2011, 2012 and 2013, 240 snow samples were collected from 15 mountain peaks over altitudes ranging from 4800 to nearly 6800 m. Several mountains were sampled each of the 3 years and some mountains were sampled multiple times during the same year. Collected snow samples were melted and filtered in the field then later analyzed using the Light Absorption Heating Method (LAHM), a new technique that measures the ability of particles on filters to absorb visible light. LAHM results have been calibrated using filters with known amounts of fullerene soot, a common industrial surrogate for black carbon (BC). As sample filters often contain dust in addition to BC, results are presented in terms of effective black carbon (eBC). During the 2013 survey, snow samples were collected and kept frozen for analysis with a Single Particle Soot Photometer (SP2). Calculated eBC mass from the LAHM analysis and the SP2 refractory black carbon (rBC) results were well correlated (r2 = 0.92). These results indicate that a substantial portion of the light-absorbing particles in the more polluted regions were likely BC. The 3 years of data show that glaciers in the Cordillera Blanca Mountains close to human population centers have substantially higher levels of eBC (as high as 70 ng g-1) than remote glaciers (as low as 2.0 ng g-1 eBC), indicating that population centers can influence local glaciers by sourcing BC.

  11. Measurements of light absorbing particulates on the glaciers in the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Schmitt, C. G.; All, J. D.; Schwarz, J. P.; Arnott, W. P.; Cole, R. J.; Lapham, E.; Celestian, A.

    2014-10-01

    Glaciers in the tropical Andes have been rapidly losing mass since the 1970s. In addition to the documented increase in air temperature, increases in light absorbing particulates deposited on glaciers could be contributing to the observed glacier loss. Here we report on measurements of light absorbing particulates sampled from glaciers during three surveys in the Cordillera Blanca in Peru. During three research expeditions in the dry seasons (May-August) of 2011, 2012 and 2013, two hundred and forty snow samples were collected from fifteen mountain peaks over altitudes ranging from 4800 to nearly 6800 m. Several mountains were sampled each of the three expeditions and some mountains were sampled multiple times during the same expedition. Collected snow samples were melted and filtered in the field then later analyzed using the Light Absorption Heating Method (LAHM), a new technique that measures the ability of particulates on filters to absorb visible light. LAHM results have been calibrated using filters with known amounts of fullerene soot, a common industrial surrogate for black carbon (BC). As sample filters often contain dust in addition to BC, results are presented in terms of effective Black Carbon (eBC). During the 2013 survey, snow samples were collected and kept frozen for analysis with a Single Particle Soot Photometer (SP2). Calculated eBC mass from the filter analysis and the SP2 refractory Black Carbon (rBC) results were well correlated (r2 = 0.92). These results indicate that a substantial portion of the light absorbing particulates in the more polluted areas were likely BC. The three years of data show that glaciers in the Cordillera Blanca Mountains close to human population centers have substantially higher levels of eBC (as high as 70 ng g-1) than remote glaciers (as low as 2.0 ng g-1 eBC), indicating that population centers can influence local glaciers by sourcing BC.

  12. Co doped ZnO nanowires as visible light photocatalysts

    NASA Astrophysics Data System (ADS)

    Šutka, Andris; Käämbre, Tanel; Pärna, Rainer; Juhnevica, Inna; Maiorov, Mihael; Joost, Urmas; Kisand, Vambola

    2016-06-01

    High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV-visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10-3 min-1 in case of nanoparticles and 4.2·10-3 min-1 in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn0.95Co0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.

  13. Source apportionment of light absorbing WSOC in South Asian outflow

    NASA Astrophysics Data System (ADS)

    Bosch, Carme; Kirillova, Elena; Andersson, August; Kruså, Martin; Budhavant, Krishnakant; Tiwari, Suresh; Gustafsson, Örjan

    2013-04-01

    Carbonaceous aerosols (CA) formed over South Asia are of special concern for human health and regional climate impacts. Anthropogenic emissions forming CA are generally high throughout the region and particularly over the Indo-Gangetic Plain. The net effects of CA on radiative climate forcing are still uncertain. One of the components of CA is black carbon (BC), dominated by soot-like elemental carbon, a strong absorber of solar radiation. Another component is organic carbon (OC), traditionally considered as a light scattering particle. However, recent field studies have shown OC to absorb at lower wavelengths. Thus OC, in addition to BC, may also contribute to light absorption and have a positive direct radiative effect on climate. Light absorbing organic aerosol is usually termed brown carbon (BrC). A significant fraction of BrC is water-soluble, therefore its dissolution into clouds could result in absorbing droplets that affect the cloud absorption and thus contributing to the indirect aerosol climate effects. In this study, light absorption and δ13C + Δ14C isotopic measurements of WSOC were studied in fine aerosols (PM 2.5) at two sites during early pre-monsoon season. New Delhi, one of the most densely populated and industrialized urban megacities in South Asia, was chosen to represent a strong source and Maldives Climate Observatory at Hanimaadhoo (MCOH) was chosen as a regional receptor which in wintertime is located downwind of the Indian subcontinent. Sampling in Delhi was done from mid-February to mid-March 2011 and in MCOH during March 2012. WSOC concentrations were 12±4.5 and 0.71±0.30 μg m-3 in Delhi and MCOH respectively. Whereas in Delhi WSOC contributed 31±4% of total organic carbon, this contribution was slightly higher in MCOH (40±12%). Light absorption by WSOC exhibited strong wavelength (?) dependence. In Maldives, WSOC Absorption Ångström Exponent (AAE) was found to be 6.9±0.4 and Mass Absorption Efficiency (MAE) measured at 365 nm

  14. Almost-total absorption of light in thin, biperiodic, weakly-absorbing semiconductor gratings.

    PubMed

    Popov, Evgeny; Fehrembach, Anne-Laure; McPhedran, Ross C

    2016-07-25

    We consider the design of optical systems capable of providing near 100% absorption of visible light, consisting of a structured thin layer of a weakly absorbing semiconductor placed on top of a dielectric spacer layer and a metallic mirror layer. We generalise a system recently studied semi-analytically and experimentally by Stürmberg et al [Optica 3, 556 2016] which incorporated a grating layer of antimony sulphide and delivered high, narrow-band absorptance of normally-incident light for a single polarisation. We demonstrate that bi-periodic gratings can be optimised to deliver near-perfect absorptance of unpolarised light in the system, and comment on the wavelength and angular ranges over which the absorptance remains near 100%. We show that the properties of the systems studied depend on the interaction of multiple modes, and cannot be accurately modelled within the quasistatic approximation. PMID:27464093

  15. Almost-total absorption of light in thin, biperiodic, weakly-absorbing semiconductor gratings.

    PubMed

    Popov, Evgeny; Fehrembach, Anne-Laure; McPhedran, Ross C

    2016-07-25

    We consider the design of optical systems capable of providing near 100% absorption of visible light, consisting of a structured thin layer of a weakly absorbing semiconductor placed on top of a dielectric spacer layer and a metallic mirror layer. We generalise a system recently studied semi-analytically and experimentally by Stürmberg et al [Optica 3, 556 2016] which incorporated a grating layer of antimony sulphide and delivered high, narrow-band absorptance of normally-incident light for a single polarisation. We demonstrate that bi-periodic gratings can be optimised to deliver near-perfect absorptance of unpolarised light in the system, and comment on the wavelength and angular ranges over which the absorptance remains near 100%. We show that the properties of the systems studied depend on the interaction of multiple modes, and cannot be accurately modelled within the quasistatic approximation.

  16. Monitoring of slaughterhouse wastewater biodegradation in a SBR using fluorescence and UV-Visible absorbance.

    PubMed

    Louvet, J N; Homeky, B; Casellas, M; Pons, M N; Dagot, C

    2013-04-01

    The aim of this study was to demonstrate that the effectiveness of slaughterhouse wastewater treatment by activated sludge could be enhanced through the use of optical techniques, such as UV-Visible absorbance and fluorescence spectroscopy, to estimate the hydraulic retention time necessary to remove the biodegradable chemical oxygen demand (COD). Two experiments were conducted. First, a batch aerobic degradation was performed on four wastewater samples collected from four different cattle processing sites in order to study the changes in the spectroscopic properties of wastewater during biodegradation. Second, a sequencing batch reactor was used in order to confirm that the wastewater fluorescence could be successfully used to monitor wastewater biodegradation in a pilot-scale experiment. Residual blood was the main source of organic matter in the wastewater samples. The absorbance at 416 nm, related to porphyrins, was correlated to the COD during wastewater biodegradation. The tryptophan-like/fulvic-like fluorescence intensity ratio was related to the extent of biodegradation. The COD removal efficiency ranged from 74% to 94% with an hydraulic retention time (HRT) of 23 h. A ratio of tryptophan-like/fulvic-like fluorescence intensities higher than 1.2 indicated incomplete biodegradation of the wastewater and the need to increase the HRT.

  17. Wireless visible light communication technology using optical beamforming

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Man; Kim, Seong-Min

    2013-10-01

    We propose and demonstrate a new wireless visible light communication (VLC) technology using optical beamforming to improve signal-to-noise ratio (SNR) and transmission distance. Optical beamforming is a technology that can focus light-emitting diode (LED) light on a desired target device. Our experimental results show that SNR can be improved by 12 dB and transmission distance can be almost doubled by using optical beamforming. We can also control the modulation depth of the optical beamforming if we want to use the LED light as illumination at the same time. We also propose an algorithm to direct the beam to the target device automatically.

  18. A femtosecond visible/visible and visible/mid-infrared transient absorption study of the light harvesting complex II.

    PubMed

    Stahl, Andreas D; Di Donato, Mariangela; van Stokkum, Ivo; van Grondelle, Rienk; Groot, Marie Louise

    2009-12-16

    Light harvesting complex II (LHCII) is the most abundant protein in the thylakoid membrane of higher plants and green algae. LHCII acts to collect solar radiation, transferring this energy mainly toward photosystem II, with a smaller amount going to photosystem I; it is then converted into a chemical, storable form. We performed time-resolved femtosecond visible pump/mid-infrared probe and visible pump/visible probe absorption difference spectroscopy on purified LHCII to gain insight into the energy transfer in this complex occurring in the femto-picosecond time regime. We find that information derived from mid-infrared spectra, together with structural and modeling information, provides a unique visualization of the flow of energy via the bottleneck pigment chlorophyll a604.

  19. Optical properties and aging of light-absorbing secondary organic aerosol

    DOE PAGES

    Liu, Jiumeng; Lin, Peng; Laskin, Alexander; Laskin, Julia; Kathmann, Shawn M.; Wise, Matthew; Caylor, Ryan; Imholt, Felisha; Selimovic, Vanessa; Shilling, John E.

    2016-10-14

    The light-absorbing organic aerosol (OA) commonly referred to as “brown carbon” (BrC) has attracted considerable attention in recent years because of its potential to affect atmospheric radiation balance, especially in the ultraviolet region and thus impact photochemical processes. A growing amount of data has indicated that BrC is prevalent in the atmosphere, which has motivated numerous laboratory and field studies; however, our understanding of the relationship between the chemical composition and optical properties of BrC remains limited. We conducted chamber experiments to investigate the effect of various volatile organic carbon (VOC) precursors, NOx concentrations, photolysis time, and relative humidity (RH) on the light absorptionmore » of selected secondary organic aerosols (SOA). Light absorption of chamber-generated SOA samples, especially aromatic SOA, was found to increase with NOx concentration, at moderate RH, and for the shortest photolysis aging times. The highest mass absorption coefficient (MAC) value is observed from toluene SOA products formed under high-NOx conditions at moderate RH, in which nitro-aromatics were previously identified as the major light-absorbing compounds. BrC light absorption is observed to decrease with photolysis time, correlated with a decline of the organic nitrate fraction of SOA. SOA formed from mixtures of aromatics and isoprene absorb less visible (Vis) and ultraviolet (UV) light than SOA formed from aromatic precursors alone on a mass basis. However, the mixed SOA absorption was underestimated when optical properties were predicted using a two-product SOA formation model, as done in many current climate models. Further investigation, including analysis on detailed mechanisms, are required to explain the discrepancy.« less

  20. Optical properties and aging of light-absorbing secondary organic aerosol

    NASA Astrophysics Data System (ADS)

    Liu, Jiumeng; Lin, Peng; Laskin, Alexander; Laskin, Julia; Kathmann, Shawn M.; Wise, Matthew; Caylor, Ryan; Imholt, Felisha; Selimovic, Vanessa; Shilling, John E.

    2016-10-01

    The light-absorbing organic aerosol (OA) commonly referred to as "brown carbon" (BrC) has attracted considerable attention in recent years because of its potential to affect atmospheric radiation balance, especially in the ultraviolet region and thus impact photochemical processes. A growing amount of data has indicated that BrC is prevalent in the atmosphere, which has motivated numerous laboratory and field studies; however, our understanding of the relationship between the chemical composition and optical properties of BrC remains limited. We conducted chamber experiments to investigate the effect of various volatile organic carbon (VOC) precursors, NOx concentrations, photolysis time, and relative humidity (RH) on the light absorption of selected secondary organic aerosols (SOA). Light absorption of chamber-generated SOA samples, especially aromatic SOA, was found to increase with NOx concentration, at moderate RH, and for the shortest photolysis aging times. The highest mass absorption coefficient (MAC) value is observed from toluene SOA products formed under high-NOx conditions at moderate RH, in which nitro-aromatics were previously identified as the major light-absorbing compounds. BrC light absorption is observed to decrease with photolysis time, correlated with a decline of the organic nitrate fraction of SOA. SOA formed from mixtures of aromatics and isoprene absorb less visible (Vis) and ultraviolet (UV) light than SOA formed from aromatic precursors alone on a mass basis. However, the mixed SOA absorption was underestimated when optical properties were predicted using a two-product SOA formation model, as done in many current climate models. Further investigation, including analysis on detailed mechanisms, are required to explain the discrepancy.

  1. Selective Cell Targeting with Light-Absorbing Microparticles and Nanoparticles

    PubMed Central

    Pitsillides, Costas M.; Joe, Edwin K.; Wei, Xunbin; Anderson, R. Rox; Lin, Charles P.

    2003-01-01

    We describe a new method for selective cell targeting based on the use of light-absorbing microparticles and nanoparticles that are heated by short laser pulses to create highly localized cell damage. The method is closely related to chromophore-assisted laser inactivation and photodynamic therapy, but is driven solely by light absorption, without the need for photochemical intermediates (particularly singlet oxygen). The mechanism of light-particle interaction was investigated by nanosecond time-resolved microscopy and by thermal modeling. The extent of light-induced damage was investigated by cell lethality, by cell membrane permeability, and by protein inactivation. Strong particle size dependence was found for these interactions. A technique based on light to target endogenous particles is already being exploited to treat pigmented cells in dermatology and ophthalmology. With exogenous particles, phamacokinetics and biodistribution studies are needed before the method can be evaluated against photodynamic therapy for cancer treatment. However, particles are unique, unlike photosensitizers, in that they can remain stable and inert in cells for extended periods. Thus they may be particularly useful for prelabeling cells in engineered tissue before implantation. Subsequent irradiation with laser pulses will allow control of the implanted cells (inactivation or modulation) in a noninvasive manner. PMID:12770906

  2. Emission of Visible Light by Hot Dense Metals

    SciTech Connect

    More, R.M.; Goto, M.; Graziani, F.; Ni, P.A.; Yoneda, H.

    2009-12-01

    We consider the emission of visible light by hot metal surfaces having uniform and non-uniform temperature distributions and by small droplets of liquid metal. The calculations employ a nonlocal transport theory for light emission, using the Kubo formula to relate microscopic current fluctuations to the dielectric function of the material. We describe a related algorithm for calculating radiation emission in particle simulation of hot fusion plasmas.

  3. Hybrid bilayer plasmonic metasurface efficiently manipulates visible light

    PubMed Central

    Qin, Fei; Ding, Lu; Zhang, Lei; Monticone, Francesco; Chum, Chan Choy; Deng, Jie; Mei, Shengtao; Li, Ying; Teng, Jinghua; Hong, Minghui; Zhang, Shuang; Alù, Andrea; Qiu, Cheng-Wei

    2016-01-01

    Metasurfaces operating in the cross-polarization scheme have shown an interesting degree of control over the wavefront of transmitted light. Nevertheless, their inherently low efficiency in visible light raises certain concerns for practical applications. Without sacrificing the ultrathin flat design, we propose a bilayer plasmonic metasurface operating at visible frequencies, obtained by coupling a nanoantenna-based metasurface with its complementary Babinet-inverted copy. By breaking the radiation symmetry because of the finite, yet small, thickness of the proposed structure and benefitting from properly tailored intra- and interlayer couplings, such coupled bilayer metasurface experimentally yields a conversion efficiency of 17%, significantly larger than that of earlier single-layer designs, as well as an extinction ratio larger than 0 dB, meaning that anomalous refraction dominates the transmission response. Our finding shows that metallic metasurface can counterintuitively manipulate the visible light as efficiently as dielectric metasurface (~20% in conversion efficiency in Lin et al.’s study), although the metal’s ohmic loss is much higher than dielectrics. Our hybrid bilayer design, still being ultrathin (~λ/6), is found to obey generalized Snell’s law even in the presence of strong couplings. It is capable of efficiently manipulating visible light over a broad bandwidth and can be realized with a facile one-step nanofabrication process. PMID:26767195

  4. Developing Tools for Undergraduate Spectroscopy: An Inexpensive Visible Light Spectrometer

    ERIC Educational Resources Information Center

    Vanderveen, Jesse R.; Martin, Brian; Ooms, Kristopher J.

    2013-01-01

    The design and implementation of an inexpensive, high-resolution Littrow-type visible light spectrometer is presented. The instrument is built from low-cost materials and interfaced with the program RSpec for real-time spectral analysis, making it useful for classroom and laboratory exercises. Using a diffraction grating ruled at 1200 lines/mm and…

  5. A possible mechanism for visible-light-induced skin rejuvenation

    NASA Astrophysics Data System (ADS)

    Longo, Leonardo; Lubart, Rachel; Friedman, Harry; Lavie, R.

    2004-09-01

    In recent years there has been intensive research in the field of non-ablative skin rejuvenation. This comes as a response to the desire for a simple method of treating rhytids caused by aging, UV exposure and acne scars. In numerous studies intense visible light pulsed systems (20-30J/cm2) are used. The mechanism of action was supposed to be a selective heat induced denaturalization of dermal collagen that leads to subsequent reactive synthesis. In this study we suggest a different mechanism for photorejuvenation based on light induced Reactive Oxygen Species (ROS) formation. We irradiated collagen in-vitro with a broad band of visible light, 400-800 nm, 12-22J/cm2, and used the spin trapping coupled with electron paramagnetic resonance (EPR) spectroscopy to detect ROS. In vivo, we used dose 30 J in average (35 for acnis scars, 25 for wrinkles and redness). Irradiated collagen results in hydroxyl and methyl radicals formation. We propose, as a new concept, that visible light at the intensity used for skin rejuvenation, 20-30J/cm2, produces high amounts of ROS which destroy old collagen fibers encouraging the formation of new ones. On the other hand at inner depths of the skin, where the light intensity is much weaker, low amounts of ROS are formed which are well known to stimulate fibroblast proliferation.

  6. Conducting polymer nanostructures for photocatalysis under visible light

    NASA Astrophysics Data System (ADS)

    Ghosh, Srabanti; Kouamé, Natalie A.; Ramos, Laurence; Remita, Samy; Dazzi, Alexandre; Deniset-Besseau, Ariane; Beaunier, Patricia; Goubard, Fabrice; Aubert, Pierre-Henri; Remita, Hynd

    2015-05-01

    Visible-light-responsive photocatalysts can directly harvest energy from solar light, offering a desirable way to solve energy and environment issues. Here, we show that one-dimensional poly(diphenylbutadiyne) nanostructures synthesized by photopolymerization using a soft templating approach have high photocatalytic activity under visible light without the assistance of sacrificial reagents or precious metal co-catalysts. These polymer nanostructures are very stable even after repeated cycling. Transmission electron microscopy and nanoscale infrared characterizations reveal that the morphology and structure of the polymer nanostructures remain unchanged after many photocatalytic cycles. These stable and cheap polymer nanofibres are easy to process and can be reused without appreciable loss of activity. Our findings may help the development of semiconducting-based polymers for applications in self-cleaning surfaces, hydrogen generation and photovoltaics.

  7. Controlled release of fragrant molecules with visible light.

    PubMed

    Wang, Zhuozhi; Johns, Valentine K; Liao, Yi

    2014-11-01

    Controlled release of odorous molecules is the key to digital scent technology which will add another dimension to electronics. Photorelease is a cold mechanism that promises better temporal and spatial control than thermal release. Herein we report a novel material composed of an acid-sensitive polymer carrying a fragrant aldehyde and a reversible metastable-state photoacid. It releases the fragrant molecule under visible light, and stops releasing it after the light is turned off. A metastable-state photoacid with a fast reverse-reaction rate was developed to quickly stop the release after irradiation. Both the carrier polymer and the photoacid can be reused after all the fragrant molecules have been released. The material combines the advantages of visible-light activity, fast on/off rate, easy preparation, and recyclability, and thus is promising for digital scent technology. PMID:25284277

  8. A Z-scheme photocatalyst constructed with an yttrium-tantalum oxynitride and a binuclear Ru(ii) complex for visible-light CO2 reduction.

    PubMed

    Muraoka, Kanemichi; Kumagai, Hiromu; Eguchi, Miharu; Ishitani, Osamu; Maeda, Kazuhiko

    2016-06-14

    An yttrium-tantalum oxynitride having a band gap of 2.1 eV (absorbing visible light at <580 nm) was applicable as a semiconductor component of a Z-scheme CO2 reduction system operable under visible light, in combination with a binuclear Ru(ii) complex that has strong absorption in the visible region (<600 nm). Excitation of this system with visible light under a CO2 atmosphere induced photocatalytic formation of formic acid with very high selectivity (>99%). PMID:27251369

  9. Resource allocation for multichannel broadcasting visible light communication

    NASA Astrophysics Data System (ADS)

    Le, Nam-Tuan; Jang, Yeong Min

    2015-11-01

    Visible light communication (VLC), which offers the possibility of using light sources for both illumination and data communications simultaneously, will be a promising incorporation technique with lighting applications. However, it still remains some challenges especially coverage because of field-of-view limitation. In this paper, we focus on this issue by suggesting a resource allocation scheme for VLC broadcasting system. By using frame synchronization and a network calculus QoS approximation, as well as diversity technology, the proposed VLC architecture and QoS resource allocation for the multichannel-broadcasting MAC (medium access control) protocol can solve the coverage limitation problem and the link switching problem of exhibition service.

  10. Laser Writing Block Copolymer Self-Assembly on Graphene Light-Absorbing Layer.

    PubMed

    Jin, Hyeong Min; Lee, Seung Hyun; Kim, Ju Young; Son, Seung-Woo; Kim, Bong Hoon; Lee, Hwan Keon; Mun, Jeong Ho; Cha, Seung Keun; Kim, Jun Soo; Nealey, Paul F; Lee, Keon Jae; Kim, Sang Ouk

    2016-03-22

    Recent advance of high-power laser processing allows for rapid, continuous, area-selective material fabrication, typically represented by laser crystallization of silicon or oxides for display applications. Two-dimensional materials such as graphene exhibit remarkable physical properties and are under intensive development for the manufacture of flexible devices. Here we demonstrate an area-selective ultrafast nanofabrication method using low intensity infrared or visible laser irradiation to direct the self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12 nm. The fundamental principles underlying this light-induced nanofabrication mechanism include the self-assembly of block copolymers to proceed across the disorder-order transition under large thermal gradients, and the use of chemically modified graphene films as a flexible and conformal light-absorbing layers for transparent, nonplanar, and mechanically flexible surfaces. PMID:26871736

  11. Laser Writing Block Copolymer Self-Assembly on Graphene Light-Absorbing Layer.

    PubMed

    Jin, Hyeong Min; Lee, Seung Hyun; Kim, Ju Young; Son, Seung-Woo; Kim, Bong Hoon; Lee, Hwan Keon; Mun, Jeong Ho; Cha, Seung Keun; Kim, Jun Soo; Nealey, Paul F; Lee, Keon Jae; Kim, Sang Ouk

    2016-03-22

    Recent advance of high-power laser processing allows for rapid, continuous, area-selective material fabrication, typically represented by laser crystallization of silicon or oxides for display applications. Two-dimensional materials such as graphene exhibit remarkable physical properties and are under intensive development for the manufacture of flexible devices. Here we demonstrate an area-selective ultrafast nanofabrication method using low intensity infrared or visible laser irradiation to direct the self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12 nm. The fundamental principles underlying this light-induced nanofabrication mechanism include the self-assembly of block copolymers to proceed across the disorder-order transition under large thermal gradients, and the use of chemically modified graphene films as a flexible and conformal light-absorbing layers for transparent, nonplanar, and mechanically flexible surfaces.

  12. Thickness-dependent photocatalytic performance of graphite oxide for degrading organic pollutants under visible light.

    PubMed

    Oh, Junghoon; Chang, Yun Hee; Kim, Yong-Hyun; Park, Sungjin

    2016-04-28

    Photocatalysts use sustainable solar light energy to trigger various catalytic reactions. Metal-free nanomaterials have been suggested as cost-effective and environmentally friendly photocatalysts. In this work, we propose thickness-controlled graphite oxide (GO) as a metal-free photocatalyst, which is produced by exfoliating thick GO particles via stirring and sonication. All GO samples exhibit photocatalytic activity for degrading an organic pollutant, rhodamine B under visible light, and the thickest sample shows the best catalytic performance. UV-vis-NIR diffuse reflectance absorption spectra indicate that thicker GO samples absorb more vis-NIR light than thinner ones. Density-functional theory calculations show that GO has a much smaller band gap than that of single-layer graphene oxide, and thus suggest that the largely-reduced band gap is responsible for this trend of light absorption. PMID:27040040

  13. Increased visible-light photocatalytic activity of TiO2 via band gap manipulation

    NASA Astrophysics Data System (ADS)

    Pennington, Ashley Marie

    Hydrogen gas is a clean burning fuel that has potential applications in stationary and mobile power generation and energy storage, but is commercially produced from non-renewable fossil natural gas. Using renewable biomass as the hydrocarbon feed instead could provide sustainable and carbon-neutral hydrogen. We focus on photocatalytic oxidation and reforming of methanol over modified titanium dioxide (TiO2) nanoparticles to produce hydrogen gas. Methanol is used as a model for biomass sugars. By using a photocatalyst, we aim to circumvent the high energy cost of carrying out endothermic reactions at commercial scale. TiO2 is a semiconductor metal oxide of particular interest in photocatalysis due to its photoactivity under ultraviolet illumination and its stability under catalytic reaction conditions. However, TiO2 primarily absorbs ultraviolet light, with little absorption of visible light. While an effective band gap for absorbance of photons from visible light is 1.7 eV, TiO2 polymorphs rutile and anatase, have band gaps of 3.03 eV and 3.20 eV respectively, which indicate ultraviolet light. As most of incident solar radiation is visible light, we hypothesize that decreasing the band gap of TiO2 will increase the efficiency of TiO2 as a visible-light active photocatalyst. We propose to modify the band gap of TiO2 by manipulating the catalyst structure and composition via metal nanoparticle deposition and heteroatom doping in order to more efficiently utilize solar radiation. Of the metal-modified Degussa P25 TiO2 samples (P25), the copper and nickel modified samples, 1%Cu/P25 and 1%Ni/P25 yielded the lowest band gap of 3.05 eV each. A difference of 0.22 eV from the unmodified P25. Under visible light illumination 1%Ni/P25 and 1%Pt/P25 had the highest conversion of methanol of 9.9% and 9.6%, respectively.

  14. Contribution of chlorophyll to photooxidation of soybean oil at specific visible wavelengths of light.

    PubMed

    Bianchi, Laurie M; Duncan, Susan E; Webster, Janet B; Neilson, Andrew P; O'Keefe, Sean F

    2015-02-01

    Photosensitizers in foods and beverages are important considerations when selecting packaging materials. Chlorophyll is found at low concentrations in many food products. The objective of this study was to determine the photosensitizing effect of chlorophyll on soybean oil (SO) using broad-spectrum light and 3 visible wavelength regions of light. SO with added chlorophyll (0, 1, or 2 μg chlorophyll added/mL SO) was exposed to 5 light conditions, using a photochemical reactor (10 °C; 4 h). Light treatments included broad-spectrum (BS; no filter; 157.6 ± 4.7 mW intensity), 430 nm (10 nm; 1.8 ± 0.7 mW), and 660 nm (10 nm; 0.332 ± 0.05 mW) wavelengths compared to a no-light control. Chlorophyll a (but not b) absorbs light in the selected visible wavelength regions. Chlorophyll degradation was evaluated. Oxidative changes in SO were assessed by peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) assay, which measures malondialdehyde (MDA). Chlorophyll was completely degraded at BS and 430 nm conditions and degraded to 36% of original concentration at 660 nm wavelength. PV and MDA concentration significantly increased with chlorophyll addition (1 μg/mL) at BS and 430 nm wavelengths compared to no-light control. Lower light intensity at 660 nm initiated oxidation reactions as measured by PV, but not significantly. There were differences in PV (BS, 430 nm) and TBARS (BS) between the no-light and light-exposed SO without chlorophyll added. There was very little effect at 450 nm. This study suggests that broad-spectrum light and at least light wavelengths at or near 430 nm and 660 nm excite chlorophyll, resulting in initiation of oxidation reactions. Packaging material selection for foods and beverages should consider blocking excitation wavelengths of photosensitizing molecules, including chlorophyll, to protect product quality.

  15. [Degrading anticancer drugs in the medical environment using a visible light-driven photocatalyst].

    PubMed

    Sato, Junya; Kikuchi, Satomi; Kudo, Kenzo

    2014-01-01

      Occupational exposure to anticancer drugs is recognized as a risk for healthcare workers. Reducing anticancer drugs in the environment is important to prevent the exposure of individuals to anticancer drugs. However, there are currently no effective degrading agents for all anticancer drugs used in clinical settings. We previously reported the resolution of an anticancer drug with the use of a photocatalyst (TiO2), which acts by absorbing ultraviolet light to degrade organic compounds. In this study, we evaluated anticancer drug degradation using a visible light-driven photocatalyst (Cu/WO3). Anticancer drugs [cyclophosphamide (CPA), paclitaxel (PTX), methotrexate (MTX), irinotecan (CPT-11), cytarabine (Ara-C), and 5-fluorouracil (5-FU)], were experimentally deposited on a stainless steel plate. The visible light-driven photocatalytic agent (0.075% Cu/WO3 solution) was sprayed onto the plate, and the plate was then left under a fluorescent lamp for 12 h. The anticancer drugs remaining on the plate were assayed by high-performance liquid chromatography (HPLC). CPA, PTX, MTX, CPT-11, Ara-C, and 5-FU were found to be degraded by up to 37.7%, >99.0%, 57.1%, 54.6%, 69.5%, and 36.3%, respectively. The visible light-driven photocatalyst was therefore confirmed to degrade anticancer drugs under a fluorescent lamp. The ability of the visible light-driven photocatalyst to degrade multiple chemotherapeutic agents without the need for altering the light source could make it a useful tool for reducing anticancer drug pollution in clinical settings.

  16. Modulation selection for visible light communications using lighting LEDs

    NASA Astrophysics Data System (ADS)

    Siuzdak, Jerzy

    2015-09-01

    The paper analyzes suitability of various spectrally efficient modulations (PAM, CAP, OFDM/DMT) in a VLC system using lighting LEDs as a transmitter. Although under ideal conditions all modulation have similar efficiency i.e. they produce similar throughputs with a given BER, their practical performances are different. For example, the level of nonlinear distortions generated by each modulation is the least for PAM and by far the greatest for OFDM/DMT locating CAP in the middle. The suitability of various OFDM/DMT variants in a VLC LED link was also analyzed proving that the asymmetrically clipped (ACO) OFDM has a worse performance as compared with DC biased (DCO) OFDM.

  17. Heterogeneous visible light photocatalysis for selective organic transformations.

    PubMed

    Lang, Xianjun; Chen, Xiaodong; Zhao, Jincai

    2014-01-01

    The future development of chemistry entails environmentally friendly and energy sustainable alternatives for organic transformations. Visible light photocatalysis can address these challenges, as reflected by recent intensive scientific endeavours to this end. This review covers state-of-the-art accomplishments in visible-light-induced selective organic transformations by heterogeneous photocatalysis. The discussion comprises three sections based on the photocatalyst type: metal oxides such as TiO2, Nb2O5 and ZnO; plasmonic photocatalysts like nanostructured Au, Ag or Cu supported on metal oxides; and polymeric graphitic carbon nitride. Finally, recent strides in bridging the gap between photocatalysis and other areas of catalysis will be highlighted with the aim of overcoming the existing limitations of photocatalysis by developing more creative synthetic methodologies.

  18. Hydrogen generation under visible light using nitrogen doped titania anodes

    SciTech Connect

    Lin, H.; Rumaiz, A.; Schulz, M.; Huang, C.P.; Sha, S. I.

    2010-06-16

    Hydrogen is among several energy sources that will be needed to replace the quickly diminishing fossil fuels. Free hydrogen is not available naturally on earth and the current processes require a fossil fuel, methane, to generate hydrogen. Electrochemical splitting of water on titania proposed by Fujishima suffers from low efficiency. The efficiency could be enhanced if full sun spectrum can be utilized. Using pulsed laser deposition technique we synthesized nitrogen doped titanium dioxide (TiO{sub 2-x}N{sub x}) thin films with improved visible light sensitivity. The photoactivity was found to be N concentration dependent. Hydrogen evolution was observed under visible light irradiation (wavelength > 390 nm) without the presence of any organic electron donor.

  19. Hexaarylbiimidazoles as Visible Light Thiol–Ene Photoinitiators

    PubMed Central

    Clarkson, Brian H.; Scott, Timothy F.

    2015-01-01

    Objectives The aim of this study is to determine if hexaarylbiimidazoles (HABIs) are efficient, visible light-active photoinitiators for thiol–ene systems. We hypothesize that, owing to the reactivity of lophyl radicals with thiols and the necessarily high concentration of thiol in thiol–ene formulations, HABIs will effectively initiate thiol–ene polymerization upon visible light irradiation. Methods UV-vis absorption spectra of photoinitiator solutions were obtained using UV-vis spectroscopy, while EPR spectroscopy was used to confirm radical species generation upon HABI photolysis. Functional group conversions during photopolymerization were monitored using FTIR spectroscopy, and thermomechanical properties were determined using dynamic mechanical analysis. Results The HABI derivatives investigated exhibit less absorptivity than camphorquinone at 469 nm; however, they afford increased sensitivity at this wavelength when compared with bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide. Photolysis of the investigated HABIs affords lophyl radicals. Affixing hydroxyhexyl functional groups to the HABI core significantly improved solubility. Thiol–ene resins formulated with HABI photoinitiators polymerized rapidly upon irradiation with 469 nm. The glass transition temperatures of the thiol–ene resin formulated with a bis(hydroxyhexyl)-functionalized HABI and photopolymerized at room and body temperature were 49.5±0.5°C and 52.2±0.1°C, respectively. Significance Although thiol–enes show promise as continuous phases for composite dental restorative materials, they show poor reactivity with the conventional camphorquinone/tertiary amine photoinitiation system. Conversely, despite their relatively low visible light absorptivity, HABI photoinitiators afford rapid thiol–ene photopolymerization rates. Moreover, minor structural modifications suggest pathways for improved HABI solubility and visible light absorption. PMID:26119702

  20. Trifluoromethylation of alkenes by visible light photoredox catalysis.

    PubMed

    Iqbal, Naeem; Choi, Sungkyu; Kim, Eunjin; Cho, Eun Jin

    2012-12-21

    A method for trifluoromethylation of alkenes has been developed employing visible light photoredox catalysis with CF(3)I, Ru(Phen)(3)Cl(2), and DBU. This process works especially well for terminal alkenes to give alkenyl-CF(3) products with only E-stereochemistry. The mild reaction conditions enable the trifluoromethylation of a range of alkenes that bear various functional groups. PMID:23167602

  1. Nonmetal species in the carbon modified TiO2 and its visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Shi, Yanfen; Chen, Feng; Zhang, Jinlong

    2013-01-01

    A carbon modified TiO2 (CT) was synthesized by hydrolyzing titanium tetrachloride with diethylamine and calcination at 400 °C. CT was then handled with a NaOH aqueous solution elution and a subsequent re-assembling treatment. X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption analysis, X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermal analysis (TG-DTA), chemical oxygen demand (COD) and UV-vis diffuse reflectance spectroscopy (DRS) were then used to assess the changes of CT during the whole process. It is revealed that carbon in the CT should mostly be presented as surface deposited organic matters but not likely doped into the TiO2 lattice. CT exhibits obvious visible absorption and high photocatalytic activity for the degradation of 2,4-dichlorophenol (DCP) under visible light irradiation. Meanwhile, CT photocatalyst possesses excellent stability and reusability. NaOH solution elution washes off a large amount of surface deposited organics and worsens the visible absorbance and photocatalytic activity of CT, which can be well recovered by the re-assembling treatment. The re-assembled photocatalyst, CTSL, exhibits exhibits a very similar photocataytic activity with CT for degradation of DCP under the visible light irradiation, but is much higher than that of CTS.

  2. Photocontrolled release using one-photon absorption of visible or NIR light.

    PubMed

    Olejniczak, Jason; Carling, Carl-Johan; Almutairi, Adah

    2015-12-10

    Light is an excellent means to externally control the properties of materials and small molecules for many applications. Light's ability to initiate chemistries largely independent of a material's local environment makes it particularly useful as a bio-orthogonal and on-demand trigger in living systems. Materials responsive to UV light are widely reported in the literature; however, UV light has substantial limitations for in vitro and in vivo applications. Many biological molecules absorb these energetic wavelengths directly, not only preventing substantial tissue penetration but also causing detrimental photochemical reactions. The more innocuous nature of long-wavelength light (>400nm) and its ability at longer wavelengths (600-950nm) to effectively penetrate tissues is ideal for biological applications. Multi-photon processes (e.g. two-photon excitation and upconversion) using longer wavelength light, often in the near-infrared (NIR) range, have been proposed as a means of avoiding the negative characteristics of UV light. However, high-power focused laser light and long irradiation times are often required to initiate photorelease using these inefficient non-linear optical methods, limiting their in vivo use in mammalian tissues where NIR light is readily scattered. The development of materials that efficiently convert a single photon of long-wavelength light to chemical change is a viable solution to achieve in vivo photorelease. However, to date only a few such materials have been reported. Here we review current technologies for photo-regulated release using photoactive organic materials that directly absorb visible and NIR light.

  3. Scavenging insoluble light-absorbing particulates (ILAP) in seasonal snow over northern China

    NASA Astrophysics Data System (ADS)

    Wang, X.; Huang, J.

    2013-12-01

    It has been long believed that Black Carbon (BC) from biomass burning, fossil fuel and biofuel plays an important role in the earth's system through its climate effect. Compared with other insoluble light-absorbing particulates (ILAP), BC is a main component of the most effective light-absorbing particulates, which can dominates the absorption of solar radiation at the visible wavelengths. Furthermore, once deposits on snow, it could significant reduces the snow reflectance and accelerate the snow melting, therefore, it is considered as the second most important component as the CO2 to affect the globe warming. Although several experiments have already been performed for collecting and measuring the scavenging BC in snow on a global scale. Little attention has been given to the quantitative measurements of ILAP deposit on the snowpack at mid-latitude regions in Asia, especially over Northern China. Recently, there are two field campaigns were conducted in January and February 2010 and 2012 to measuring the ILAP in snow across northern China. About 700 snow samples were collected at 84 sites in seven provinces. The BC mass fractions in seasonal snow across northern Xinjiang have a median value of 70 ng g-1, and the concentrations of BC were in the remote northeast on the border of Siberia, with a median concentration in surface snow of 120 ng g-1. South of this, in the industrial northeast, the median snow BC concentration was 1200 ng g-1. In the northeast, snow particulate light absorption was dominated by BC. Across the grassland of Inner Mongolia, OC, likely mostly from local soil, dominates light absorption, with median BC concentrations of 340 ng g-1 responsible for only about one third of total particulate light absorption. In the Qilian Mountains, at the northern boundary of the Tibetan Plateau, snow particulate light absorption is dominated by local soil and desert dust.

  4. Asynchronous indoor positioning system based on visible light communications

    NASA Astrophysics Data System (ADS)

    Zhang, Weizhi; Chowdhury, M. I. Sakib; Kavehrad, Mohsen

    2014-04-01

    Indoor positioning has become an attractive research topic within the past two decades. However, no satisfying solution has been found with consideration of both accuracy and system complexity. Recently, research on visible light communications (VLC) offer new opportunities in realizing accurate indoor positioning with relatively simple system configuration. An indoor positioning system based on VLC technology is introduced, with no synchronization requirement on the transmitters. Simulation results show that, with over 95% confidence, the target receiver can be located with an accuracy of 5.9 cm, assuming indirect sunlight exposure and proper installation of light-emitting diode bulbs.

  5. The physical properties of black carbon and other light-absorbing material emitted from prescribed fires in the United States

    NASA Astrophysics Data System (ADS)

    McMeeking, G. R.; Kreidenweis, S. M.; Yokelson, R. J.; Sullivan, A. P.; Lee, T.; Collett, J. L.; Fortner, E.; Onasch, T. B.; Akagi, S. K.; Taylor, J.; Coe, H.

    2012-12-01

    Black carbon (BC) aerosol emitted from fires absorbs light, leading to visibility degradation as well as regional and global climate impacts. Fires also emit a wide range of trace gases and particulates that can interact with emitted BC and alter its optical properties and atmospheric lifetime. Non-BC particulate species emitted by fires can also scatter and absorb light, leading to additional effects on visibility. Recent work has shown that certain organic species can absorb light strongly at shorter wavelengths, giving it a brown or yellow color. This material has been classified as brown carbon, though it is not yet well defined. Land managers must find a balance between the negative impacts of prescribed fire emissions on visibility and air quality and the need to prevent future catastrophic wildfire as well as manage ecosystems for habitat restoration or other purposes. This decision process requires accurate assessments of the visibility impacts of fire emissions, including BC and brown carbon, which in turn depend on their optical properties. We present recent laboratory and aircraft measurements of black carbon and aerosol optical properties emitted from biomass burning. All measurement campaigns included a single particle soot photometer (SP2) instrument capable of providing size-resolved measurements of BC mass and number distributions and mixing state, which are needed to separate the BC and brown carbon contributions to total light absorption. The laboratory experiments also included a three-wavelength photoacoustic spectrometer that provided accurate measurements of aerosol light absorption. The laboratory systems also characterized emissions after they had been treated with a thermal denuder to remove semi-volatile coatings, allowing an assessment of the role of non-BC coatings on bulk aerosol optical properties. Emissions were also aged in an environmental smog chamber to examine the role of secondary aerosol production on aerosol optical properties.

  6. Modeling the Effect of Polychromatic Light in Quantitative Absorbance Spectroscopy

    ERIC Educational Resources Information Center

    Smith, Rachel; Cantrell, Kevin

    2007-01-01

    Laboratory experiment is conducted to give the students practical experience with the principles of electronic absorbance spectroscopy. This straightforward approach creates a powerful tool for exploring many of the aspects of quantitative absorbance spectroscopy.

  7. Warming of the Arctic Lower Stratosphere by Light Absorbing Particle

    NASA Astrophysics Data System (ADS)

    Baumgardner, D.; Raga, G. B.; Kok, G.; Anderson, B.

    2003-12-01

    Light absorption by particles such as soot and dust change the thermodynamic structure of the atmosphere and contribute to regional and global climate change. The lower stratosphere is particularly sensitive to the presence of light absorbing particles (LAP) since particles in this region can reside from months to years, in contrast to upper tropospheric lifetimes of days to weeks. The source of particles in the lower stratosphere may be aircraft, meteorites or transport from tropospheric sources. There is a serious deficiency of accurate and quantitative measurements of these particles that limits our understanding of the origin and lifetime of aerosols in this region of the atmosphere and how their presence alters radiative fluxes that lead to climate change. Here we present measurements in the Arctic lower stratosphere with a new, single particle soot photometer (SP2) that has detected black carbon (BC) mass concentrations of 20-1000 ng m-3. These concentrations are 10-1000 times larger than those reported in previous experimental studies and are at least 30 times larger than predictions based on fuel consumption by commercial aircraft. The comparison of the measurements of BC with published 3D model predictions suggests that particles transported from the troposphere are the likely source of LAP in the Arctic lower stratosphere. Radiative transfer calculations that include the presence of a layer of LAP between 9 and 12 km, indicate an increase in the localised heating of this layer by approximately 25%.

  8. Visible light photocatalysis as a greener approach to photochemical synthesis

    NASA Astrophysics Data System (ADS)

    Yoon, Tehshik P.; Ischay, Michael A.; Du, Juana

    2010-07-01

    Light can be considered an ideal reagent for environmentally friendly, 'green' chemical synthesis; unlike many conventional reagents, light is non-toxic, generates no waste, and can be obtained from renewable sources. Nevertheless, the need for high-energy ultraviolet radiation in most organic photochemical processes has limited both the practicality and environmental benefits of photochemical synthesis on industrially relevant scales. This Perspective describes recent approaches to the use of metal polypyridyl photocatalysts in synthetic organic transformations. Given the remarkable photophysical properties of these complexes, these new transformations, which use Ru(bpy)32+ and related photocatalysts, can be conducted using almost any source of visible light, including both store-bought fluorescent light bulbs and ambient sunlight. Transition metal photocatalysis thus represents a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.

  9. Visible light-responsive titanium dioxide thin film prepared by reactive sputtering.

    PubMed

    Jeong, Woon-Jo; Moon, In-Seob; Cho, Soon-Kye; Yang, Hyeon-Hun; Park, Gye-Choon; Gu, Hal-Bon; Kim, Ki-Joong; Ahn, Ho-Geun

    2011-02-01

    TiO2 is a wide band-gap semiconductor (3.4 eV) and can only absorb about 5% of sun light in the ultraviolet light region, which largely limits its practical applications because of the lower utility of sun light and quantum yield. In order to move the absorption edge of TiO2 films to visible spectrum range, we have made the impurity level within a band-gap of TiO2 thin film by introduction of oxygen vacancy. Oxygen-defected TiO2 photo-catalyst have prepared by reactive sputtering with the partial pressure of Ar:O2 = 76.7:23.3 approximately 98.5:1.5 ratios. As a result, we could have the impurity level of about 2.75 eV on condition that oxygen partial pressure is 2.9%. And the photocatalytic activity was realized at 400 nm wavelength.

  10. Optical motion detector detecting visible and near infrared light

    NASA Astrophysics Data System (ADS)

    Everett, Hobart R., Jr.

    1990-02-01

    An optical motion detector detects changes in scene lighting indicative of motion and is also capable of detecting surveillance by active night vision devices using near-infrared light. The detector includes two photodetectors which each provide data to a signal processing network. One photodetector is sensitive to visible light; the other to near-infrared light. Both signal processing networks are identical and include a sample-and-hold, a comparator network, and a pulse stretcher. The output of a photodetector is provided to the sample-and-hold and comparator network. The comparator network compares a voltage corresponding to the instantaneously detected ambient lighting scene with a voltage corresponding to a reference lighting scene. The pulse stretcher receives the output of the comparator network and in turn provides an output to a logical processor. The logical processor compares the outputs of both signal processing networks and provides an output indicating surveillance with near-infrared light. The logical processor also indicates any perturbations in intensities of incandescent and fluorescent light.

  11. Visible-light system for detecting doxorubicin contamination on skin and surfaces.

    PubMed

    Van Raalte, J; Rice, C; Moss, C E

    1990-05-01

    A portable system that uses fluorescence stimulated by visible light to identify doxorubicin contamination on skin and surfaces was studied. When activated by violet-blue light in the 465-nm range, doxorubicin fluoresces, emitting orange-red light in the 580-nm range. The light source to stimulate fluorescence was a slide projector with a filter to selectively pass short-wave (blue) visible light. Fluorescence was both observed visually with viewing spectacles and photographed. Solutions of doxorubicin in sterile 0.9% sodium chloride injection were prepared in nine standard concentrations ranging from 2 to 0.001 mg/mL. Droplets of each admixture were placed on stainless steel, laboratory coat cloth, pieces of latex examination glove, bench-top absorbent padding, and other materials on which antineoplastics might spill or leak. These materials then were stored for up to eight weeks and photographed weekly. The relative ability of water, household bleach, hydrogen peroxide solution, and soap solution to deactivate doxorubicin was also measured. Finally, this system was used to inspect the antineoplastic-drug preparation and administration areas of three outpatient cancer clinics for doxorubicin contamination. Doxorubicin fluorescence was easily detectable with viewing spectacles when a slide projector was used as the light source. The photographic method was sensitive for doxorubicin concentrations from 2.0 to 0.001 mg/mL. Immersion of study materials in bleach for one minute eliminated detectable fluorescence. Doxorubicin contamination is detectable for at least eight weeks in the ambient environment. Probable doxorubicin contamination was detected in two of the three clinics surveyed. A safe, portable system that uses fluorescence stimulated by visible light is a sensitive method for detecting doxorubicin on skin and surfaces.

  12. Soot on snow experiments: light-absorbing impurities effect on the natural snowpack

    NASA Astrophysics Data System (ADS)

    Svensson, J.; Virkkula, A.; Meinander, O.; Kivekäs, N.; Hannula, H.-R.; Järvinen, O.; Peltoniemi, J. I.; Gritsevich, M.; Heikkilä, A.; Kontu, A.; Hyvärinen, A.-P.; Neitola, K.; Brus, D.; Dagsson-Waldhauserova, P.; Anttila, K.; Hakala, T.; Kaartinen, H.; Vehkamäki, M.; de Leeuw, G.; Lihavainen, H.

    2015-02-01

    Light-absorbing impurities affect snow and ice via a decrease in albedo and a consequent disturbance to the radiative energy balance. Experimentally, these matters have only been examined in a few studies. Here we present results from a series of experiments in which we deposited different soot concentrations onto natural snow in different regions of Finland, and thereafter monitored the changes of the snowpack through the melting season. Measurements of the particulates in the snow indicated concentrations in the range of thousands of ppb to have clear effects on the snow properties, including the albedo, the physical snow characteristics, and an increased melt rate. For soot concentrations in the hundreds of ppb range, the effects were not as clearly visible, and it was more difficult to attribute the effects solely to the soot on the snow. Comparisons between our experimental data and the widely used Snow, Ice and Aerosol Radiation (SNICAR) model showed a general agreement when the model was specifically tuned to our measurements. This study highlights the importance of additional experimental studies, to further articulate and quantify the effects of light-absorbing impurities on snow.

  13. Light-driven tunable dual-band plasmonic absorber using liquid-crystal-coated asymmetric nanodisk array

    NASA Astrophysics Data System (ADS)

    Zhao, Yanhui; Hao, Qingzhen; Ma, Yi; Lu, Mengqian; Zhang, Bingxin; Lapsley, Michael; Khoo, Iam-Choon; Jun Huang, Tony

    2012-01-01

    We experimentally demonstrated a light-driven reconfigurable near perfect plasmonic absorber working at dual frequencies in infrared range. By employing nanodisks with different sizes in certain arrangement, near perfect absorption of incident electromagnetic waves can be achieved for different working frequencies due to the resonance between the incident light and the nanodisk of different sizes. We showed that optically induced changes in the dielectric constant of the adjacent liquid crystal layer is an effective means to tune the absorption bands of an asymmetric gold nanodisk array. Our liquid crystal based infrared plasmonic absorber can be tuned by using visible light in real time. A tunable range of 25 nm has been confirmed by both simulation and experiment.

  14. Ultra-thin metamaterial absorber with extremely bandwidth for solar cell and sensing applications in visible region

    NASA Astrophysics Data System (ADS)

    Tang, Jingyao; Xiao, Zhongyin; Xu, Kaikai

    2016-10-01

    In this paper, we proposed a broadband and ultra-thin metamaterial absorber in the visible region. The absorber is composed of three layers, and the most remarkable difference is that the split ring resonators (SRR) made of metal stannum are encrusted in the indium antimonide (InSb) plane on the top layer. Numerical results reveal that a broadband absorption spectrum above 90% can be realized from 353.9 THz to 613.2 THz due to the coupling effect between the material of stannum and InSb. The metamaterial absorber is ultra-thin, having the total thickness of 56 nm, i.e. less than λ/10 with respect to the center frequency of the absorption band more than 90%. In addition, the impedance matching theory, surface current distributions, E-field and H-field are investigated to explain the physical mechanism of the absorption. The sensing applications are discussed and the simulated results show that the proposed absorber operates well with a good efficiency. Moreover, the visible absorber has potential applications in the aspects of solar energy harvest, integrated photodetectors and so on.

  15. Quantum-confined bandgap narrowing of TiO2 nanoparticles by graphene quantum dots for visible-light-driven applications.

    PubMed

    Wang, Shujun; Cole, Ivan S; Li, Qin

    2016-07-28

    We for the first time report a quantum-confined bandgap narrowing mechanism through which the absorption of two UV absorbers, namely the graphene quantum dots (GQDs) and TiO2 nanoparticles, can be easily extended into the visible light range in a controllable manner. Such a mechanism may be of great importance for light harvesting, photocatalysis and optoelectronics. PMID:27297746

  16. Theory of Visible Light Emission from Scanning Tunneling Microscope

    NASA Astrophysics Data System (ADS)

    Uehara, Yoichi; Kimura, Yuichi; Ushioda, Sukekatsu; Takeuchi, Koichiro

    1992-08-01

    The mechanism for visible light emission from the scanning tunneling microscope (STM) has been investigated theoretically by adapting a theory for light emitting tunnel junctions (LETJ). From the analysis of the calculated results and available experimental data, the following picture emerges. The tunneling current first excites localized surface plasmons (LSP) that are localized in a region of a few tens of Angstroms between the STM tip-front and the sample surface. Some of them decay into surface plasmon polaritons (SPP) that propagate along the sample surface. There are two channels of light emission: one is direct emission from LSP and the other is emission through SPP. The relative branching ratio between these two channels depends on the experimental configuration. The effect of sample surface roughness is very small and negligible.

  17. Experimental Verification of n=0 Structures for Visible Light

    NASA Astrophysics Data System (ADS)

    Vesseur, Ernst Jan R.; Coenen, Toon; Caglayan, Humeyra; Engheta, Nader; Polman, Albert

    2013-01-01

    We fabricate and characterize a metal-dielectric nanostructure with an effective refractive index n=0 in the visible spectral range. Light is excited in the material at deep subwavelength resolution by a 30-keV electron beam. From the measured spatially and angle-resolved emission patterns, a vanishing phase advance, corresponding to an effective ɛ=0 and n=0, is directly observed at the cutoff frequency. The wavelength at which this condition is observed can be tuned over the entire visible or near-infrared spectral range by varying the waveguide width. This n=0 plasmonic nanostructure may serve as a new building block in nanoscale optical integrated circuits and to control spontaneous emission as experimentally demonstrated by the strongly enhanced radiative optical density of states over the entire n=0 structure.

  18. Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties

    NASA Astrophysics Data System (ADS)

    Mumin, Md Abdul; Xu, William Z.; Charpentier, Paul A.

    2015-08-01

    The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (˜65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (˜90%) and decreased UV transmission (˜75%).

  19. Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties.

    PubMed

    Mumin, Md Abdul; Xu, William Z; Charpentier, Paul A

    2015-08-01

    The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (∼65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (∼90%) and decreased UV transmission (∼75%). PMID:26177824

  20. Quantum dots/silica/polymer nanocomposite films with high visible light transmission and UV shielding properties.

    PubMed

    Mumin, Md Abdul; Xu, William Z; Charpentier, Paul A

    2015-08-01

    The dispersion of light-absorbing inorganic nanomaterials in transparent plastics such as poly(ethylene-co-vinyl acetate) (PEVA) is of enormous current interest in emerging solar materials, including photovoltaic (PV) modules and commercial greenhouse films. Nanocrystalline semiconductor or quantum dots (QDs) have the potential to absorb UV light and selectively emit visible light, which can control plant growth in greenhouses or enhance PV panel efficiencies. This work provides a new and simple approach for loading mesoporous silica-encapsulated QDs into PEVA. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm size were synthesized using a modified facile approach based on pyrolysis of the single-molecule precursors and capping the CdS QDs with a thin layer of ZnS. To make both the bare and core-shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interactions. By careful experimental tuning, this encapsulation technique enhanced the quantum yield (∼65%) and photostability compared to the bare QDs. Both the encapsulated bare and core-shell QDs were then melt-mixed with EVA pellets using a mini twin-screw extruder and pressed into thin films with controlled thickness. The results demonstrated for the first time that mesoporous silica not only enhanced the quantum yield and photostability of the QDs but also improved the compatibility and dispersibility of QDs throughout the PEVA films. The novel light selective films show high visible light transmission (∼90%) and decreased UV transmission (∼75%).

  1. Studies on microleakage associated with visible light cured dental composites.

    PubMed

    Krishnan, V K; Bindhu, D B; Manjusha, K

    1996-04-01

    The objective of this investigation was twofold: 1) to determine the extent of microleakage associated with two visible light cured dental composites, one of which is an indigenously developed light cure composite (chitra light cure system) compared with a commercially available control material (Prisma APH light cure system), and 2) to study the effect of using bonding agents upon the above phenomena. The bonding agents used along with the above composites during restoration were chitra bonding agent system containing chitra primer/chitra resin and a control (Probond) which was purchased commercially. A comparison of microleakage in freshly restored human premolar teeth by silver nitrate staining technique was made during the above study. Cavities were restored with both composites with and without bonding agents, stored in 50 percent silver nitrate, and sections were cut after developing. The microtomed sections were observed under the optical light microscope and scanning electron microscope. Results indicate that bonding agents are mandatory for effective bonding at the tooth/resin interface and subsequent reduction in marginal leakage. Chitra bonding agent showed excellent adhesive bonding characteristics at the dentine/composite interface with minimal marginal leakage compared to the control bonding system. The chitra light cure composite material also showed lower shrinkage characteristics compared to Prisma APH composite. PMID:8859406

  2. Bactericidal mechanisms of Au@TNBs under visible light irradiation.

    PubMed

    Guo, Lingqiao; Shan, Chao; Liang, Jialiang; Ni, Jinren; Tong, Meiping

    2015-04-01

    Au@TNBs nanocomposites were synthesized by depositing Au nanoparticles onto the surfaces of TiO2 nanobelts (TNBs). The disinfection activities of Au@TNBs on model cell type, Gram-negative Escherichia coli (E. coli), were examined under visible light irradiation conditions. Au@TNBs exhibited stronger bactericidal properties toward E. coli than those of TNBs and Au NPs under visible light irradiation. The bactericidal mechanisms of Au@TNBs under light conditions were explored, specifically, the specific active species controlling the inactivation of bacteria were determined. Active species (H2O2, diffusing ∙OH, ∙O2-, 1O2, and e-) generated by Au@TNBs were found to play important roles on the inactivation of bacteria. Moreover, the concentrations of H2O2, ·OH, ·O2-, and 1O2 generated in the antimicrobial system were estimated. Without the presence of active species, the direct contact of Au@TNBs with bacterial cells was found to have no bactericidal effect. The reusability of Au@TNBs were also determined. Au@TNBs exhibited strong antibacterial activity toward E. coli even in five consecutively reused cycles. This study indicated that the fabricated Au@TNBs could be potentially utilized to inactivate bacteria in water.

  3. Asymmetric photoredox transition-metal catalysis activated by visible light

    NASA Astrophysics Data System (ADS)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

    2014-11-01

    Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

  4. Visible Light Communication System Using an Organic Bulk Heterojunction Photodetector

    PubMed Central

    Arredondo, Belén; Romero, Beatriz; Pena, José Manuel Sánchez; Fernández-Pacheco, Agustín; Alonso, Eduardo; Vergaz, Ricardo; de Dios, Cristina

    2013-01-01

    A visible light communication (VLC) system using an organic bulk heterojunction photodetector (OPD) is presented. The system has been successfully proven indoors with an audio signal. The emitter consists of three commercial high-power white LEDs connected in parallel. The receiver is based on an organic photodetector having as active layer a blend of poly(3-hexylthiophene) (P3HT) and phenyl C61-butyric acid methyl ester (PCBM). The OPD is opto-electrically characterized, showing a responsivity of 0.18 A/W and a modulation response of 790 kHz at −6 V. PMID:24036584

  5. Performance Analysis of Visible Light Communication Using CMOS Sensors

    PubMed Central

    Do, Trong-Hop; Yoo, Myungsik

    2016-01-01

    This paper elucidates the fundamentals of visible light communication systems that use the rolling shutter mechanism of CMOS sensors. All related information involving different subjects, such as photometry, camera operation, photography and image processing, are studied in tandem to explain the system. Then, the system performance is analyzed with respect to signal quality and data rate. To this end, a measure of signal quality, the signal to interference plus noise ratio (SINR), is formulated. Finally, a simulation is conducted to verify the analysis. PMID:26938535

  6. Organocatalyzed atom transfer radical polymerization driven by visible light.

    PubMed

    Theriot, Jordan C; Lim, Chern-Hooi; Yang, Haishen; Ryan, Matthew D; Musgrave, Charles B; Miyake, Garret M

    2016-05-27

    Atom transfer radical polymerization (ATRP) has become one of the most implemented methods for polymer synthesis, owing to impressive control over polymer composition and associated properties. However, contamination of the polymer by the metal catalyst remains a major limitation. Organic ATRP photoredox catalysts have been sought to address this difficult challenge but have not achieved the precision performance of metal catalysts. Here, we introduce diaryl dihydrophenazines, identified through computationally directed discovery, as a class of strongly reducing photoredox catalysts. These catalysts achieve high initiator efficiencies through activation by visible light to synthesize polymers with tunable molecular weights and low dispersities.

  7. Location-adaptive transmission for indoor visible light communication

    NASA Astrophysics Data System (ADS)

    Wang, Chun-yue; Wang, Lang; Chi, Xue-fen

    2016-01-01

    A location-adaptive transmission scheme for indoor visible light communication (VLC) system is proposed in this paper. In this scheme, the symbol error rate ( SER) of less than 10-3 should be guaranteed. And the scheme is realized by the variable multilevel pulse-position modulation (MPPM), where the transmitters adaptively adjust the number of time slots n in the MPPM symbol according to the position of the receiver. The purpose of our scheme is to achieve the best data rate in the indoor different locations. The results show that the location-adaptive transmission scheme based on the variable MPPM is superior in the indoor VLC system.

  8. A Spinel Oxynitride with Visible-Light Photocatalytic Activity

    SciTech Connect

    Boppana, V.; Doren, D; Lobo, R

    2010-01-01

    Spinel zinc gallium oxynitride photocatalysts are prepared by the sol-gel method, at 550 C. In these materials, of base composition ZnGa{sub 2}O{sub 4} (octahedral Ga), reaction with ammonia leads to ZnGa{sub 2}O{sub x}N{sub y}, with a dramatic reduction of the bandgap to 2.7 eV, with just 1.3% N and no loss of Zn. At 850 C this phase is converted into wurzite (tetrahedral Ga). The novel oxynitrides also show visible-light photocatalytic activity towards the degradation of methylene blue.

  9. Synthesis, characterization and application of iodine modified titanium dioxide in phototcatalytical reactions under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Bagwasi, Segomotso; Tian, Baozhu; Chen, Feng; Zhang, Jinlong

    2012-02-01

    Iodine doped titanium dioxide has been successfully prepared by simple hydrolysis of tetrabutyl titanate in the presence of iodic acid. The adopted method allowed for the production of spherical iodine doped titaniun dioxide nanoparticles with varied amount of iodine content. Analysis by X-ray diffraction, Raman, transmission electron microscopy as well as UV-vis DRS revealed that titanium dioxide nanostructures were doped with iodine which existed in two different valence states I5+ and I-. The iodine in the form of I5+ is believed to have doped into the lattice whereas I- was well dispersed on the surface of TiO2 probably as iodine adducts hence rendering it to be highly absorbing in visible light region. The I-TiO2 exhibited improved photocatalytic activity toward degradation of acid orange 7 (AO7), methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP) under visible light over the pristine TiO2 prepared by the same method. High catalytic properties are attributed to iodine doping which led to high specific surface area, absorption in visible region as well as alleviation of charge carrier recombination. The most probable route undertaken in the degradation of AO7 is through indirect oxidation by the hydroxyl radicals.

  10. Short-wavelength visible light emission from silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Pi, Xiaodong; Liptak, Rick; Campbell, Stephen; Kortshagen, Uwe

    2007-03-01

    Si is the material of choice for modern microelectronics but, as an indirect-bandgap semiconductor, it is not an efficient light emitter. An electrically pumped Si laser would present a breakthrough for optoelectronic integration that may enable optical interconnect to make computers faster. Si light emitting diodes may revolutionize solid-state lighting and displays because of the low cost and environmental friendliness of Si. One of the most challenging problems of Si-based lighting and displays is the lack of a reliable and efficient full visible spectrum emission. Si nanocrystals (Si-NCs) have so far been the most promising form of Si to emit light. Most of the synthesis approaches of Si-NCs, however, only lead to red light emission. Our recent work on Si-NCs synthesized by non-thermal plasmas has focused on extending their light emission into the short-wavelength range. Firstly, the process of oxidation-etching-oxidation of Si-NCs is investigated. This process causes the size of Si-NCs to decrease, leading to shorter wavelength light emission from Si-NCs. Yellow or green photoluminescence (PL) has been observed from initially oxidized red light emitting Si-NCs after HF vapour etching and atmospheric oxidation. The intensity of PL from Si-NCs, however, decreases by a factor up to 100. It is found that HF etching restructures the surface of Si-NCs. This leads to a decrease in the incorporation of O during subsequent oxidation, which finally results in silicon suboxide SiO1.9. Such an understoichiometry indicates a high density of defects such as Si dangling bonds at the Si-NC/oxide interface. Therefore, the PL efficiency is extremely low for short-wavelength light emitting Si-NCs obtained by the process of oxidation-etching-oxidation. Secondly, an integrated two-stage plasma system is employed to achieve the light emission from Si-NCs in the full visible spectrum range. Red-light-emitting Si-NCs are produced in the first stage by the plasma decomposition of SiH4

  11. Visible-light-accelerated oxygen vacancy migration in strontium titanate

    PubMed Central

    Li, Y.; Lei, Y.; Shen, B. G.; Sun, J. R.

    2015-01-01

    Strontium titanate is a model transition metal oxide that exhibits versatile properties of special interest for both fundamental and applied researches. There is evidence that most of the attractive properties of SrTiO3 are closely associated with oxygen vacancies. Tuning the kinetics of oxygen vacancies is then highly desired. Here we reported on a dramatic tuning of the electro-migration of oxygen vacancies by visible light illumination. It is found that, through depressing activation energy for vacancy diffusion, light illumination remarkably accelerates oxygen vacancies even at room temperature. This effect provides a feasible approach towards the modulation of the anionic processes. The principle proved here can be extended to other perovskite oxides, finding a wide application in oxide electronics. PMID:26420376

  12. A Reversible Photoacid Functioning in PBS Buffer under Visible Light.

    PubMed

    Abeyrathna, Nawodi; Liao, Yi

    2015-09-01

    A metastable-state photoacid that can reversibly release a proton in PBS buffer (pH = 7.4) under visible light is reported. The design is based on the dual acid-base property and tautomerization of indazole. The quantum yield was as high as 0.73, and moderate light intensity (10(2) μmol·m(2)·s(-1)) is sufficient for the photoreaction. Reversible pH change of 1.7 units was demonstrated using a 0.1 mM aqueous solution. This type of photoacid is promising for control of proton-transfer processes in physiological conditions and may find applications in biomedical areas.

  13. Dual-polarity plasmonic metalens for visible light.

    PubMed

    Chen, Xianzhong; Huang, Lingling; Mühlenbernd, Holger; Li, Guixin; Bai, Benfeng; Tan, Qiaofeng; Jin, Guofan; Qiu, Cheng-Wei; Zhang, Shuang; Zentgraf, Thomas

    2012-01-01

    Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light. Specifically, by controlling the helicity of the input light, the positive and negative polarity are interchangeable in one identical flat lens. Helicity-controllable real and virtual focal planes, as well as magnified and demagnified imaging, are observed on the same plasmonic lens at visible and near-infrared wavelengths. The plasmonic metalens with dual polarity may empower advanced research and applications in helicity-dependent focusing and imaging devices, angular-momentum-based quantum information processing and integrated nano-optoelectronics.

  14. Dual-polarity plasmonic metalens for visible light

    NASA Astrophysics Data System (ADS)

    Chen, Xianzhong; Huang, Lingling; Mühlenbernd, Holger; Li, Guixin; Bai, Benfeng; Tan, Qiaofeng; Jin, Guofan; Qiu, Cheng-Wei; Zhang, Shuang; Zentgraf, Thomas

    2012-11-01

    Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light. Specifically, by controlling the helicity of the input light, the positive and negative polarity are interchangeable in one identical flat lens. Helicity-controllable real and virtual focal planes, as well as magnified and demagnified imaging, are observed on the same plasmonic lens at visible and near-infrared wavelengths. The plasmonic metalens with dual polarity may empower advanced research and applications in helicity-dependent focusing and imaging devices, angular-momentum-based quantum information processing and integrated nano-optoelectronics.

  15. Dual-polarity plasmonic metalens for visible light

    PubMed Central

    Chen, Xianzhong; Huang, Lingling; Mühlenbernd, Holger; Li, Guixin; Bai, Benfeng; Tan, Qiaofeng; Jin, Guofan; Qiu, Cheng-Wei; Zhang, Shuang; Zentgraf, Thomas

    2012-01-01

    Surface topography and refractive index profile dictate the deterministic functionality of a lens. The polarity of most lenses reported so far, that is, either positive (convex) or negative (concave), depends on the curvatures of the interfaces. Here we experimentally demonstrate a counter-intuitive dual-polarity flat lens based on helicity-dependent phase discontinuities for circularly polarized light. Specifically, by controlling the helicity of the input light, the positive and negative polarity are interchangeable in one identical flat lens. Helicity-controllable real and virtual focal planes, as well as magnified and demagnified imaging, are observed on the same plasmonic lens at visible and near-infrared wavelengths. The plasmonic metalens with dual polarity may empower advanced research and applications in helicity-dependent focusing and imaging devices, angular-momentum-based quantum information processing and integrated nano-optoelectronics. PMID:23149743

  16. Facile fabrication of visible light induced Bi2O3 nanorod using conventional heat treatment method

    NASA Astrophysics Data System (ADS)

    Raza, Waseem; Khan, Azam; Alam, Umair; Muneer, M.; Bahnemann, D.

    2016-03-01

    In this paper, a new Bi2O3 based photocatalyst doped with varying concentration of Nb and Mn metal ion was fabricated by conventional heat treatment method and their photocatalytic activity was investigated. The prepared material was characterized by X-ray diffraction (XRD), UV-Visible Spectroscopy, Fourier transform infrared (FTIR) and Scanning Electron Microscopic (SEM) techniques. The XRD analysis of synthesized photocatalyst was found to exhibit characteristic peaks of well crystallized monoclinic α-Bi2O3. The XRD pattern of pure and metal doped Bi2O3 were found to more or less similar. The crystallite size of doped materials were smaller than pure Bi2O3 and size decreases with increasing dopant concentration from 0.5 to 2.0% for Nb & 1.0-3.0% for Mn and remains almost constant at higher dopant concentration. The SEM analysis clearly indicate the formation of nanorod like morphologies. The UV-Vis absorption spectra of synthesized nanorods revealed that the absorption edge shift towards longer wavelength on doping with Nb and Mn metal ions which is beneficial for absorbing more visible light in the solar spectrum. The prepared doped Bi2O3 nanorod showed the excellent photocatalytic activity for degradation of selected organic pollutants, such as Methylene Blue (MB) and Rodaamime B (RhB) under visible light source. The higher activity of doped Bi2O3 nanorod may be attributed to absorption of more visible light leading to generation of higher photogenerated electron hole pairs and efficient separation of photoinduced charge carrier to inhibit the recombination rate.

  17. Invisibility Cloaking Based on Geometrical Optics for Visible Light

    NASA Astrophysics Data System (ADS)

    Ichikawa, H.; Oura, M.; Taoda, T.

    2013-06-01

    Optical cloaking has been one of unattainable dreams and just a subject in fiction until recently. Several different approaches to cloaking have been proposed and demonstrated: stealth technology, active camouflage and transformation optics. The last one would be the most formal approach modifying electromagnetic field around an object to be cloaked with metamaterials. While cloaking based on transformation optics, though valid only at single frequency, is experimentally demonstrated in microwave region, its operation in visible spectrum is still distant from realisation mainly owing to difficulty in fabricating metamaterial structure whose elements are much smaller than wavelength of light. Here we show that achromatic optical cloaking in visible spectrum is possible with the mere principle based on geometrical optics. In combining a pair of polarising beam splitters and right-angled prisms, rays of light to be obstructed by an object can make a detour to an observer, while unobstructed rays go straight through two polarising beam splitters. What is observed eventually through the device is simply background image as if nothing exists in between.

  18. Light source design for double reflection transmission-type visibility meter

    NASA Astrophysics Data System (ADS)

    Zhen, Xiaoqiong; Yang, Ling; Niu, Zhiqiang; Zeng, Qiangyu

    2015-07-01

    In this paper, a novel transmission-type visibility meter which is also named double reflection transmission-type visibility meter is introduced and developed. The novel visibility meter uses a charge coupled device (CCD) as an image acquiring unit, the CCD acquires light spot images which generated by a light source, an air extinction coefficient is calculated, and then the meteorology visibility is obtained. The light source is an important unit in this novel visibility meter, and influences the meteorology visibility calculation results. In this paper, several light source design schemes are proposed and researched. Each light source scheme is tested and the experimental results are analyzed. Finally the novel visibility meter which employs a determined light source design scheme finished a measurement result comparison experiment and the reliability and accuracy of the visibility meter are proved.

  19. Visible light photoinitiation of mesenchymal stem cell-laden bioresponsive hydrogels.

    PubMed

    Bahney, C S; Lujan, T J; Hsu, C W; Bottlang, M; West, J L; Johnstone, B

    2011-07-15

    Biological activity can be added to synthetic scaffolds by incorporating functional peptide sequences that provide enzyme-mediated degradation sites, facilitate cellular adhesion or stimulate signaling pathways. Poly(ethylene glycol) diacrylate is a popular synthetic base for tissue engineering scaffolds because it creates a hydrophilic environment that can be chemically manipulated to add this biological functionality. Furthermore, the acrylate groups allow for encapsulation of cells using photopolymerization under physiological conditions. One complication with the addition of these peptides is that aromatic amino acids absorb light at 285 nm and compete with the ultraviolet (UV)-sensitive photoinitiators such as IrgacureTM 2959 (I2959), the most commonly used initiator for cytocompatible photoencapsulation of cells into synthetic scaffolds. In this study we define non-toxic conditions for photoencapsulation of human mesenchymal stem cells (hMSC) in PEGDA scaffolds using a visible light photoinitiator system composed of eosin Y, triethanolamine and 1-vinyl-2-pyrrolidinone. This visible light photoinitiator produced hydrogel scaffolds with an increased viability of encapsulated hMSCs and a more tightly crosslinked network in one-third the time of UV polymerization with I2959.

  20. VISIBLE LIGHT PHOTOINITIATION OF MESENCHYMAL STEM CELL-LADEN BIORESPONSIVE HYDROGELS

    PubMed Central

    Bahney, C.S.; Lujan, T.J.; Hsu, C.W.; Bottlang, M.; West, J.L.; Johnstone, B.

    2016-01-01

    Biological activity can be added to synthetic scaffolds by incorporating functional peptide sequences that provide enzyme-mediated degradation sites, facilitate cellular adhesion or stimulate signaling pathways. Poly(ethylene glycol) diacrylate is a popular synthetic base for tissue engineering scaffolds because it creates a hydrophilic environment that can be chemically manipulated to add this biological functionality. Furthermore, the acrylate groups allow for encapsulation of cells using photopolymerization under physiological conditions. One complication with the addition of these peptides is that aromatic amino acids absorb light at 285nm and compete with the ultraviolet (UV)-sensitive photoinitiators such as Irgacure™ 2959 (I2959), the most commonly used initiator for cytocompatible photoencapsulation of cells into synthetic scaffolds. In this study we define non-toxic conditions for photoencapsulation of human mesenchymal stem cells (hMSC) in PEGDA scaffolds using a visible light photoinitiator system composed of eosin Y, triethanolamine and 1-vinyl-2-pyrrolidinone. This visible light photoinitiator produced hydrogel scaffolds with an increased viability of encapsulated hMSCs and a more tightly crosslinked network in one-third the time of UV polymerization with I2959. PMID:21761391

  1. Photocatalytic activities of various pentavalent bismuthates under visible light irradiation

    SciTech Connect

    Takei, Takahiro; Haramoto, Rie; Dong, Qiang; Kumada, Nobuhiro; Yonesaki, Yoshinori; Kinomura, Nobukazu; Mano, Takayuki; Nishimoto, Shunsuke; Kameshima, Yoshikazu; Miyake, Michihiro

    2011-08-15

    LiBiO{sub 3}, NaBiO{sub 3}, MgBi{sub 2}O{sub 6}, KBiO{sub 3}, ZnBi{sub 2}O{sub 6}, SrBi{sub 2}O{sub 6}, AgBiO{sub 3}, BaBi{sub 2}O{sub 6} and PbBi{sub 2}O{sub 6} were synthesized by various processes such as hydrothermal treatment, heating and so on. These materials were examined for their photocatalytic activities in the decolorization of methylene blue and decomposition of phenol under visible light irradiation. For methylene blue decolorization, the presence of KBiO{sub 3} resulted in complete decoloration within 5 min. For phenol decomposition, NaBiO{sub 3} showed the highest activity, while LiBiO{sub 3}, SrBi{sub 2}O{sub 6} and BaBi{sub 2}O{sub 6} possessed almost comparable decomposition rates. Their decomposition rates were apparently higher than that by anatase (P25) under UV irradiation. - Graphical abstract: Nine pentavalent bismuthates were synthesized and were examined for their photocatalytic activities by decomposition of phenol under visible light irradiation. NaBiO{sub 3}, LiBiO{sub 3}, SrBi{sub 2}O{sub 6} and BaBi{sub 2}O{sub 6} indicated faster decomposition rate than that of anatase (P25) under UV-vis light irradiation. Highlights: > KBiO{sub 3} decolorize methylene blue aqueous solution immediately within 5 min. > NaBiO{sub 3}, LiBiO{sub 3}, SrBi{sub 2}O{sub 6} and BaBi{sub 2}O{sub 6} indicated high decomposition rate of phenol. > The d electron of Zn, Ag and Pb form broad conduction band. > The broad conduction band poses to diminish photocatalytic activity.

  2. Optimum combinations of visible and near-infrared reflectances for estimating the fraction of photosynthetically available radiation absorbed by plants

    NASA Technical Reports Server (NTRS)

    Podaire, Alain; Deschamps, Pierre-Yves; Frouin, R.; Asrar, Ghassem

    1991-01-01

    A useful parameter to estimate terrestrial primary productivity, that can be sensed from space, is the daily averaged fraction of Photosynthetically Available Radiation (PAR) absorbed by plants. To evaluate this parameter, investigators have relied on the fact that the relative amount of radiation reflected by a vegetated surface in the visible and near infrared depends on the fraction of the surface covered by the vegetation and therefore, correlates with absorbed PAR. They have used vegetation indices, namely normalized difference and simple ratio, to derive absorbed PAR. The problem with normalized difference and simple ratio is first, they are non linear functions of radiance or reflectance and therefore, cannot be readily applied to heterogeneous targets, second, they are used in generally nonlinear relationships, which make time integrals of the indices not proportional to primary productivity, and third, the relationships depend strongly on the type of canopy and background. To remove these limitations, linear combinations of visible and near infrared reflectances at optimum (one or two) viewing zenith angles are proposed.

  3. Mobile health-monitoring system through visible light communication.

    PubMed

    Tan, Yee-Yong; Chung, Wan-Young

    2014-01-01

    Promising development in the light emitting diode (LED) technology has spurred the interest to adapt LED for both illumination and data transmission. This has fostered the growth of interest in visible light communication (VLC), with on-going research to utilize VLC in various applications. This paper presents a mobile-health monitoring system, where healthcare information such as biomedical signals and patient information are transmitted via the LED lighting. A small and portable receiver module is designed and developed to be attached to the mobile device, providing a seamless monitoring environment. Three different healthcare information including ECG, PPG signals and HL7 text information is transmitted simultaneously, using a single channel VLC. This allows for a more precise and accurate monitoring and diagnosis. The data packet size is carefully designed, to transmit information in a minimal packet error rate. A comprehensive monitoring application is designed and developed through the use of a tablet computer in our study. Monitoring and evaluation such as heart rate and arterial blood pressure measurement can be performed concurrently. Real-time monitoring is demonstrated through experiment, where non-hazardous transmission method can be implemented alongside a portable device for better and safer healthcare service.

  4. Black carbon and other light-absorbing particles in snow of central North America

    NASA Astrophysics Data System (ADS)

    Doherty, Sarah J.; Dang, Cheng; Hegg, Dean A.; Zhang, Rudong; Warren, Stephen G.

    2014-11-01

    Vertical profiles of light-absorbing particles in seasonal snow were sampled from 67 North American sites. Over 500 snow samples and 55 soil samples from these sites were optically analyzed for spectrally resolved visible light absorption. The optical measurements were used to estimate black carbon (BC) mixing ratios in snow (CBCest), contributions to absorption by BC and non-BC particles, and the absorption Ångström exponent of particles in snow and local soil. Sites in Canada tended to have the lowest BC mixing ratios (typically ~5-35 ng g-1), with somewhat higher CBCest in the Pacific Northwest (typically ~5-40 ng g-1) and Intramountain Northwest (typically 10-50 ng g-1). The Northern U.S. Plains sites were the dirtiest, with CBCest typically ~15-70 ng g-1 and multiple sample layers with >100 ng g-1 BC in snow. Snow water samples were also chemically analyzed for standard anions, selected carbohydrates, and various elements. The chemical and optical data were input to a Positive Matrix Factorization analysis of the sources of particulate light absorption. These were soil, biomass/biofuel burning, and fossil fuel pollution. Comparable analyses have been conducted for the Arctic and North China, providing a broad, internally consistent data set. As in North China, soil is a significant contributor to snow particulate light absorption in the Great Plains. We also examine the concentrations and sources of snow particulate light absorption across a latitudinal transect from the northern U.S. Great Plains to Arctic Canada by combining the current data with our earlier Arctic survey.

  5. Imaging of Biological Tissues by Visible Light CDI

    NASA Astrophysics Data System (ADS)

    Karpov, Dmitry; Dos Santos Rolo, Tomy; Rich, Hannah; Fohtung, Edwin

    Recent advances in the use of synchrotron and X-ray free electron laser (XFEL) based coherent diffraction imaging (CDI) with application to material sciences and medicine proved the technique to be efficient in recovering information about the samples encoded in the phase domain. The current state-of-the-art algorithms of reconstruction are transferable to optical frequencies, which makes laser sources a reasonable milestone both in technique development and applications. Here we present first results from table-top laser CDI system for imaging of biological tissues and reconstruction algorithms development and discuss approaches that are complimenting the data quality improvement that is applicable to visible light frequencies due to it's properties. We demonstrate applicability of the developed methodology to a wide class of soft bio-matter and condensed matter systems. This project is funded by DOD-AFOSR under Award No FA9550-14-1-0363 and the LANSCE Professorship at LANL.

  6. Performance of indoor optical femtocell by visible light communication

    NASA Astrophysics Data System (ADS)

    Cui, Kaiyun; Quan, Jinguo; Xu, Zhengyuan

    2013-07-01

    Femotocell has been proposed and deployed to improve the indoor coverage and capacity of a cellular network. One big challenge in its deployment is the interference between the macrocell and femtocell cellular networks. In this paper we propose a new physical layer for the implementation of indoor femtocells - optical femtocells by LED-based visible light communication. A general system structure of the indoor optical femtocell network is first introduced. A combined wavelength division and code division multiple access scheme is proposed to differentiate cells and multiple users within a cell. This scheme coupled with directional beaming characteristics of the LEDs helps to mitigate intercell interference and intracell inference. The communication performance adopting the dimming compatible variable-PPM modulation suggested by the IEEE standard is analyzed. Monte-Carlo simulation is then carried out to reveal the system performance numerically under typical system settings and effects of various parameters.

  7. Visible light responsive systems based on metastable-state photoacids

    NASA Astrophysics Data System (ADS)

    Liao, Yi

    2015-09-01

    Proton transfer is one of the most fundamental processes in nature. Metastable-state photoacids can reversibly generate a large proton concentration under visible light with moderate intensity. which provides a general approach to control various proton transfer processes. Several applications of mPAHs have been demonstrated recently including control of acid-catalyzed reactions, volume-change of hydrogels, polymer conductivity, bacteria killing, odorant release, and color change of materials. They have also been utilized to control supramolecular assemblies, molecular switches, microbial fuel cells and cationic sensors. In this talk, the mechanism, structure design, and applications of metastable-state photoacids are introduced. Recent development of different types of metastable-state photoacids is presented. Challenges and future work are also discussed.

  8. An integrated PIN-array receiver for visible light communication

    NASA Astrophysics Data System (ADS)

    Li, Jie-Hui; Huang, Xing-Xing; Ji, Xin-Ming; Chi, Nan; Shi, Jian-Yang

    2015-10-01

    This paper first designs and demonstrates an integrated receiver for a visible light communication (VLC) system based on RGB LED and an array of silicon PIN diode detectors. The system uses a maximal ratio combining (MRC) algorithm to enhance system performance. The novel integrated PIN diode array design yields a high date rate of 1.2 Gbit s-1 by 16QAM-OFDM based on a commercially available RGB LED in a VLC system with bit error rate under a 7% pre-forward-error-correction (FEC) threshold of 3.8 × 10-3 after 30 cm free-space transmission. The results show that the use of integrated antennas in VLC systems will become a trend in the future.

  9. CO2 SEQUESTRATION AND RECYCLE BY PHOTOCATALYSIS WITH VISIBLE LIGHT

    SciTech Connect

    Steven S.C. Chuang

    2001-10-01

    Visible light-photocatalysis could provide a cost-effective route to recycle CO{sub 2} to useful chemicals or fuels. Development of an effective catalyst for the photocatalytic synthesis requires (i) the knowledge of the surface band gap and its relation to the surface structure, (ii) the reactivity of adsorbates and their reaction pathways, and (iii) the ability to manipulate the actives site for adsorption, surface reaction, and electron transfer. The objective of this research is to study the photo-catalytic activity of TiO{sub 2}-base catalyst. A series of TiO{sub 2}-supported metal catalysts were prepared for determining the activity and selectivity for the synthesis of methane and methanol. 0.5 wt% Cu/SrTiO{sub 3} was found to be the most active and selective catalyst for methanol synthesis. The activity of the catalyst decreased in the order: Ti silsesquioxane > Cu/SrTiO{sub 3} > Pt/TiO{sub 2} > Cu/TiO{sub 2} > TiO{sub 2} > Rh/TiO{sub 2}. To further increase the number of site for the reaction, we propose to prepare monolayer and multiplayer TiOx on high surface area mesoporous oxides. These catalysts will be used for in situ IR study in the Phase II research project to determine the reactivity of adsorbates. Identification of active adsorbates and sites will allow incorporation of acid/basic sites to alter the nature of CO{sub 2} and H{sub 2}O adsorbates and with Pt/Cu sites to direct reaction pathways of surface intermediates, enhancing the overall activity and selectivity for methanol and hydrocarbon synthesis. The overall goal of this research is to provide a greater predictive capability for the design of visible light-photosynthesis catalysts by a deeper understanding of the reaction kinetics and mechanism as well as by better control of the coordination/chemical environment of active sites.

  10. Functional inactivation of lymphocytes by methylene blue with visible light.

    PubMed

    Zhang, Bo; Cheng, Zhenzhen; Mo, Qin; Wang, Li; Wang, Xun; Wu, Xiaofei; Jia, Yao; Huang, Yuwen

    2015-10-01

    Transfusion of allogeneic white blood cells (WBCs) may cause adverse reactions in immunocompromised recipients, including transfusion-associated graft-versus-host disease (TA-GVHD), which is often fatal and incurable. In this study, the in vitro effect of methylene blue with visible light (MB + L) treatment on lymphocyte proliferation and cytokine production was measured to investigate whether MB + L can be used to prevent immune reactions that result from transfused lymphocytes. WBCs and 3 μM of MB were mixed and transferred into medical PVC bags, which were then exposed to visible light. Gamma irradiation was conducted as a parallel positive control. The cells without treatment were used as untreated group. All the groups were tested for the ability of cell proliferation and cytokine production upon stimulation. After incubation with mitogen phytohemagglutinin (PHA) or plate-bound anti-CD3 plus anti-CD28, the proliferation of MB + L/gamma-irradiation treated lymphocytes was significantly inhibited (P < 0.01) as compared to the untreated ones; the proliferation inhibitive rate of the MB + L group was even higher than that of gamma-irradiated cells (73.77% ± 28.75% vs. 44.72% ± 38.20%). MB + L treated cells incubated up to 7 days with PHA also showed no significant proliferation. The levels of TNF-α, IFN-γ, IL-6, IL-8, IL-10 and IL-1β present in the supernatant of MB + L treated lymphocytes upon stimulation were significantly lower than those of untreated lymphocytes. These results demonstrated that MB + L treatment functionally and irreversibly inactivated lymphocytes by inhibiting lymphocyte proliferation and the production of cytokines. MB + L treatment might be a promising method for the prevention of adverse immune responses caused by WBCs. PMID:26295729

  11. Imaging spectroscopy of albedo and radiative forcing by light-absorbing impurities in mountain snow

    NASA Astrophysics Data System (ADS)

    Painter, Thomas H.; Seidel, Felix C.; Bryant, Ann C.; McKenzie Skiles, S.; Rittger, Karl

    2013-09-01

    Recent studies show that deposition of dust and black carbon to snow and ice accelerates snowmelt and perturbs regional climate and hydrologic cycles. Radiative forcing by aerosols is often neglected in climate and hydrological models in part due to scarcity of observations. Here we describe and validate an algorithm suite (Imaging Spectrometer-Snow Albedo and Radiative Forcing (IS-SnARF)) that provides quantitative retrievals of snow grain size, snow albedo, and radiative forcing by light-absorbing impurities in snow and ice (LAISI) from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data collected on 15 June 2011 in the Senator Beck Basin Study Area (SBBSA), SW Colorado, USA. Radiative forcing by LAISI is retrieved by the integral of the convolution of spectral irradiance with spectral differences between the spectral albedo (scaled from the observed hemispherical-directional reflectance factor (HDRF)) and modeled clean snow spectral albedo. The modeled surface irradiance at time of acquisition at test sites was 1052 W m-2 compared to 1048 W m-2 measured with the field spectroradiometer measurements, a relative difference of 0.4%. HDRF retrievals at snow and bare soil sites had mean errors relative to in situ measurements of -0.4 ± 0.1% reflectance averaged across the spectrum and root-mean-square errors of 1.5 ± 0.1%. Comparisons of snow albedo and radiative forcing retrievals from AVIRIS with in situ measurements in SBBSA showed errors of 0.001-0.004 and 2.1 ± 5.1 W m-2, respectively. A counterintuitive result was that, in the presence of light absorbing impurities, near-surface snow grain size increased with elevation, whereas we generally expect that at lower elevation the grain size would be larger.

  12. Biogenic C-doped titania templated by cyanobacteria for visible-light photocatalytic degradation of Rhodamine B.

    PubMed

    He, Jiao; Zi, Guoli; Yan, Zhiying; Li, Yongli; Xie, Jiao; Duan, Deliang; Chen, Yongjuan; Wang, Jiaqiang

    2014-05-01

    Cyanobacteria, which occurred in eutrophic water harvest solar light to carry out photosynthesis with high efficiency. In this work, cyanobacteria (Microcystis sp.) were used as biotemplate to synthesize titania structure. The synthesized titania sample had similar morphology to that of the original template in spite of the fragile unicellular structures and extremely high water content of cyanobacterial cells. Incorporation of biogenic C, as well as the morphology inherited from biotemplate improved visible-light absorbance of the titania structure. The sample exhibited higher visible-light photocatalytic activity than commercial titania photocatalyst Degussa P25 for Rhodamine B (RhB) degradation. Compared with those C-doped titania photocatalysts prepared by other methods, cyanobacteria templated titania photocatalyst offer some potential for competitive advantages. The reported strategy opened up a new use for the cyanobacteria. It could also be used for titania in applications such as treatment of polluted water, dye-sensitized solar cells, or other regions.

  13. Colloidal metasurfaces displaying near-ideal and tunable light absorbance in the infrared.

    PubMed

    Rozin, Matthew J; Rosen, David A; Dill, Tyler J; Tao, Andrea R

    2015-01-01

    Metasurfaces are ultrathin, two-dimensional arrays of subwavelength resonators that have been demonstrated to control the flow of light in ways that are otherwise unattainable with natural materials. These arrays are typically composed of metallic Ag or Au nanostructures shaped like split rings, nanowire pairs or nanorods (commonly referred to as meta-atoms) that are arranged to produce a collective optical response spanning an impressive range of properties, from the perfect absorption of incident light to superresolution imaging. However, metasurfaces pose major challenges in their fabrication over large areas, which can be prohibitively expensive and time consuming using conventional nanolithography techniques. Here we show that differently shaped colloidal nanocrystals can be organized into metasurface architectures using robust, scalable assembly methods. These metasurfaces exhibit extreme in-plane electromagnetic coupling that is strongly dependent on nanocrystal size, shape and spacing. Colloidal metasurfaces that display near-ideal electromagnetic absorbance can be tuned from the visible into the mid-infrared wavelengths. PMID:26099835

  14. Thermal mechanisms of laser marking in transparent polymers with light-absorbing microparticles

    NASA Astrophysics Data System (ADS)

    Zelenska, K. S.; Zelensky, S. E.; Poperenko, L. V.; Kanev, K.; Mizeikis, V.; Gnatyuk, V. A.

    2016-01-01

    Interaction of highly viscous polystyrene suspensions of light-absorbing microparticles with pulsed radiation of a Q-switched YAG:Nd3+ laser is investigated. Absorption of laser radiation by the suspended microparticles causes thermal decomposition (pyrolysis) of the polymer in the vicinity of the overheated particles. Laser-induced incandescence (LII) of light-absorbing microparticles under irradiation by a sequence of laser pulses is observed. The mechanism of laser marking includes formation of light-absorbing and scattering centers by accumulation of carbonaceous and gaseous products of pyrolysis.

  15. Visible photoluminescence of color centers in LiF crystals for absorbed dose evaluation in clinical dosimetry

    NASA Astrophysics Data System (ADS)

    Villarreal-Barajas, J. E.; Piccinini, M.; Vincenti, M. A.; Bonfigli, F.; Khan, R. F.; Montereali, R. M.

    2015-04-01

    Among insulating materials, lithium fluoride (LiF) has been successfully used as ionizing radiation dosemeter for more than 60 years. Thermoluminescence (TL) has been the most commonly used reading technique to evaluate the absorbed dose. Lately, optically stimulated luminescence (OSL) of visible emitting color centers (CCs) has also been explored in pure and doped LiF. This work focuses on the experimental behaviour of nominally pure LiF crystals dosemeters for 6 MV x rays at low doses based on photoluminescence (PL) of radiation induced CCs. Polished LiF crystals were irradiated using 6 MV x rays produced by a clinical linear accelerator. The doses (absorbed dose to water) covered the 1-100 Gy range. Optical absorption spectra show stable formation of primary F defects up to a maximum concentration of 2×1016 cm-3, while no significant M absorption band at around 450 nm was detected. On the other hand, under Argon laser excitation at 458 nm, PL spectra of the irradiated LiF crystals clearly exhibited the characteristic F2 and F+3 visible broad emission bands. Their sum intensity is linearly proportional to the absorbed dose in the investigated range. PL integrated intensity was also measured using a conventional fluorescence optical microscope under blue lamp illumination. The relationship between the absorbed dose and the integrated F2 and F+3 PL intensities, represented by the net average pixel number in the optical fluorescence images, is also fairly linear. Even at the low point defect densities obtained at the investigated doses, these preliminary experimental results are encouraging for further investigation of CCs PL in LiF crystals for clinical dosimetry.

  16. Turn on the lights: leveraging visible light for communications and positioning

    NASA Astrophysics Data System (ADS)

    Hranilovic, Steve

    2015-01-01

    The need for ubiquitous broadband connectivity is continually growing, however, radio spectrum is increasingly scarce and limited by interference. In addition, the energy efficiency of many radio transmitters is low and most input energy is converted to heat. A widely overlooked resource for positioning and broadband access is optical wireless communication reusing existing illumination installations. As many of the 14 billion incandescent bulbs in use worldwide are converted to energy efficient LED lighting, a unique opportunity exists to augment them with visible light communications (VLC) and visible light positioning (VLP). VLC- and VLP- enabled LED lighting is not only energy efficient but enables a host of new use cases such as location-aware ubiquitous high-speed wireless communication links. This talk presents the recent work of the Free-space Optical Communication Algorithms Laboratory (FOCAL) at McMaster University in Hamilton, Canada in developing novel signaling and indoor localization techniques using illumination devices. Developments in the signaling design for VLC systems will be presented along with several prototype VLC communication systems. Novel approaches to the integration of VLC networks with power line communications (PLC) are discussed. The role of visible light communications and ranging for automotive safety will also be highlighted. Several approaches to indoor positioning using illumination devices and simple smartphone-based receivers will be presented. Finally, a vision for VLC and VLP technologies will be presented along with our ongoing research directions.

  17. Plasmonic interaction of visible light with gold nanoscale checkerboards

    NASA Astrophysics Data System (ADS)

    Ramakrishna, S. Anantha; Mandal, P.; Jeyadheepan, K.; Shukla, N.; Chakrabarti, S.; Kadic, M.; Enoch, S.; Guenneau, S.

    2011-12-01

    Intersecting corners and checkerboards of negative refractive index materials (NRIM) represent highly singular electromagnetic systems that involve very highly enhanced local fields and the local density of modes. It is well known that plasmonic metallic systems can mimic the behavior of NRIM in the near-field limit at optical frequencies. Opaque gold films have been structured by focused ion-beam technologies at submicrometer scales in a checkerboard fashion and their optical properties measured. Subwavelength square holes in thick gold films placed in checkerboard fashion show a broadband extraordinary transmission of light at visible wavelengths. We find that the smaller the square holes, the larger is the transmission over a band of wavelengths from 650 to 950 nm suggesting that such structured surfaces have very unusual effective medium properties, which is confirmed by the band-structure diagrams computed with finite elements. Theoretical results also confirm the experimental transmission measured to be well over 80% from 750 to 950 nm for a checkerboard with 150nm×150 nm square holes. This unusual broadband nature of checkerboard structured films is confirmed by the dark-field reflection spectra. Microscopic studies reveal that these structures have enhanced interaction of light at the edges and corners. These checkerboards are also found to give rise to an enhancement of fluorescence by imbedded dye molecules. There is a strong correspondence between the theoretical predictions and the experimental measurements.

  18. Distributed user-centric scheduling for visible light communication networks.

    PubMed

    Chen, Lingjiao; Wang, Jiaheng; Zhou, Jiantao; Ng, Derrick Wing Kwan; Schober, Robert; Zhao, Chunming

    2016-07-11

    Visible light communication (VLC) networks, consisting of multiple light-emitting diodes (LEDs) acting as optical access points (APs), can provide low-cost high-rate data transmission to multiple users simultaneously in indoor environments. However, the performance of VLC networks is severely limited by the interference between different users. In this paper, we establish a distributed user-centric scheduling framework based on stable marriage theory, and propose a novel decentralized scheduling method to manage interference by forming flexible amorphous cells for all users. The proposed scheduling method has provable low computational complexity and requires only the exchange of a few 1-bit messages between the APs and the users but not the feedback of the channel state information of the entire network. We further show that the proposed method can achieve both user-wise and system-wise optimality as well as a certain level of fairness. Simulation results indicate that our decentralized user-centric scheduling method outperforms existing centralized approaches in terms of throughput, fairness, and computational complexity.

  19. Distributed user-centric scheduling for visible light communication networks.

    PubMed

    Chen, Lingjiao; Wang, Jiaheng; Zhou, Jiantao; Ng, Derrick Wing Kwan; Schober, Robert; Zhao, Chunming

    2016-07-11

    Visible light communication (VLC) networks, consisting of multiple light-emitting diodes (LEDs) acting as optical access points (APs), can provide low-cost high-rate data transmission to multiple users simultaneously in indoor environments. However, the performance of VLC networks is severely limited by the interference between different users. In this paper, we establish a distributed user-centric scheduling framework based on stable marriage theory, and propose a novel decentralized scheduling method to manage interference by forming flexible amorphous cells for all users. The proposed scheduling method has provable low computational complexity and requires only the exchange of a few 1-bit messages between the APs and the users but not the feedback of the channel state information of the entire network. We further show that the proposed method can achieve both user-wise and system-wise optimality as well as a certain level of fairness. Simulation results indicate that our decentralized user-centric scheduling method outperforms existing centralized approaches in terms of throughput, fairness, and computational complexity. PMID:27410830

  20. Ultraviolet and visible imaginary refractive index of strongly absorbing atmospheric particulate matter.

    PubMed

    Gillespie, J B; Lindberg, J D

    1992-04-20

    Determinations of the imaginary refractive index in the ultraviolet and visible spectral regions as determined from diffuse reflectance measurements are presented. Materials examined are carbon black and oxides of iron, lead, mercury, copper, manganese, and vanadium along with lead iodide and iron sulfide.

  1. Luminescence- and nanoparticle-mediated increase of light absorption by photoreceptor cells: Converting UV light to visible light

    PubMed Central

    Li, Lei; Sahi, Sunil K.; Peng, Mingying; Lee, Eric B.; Ma, Lun; Wojtowicz, Jennifer L.; Malin, John H.; Chen, Wei

    2016-01-01

    We developed new optic devices – singly-doped luminescence glasses and nanoparticle-coated lenses that convert UV light to visible light – for improvement of visual system functions. Tb3+ or Eu3+ singly-doped borate glasses or CdS-quantum dot (CdS-QD) coated lenses efficiently convert UV light to 542 nm or 613 nm wavelength narrow-band green or red light, or wide-spectrum white light, and thereby provide extra visible light to the eye. In zebrafish (wild-type larvae and adult control animals, retinal degeneration mutants, and light-induced photoreceptor cell degeneration models), the use of Tb3+ or Eu3+ doped luminescence glass or CdS-QD coated glass lenses provide additional visible light to the rod and cone photoreceptor cells, and thereby improve the visual system functions. The data provide proof-of-concept for the future development of optic devices for improvement of visual system functions in patients who suffer from photoreceptor cell degeneration or related retinal diseases. PMID:26860393

  2. Luminescence- and nanoparticle-mediated increase of light absorption by photoreceptor cells: Converting UV light to visible light.

    PubMed

    Li, Lei; Sahi, Sunil K; Peng, Mingying; Lee, Eric B; Ma, Lun; Wojtowicz, Jennifer L; Malin, John H; Chen, Wei

    2016-02-10

    We developed new optic devices - singly-doped luminescence glasses and nanoparticle-coated lenses that convert UV light to visible light - for improvement of visual system functions. Tb(3+) or Eu(3+) singly-doped borate glasses or CdS-quantum dot (CdS-QD) coated lenses efficiently convert UV light to 542 nm or 613 nm wavelength narrow-band green or red light, or wide-spectrum white light, and thereby provide extra visible light to the eye. In zebrafish (wild-type larvae and adult control animals, retinal degeneration mutants, and light-induced photoreceptor cell degeneration models), the use of Tb(3+) or Eu(3+) doped luminescence glass or CdS-QD coated glass lenses provide additional visible light to the rod and cone photoreceptor cells, and thereby improve the visual system functions. The data provide proof-of-concept for the future development of optic devices for improvement of visual system functions in patients who suffer from photoreceptor cell degeneration or related retinal diseases.

  3. Ultraviolet light absorbers having two different chromophors in the same molecule

    DOEpatents

    Vogl, O.; Li, S.

    1983-10-06

    This invention relates to novel ultraviolet light absorbers having two chromophors in the same molecule, and more particularly to benzotriazole substituted dihydroxybenzophenones and acetophenones. More particularly, this invention relates to 3,5-(di(2H-benzotriazole-2-yl))-2,4-dihydroxybenzophenone and 3,5-(di(2H-benzotriazole-2-yl))-2,4-dihydroxyacetophenone which are particularly useful as an ultraviolet light absorbers.

  4. Visible Light Induces Melanogenesis in Human Skin through a Photoadaptive Response.

    PubMed

    Randhawa, Manpreet; Seo, InSeok; Liebel, Frank; Southall, Michael D; Kollias, Nikiforos; Ruvolo, Eduardo

    2015-01-01

    Visible light (400-700 nm) lies outside of the spectral range of what photobiologists define as deleterious radiation and as a result few studies have studied the effects of visible light range of wavelengths on skin. This oversight is important considering that during outdoors activities skin is exposed to the full solar spectrum, including visible light, and to multiple exposures at different times and doses. Although the contribution of the UV component of sunlight to skin damage has been established, few studies have examined the effects of non-UV solar radiation on skin physiology in terms of inflammation, and limited information is available regarding the role of visible light on pigmentation. The purpose of this study was to determine the effect of visible light on the pro-pigmentation pathways and melanin formation in skin. Exposure to visible light in ex-vivo and clinical studies demonstrated an induction of pigmentation in skin by visible light. Results showed that a single exposure to visible light induced very little pigmentation whereas multiple exposures with visible light resulted in darker and sustained pigmentation. These findings have potential implications on the management of photo-aggravated pigmentary disorders, the proper use of sunscreens, and the treatment of depigmented lesions.

  5. Removal of fluorescence and ultraviolet absorbance of dissolved organic matter in reclaimed water by solar light.

    PubMed

    Wu, Qianyuan; Li, Chao; Wang, Wenlong; He, Tao; Hu, Hongying; Du, Ye; Wang, Ting

    2016-05-01

    Storing reclaimed water in lakes is a widely used method of accommodating changes in the consumption of reclaimed water during wastewater reclamation and reuse. Solar light serves as an important function in degrading pollutants during storage, and its effect on dissolved organic matter (DOM) was investigated in this study. Solar light significantly decreased the UV254 absorbance and fluorescence (FLU) intensity of reclaimed water. However, its effect on the dissolved organic carbon (DOC) value of reclaimed water was very limited. The decrease in the UV254 absorbance intensity and FLU excitation-emission matrix regional integration volume (FLU volume) of reclaimed water during solar light irradiation was fit with pseudo-first order reaction kinetics. The decrease of UV254 absorbance was much slower than that of the FLU volume. Ultraviolet light in solar light had a key role in decreasing the UV254 absorbance and FLU intensity during solar light irradiation. The light fluence-based removal kinetic constants of the UV254 and FLU intensity were independent of light intensity. The peaks of the UV254 absorbance and FLU intensity with an apparent molecular weight (AMW) of 100Da to 2000Da decreased after solar irradiation, whereas the DOC value of the major peaks did not significantly change.

  6. Removal of fluorescence and ultraviolet absorbance of dissolved organic matter in reclaimed water by solar light.

    PubMed

    Wu, Qianyuan; Li, Chao; Wang, Wenlong; He, Tao; Hu, Hongying; Du, Ye; Wang, Ting

    2016-05-01

    Storing reclaimed water in lakes is a widely used method of accommodating changes in the consumption of reclaimed water during wastewater reclamation and reuse. Solar light serves as an important function in degrading pollutants during storage, and its effect on dissolved organic matter (DOM) was investigated in this study. Solar light significantly decreased the UV254 absorbance and fluorescence (FLU) intensity of reclaimed water. However, its effect on the dissolved organic carbon (DOC) value of reclaimed water was very limited. The decrease in the UV254 absorbance intensity and FLU excitation-emission matrix regional integration volume (FLU volume) of reclaimed water during solar light irradiation was fit with pseudo-first order reaction kinetics. The decrease of UV254 absorbance was much slower than that of the FLU volume. Ultraviolet light in solar light had a key role in decreasing the UV254 absorbance and FLU intensity during solar light irradiation. The light fluence-based removal kinetic constants of the UV254 and FLU intensity were independent of light intensity. The peaks of the UV254 absorbance and FLU intensity with an apparent molecular weight (AMW) of 100Da to 2000Da decreased after solar irradiation, whereas the DOC value of the major peaks did not significantly change. PMID:27155416

  7. Performance study for indoor visible light communication systems

    NASA Astrophysics Data System (ADS)

    Gao, Shuo

    The field of Optical Wireless Communications (OWC) has seen rapid development during the recent years. This growing popularity is due to several characteristics of considerable importance to consumer electronics products, such as large bandwidth that is also not having spectrum regulations imposed, low cost, and license free operation. As a branch of OWC, visible light communication (VLC) systems have their own unique advantages, with several new technologies, products and patents having been developed during since the end of last century. In this research, a VLC system for indoor application is proposed. In this work, we focus on reducing cost, and for that, we had to make appropriate selection of system's components, e.g. modulation, coding, filtering. Our objective was to achieve acceptable bit error rate (BER) performance for indoor use, with a low cost system. Through our research we met this objective. Our designs were evaluated through computer simulations. The acquired results proved the suitability of the proposed schemes and the performance's degree of dependency on several parameters such as distance, incidence angle and irradiance angle. A software tool was created allowing easy assessment of the communication system. It is using a user friendly GUI through which the user enters the system's parameters and the system outputs the corresponding BER value.

  8. Visible light to electrical energy conversion using photoelectrochemical cells

    NASA Technical Reports Server (NTRS)

    Wrighton, Mark S. (Inventor); Ellis, Arthur B. (Inventor); Kaiser, Steven W. (Inventor)

    1983-01-01

    Sustained conversion of low energy visible or near i.r. light (>1.25 eV) to electrical energy has been obtained using wet photoelectrochemical cells where there are no net chemical changes in the system. Stabilization of n-type semi-conductor anodes of CdS, CdSe, CdTe, GaP, GaAs and InP to photoanodic dissolution is achieved by employing selected alkaline solutions of Na.sub.2 S, Na.sub.2 S/S, Na.sub.2 Se, Na.sub.2 Se/Se, Na.sub.2 Te and Na.sub.2 Te/Te as the electrolyte. The oxidation of (poly) sulfide, (poly)selenide or (poly)telluride species occurs at the irradiated anode, and reduction of polysulfide, polyselenide or polytelluride species occurs at the dark Pt cathode of the photoelectrochemical cell. Optical to electrical energy conversion efficiencies approaching 15% at selected frequencies have been observed in some cells. The wavelength for the onset of photocurrent corresponds to the band gap of the particular anode material used in the cell.

  9. Toward user mobility for OFDM-based visible light communications.

    PubMed

    Hong, Yang; Chen, Lian-Kuan

    2016-08-15

    We propose and experimentally demonstrate a mobile visible light communications (mobi-VLC) transmission system. The impact of user mobility on the performance of the mobi-VLC system is characterized, and we propose the use of the channel-independent orthogonal circulant matrix transform (OCT) precoding to combat the packet loss performance degradation induced by mobility. A mobile user terminal is used to detect the signal from a blue laser placed at 1 m away from the moving track. Various moving speeds (20, 40, 60, and 80  cm/s) and lateral moving distances (30, 40, and 50 cm) of the user terminal are investigated. The effectiveness of the OCT precoding is evaluated by the comparison with the conventional orthogonal frequency division multiplexing (OFDM) scheme and the adaptive-loaded discrete multi-tone (DMT) scheme. Experimental results show that the system performance degrades with the increase in user mobility speed and in moving distance. Furthermore, the OCT precoding provides performance improvement that is superior over that of conventional OFDM schemes, and it exhibits lower packet loss rate than that of adaptive-loaded DMT. No packet loss for 300  Mb/s transmission is achieved with a 30 cm lateral moving distance at 20  cm/s. PMID:27519083

  10. Water splitting on semiconductor catalysts under visible-light irradiation.

    PubMed

    Navarro Yerga, Rufino M; Alvarez Galván, M Consuelo; del Valle, F; Villoria de la Mano, José A; Fierro, José L G

    2009-01-01

    Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. The Sun is a source of silent and precious energy that is distributed fairly all over the Earth daily. However, its tremendous potential as a clean, safe, and economical energy source cannot be exploited unless the energy is accumulated or converted into more useful forms. The conversion of solar energy into hydrogen via the water-splitting process, assisted by photo-semiconductor catalysts, is one of the most promising technologies for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. This Minireview provides an overview of the principles, approaches, and research progress on solar hydrogen production via the water-splitting reaction on photo-semiconductor catalysts. It presents a survey of the advances made over the last decades in the development of catalysts for photochemical water splitting under visible-light irradiation. The Minireview also analyzes the energy requirements and main factors that determine the activity of photocatalysts in the conversion of water into hydrogen and oxygen using sunlight. Remarkable progress has been made since the pioneering work by Fujishima and Honda in 1972, but he development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy still faces major challenges. Research strategies and approaches adopted in the search for active and efficient photocatalysts, for example through new materials and synthesis methods, are presented and analyzed.

  11. Microwave-assisted hydrothermal synthesis of N-doped titanate nanotubes for visible-light-responsive photocatalysis.

    PubMed

    Peng, Yen-Ping; Lo, Shang-Lien; Ou, Hsin-Hung; Lai, Shiau-Wu

    2010-11-15

    This study employs a rapid, energy frugal and environmental friendly method to synthesize nitrogen doped titanate nanotubes (NTNTs), and uses TEM, XRD, Raman, nitrogen adsorption-desorption isotherms analysis, and UV-vis spectroscopy to characterize the obtained NTNTs. TEM results demonstrate that the current research successfully synthesized one-dimensional NTNTs via the microwave hydrothermal (M-H) method, and show that NTNTs retain a tubular structure after sintering at a temperature of 350°C. XRD results agree well with Raman spectrum findings. Both show that the intensity of anatase crystallization increases with an increase in sintering temperature. After sintering at high temperature, above 250°C, the UV-vis absorbance edges of NTNTs significantly shift to the visible-light region, which illustrates N atom doping into nanotubes. Photocatalytic tests conclude that the NTNTs-350 shows good efficiency with visible-light response.

  12. Towards efficient visible-light active photocatalysts: CdS/Au sensitized TiO2 nanotube arrays.

    PubMed

    Nguyen, VanManh; Cai, Qingyun; Grimes, Craig A

    2016-12-01

    A visible-light active photocatalyst, CdS/Au/TiO2 nanotube array (NTA) photoelectrode, was prepared by electrodeposition of Au nanoparticles onto TiO2 NTA with subsequent deposition of visible-light absorbable 2.4eV band-gap CdS quantum dots using successive ion layer adsorption and reaction (SILAR). The Au nanoparticles here act as electron sinks facilitating charge carrier separation. Under AM1.5G illumination a photoconversion efficiency of 4.06% was achieved for the CdS/Au/TiO2 NTA photoelectrode, suggesting the promise of the material architecture for achieving high-performance cost-effective materials. PMID:27565960

  13. Microwave-assisted hydrothermal synthesis of N-doped titanate nanotubes for visible-light-responsive photocatalysis.

    PubMed

    Peng, Yen-Ping; Lo, Shang-Lien; Ou, Hsin-Hung; Lai, Shiau-Wu

    2010-11-15

    This study employs a rapid, energy frugal and environmental friendly method to synthesize nitrogen doped titanate nanotubes (NTNTs), and uses TEM, XRD, Raman, nitrogen adsorption-desorption isotherms analysis, and UV-vis spectroscopy to characterize the obtained NTNTs. TEM results demonstrate that the current research successfully synthesized one-dimensional NTNTs via the microwave hydrothermal (M-H) method, and show that NTNTs retain a tubular structure after sintering at a temperature of 350°C. XRD results agree well with Raman spectrum findings. Both show that the intensity of anatase crystallization increases with an increase in sintering temperature. After sintering at high temperature, above 250°C, the UV-vis absorbance edges of NTNTs significantly shift to the visible-light region, which illustrates N atom doping into nanotubes. Photocatalytic tests conclude that the NTNTs-350 shows good efficiency with visible-light response. PMID:20732743

  14. Spectroscopic refractometer for transparent and absorbing liquids by reflection of white light near the critical angle

    SciTech Connect

    Sanchez-Perez, C.; Garcia-Valenzuela, A.

    2012-11-15

    We propose and evaluate a spectroscopic refractometer device to measure the refractive index dispersion of transparent and absorbing solutions. The angle-dependent reflectivity of a white beam of light in an internal reflection configuration around the critical angle is spectrally analyzed. The refractive index in a wavelength range from 400 nm to 900 nm is obtained from the angle-reflectivity curve around the critical angle at each wavelength. The device does not use angle scanning mechanisms, decreasing considerably the complexity of the instrument in comparison to previous proposals. As a result, the measurements are obtained relatively fast. Nevertheless, a good experimental resolution in refractive index of about {Delta}n Almost-Equal-To 10{sup -4} at all the wavelengths is achieved in the case of transparent solutions. The calibration procedure of the device is discussed in detail. We also present measurements of the refractive index dispersion of rhodamine 6G-methanol solutions, which has a strong absorption band in the visible spectra.

  15. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Maruo, Daiki; Hai, Pham Nam; Tanaka, Masaaki

    2015-03-01

    We demonstrate visible-light electroluminescence (EL) due to d- d transitions in GaAs:Mn based LEDs. We design p+-n junctions with a p+ GaAs:Mn layer, in which at a reverse bias voltage (-3 to -6 V), an intense electric field builds up in the depletion layers of the p+-n junctions. Holes are injected to the depletion layer by Zener tunneling from the conduction band or by diffusion of minority holes from the valence band of the n-type layer. These holes are accelerated by the intense electric field in the depletion layer, and excite the d electrons of Mn in the p+ GaAs:Mn layer by impact excitations. We observe visible-light emission at E1 = 1.89 eV and E2 = 2.16 eV, which are exactly the same as the 4T1-->6A1 and 4A2-->4T1 transition energy of Mn. The threshold voltage for observation of visible-light EL is -4 V, corresponding to -(E1 +E2) / e. This indicates that the impact excitation is most effective for the one step excitation from the ground state 6A1 to the highest excited state 4A2 .

  16. Light-concentrating plasmonic Au superstructures with significantly visible-light-enhanced catalytic performance.

    PubMed

    Yang, Jinhu; Li, Ying; Zu, Lianhai; Tong, Lianming; Liu, Guanglei; Qin, Yao; Shi, Donglu

    2015-04-22

    Noble metals are well-known for their surface plasmon resonance effect that enables strong light absorption typically in the visible regions for gold and silver. However, unlike semiconductors, noble metals are commonly considered incapable of catalyzing reactions via photogenerated electron-hole pairs due to their continuous energy band structures. So far, photonically activated catalytic system based on pure noble metal nanostructures has seldom been reported. Here, we report the development of three different novel plasmonic Au superstructures comprised of Au nanoparticles, multiple-twinned nanoparticles and nanoworms assembling on the surfaces of SiO2 nanospheres respectively via a well-designed synthetic strategy. It is found that these novel Au superstructures show enhanced broadband visible-light absorption due to the plasmon resonance coupling within the superstructures, and thus can effectively focus the energy of photon fluxes to generate much more excited hot electrons and holes for promoting catalytic reactions. Accordingly, these Au superstructures exhibit significantly visible-light-enhanced catalytic efficiency (up to ∼264% enhancement) for the commercial reaction of p-nitrophenol reduction. PMID:25840556

  17. Nature of light scattering in dental enamel and dentin at visible and near-infrared wavelengths

    NASA Astrophysics Data System (ADS)

    Fried, Daniel; Glena, Richard E.; Featherstone, John D. B.; Seka, Wolf

    1995-03-01

    The light-scattering properties of dental enamel and dentin were measured at 543, 632, and 1053 nm. Angularly resolved scattering distributions for these materials were measured from 0 deg to 180 deg using a rotating goniometer. Surface scattering was minimized by immersing the samples in an index-matching bath. The scattering and absorption coefficients and the scattering phase function were deduced by comparing the measured scattering data with angularly resolved Monte Carlo light-scattering simulations. Enamel and dentin were best represented by a linear combination of a highly forward-peaked Henyey-Greenstein (HG) phase function and an isotropic phase function. Enamel weakly scatters light between 543 nm and 1.06 mu m, with the scattering coefficient ( mu s) ranging from mu s = 15 to 105 cm-1. The phase function is a combination of a HG function with g = 0.96 and a 30-60% isotropic phase function. For enamel, absorption is negligible. Dentin scatters strongly in the visible and near IR ( mu s approximately equals 260 cm-1) and absorbs weakly ( mu a approximately equals 4 cm-1). The scattering phase function for dentin is described by a HG function with g = 0.93 and a very weak isotropic scattering component ( approximately 2%).

  18. Measurements of a prototype synchrotron radiation pumped absorber for future light sources

    SciTech Connect

    Chou, T.S.; Foerster, C.L.; Halama, H.; Lanni, C.

    1988-01-01

    In the new generation of advanced synchrotron light sources, the conventional concept of distributed pumping is no longer suitable for removing the gas load caused by photon stimulated desorption (PSD). A new concept using a combination of photon absorber and pumping station has been designed, constructed, and installed in the U1OB beam line at the VUV ring of the National Synchrotron Light Source. The system consists of an electrically insulated water cooled copper block, a titanium sublimation pump, calibrated BA gauges, a calibrated RGA, and a known conductance. A photon beam 10 milliradian wide and 3.26 milliradian high, having critical energy of 500 eV, is directed on the absorber. PSD yield is studied as a function of total beam dose and absorber surface preparation. The results from this experiment, pump characteristics, design of an absorber pump for future light sources, and the pressure improvement factors will be presented. 5 refs., 7 figs., 1 tab.

  19. Visible light water splitting using dye-sensitized oxide semiconductors.

    PubMed

    Youngblood, W Justin; Lee, Seung-Hyun Anna; Maeda, Kazuhiko; Mallouk, Thomas E

    2009-12-21

    Researchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO(2) to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts. Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor-acceptor systems and semiconductor particles. Unfortunately, energetically favorable charge recombination reactions tend to be much faster than the slow multielectron processes of water oxidation and reduction. Consequently, visible light water splitting has only recently been achieved in semiconductor-based photocatalytic systems and remains an inefficient process. This Account describes our approach to two problems in solar water splitting: the organization of molecules into assemblies that promote long-lived charge separation, and catalysis of the electrolysis reactions, in particular the four-electron oxidation of water. The building blocks of our artificial photosynthetic systems are wide band gap semiconductor particles, photosensitizer and electron relay molecules, and nanoparticle catalysts. We intercalate layered metal oxide semiconductors with metal nanoparticles. These intercalation compounds, when sensitized with [Ru(bpy)(3)](2+) derivatives, catalyze the photoproduction of hydrogen from sacrificial

  20. Light scattering by absorbing hexagonal ice crystals in cirrus clouds.

    PubMed

    Zhang, J; Xu, L

    1995-09-01

    An improved ray-optics theory for single scattering and polarization of hexagonal columns and plates randomly oriented in space has been developed by considering absorption and by using the Chebyshev solution for diffraction integrals. The vector-tracing method and statistics technique of random sampling are employed. The equivalent forms of Snell's law and Fresnel formulas for absorbing ice crystals are derived, and two equivalent optical constants, m' and m″, are obtained. Comparison is made of the computed results of our model and the Takano and Liou model for asymmetry factors, single-scattering albedos, and scattering phase matrix elements. Some characteristics of our model are discussed, and these analyses demonstrate that our ray-optics model is practical and much improved.

  1. Soluble, light-absorbing species in snow at Barrow, Alaska

    NASA Astrophysics Data System (ADS)

    Beine, Harry; Anastasio, Cort; Esposito, Giulio; Patten, Kelley; Wilkening, Elizabeth; Domine, Florent; Voisin, Didier; Barret, Manuel; Houdier, Stephan; Hall, Sam

    2011-07-01

    As part of the international multidisciplinary Ocean - Atmosphere - Sea Ice - Snowpack (OASIS) program we analyzed more than 500 terrestrial (melted) snow samples near Barrow, AK between February and April 2009 for light absorption, as well as H2O2 and inorganic anion concentrations. For light absorption in the photochemically active region (300-450 nm) of surface snows, H2O2 and NO3- make minor contributions (combined < 9% typically), while HUmic LIke Substances (HULIS) and unknown chromophores each account for approximately half of the total absorption. We have identified four main sources for our residual chromophores (i.e., species other than H2O2 or NO3-): (1) vegetation and organic debris impact mostly the lowest 20 cm of the snowpack, (2) marine inputs, which are identified by high Cl- and SO42- contents, (3) deposition of diamond dust to surface snow, and (4) gas-phase exchange between the atmosphere and surface snow layers. The snow surfaces, and accompanying chromophore concentrations, are strongly modulated by winds and snowfall at Barrow. However, even with these physical controls on light absorption, we see an overall decline of light absorption in near-surface snow during the 7 weeks of our campaign, likely due to photo-bleaching of chromophores. While HULIS and unknown chromophores dominate light absorption by soluble species in Barrow snow, we know little about the photochemistry of these species, and thus we as a community are probably overlooking many snowpack photochemical reactions.

  2. Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices

    PubMed Central

    O'Toole, Martina; Diamond, Dermot

    2008-01-01

    The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements.

  3. Absorption of visible radiation in atmosphere containing mixtures of absorbing and nonabsorbing particles

    NASA Technical Reports Server (NTRS)

    Ackerman, T. P.; Toon, O. B.

    1981-01-01

    The presence of a strongly absorbing material, tentatively identified as graphitic carbon, or 'soot', is indicated by measurements of single-scattering albedo of tropospheric aerosols. Although theoretical calculations based on models of the ways in which soot may mix with other aerosol materials yield the single-scattering albedo values of 0.6, accounted for by a minimum 20% soot by volume, in urban regions and 0.8, yielded by 1-5% soot by volume, in rural settings, it is found that these same values can be produced by similar amounts of the iron oxide magnetite. Magnetite is shown to be indistinguishable from soot by optical measurements performed on bulk samples, and calculation of various mixtures of soot indicate the difficulty of determining aerosol composition by optical scattering techniques.

  4. Visible-light emission at room temperature in Mn-doped Si light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Hai, Pham Nam; Maruo, Daiki; Anh, Le Duc; Tanaka, Masaaki

    2016-03-01

    We demonstrate Si-based light-emitting diodes that continuously emit reddish-yellow visible light at room temperature by utilizing optical transitions between the p-d hybrid orbitals of Mn atoms doped in Si. Our light-emitting diodes show clear visible-light electroluminescence with two peaks at E1=1.75 and E2=2.30 eV , corresponding to optical transitions between p-d hybrid orbitals of Mn atoms. The electrons at the p-d hybrid orbitals of Mn in Si are excited by hot holes that are accelerated by an intensive electric field in the depletion layer of reverse biased Si p -n junctions containing a Mn-doped Si (Si:Mn) layer. The observed two peaks at E1=1.75 and E2=2.30 eV are redshifted and blueshifted by 0.14 eV, respectively, from those of GaAs:Mn or ZnS:Mn. Our observations are consistent with the p -d hybridized electronic structure of Mn atoms doped in Si as predicted by first-principles calculations.

  5. Fluorescence enhancement in visible light: dielectric or noble metal?

    PubMed

    Sun, S; Wu, L; Bai, P; Png, C E

    2016-07-28

    A high permittivity dielectric gives the impression of outperforming plasmonic noble metal in visible light fluorescence enhancement primarily because of its small loss. Nonetheless, the performances of these two platforms in various situations remain obscure due to the different optical confinement mechanisms as well as the complexity in the fluorescence enhancement process. This study presents a comprehensive comparison between these two platforms based on nanoparticles (NPs) to evaluate their capability and applicability in fluorescence enhancement by taking into account the fluorescence excitation rate, the quantum yield, the fluorophore wavelengths and Stokes shifts as well as the far field intensity. In a low permittivity sensing medium (e.g. air), the dielectric NP can achieve comparable or higher fluorescence enhancement than the metal NP due to its decent NP-enhanced excitation rate and larger quantum yield. In a relatively high permittivity sensing medium (e.g. water), however, there is a significant decrement of the excitation rate of the dielectric NP as the permittivity contrast decreases, leading to a smaller fluorescence enhancement compared to the metallic counterpart. Combining the fluorescence enhancement and the far field intensity studies, we further conclude that for both dielectric and plasmonic NPs, the optimal situation occurs when the fluorescence excitation wavelength, the fluorescence emission wavelength and the electric-dipole-mode of the dielectric NP (or the plasmonic resonance of the metal NP) are the same and all fall in the low conductivity region of the NP material. We also find that the electric-dipole-mode of the dielectric NP performs better than the magnetic-dipole-mode for fluorescence enhancement applications because only the electric-dipole-mode can be strongly excited by the routinely used fluorescent dyes and quantum dots, which behave as electric dipoles by nature.

  6. Fluorescence enhancement in visible light: dielectric or noble metal?

    PubMed

    Sun, S; Wu, L; Bai, P; Png, C E

    2016-07-28

    A high permittivity dielectric gives the impression of outperforming plasmonic noble metal in visible light fluorescence enhancement primarily because of its small loss. Nonetheless, the performances of these two platforms in various situations remain obscure due to the different optical confinement mechanisms as well as the complexity in the fluorescence enhancement process. This study presents a comprehensive comparison between these two platforms based on nanoparticles (NPs) to evaluate their capability and applicability in fluorescence enhancement by taking into account the fluorescence excitation rate, the quantum yield, the fluorophore wavelengths and Stokes shifts as well as the far field intensity. In a low permittivity sensing medium (e.g. air), the dielectric NP can achieve comparable or higher fluorescence enhancement than the metal NP due to its decent NP-enhanced excitation rate and larger quantum yield. In a relatively high permittivity sensing medium (e.g. water), however, there is a significant decrement of the excitation rate of the dielectric NP as the permittivity contrast decreases, leading to a smaller fluorescence enhancement compared to the metallic counterpart. Combining the fluorescence enhancement and the far field intensity studies, we further conclude that for both dielectric and plasmonic NPs, the optimal situation occurs when the fluorescence excitation wavelength, the fluorescence emission wavelength and the electric-dipole-mode of the dielectric NP (or the plasmonic resonance of the metal NP) are the same and all fall in the low conductivity region of the NP material. We also find that the electric-dipole-mode of the dielectric NP performs better than the magnetic-dipole-mode for fluorescence enhancement applications because only the electric-dipole-mode can be strongly excited by the routinely used fluorescent dyes and quantum dots, which behave as electric dipoles by nature. PMID:27374052

  7. Optical closure study on light-absorbing aerosols

    NASA Astrophysics Data System (ADS)

    Petzold, Andreas; Bundke, Ulrich; Freedman, Andrew; Onasch, Timothy B.; Massoli, Paola; Andrews, Elizabeth; Hallar, Anna G.

    2014-05-01

    The in situ measurement of atmospheric aerosol optical properties is an important component of quantifying climate change. In particular, the in-situ measurement of the aerosol single-scattering albedo (SSA), which is the ratio of aerosol scattering to aerosol extinction, is identified as a key challenge in atmospheric sciences and climate change research. Ideally, the complete set of aerosol optical properties is measured through optical closure studies which simultaneous measure aerosol extinction, scattering and absorption coefficients. The recent development of new optical instruments have made real-time in situ optical closure studies attainable, however, many of these instruments are state-of-the-art but not practical for routine monitoring. In our studies we deployed a suit of well-established and recently developed instruments including the cavity attenuated phase shift (CAPS) method for aerosol light extinction, multi-angle absorption photometer (MAAP) and particle soot absorption photometer (PSAP) for aerosol light absorption, and an integrating nephelometer (NEPH) for aerosol light scattering measurements. From these directly measured optical properties we calculated light absorption from extinction minus scattering (difference method), light extinction from scattering plus absorption, and aerosol single-scattering albedo from combinations CAPS + MAAP, NEPH + PSAP, NEPH + MAAP, CAPS + NEPH. Closure studies were conducted for laboratory-generated aerosols composed of various mixtures of black carbon (Regal 400R pigment black, Cabot Corp.) and ammonium sulphate, urban aerosol (Billerica, MA), and background aerosol (Storm Peak Lab.). Key questions addressed in our closure studies are: (1) how well can we measure aerosol light absorption by various methods, and (2) how well can we measure the aerosol single-scattering albedo by various instrument combinations? In particular we investigated (3) whether the combination of a CAPS and NEPH provides a reasonable

  8. Effect of various visible light photoinitiators on the polymerization and color of light-activated resins.

    PubMed

    Arikawa, Hiroyuki; Takahashi, Hideo; Kanie, Takahito; Ban, Seiji

    2009-07-01

    The purpose of this study was to investigate effects of various visible light photoinitiators on the polymerization efficiency and color of the light-activated resins. Four photoinitiators, including camphorquinone, phenylpropanedione, monoacrylphosphine oxide (TPO), and bisacrylphosphine oxide (Ir819), were used. Each photoinitiator was dissolved in a Bis-GMA and TEGDMA monomer mixture. Materials were polymerized using dental quartz-tungsten halogen lamp (QTH), plasma-ark lamp and blue LED light-curing units, and a custom-made violet LED light unit. The degree of monomer conversion and CIE L*a*b* color values of the resins were measured using a FTIR and spectral transmittance meter. The degree of monomer conversions of TPO- and Ir819-containing resins polymerized with the violet-LED unit were higher than camphorquinone-containing resin polymerized with the QTH light-curing unit. The lowest color values were observed for the TPO-containing resin. Our results indicate that the TPO photoinitiator and the violet-LED light unit may provide a useful and improved photopolymerization system for dental light-activated resins. PMID:19721283

  9. Analysis of the sensitivity of absorbed light and incident light profile to various canopy architecture and stand conditions.

    PubMed

    Kim, Hyun-Seok; Palmroth, Sari; Thérézien, Mathieu; Stenberg, Pauline; Oren, Ram

    2011-01-01

    We analyzed the effect of simplifying assumptions in canopy representation of radiation transfer models, comparing modeled diffuse non-interceptance and photosynthetic photon flux density with measurements at different layers of complex pine-broadleaved canopy with large seasonal variation of leaf area index. The most detailed model included clumping of trees (i.e., stand density) and a vertical specification of leaf angle distribution and shoot clumping. A less detailed model replaced the vertically specified variables with their means. The most parsimonious model accounted for neither shoot clumping nor stand density. The vertical specification of shoot clumping and leaf angle distribution only slightly improved vertical and seasonal openness and light estimates over using mean values. Further simplification had little effect on total absorbed light but was more risky for estimates of the vertical distributions of openness and light absorbed by the canopy, which will affect photosynthesis estimates due to the non-linearity of photosynthetic light response. Including woody surfaces in winter, when leaf area was low, was essential for reproducing the measurements correctly. A sensitivity analysis showed that ignoring (i) shoot clumping could result in a substantial overestimation of total absorbed light with errors increasing with decreasing leaf area and (ii) stand density in sparse stands could lead to substantial overestimation of total absorbed light, and the effect is largely independent of leaf area. Also, (iii) the effect of changing leaf angle distribution increased with decreasing leaf area, and was larger and more persistent along the leaf area range with increasing shoot clumping. Overall, accounting for the effect of tree clumping on absorbed light is most important in stands composed of species where leaves are not very clumped (e.g., broadleaved). However, even in forests with highly clumped shoots (i.e., coniferous), an accurate estimation of

  10. Intimate Coupling of Photocatalysis and Biodegradation for Degrading Phenol Using Different Light Types: Visible Light vs UV Light.

    PubMed

    Zhou, Dandan; Xu, Zhengxue; Dong, Shanshan; Huo, Mingxin; Dong, Shuangshi; Tian, Xiadi; Cui, Bin; Xiong, Houfeng; Li, Tingting; Ma, Dongmei

    2015-07-01

    Intimate coupling of photocatalysis and biodegradation (ICPB) technology is attractive for phenolic wastewater treatment, but has only been investigated using UV light (called UPCB). We examined the intimate coupling of visible-light-induced photocatalysis and biodegradation (VPCB) for the first time. Our catalyst was prepared doping both of Er(3+) and YAlO3 into TiO2 which were supported on macroporous carriers. The macroporous carriers was used to support for the biofilms as well. 99.8% removal efficiency of phenol was achieved in the VPCB, and this was 32.6% higher than that in the UPCB. Mineralization capability of UPCB was even worse, due to less adsorbable intermediates and cell lysis induced soluble microbial products release. The lower phenol degradation in the UPCB was due to the serious detachment of the biofilms, and then the microbes responsible for phenol degradation were insufficient due to disinfection by UV irradiation. In contrast, microbial communities in the carriers were well protected under visible light irradiation and extracellular polymeric substances secretion was enhanced. Thus, we found that the photocatalytic reaction and biodegradation were intimately coupled in the VPCB, resulting in 64.0% removal of dissolved organic carbon. Therefore, we found visible light has some advantages over UV light in the ICPB technology.

  11. Mobile-phone based visible light communication using region-grow light source tracking for unstable light source.

    PubMed

    Liang, Kevin; Chow, Chi-Wai; Liu, Yang

    2016-07-25

    In order to increase the data rate of the camera-based visible light communication (VLC) system, using rolling shutter effect has been demonstrated successfully, in which the pixel rows of the complementary-metal-oxide-semiconductor (CMOS) image sensor are activated sequentially. Previous camera-based VLCs focused on using a stable LED light source, and its illumination area is positioned at the center of an image frame. In this work, we investigate the performance of a camera-based VLC with light source at different parts of an image frame. We propose and demonstrate using region-grow algorithm to track the light source. We also evaluate and discuss different scenarios when the light source is moved. Besides, a recorded > 5 kbit/s net data rate can be achieved by using only a single phosphor-based white-light LED source. Here, we demonstrate that 4.502 pixel/bit can be achieved.

  12. Theoretical model of homogeneous metal-insulator-metal perfect multi-band absorbers for the visible spectrum

    NASA Astrophysics Data System (ADS)

    Kajtár, G.; Kafesaki, M.; Economou, E. N.; Soukoulis, C. M.

    2016-02-01

    We present a rigorous study of the perfect absorption properties of metal-insulator-metal (MIM) structures in the visible spectrum. We provide a derivation (based on the transfer matrix method) and analysis of the conditions for which the perfect absorption occurs. We show that these conditions are fulfilled when the incident wave excites the eigenmodes of the structure. The quantitative analysis allows us to design specific perfect absorbers for our needs. The analytical model is verified by rigorous simulations based on rigorous coupled wave analysis, which demonstrate also the angle and polarization insensitivity of the absorption properties of such a structure. Employing the MIM approach and results, we also investigate and demonstrate multiple perfect absorption bands and broad-band absorption in properly designed multilayer metal-insulator systems.

  13. Broadband visible light source based on AllnGaN light emitting diodes

    DOEpatents

    Crawford, Mary H.; Nelson, Jeffrey S.

    2003-12-16

    A visible light source device is described based on a light emitting diode and a nanocluster-based film. The light emitting diode utilizes a semiconductor quantum well structure between n-type and p-type semiconductor materials on the top surface a substrate such as sapphire. The nanocluster-based film is deposited on the bottom surface of the substrate and can be derived from a solution of MoS.sub.2, MoSe.sub.2, WS.sub.2, and WSe.sub.2 particles of size greater than approximately 2 nm in diameter and less than approximately 15 nm in diameter, having an absorption wavelength greater than approximately 300 nm and less than approximately 650 nm.

  14. Hydroxyapatite supported Ag3PO4 nanoparticles with higher visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Hong, Xiaoting; Wu, Xiaohui; Zhang, Qiuyun; Xiao, Mingfeng; Yang, Gelin; Qiu, Meirong; Han, Guocheng

    2012-03-01

    Hydroxyapatite supported Ag3PO4 nanocomposites have been synthesized by a wet impregnation process. UV-vis absorption spectra show a red shift of the absorption edges for the composite systems compared to pure hydroxyapatite support. The surface structure and morphology of the nanocomposites were characterized by Brunauer-Emmett-Teller (BET) apparatus, X-ray diffraction (XRD), transmission electron microscopy (TEM). The results suggest that Ag3PO4 nanoparticles (6-17 nm in diameter) are well dispersed on the hydroxyapatite support and Ag3PO4 nanoparticles density is larger for the higher Ag+ loading sample. The as-prepared nanocomposite photocatalysts showed a pronounced photocatalytic activity upon decomposition of methylene blue dye in aqueous solution under both visible light (wavelength > 400 nm) and UV-vis light irradiation. A synergic mechanism of inherent photocatalytic capability of Ag3PO4 and the accelerated electron/hole separation resulting from the photoinduced electrons captured by the slow-released Ag+ at the interface of Ag3PO4 and hydroxyapatite is proposed for the nanocomposites on the enhancement of photocatalytic performance in comparison to that of pure Ag3PO4 nanoparticles. The support of hydroxyapatite may also act as an absorbent which favors the mass transfer in heterogeneous photocatalysis reaction.

  15. Enhancing Localized Evaporation through Separated Light Absorbing Centers and Scattering Centers

    PubMed Central

    Zhao, Dengwu; Duan, Haoze; Yu, Shengtao; Zhang, Yao; He, Jiaqing; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

    2015-01-01

    This report investigates the enhancement of localized evaporation via separated light absorbing particles (plasmonic absorbers) and scattering particles (polystyrene nanoparticles). Evaporation has been considered as one of the most important phase-change processes in modern industries. To improve the efficiency of evaporation, one of the most feasible methods is to localize heat at the top water layer rather than heating the bulk water. In this work, the mixture of purely light absorptive plasmonic nanostructures such as gold nanoparticles and purely scattering particles (polystyrene nanoparticles) are employed to confine the incident light at the top of the solution and convert light to heat. Different concentrations of both the light absorbing centers and the light scattering centers were evaluated and the evaporation performance can be largely enhanced with the balance between absorbing centers and scattering centers. The findings in this study not only provide a new way to improve evaporation efficiency in plasmonic particle-based solution, but also shed lights on the design of new solar-driven localized evaporation systems. PMID:26606898

  16. Enhancing Localized Evaporation through Separated Light Absorbing Centers and Scattering Centers.

    PubMed

    Zhao, Dengwu; Duan, Haoze; Yu, Shengtao; Zhang, Yao; He, Jiaqing; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

    2015-11-26

    This report investigates the enhancement of localized evaporation via separated light absorbing particles (plasmonic absorbers) and scattering particles (polystyrene nanoparticles). Evaporation has been considered as one of the most important phase-change processes in modern industries. To improve the efficiency of evaporation, one of the most feasible methods is to localize heat at the top water layer rather than heating the bulk water. In this work, the mixture of purely light absorptive plasmonic nanostructures such as gold nanoparticles and purely scattering particles (polystyrene nanoparticles) are employed to confine the incident light at the top of the solution and convert light to heat. Different concentrations of both the light absorbing centers and the light scattering centers were evaluated and the evaporation performance can be largely enhanced with the balance between absorbing centers and scattering centers. The findings in this study not only provide a new way to improve evaporation efficiency in plasmonic particle-based solution, but also shed lights on the design of new solar-driven localized evaporation systems.

  17. Effect of light units on tooth bleaching with visible-light activating titanium dioxide photocatalyst.

    PubMed

    Kishi, Ayaka; Otsuki, Masayuki; Sadr, Alireza; Ikeda, Masaomi; Tagami, Junji

    2011-01-01

    This study evaluated the influence of different light sources on the efficiency of an office bleaching agent containing visible-light activating titanium dioxide photocatalyst (VL-TiO(2)) using an artificial discoloration tooth model. Extracted bovine teeth were stained by black tea. The CIE L*a*b* values were measured before and after nine consecutive treatments by the VL-TiO(2)-containing bleaching agent (TiON in Office, GC, Tokyo, Japan). A halogen light unit (CB; CoBee, GC) or an LED unit (G-light, GC) with two modes (blue and violet: GL-BV, blue: GL-B) were used to activate the bleaching agent in three groups (n=8). Brightness (ΔL) and color difference (ΔE) increased as bleaching repeated in all groups. Two-way ANOVA showed that both number of treatments and light sources significantly affected ΔE (p<0.05). GL-BV showed better bleaching effect than GL-B. In measurement of irradiation spectra, CB showed a wide spectrum (380-530 nm), GL-B had a sharp peak at 470 nm and GL-BV showed an additional peak at 405 nm. It was concluded that the light source influenced the efficiency of the tooth bleaching with VL-TiO(2). PMID:21946494

  18. Penning plasma based simultaneous light emission source of visible and VUV lights

    NASA Astrophysics Data System (ADS)

    Vyas, G. L.; Prakash, R.; Pal, U. N.; Manchanda, R.; Halder, N.

    2016-06-01

    In this paper, a laboratory-based penning plasma discharge source is reported which has been developed in two anode configurations and is able to produce visible and VUV lights simultaneously. The developed source has simultaneous diagnostics facility using Langmuir probe and optical emission spectroscopy. The two anode configurations, namely, double ring and rectangular configurations, have been studied and compared for optimum use of the geometry for efficient light emissions and recording. The plasma is produced using helium gas and admixture of three noble gases including helium, neon, and argon. The source is capable to produce eight spectral lines for pure helium in the VUV range from 20 to 60 nm and total 24 spectral lines covering the wavelength range 20-106 nm for the admixture of gases. The large range of VUV lines is generated from gaseous admixture rather from the sputtered materials. The recorded spectrum shows that the plasma light radiations in both visible and VUV range are larger in double ring configuration than that of the rectangular configurations at the same discharge operating conditions. To clearly understand the difference, the imaging of the discharge using ICCD camera and particle-in-cell simulation using VORPAL have also been carried out. The effect of ion diffusion, metastable collision with the anode wall and the nonlinear effects are correlated to explain the results.

  19. Isotope effects in photo dissociation of ozone with visible light

    NASA Astrophysics Data System (ADS)

    Früchtl, Marion; Janssen, Christof; Röckmann, Thomas

    2014-05-01

    Ozone (O3) plays a key role for many chemical oxidation processes in the Earth's atmosphere. In these chemical reactions, ozone can transfer oxygen to other trace gases. This is particularly interesting, since O3 has a very peculiar isotope composition. Following the mass dependent fractionation equation δ17O = 0.52 * δ18O, most fractionation processes depend directly on mass. However, O3 shows an offset to the mass dependent fractionation line. Processes, which show such anomalies, are termed mass independent fractionations (MIF). A very well studied example for a chemical reaction that leads to mass independent fractionation is the O3 formation reaction. To what degree O3 destruction reactions need to be considered in order to understand the isotope composition of atmospheric O3 is still not fully understood and an open question within scientific community. We set up new experiments to investigate the isotope effect resulting from photo dissociation of O3 in the Chappuis band (R1). Initial O3 is produced by an electric discharge. After photolysis O3 is collected in a cold trap at the triple point temperature of nitrogen (63K). O3 is then converted to O2 in order to measure the oxygen isotopes of O3 using isotope ratio mass spectrometry. To isolate O3 photo dissociation (R1) from O3 decomposition (R2) and secondary O3 formation (R3), we use varying amounts of carbon monoxide (CO) as O atom quencher (R4). In this way we suppress the O + O3 reaction (R3) and determine the isotope fractionation in R1 and R2 separately. We present first results on the isotope effects in O3 photo dissociation with visible light in the presence of different bath gases. Results are interpreted based on chemical kinetics modeling. (R1) O3 + hυ → O (3P) + O2 (R2) O3 + O (3P) → 2 O2 (R3) O + O2 + M → O3 + M (R4) O (3P) + CO + M → CO2 + M

  20. Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts

    NASA Astrophysics Data System (ADS)

    Qu, Dan; Zheng, Min; Du, Peng; Zhou, Yue; Zhang, Ligong; Li, Di; Tan, Huaqiao; Zhao, Zhao; Xie, Zhigang; Sun, Zaicheng

    2013-11-01

    A facile hydrothermal synthesis route to N and S, N co-doped graphene quantum dots (GQDs) was developed by using citric acid as the C source and urea or thiourea as N and S sources. Both N and S, N doped GQDs showed high quantum yield (78% and 71%), excitation independent under excitation of 340-400 nm and single exponential decay under UV excitation. A broad absorption band in the visible region appeared in S, N co-doped GQDs due to doping with sulfur, which alters the surface state of GQDs. However, S, N co-doped GQDs show different color emission under excitation of 420-520 nm due to their absorption in the visible region. The excellent photocatalytic performance of the S, N co-doped GQD/TiO2 composites was demonstrated by degradation of rhodamine B under visible light. The apparent rate of S, N:GQD/TiO2 is 3 and 10 times higher than that of N:GQD/TiO2 and P25 TiO2 under visible light irradiation, respectively.A facile hydrothermal synthesis route to N and S, N co-doped graphene quantum dots (GQDs) was developed by using citric acid as the C source and urea or thiourea as N and S sources. Both N and S, N doped GQDs showed high quantum yield (78% and 71%), excitation independent under excitation of 340-400 nm and single exponential decay under UV excitation. A broad absorption band in the visible region appeared in S, N co-doped GQDs due to doping with sulfur, which alters the surface state of GQDs. However, S, N co-doped GQDs show different color emission under excitation of 420-520 nm due to their absorption in the visible region. The excellent photocatalytic performance of the S, N co-doped GQD/TiO2 composites was demonstrated by degradation of rhodamine B under visible light. The apparent rate of S, N:GQD/TiO2 is 3 and 10 times higher than that of N:GQD/TiO2 and P25 TiO2 under visible light irradiation, respectively. Electronic supplementary information (ESI) available: More XPS and UV-Vis spectra. See DOI: 10.1039/c3nr04402e

  1. Damaging effects of visible light. Comprehensive progress report

    SciTech Connect

    1981-01-01

    Research progress is reported on studies of retinal light damage. A myriad of variables effect the production of light damage. These include age, prior light history, body temperature, vitamin A status, intensity, wavelength and duration of light. The intensity-duration function and the age function have been studied in detail in rats. Studies have been begun on the wavelength variable. (ACR)

  2. 33 CFR 83.22 - Visibility of lights (Rule 22).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...; (4) A towing light, 3 miles; (5) A white, red, green or yellow all-round light, 3 miles; and (6) A... sidelight, 2 miles; (3) A sternlight, 2 miles; (4) A towing light, 2 miles; (5) A white, red, green or... sidelight, 1 mile; (3) A sternlight, 2 miles; (4) A towing light, 2 miles; (5) A white, red, green or...

  3. 33 CFR 83.22 - Visibility of lights (Rule 22).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...; (4) A towing light, 3 miles; (5) A white, red, green or yellow all-round light, 3 miles; and (6) A... sidelight, 2 miles; (3) A sternlight, 2 miles; (4) A towing light, 2 miles; (5) A white, red, green or... sidelight, 1 mile; (3) A sternlight, 2 miles; (4) A towing light, 2 miles; (5) A white, red, green or...

  4. Lidar remote sensing of laser-induced incandescence on light absorbing particles in the atmosphere.

    PubMed

    Miffre, Alain; Anselmo, Christophe; Geffroy, Sylvain; Fréjafon, Emeric; Rairoux, Patrick

    2015-02-01

    Carbon aerosol is now recognized as a major uncertainty on climate change and public health, and specific instruments are required to address the time and space evolution of this aerosol, which efficiently absorbs light. In this paper, we report an experiment, based on coupling lidar remote sensing with Laser-Induced-Incandescence (LII), which allows, in agreement with Planck's law, to retrieve the vertical profile of very low thermal radiation emitted by light-absorbing particles in an urban atmosphere over several hundred meters altitude. Accordingly, we set the LII-lidar formalism and equation and addressed the main features of LII-lidar in the atmosphere by numerically simulating the LII-lidar signal. We believe atmospheric LII-lidar to be a promising tool for radiative transfer, especially when combined with elastic backscattering lidar, as it may then allow a remote partitioning between strong/less light absorbing carbon aerosols.

  5. Harnessing and storing visible light using a heterojunction of WO3 and CdS for sunlight-free catalysis.

    PubMed

    Kim, Seonghun; Park, Yiseul; Kim, Wooyul; Park, Hyunwoong

    2016-08-01

    CdS and WO3 (CdS/WO3) bilayer film electrodes are fabricated to harness solar visible light (λ > 420 nm) and store photogenerated electrons for possible use during periods of unavailable sunlight. The overall film thickness is approximately 50-60 μm, while the CdS underlayer is slightly thinner than WO3 owing to a packing effect. The energetics of CdS and WO3 determined by optical and electrochemical analyses enables cascaded electron transfer from CdS to WO3. The open circuit potential (EOCP) of CdS/WO3 under visible light (approximately -0.35 V vs. SCE) is nearly maintained even in the absence of light, with a marginal decrease (∼0.15 V) in ∼20 h of darkness. Neither CdS nor WO3 alone exhibits such behavior. The electron lifetimes (τ) of CdS and WO3 are each less than 100 s, whereas coupling of the two increases τ to ∼2500 s at the EOCP. In the absence of dissolved O2, τ further increases, suggesting that O2 is the primary electron acceptor. In spite of oxic conditions, CdS/WO3 is capable of continuously reducing Cr(6+) to Cr(3+) and Ag(+) to Ag(0) after removal of visible light. The number of utilized (i.e., stored) electrons in the reductions of Cr(6+) and Ag(+) are estimated to be ∼1.08 × 10(17) and ∼0.87 × 10(17), respectively. The primary role of CdS is to be a visible-light absorber in the 420-565 nm wavelength range, transferring the photogenerated electrons to WO3. The electrons stored in WO3 are gradually released to electron acceptors with suitable redox potentials. PMID:27411566

  6. Ag/AgBr/TiO2 visible light photocatalyst for destruction of azodyes and bacteria.

    PubMed

    Hu, Chun; Lan, Yongqing; Qu, Jiuhui; Hu, Xuexiang; Wang, Aimin

    2006-03-01

    Ag/AgBr/TiO2 was prepared by the deposition-precipitation method and was found to be a novel visible light driven photocatalyst. The catalyst showed high efficiency for the degradation of nonbiodegradable azodyes and the killing of Escherichia coli under visible light irradiation (lambda>420 nm). The catalyst activity was maintained effectively after successive cyclic experiments under UV or visible light irradiation without the destruction of AgBr. On the basis of the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, and Auger electron spectroscopy, the surface Ag species mainly exist as Ag0 in the structure of all samples before and after reaction, and Ag0 species scavenged hVB+ and then trapped eCB- in the process of photocatalytic reaction, inhibiting the decomposition of AgBr. The studies of ESR and H2O2 formation revealed that *OH and O2*- were formed in visible light irradiated aqueous Ag/AgBr/TiO2 suspension, while there was no reactive oxygen species in the visible light irradiated Ag0/TiO2 system. The results indicate that AgBr is the main photoactive species for the destruction of azodyes and bacteria under visible light. In addition, the bactericidal efficiency and killing mechanism of Ag/AgBr/TiO2 under visible light irradiation are illustrated and discussed. PMID:16509698

  7. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Nam Hai, Pham; Maruo, Daiki; Tanaka, Masaaki

    2014-03-01

    We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4A2(4F) → 4T1(4G) and 4T1(4G) → 6A1(6S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs.

  8. Supercritical-assistant liquid crystal template approach to synthesize mesoporous titania/multiwalled carbon nanotube composites with high visible-light driven photocatalytic performance

    SciTech Connect

    Liu, Chen; Li, Youji Xu, Peng; Li, Ming; Huo, Pingxiang

    2014-12-15

    Graphical abstract: We investigate the influence of mesoporous titania content upon the visible-light driven photocatalytic performance of MPT/MWCNTs in phenol degradation. - Highlights: • MPT/MWCNTs were fabricated by liquid-crystal template in supercritical CO{sub 2}. • MPT/MWCNTs show high visible-light driven photoactivity for phenol degradation. • MPT/MWCNTs also show high reusable photoactivity under visible irradiation. • MPT content can control visible-light driven photoactivity of MPT/MWCNTs. • MPT is not easily broken away from from MPT/MWCNT composites. - Abstract: Mesoporous titania (MPT) was deposited onto multiwalled carbon nanotubes (MWCNTs) by deposition of titanium sol containing liquid-crystal template with assistant of supercritical CO{sub 2}. The products were characterized with various analytical techniques to determine their structural, morphological, optical absorption and photocatalytic properties. The results indicate that in photocatalytic degradation of phenol under visible light, the mixtures or composites of MPT and MWCNT show the high efficiency because of synergies between absorbing visible light, releasing electrons and facilitating transfer of charge carriers of MWCNTs and providing activated centers of MPT. Because of the mutual constraint between MPT and MWCNTs on the photocatalytic efficiency, the optimal loading of MPT in MPT/MWCNT-3 for phenol degradation is 48%. Because the intimate contact between MWCNTs and MPT is more beneficial to electron transformation, photoactivity of mixture is lower than that of composites with high reusable performance. The optimum conditions of phenol degradation were obtained.

  9. Melanin photosensitization and the effect of visible light on epithelial cells.

    PubMed

    Chiarelli-Neto, Orlando; Ferreira, Alan Silva; Martins, Waleska Kerllen; Pavani, Christiane; Severino, Divinomar; Faião-Flores, Fernanda; Maria-Engler, Silvya Stuchi; Aliprandini, Eduardo; Martinez, Glaucia R; Di Mascio, Paolo; Medeiros, Marisa H G; Baptista, Maurício S

    2014-01-01

    Protecting human skin from sun exposure is a complex issue that involves unclear aspects of the interaction between light and tissue. A persistent misconception is that visible light is safe for the skin, although several lines of evidence suggest otherwise. Here, we show that visible light can damage melanocytes through melanin photosensitization and singlet oxygen (1O2) generation, thus decreasing cell viability, increasing membrane permeability, and causing both DNA photo-oxidation and necro-apoptotic cell death. UVA (355 nm) and visible (532 nm) light photosensitize 1O2 with similar yields, and pheomelanin is more efficient than eumelanin at generating 1O2 and resisting photobleaching. Although melanin can protect against the cellular damage induced by UVB, exposure to visible light leads to pre-mutagenic DNA lesions (i.e., Fpg- and Endo III-sensitive modifications); these DNA lesions may be mutagenic and may cause photoaging, as well as other health problems, such as skin cancer.

  10. Nanostructure sensitization of transition metal oxides for visible-light photocatalysis

    PubMed Central

    Chen, Hongjun

    2014-01-01

    Summary To better utilize the sunlight for efficient solar energy conversion, the research on visible-light active photocatalysts has recently attracted a lot of interest. The photosensitization of transition metal oxides is a promising approach for achieving effective visible-light photocatalysis. This review article primarily discusses the recent progress in the realm of a variety of nanostructured photosensitizers such as quantum dots, plasmonic metal nanostructures, and carbon nanostructures for coupling with wide-bandgap transition metal oxides to design better visible-light active photocatalysts. The underlying mechanisms of the composite photocatalysts, e.g., the light-induced charge separation and the subsequent visible-light photocatalytic reaction processes in environmental remediation and solar fuel generation fields, are also introduced. A brief outlook on the nanostructure photosensitization is also given. PMID:24991507

  11. Melanin Photosensitization and the Effect of Visible Light on Epithelial Cells

    PubMed Central

    Chiarelli-Neto, Orlando; Ferreira, Alan Silva; Martins, Waleska Kerllen; Pavani, Christiane; Severino, Divinomar; Faião-Flores, Fernanda; Maria-Engler, Silvya Stuchi; Aliprandini, Eduardo; Martinez, Glaucia R.; Di Mascio, Paolo; Medeiros, Marisa H. G.; Baptista, Maurício S.

    2014-01-01

    Protecting human skin from sun exposure is a complex issue that involves unclear aspects of the interaction between light and tissue. A persistent misconception is that visible light is safe for the skin, although several lines of evidence suggest otherwise. Here, we show that visible light can damage melanocytes through melanin photosensitization and singlet oxygen (1O2) generation, thus decreasing cell viability, increasing membrane permeability, and causing both DNA photo-oxidation and necro-apoptotic cell death. UVA (355 nm) and visible (532 nm) light photosensitize 1O2 with similar yields, and pheomelanin is more efficient than eumelanin at generating 1O2 and resisting photobleaching. Although melanin can protect against the cellular damage induced by UVB, exposure to visible light leads to pre-mutagenic DNA lesions (i.e., Fpg- and Endo III-sensitive modifications); these DNA lesions may be mutagenic and may cause photoaging, as well as other health problems, such as skin cancer. PMID:25405352

  12. Reduction of aryl halides by consecutive visible light-induced electron transfer processes.

    PubMed

    Ghosh, Indrajit; Ghosh, Tamal; Bardagi, Javier I; König, Burkhard

    2014-11-01

    Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis.

  13. Medical devices; labeling for menstrual tampons; ranges of absorbency, change from "junior" to "light." Final rule.

    PubMed

    2004-08-25

    The Food and Drug Administration (FDA) is issuing a final rule that amends its menstrual tampon labeling regulation to change the current term for tampons that absorb 6 grams (g) and under of fluid. A tampon with absorbency of 6 g or less is currently required to be labeled as "junior". FDA is changing the term "junior" to "light". The term "junior" implies that the tampon is only for younger or teenage women when, in fact, it may be appropriate for women of any age with light menstrual flow. FDA encourages women to use the lowest absorbency tampon appropriate for their flow to help minimize the risk of Toxic Shock Syndrome (TSS). At present, FDA requires standardized terms to be used for the labeling of a menstrual tampon to indicate its particular absorbency. This rule enables women to compare the absorbency of one brand and style of tampons with the absorbency of other brands and styles. FDA is issuing this final rule under the Federal Food, Drug, and Cosmetic Act (the act) to ensure that labeling of menstrual tampons is not misleading.

  14. A visible-light harvesting system for CO2 reduction using a Ru(II) -Re(I) photocatalyst adsorbed in mesoporous organosilica.

    PubMed

    Ueda, Yutaro; Takeda, Hiroyuki; Yui, Tatsuto; Koike, Kazuhide; Goto, Yasutomo; Inagaki, Shinji; Ishitani, Osamu

    2015-02-01

    A photocatalytic system for CO2 reduction exhibiting visible-light harvesting was developed by preparing a hybrid consisting of a supramolecular metal complex as photocatalyst and periodic mesoporous organosilica (PMO) as light harvester. A Ru(II) Re(I) binuclear complex (RuRe) with methylphosphonic acid anchor groups was adsorbed on acridone or methylacridone embedded in the walls of PMO mesochannels to yield the hybrid structure. The embedded organic groups absorbed visible light, and the excitation energy was funneled to the Ru units. The energy accumulation was followed by electron transfer and catalytic reduction of CO2 to CO on the Re unit. The light harvesting of these hybrids enhanced the photocatalytic CO evolution rate by a factor of up to ten compared with that of RuRe adsorbed on mesoporous silica without a light harvester. PMID:25524162

  15. Transition metal-modified zinc oxides for UV and visible light photocatalysis.

    PubMed

    Bloh, J Z; Dillert, R; Bahnemann, D W

    2012-11-01

    In order to use photocatalysis with solar light, finding more active and especially visible light active photocatalysts is a very important challenge. Also, studies of these photocatalysts should employ a standardized test procedure so that their results can be accurately compared and evaluated with one another. A systematic study of transition metal-modified zinc oxide was conducted to determine whether they are suitable as visible light photocatalysts. The photocatalytic activity of ZnO modified with eight different transition metals (Cu, Co, Fe, Mn, Ni, Ru, Ti, Zr) in three different concentrations (0.01, 0.1, and 1 at.%) was investigated under irradiation with UV as well as with visible light. The employed activity test is the gas-phase degradation of acetaldehyde as described by the ISO standard 22197-2. The results suggest that the UV activity can be improved with almost any modification element and that there exists an optimal modification ratio at about 0.1 at.%. Additionally, Mn- and Ru-modified ZnO display visible light activity. Especially the Ru-modified ZnO is highly active and surpasses the visible light activity of all studied titania standards. These findings suggest that modified zinc oxides may be a viable alternative to titanium dioxide-based catalysts for visible light photocatalysis. Eventually, possible underlying mechanisms are proposed and discussed.

  16. Enhanced visible light photocatalytic property of red phosphorus via surface roughening

    SciTech Connect

    Li, Weibing; Yue, Jiguang; Hua, Fangxia; Feng, Chang; Bu, Yuyu; Chen, Zhuoyuan

    2015-10-15

    Highlights: • Photocatalytic RhB degradation of red phosphorus was studied for the first time. • Surface rough can increase the photocatalysis reaction active sites. • Surface rough red phosphorus possesses high photocatalytic performance. • Surface rough red phosphorus has high industrial application value. - Abstract: Red phosphorus with rough surface (SRP) was prepared by catalyst-assisted hydrothermal synthesis using Co{sup 2+} catalyst. The photocatalytic Rhodamine B (RhB) degradation of red phosphorus (RP) and SRP was studied for the first time in this work. Rough surface can enhance the dye adsorption ability of RP. About 75% RhB was absorbed by SRP after 30-min adsorption in 100 ml RhB solution with concentration of 10 mg l{sup −1} in dark. After only 10 min of illumination by visible light, more than 95% RhB was degraded, indicating that SRP has a great application potential in the area of photocatalysis. The photocatalytic RhB degradation properties of RP are much weaker than those of SRP. The increase of the number of the active sites for the photocatalytic reactions, the electron mobility and the lifetime of the photogenerated electrons cause the significant improvement of the photocatalytic performance of SRP based on the experimental results obtained.

  17. Exploring Light’s Interactions with Bubbles and Light Absorbers in Photoelectrochemical Devices using Ray Tracing

    SciTech Connect

    Stevens, John Colby

    2012-12-01

    Ray tracing was used to perform optical optimization of arrays of photovoltaic microrods and explore the interaction between light and bubbles of oxygen gas on the surface of the microrods. The incident angle of light was varied over a wide range. The percent of incident light absorbed by the microrods and reflected by the bubbles was computed over this range. It was found that, for the 10 μm diameter, 100 μm tall SrTiO3 microrods simulated in the model, the optimal center-­to-­center spacing was 14 μm for a square grid. This geometry produced 75% average and 90% maximum absorbance. For a triangular grid using the same microrods, the optimal center-­to-­center spacing was 14 μm. This geometry produced 67% average and 85% maximum absorbance. For a randomly laid out grid of 5 μm diameter, 100 μm tall SrTiO3 microrods with an average center-­to-­center spacing of 20 μm, the average absorption was 23% and the maximum absorption was 43%. For a 50% areal coverage fraction of bubbles on the absorber surface, between 2%-­20% of the incident light energy was reflected away from the rods by the bubbles, depending upon incident angle and bubble morphology.

  18. Ultraviolet light absorbers having two different chromophors in the same molecule

    DOEpatents

    Vogl, Otto; Li, Shanjun

    1988-05-17

    Ultraviolet light absorbing compounds having two different chromophors in the same molecule, particularly the benzotriazole chromophor and either the dihydroxybenzophenone or dihydroxyacetophenone chromophor; specifically, the two compounds 3,5-[di(2H-benzotriazole-2-yl)]-2,4-dihydroxyacetophenone and 3,5-[di(2H-benzotriazole-2-yl)]2,4-dihydroxybenzophenone.

  19. Photooxidative damage to mammalian cells and proteins by visible light

    SciTech Connect

    Packer, L.; Kellogg, E.W. III

    1980-01-01

    In the present article, studies carried out in our laboratory on the effects of visible irradiation and O/sub 2/ in a variety of target systems ranging from cultured mammalian cells to purified catalase are reviewed. We will relate these studies of photooxidative damage to a scheme for the propagation of intracellular damage which traces a number of the possible pro-oxidant and anti-oxidant pathways found in the cell.

  20. Sustainable Strategy Utilizing Biomass: Visible-Light-Mediated Synthesis of γ-Valerolactone

    EPA Science Inventory

    A novel sustainable approach to valued γ-valerolactone is described that exploits visible light mediated conversion of biomass-derived levulinic acid using a bimetallic catalyst on graphitic carbon nitride, AgPd@g-C3N4.

  1. Phase-dependent photocatalytic H2 evolution of copper zinc tin sulfide under visible light.

    PubMed

    Chang, Zhi-Xian; Zhou, Wen-Hui; Kou, Dong-Xing; Zhou, Zheng-Ji; Wu, Si-Xin

    2014-10-28

    CZTS exhibited apparently phase-dependent photocatalytic H2 evolution under visible light. Possible factors for the phase-dependent photocatalytic activity of CZTS were discussed in detail. PMID:25205452

  2. TiO{sub 2}-coated carbon nanotubes: A redshift enhanced photocatalysis at visible light

    SciTech Connect

    Lu, S.-Y.; Tang, C.-W.; Lin, Y.-H.; Kuo, H.-F.; Lai, Y.-C.; Ouyang Hao; Hsu, W.-K.; Tsai, M.-Y.

    2010-06-07

    Annealing of carbon nanotubes coated with thin and uniform TiO{sub 2} results in carbon diffusion into oxygen lattices and doping induced redshift is evident by an efficient photocatalysis at visible light. The underlying mechanism is discussed.

  3. Evaluation techniques for x-ray mirrors and systems using visible light

    SciTech Connect

    Takacs, P.Z.; Colbert, J.

    1985-09-01

    Severely diffraction-broadened visible light images from grazing incidence optical systems are measured and analyzed using a diffraction integral model to predict slope errors and image quality at XUV wavelengths.

  4. Visible Light and pH Responsive Polymer-Coated Mesoporous Silica Nanohybrids for Controlled Release.

    PubMed

    Wang, Guojie; Dong, Jie; Yuan, Tingting; Zhang, Juchen; Wang, Lei; Wang, Hao

    2016-07-01

    A visible light and pH responsive anticancer drug delivery system based on polymer-coated mesoporous silica nanoparticles (MSNs) has been developed. Perylene-functionalized poly(dimethylaminoethyl methacrylates) sensitive to visible light and pH are electrostatically attached on the surface of MSNs to seal the nanopores. Stimulation of visible light and acid can unseal the nanopores to induce controlled drug release from the MSNs. More interestingly, the release can be enhanced under the combined stimulation of the dual-stimuli. The synergistic effect of visible light and acid stimulation on the efficient release of anticancer drugs from the nanohybrids endows the system with great potential for cancer therapy. PMID:26938147

  5. Microcrystalline sodium tungsten bronze nanowire bundles as efficient visible light-responsive photocatalysts.

    PubMed

    Wang, Lei; Zhan, Jinhua; Fan, Weiliu; Cui, Guanwei; Sun, Honggang; Zhuo, Linhai; Zhao, Xian; Tang, Bo

    2010-12-14

    Microcrystalline sodium tungsten bronze nanowire bundles were obtained via a facile hydrothermal synthesis, and were applied in water purification as visible-light-driven photocatalysts for the first time.

  6. Self-Assembled PDINH Supramolecular System for Photocatalysis under Visible Light.

    PubMed

    Liu, Di; Wang, Jun; Bai, Xiaojuan; Zong, Ruilong; Zhu, Yongfa

    2016-09-01

    A self-assembled perylene-3,4,9,10-tetracarboxylic diimide(PDINH) supramolecular system consisting of all-organic PDINH molecule building blocks through non-covalent interactions works as a visible light photocatalyst with high activity.

  7. Visible light photoreduction of CO.sub.2 using heterostructured catalysts

    DOEpatents

    Matranga, Christopher; Thompson, Robert L; Wang, Congjun

    2015-03-24

    The method provides for use of sensitized photocatalyst for the photocatalytic reduction of CO.sub.2 under visible light illumination. The photosensitized catalyst is comprised of a wide band gap semiconductor material, a transition metal co-catalyst, and a semiconductor sensitizer. The semiconductor sensitizer is photoexcited by visible light and forms a Type II band alignment with the wide band gap semiconductor material. The wide band gap semiconductor material and the semiconductor sensitizer may be a plurality of particles, and the particle diameters may be selected to accomplish desired band widths and optimize charge injection under visible light illumination by utilizing quantum size effects. In a particular embodiment, CO.sub.2 is reduced under visible light illumination using a CdSe/Pt/TiO2 sensitized photocatalyst with H.sub.2O as a hydrogen source.

  8. Photo-oxidation of polymer-like amorphous hydrogenated carbon under visible light illumination

    SciTech Connect

    Baxamusa, Salmaan; Laurence, Ted; Worthington, Matthew; Ehrmann, Paul

    2015-11-10

    Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been understood to exhibit optical absorption of visible light (λ > 400 nm). In this report we explain that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination.

  9. Scalable Synthesis of Piperazines Enabled by Visible-Light Irradiation and Aluminum Organometallics

    PubMed Central

    Suárez-Pantiga, Samuel; Colas, Kilian; Johansson, Magnus J; Mendoza, Abraham

    2015-01-01

    The development of more active C–H oxidation catalysts has inspired a rapid, scalable, and stereoselective assembly of multifunctional piperazines through a [3+3] coupling of azomethine ylides. A combination of visible-light irradiation and aluminum organometallics is essential to promote this transformation, which introduces visible-light photochemistry of main-group organometallics and sets the basis for new and promising catalysts. PMID:26337253

  10. Visible-light-driven photocatalysts: (La/Bi + N)-codoped NaNbO3 by first principles

    NASA Astrophysics Data System (ADS)

    Liu, Guodong; Ji, Shulin; Yin, Liangliang; Xu, Guoping; Fei, Guangtao; Ye, Changhui

    2011-03-01

    To improve the photocatalytic activity of NaNbO3 for water splitting, the bandgap and the band edges of NaNbO3 should be tailored to match the visible part of the solar spectrum and hydrogen and oxygen redox potentials. By analyzing the band structures of La/Bi-doped and (La/Bi + N)-codoped NaNbO3, we found that the pseudointermediate band (PIB) was formed in the bandgap in all the doped systems because of the orbital splitting of the Nb 4d induced by the dramatically enlarged O-Nb-O angles. The PIB could make the wide bandgap semiconductors absorb visible-light photons as long as it was degenerate or partially degenerate. Considering that the appropriate band edges and absorption properties, we believe that (La/Bi + N)-codoped NaNbO3 materials are promising photocatalysts for hydrogen production through water splitting under visible-light irradiation without other modifications.

  11. Vapor-deposited amorphous metamaterials as visible near-perfect absorbers with random non-prefabricated metal nanoparticles

    PubMed Central

    Zhang, Yun; Wei, Tiaoxing; Dong, Wenjing; Zhang, Kenan; Sun, Yan; Chen, Xin; Dai, Ning

    2014-01-01

    Spatial order or periodicity is usually required and constructed with tens of nanometers in the feature size, which makes it difficult to process the near-perfect metamaterial absorbers (PMAs) working in the visible range in large-area and mass-production scale. Although many established technologies and theoretical modeling methods used for order-based metamaterials, aperiodic or disordered structures have been gradually recognized to achieve similar functionalities for which the ordered structures are overwhelmingly used. Here, we demonstrated the vapor-deposited ‘amorphous’ metamaterials as controlled-reflectance surfaces and tunable PMAs without the use of the lithographically ordered arrays, the prefabricated colloidal metal nanoparticles (MNPs) or the multilayer of nanoparticles. The flexible construction, the control of the monolayer of MNPs and the atomic-layer-deposited (ALD) dielectric spacer layer provide more insight for understanding the controlled-reflectance surfaces. Such processes have a few key advantages of CMOS-compatible simple processing, low cost and large-area plating, allowing the PMAs to be flexibly constructed in mass-production scale. PMID:24810434

  12. Analysis of Old Copper Synchrotron Light Absorbers from the Stanford Positron Electron Accelerating Ring

    SciTech Connect

    Marshall, S.R.; Scott, B.; /SLAC

    2005-12-15

    Synchrotron light absorbers intercept synchrotron radiation to protect chamber walls from excessive heat. When subjected to the high temperature of the beam, these absorbers undergo thermal stress. If the stress is too great or fatigues the material, the absorbers may fail. These absorbers are designed to last the lifetime of the machine. Any premature cracking could result in a leak and, consequently, loss of the ultra high vacuum environment. Using secondary and backscattered electron techniques, several sections of a used copper absorber were analyzed for material damage. Chemical analyses were performed on these samples as well. Comparing the unexposed sections to the sections exposed to the electron beam, few cracks were seen in the copper. However, the exposed samples showed heavy surface damage, in addition to crevices that could eventually result in material failure. Significant corrosion was also evident along the water cooling passage of the samples. These findings suggest that further investigation and periodic inspection of absorbers in SPEAR3 are necessary to control corrosion of the copper.

  13. Plasmonic photoanodes for solar water splitting with visible light.

    PubMed

    Lee, Joun; Mubeen, Syed; Ji, Xiulei; Stucky, Galen D; Moskovits, Martin

    2012-09-12

    We report a plasmonic water splitting cell in which 95% of the effective charge carriers derive from surface plasmon decay to hot electrons, as evidenced by fuel production efficiencies up to 20-fold higher at visible, as compared to UV, wavelengths. The cell functions by illuminating a dense array of aligned gold nanorods capped with TiO(2), forming a Schottky metal/semiconductor interface which collects and conducts the hot electrons to an unilluminated platinum counter-electrode where hydrogen gas evolves. The resultant positive charges in the Au nanorods function as holes and are extracted by an oxidation catalyst which electrocatalytically oxidizes water to oxygen gas.

  14. Space-based visible all-reflective stray light telescope

    NASA Astrophysics Data System (ADS)

    Wang, Dexter; Gardner, Leo R.; Wong, Wallace K.; Hadfield, Peter

    1991-08-01

    A 6-inch diameter aperture space-based visible telescope has been optimized to perform surveillance against the space background with earth albedo as a primary source of straylight. A three mirror off-axis anastigmat has been designed to cover a 1.4 degree(s) by 6.6 degree(s) field- of-view with 60 (mu) radian spatial resolution. The telescope body and optics are constructed of 6061-T6 aluminum to provide a thermally stable optical system. The optical elements are 'superfinished' to minimize scatter. Extensive baffles and stops are utilized to further reduce straylight. The telescope will be used on the Midcourse Space Experiment platform.

  15. Patterning of silver nanoparticles on visible light-sensitive Mn-doped lithium niobate photogalvanic crystals

    SciTech Connect

    Liu Xiaoyan; Ohuchi, Fumio; Hatano, Hideki; Takekawa, Shunji; Kitamura, Kenji

    2011-08-01

    Visible light-induced polarization-dependent photochemical deposition of silver nanoparticles (AgNPs) has been demonstrated using Mn-doped congruent LiNbO{sub 3} (CLN) single crystals. Mn-doped CLN has a strong absorption over a wide region of the visible spectrum that allowed effective visible light irradiation for photochemical deposition. The AgNPs deposition on Mn-doped CLN was compared with that on non-doped congruent LiNbO{sub 3}, and together these further confirmed that the photochemical deposition on LiNbO{sub 3} is caused by the strong photogalvanic effect.

  16. Preparation and characterization of ZnO-TiO{sub 2} nanocomposite for photocatalytic disinfection of bacteria and detoxification of cyanide under visible light

    SciTech Connect

    Karunakaran, C.; Abiramasundari, G.; Gomathisankar, P.; Manikandan, G.; Anandi, V.

    2011-10-15

    Highlights: {yields} ZnO-TiO{sub 2} nanocomposite, obtained by modified ammonia-evaporation-induced synthetic method, absorbs visible light. {yields} ZnO-TiO{sub 2} nanoparticles catalyze bacteria disinfection and cyanide detoxification under sunlight. {yields} ZnO-TiO{sub 2} nanocomposite is selective in photocatalysis. -- Abstract: ZnO-TiO{sub 2} nanocomposite was prepared by modified ammonia-evaporation-induced synthetic method. It was characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray, UV-visible diffuse reflectance, photoluminescence and electrochemical impedance spectroscopies. Incorporation of ZnO leads to visible light absorption, larger charge transfer resistance and lower capacitance. The nanocomposite effectively catalyzes the inactivation of E. coli under visible light. Further, the prepared nanocomposite displays selective photocatalysis. While its photocatalytic efficiency to detoxify cyanide with visible light is higher than that of TiO{sub 2} P25, its efficiency to degrade methylene blue, sunset yellow and rhodamine B dyes under UV-A light is less than that of TiO{sub 2} P25.

  17. An ultrathin invisibility skin cloak for visible light.

    PubMed

    Ni, Xingjie; Wong, Zi Jing; Mrejen, Michael; Wang, Yuan; Zhang, Xiang

    2015-09-18

    Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up and, more critically, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object. This skin cloak conceals a three-dimensional arbitrarily shaped object by complete restoration of the phase of the reflected light at 730-nanometer wavelength. The skin cloak comprises a metasurface with distributed phase shifts rerouting light and rendering the object invisible. In contrast to bulky cloaks with volumetric index variation, our device is only 80 nanometer (about one-ninth of the wavelength) thick and potentially scalable for hiding macroscopic objects. PMID:26383946

  18. An ultrathin invisibility skin cloak for visible light

    NASA Astrophysics Data System (ADS)

    Ni, Xingjie; Wong, Zi Jing; Mrejen, Michael; Wang, Yuan; Zhang, Xiang

    2015-09-01

    Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up and, more critically, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object. This skin cloak conceals a three-dimensional arbitrarily shaped object by complete restoration of the phase of the reflected light at 730-nanometer wavelength. The skin cloak comprises a metasurface with distributed phase shifts rerouting light and rendering the object invisible. In contrast to bulky cloaks with volumetric index variation, our device is only 80 nanometer (about one-ninth of the wavelength) thick and potentially scalable for hiding macroscopic objects.

  19. An ultrathin invisibility skin cloak for visible light

    NASA Astrophysics Data System (ADS)

    Wong, Zi Jing; Ni, Xingjie; Mrejen, Michael; Wang, Yuan; Zhang, Xiang

    Metamaterial-based optical cloaks have thus far used volumetric distribution of the material properties to gradually bend light and thereby obscure the cloaked region. Hence, they are bulky and hard to scale up to macroscopic sizes. In addition, typical carpet cloaks introduce unnecessary phase shifts in the reflected light, making the cloaks detectable. Here, we demonstrate experimentally an ultrathin invisibility skin cloak wrapped over an object. This skin cloak conceals a three-dimensional arbitrarily shaped object by complete restoration of the phase of the reflected light at 730-nanometer wavelength. The skin cloak comprises a metasurface with distributed phase shifts rerouting light and rendering the object invisible. In contrast to bulky cloaks with volumetric index variation, our device is only 80 nanometer (about one-ninth of the wavelength) thick and potentially scalable to hide macroscopic objects.

  20. Visible light emitting vertical cavity surface emitting lasers

    DOEpatents

    Bryan, R.P.; Olbright, G.R.; Lott, J.A.; Schneider, R.P. Jr.

    1995-06-27

    A vertical cavity surface emitting laser that emits visible radiation is built upon a substrate, then having mirrors, the first mirror on top of the substrate; both sets of mirrors being a distributed Bragg reflector of either dielectrics or other materials which affect the resistivity or of semiconductors, such that the structure within the mirror comprises a plurality of sets, each having a thickness of {lambda}/2n where n is the index of refraction of each of the sets; each of the mirrors adjacent to spacers which are on either side of an optically active bulk or quantum well layer; and the spacers and the optically active layer are from one of the following material systems: In{sub z}(Al{sub y}Ga{sub 1{minus}y}){sub 1{minus}z}P, InAlGaAs, AlGaAs, InGaAs, or AlGaP/GaP, wherein the optically active region having a length equal to m {lambda}/2n{sub eff} where m is an integer and n{sub eff} is the effective index of refraction of the laser cavity, and the spacer layer and one of the mirrors being transmissive to radiation having a wavelength of {lambda}/n, typically within the green to red portion of the visible spectrum. 10 figs.

  1. Visible light emitting vertical cavity surface emitting lasers

    DOEpatents

    Bryan, Robert P.; Olbright, Gregory R.; Lott, James A.; Schneider, Jr., Richard P.

    1995-01-01

    A vertical cavity surface emitting laser that emits visible radiation is built upon a substrate, then having mirrors, the first mirror on top of the substrate; both sets of mirrors being a distributed Bragg reflector of either dielectrics or other materials which affect the resistivity or of semiconductors, such that the structure within the mirror comprises a plurality of sets, each having a thickness of .lambda./2n where n is the index of refraction of each of the sets; each of the mirrors adjacent to spacers which are on either side of an optically active bulk or quantum well layer; and the spacers and the optically active layer are from one of the following material systems: In.sub.z (Al.sub.y Ga.sub.1-y).sub.1-z P, InAlGaAs, AlGaAs, InGaAs, or AlGaP/GaP, wherein the optically active region having a length equal to m .lambda./2n.sub.eff where m is an integer and n.sub.eff is the effective index of refraction of the laser cavity, and the spacer layer and one of the mirrors being transmissive to radiation having a wavelength of .lambda./n, typically within the green to red portion of the visible spectrum.

  2. Harnessing structural darkness in the visible and infrared wavelengths for a new source of light

    NASA Astrophysics Data System (ADS)

    Huang, Jianfeng; Liu, Changxu; Zhu, Yihan; Masala, Silvia; Alarousu, Erkki; Han, Yu; Fratalocchi, Andrea

    2016-01-01

    Engineering broadband light absorbers is crucial to many applications, including energy-harvesting devices and optical interconnects. The performances of an ideal absorber are that of a black body, a dark material that absorbs radiation at all angles and polarizations. Despite advances in micrometre-thick films, the absorbers available to date are still far from an ideal black body. Here, we describe a disordered nanostructured material that shows an almost ideal black-body absorption of 98-99% between 400 and 1,400 nm that is insensitive to the angle and polarization of the incident light. The material comprises nanoparticles composed of a nanorod with a nanosphere of 30 nm diameter attached. When diluted into liquids, a small concentration of nanoparticles absorbs on average 26% more than carbon nanotubes, the darkest material available to date. By pumping a dye optical amplifier with nanosecond pulses of ˜100 mW power, we harness the structural darkness of the material and create a new type of light source, which generates monochromatic emission (˜5 nm wide) without the need for any resonance. This is achieved through the dynamics of light condensation in which all absorbed electromagnetic energy spontaneously generates single-colour energy pulses.

  3. Low-level visible light (LLVL) irradiation promotes proliferation of mesenchymal stem cells.

    PubMed

    Lipovsky, Anat; Oron, Uri; Gedanken, Aharon; Lubart, Rachel

    2013-07-01

    Low-level visible light irradiation was found to stimulate proliferation potential of various types of cells in vitro. Stem cells in general are of significance for implantation in regenerative medicine. The aim of the present study was to investigate the effect of low-level light irradiation on the proliferation of mesenchymal stem cells (MSCs). MSCs were isolated from the bone marrow, and light irradiation was applied at energy densities of 2.4, 4.8, and 7.2 J/cm(2). Illumination of the MSCs resulted in almost twofold increase in cell number as compared to controls. Elevated reactive oxygen species and nitric oxide production was also observed in MSCs cultures following illumination with broadband visible light. The present study clearly demonstrates the ability of broadband visible light illumination to promote proliferation of MSCs in vitro. These results may have an important impact on wound healing.

  4. A new optical method coupling light polarization and Vis-NIR spectroscopy to improve the measured absorbance signal's quality of soil samples.

    NASA Astrophysics Data System (ADS)

    Gobrecht, Alexia; Bendoula, Ryad; Roger, Jean-Michel; Bellon-Maurel, Véronique

    2014-05-01

    Visible - Near-infrared spectroscopy (Vis-NIRS) is now commonly used to measure different physical and chemical parameters of soils, including carbon content. However, prediction model accuracy is insufficient for Vis-NIRS to replace routine laboratory analysis. One of the biggest issues this technique is facing up to is light scattering due to soil particles. It causes departure in the assumed linear relationship between the Absorbance spectrum and the concentration of the chemicals of interest as stated by Beer-Lambert's Law, which underpins the calibration models. Therefore it becomes essential to improve the metrological quality of the measured signal in order to optimize calibration as light/matter interactions are at the basis of the resulting linear modeling. Optics can help to mitigate scattering effect on the signal. We put forward a new optical setup coupling linearly polarized light with a Vis-NIR spectrometer to free the measured spectra from multi-scattering effect. The corrected measured spectrum was then used to compute an Absorbance spectrum of the sample, using Dahm's Equation in the frame of the Representative Layer Theory. This method has been previously tested and validated on liquid (milk+ dye) and powdered (sand + dye) samples showing scattering (and absorbing) properties. The obtained Absorbance was a very good approximation of the Beer-Lambert's law absorbance. Here, we tested the method on a set of 54 soil samples to predict Soil Organic Carbon content. In order to assess the signal quality improvement by this method, we built and compared calibration models using Partial Least Square (PLS) algorithm. The prediction model built from new Absorbance spectrum outperformed the model built with the classical Absorbance traditionally obtained with Vis-NIR diffuse reflectance. This study is a good illustration of the high influence of signal quality on prediction model's performances.

  5. Reduced graphene oxide and Ag wrapped TiO2 photocatalyst for enhanced visible light photocatalysis

    NASA Astrophysics Data System (ADS)

    Leong, Kah Hon; Sim, Lan Ching; Bahnemann, Detlef; Jang, Min; Ibrahim, Shaliza; Saravanan, Pichiah

    2015-10-01

    A well-organised reduced graphene oxide (RGO) and silver (Ag) wrapped TiO2 nano-hybrid was successfully achieved through a facile and easy route. The inherent characteristics of the synthesized RGO-Ag/TiO2 were revealed through crystalline phase, morphology, chemical composition, Raman scattering, UV-visible absorption, and photoluminescence analyses. The adopted synthesis route significantly controlled the uniform formation of silver nanoparticles and contributed for the absorption of light in the visible spectrum through localized surface plasmon resonance effects. The wrapped RGO nanosheets triggered the electron mobility and promoted visible light shift towards red spectrum. The accomplishment of synergised effect of RGO and Ag well degraded Bisphenol A under visible light irradiation with a removal efficiency of 61.9%.

  6. Bandgap narrowing of titanium oxide semiconductors by non-compensated anion-cation codoping for enhanced visible-light photoactivity

    SciTech Connect

    Zhu, Wenguang; Qiu, Xiaofeng; Iancu, Violet; Chen, Xingqiu; Pan, Hui; Wang, Wei; Dimitrijevic, Nada; Rajh, Tijana; Meyer III, Harry M; Paranthaman, Mariappan Parans; Stocks, George Malcolm; Weitering, Hanno; Gu, Baohua; Zhang, Zhenyu

    2009-01-01

    Titanium dioxide (TiO2) is widely recognized as one of the most promising photocatalysts for solar energy utilization and environmental cleanup, but because of its wide bandgap, pure TiO2 can only absorbs ultraviolet light, which represents 4% of the solar spectrum1-6. Here we establish a conceptually novel approach, termed non-compensated n-p codoping, to narrow the bandgap of TiO2 and shift the optical response into the visible spectral range where a much larger fraction of the solar spectrum can be captured. The concept embodies two key ingredients: The electrostatic attraction within the n-p dopant pair enhances the thermodynamic and kinetic solubility in substitutional doping, and the non-compensated nature ensures the creation of broadened intermediate electronic states that effectively narrow the bandgap. The concept is demonstrated quantitatively within first-principles density functional theory. The experimental evidence for bandgap narrowing is obtained in the forms of direct measurements of the density of states by scanning tunneling spectroscopy, dramatically redshifted and increased optical absorbance, and enhanced photoactivity manifested by efficient hole-electron separation in the visible spectral region. These findings represent the first crucial steps toward development of a new class of titania-based photocatalysts with greatly enhanced efficiency of solar energy conversion facilitating environmentally friendly applications ofrenewable energy.

  7. Solid-Phase Synthesis as a Platform for the Discovery of New Ruthenium Complexes for Efficient Release of Photocaged Ligands with Visible Light

    PubMed Central

    Sharma, Rajgopal; Knoll, Jessica D.; Ancona, Nicholas; Martin, Phillip D.; Turro, Claudia; Kodanko, Jeremy J.

    2015-01-01

    Ruthenium-based photocaging groups have important applications as biological tools and show great potential as therapeutics. A method was developed to rapidly synthesize, screen and identify ruthenium-based caging groups that release nitriles upon irradiation with visible light. A diverse library of tetra- and pentadentate ligands was synthesized on polystyrene resin. Ruthenium complexes of the general formula [Ru(L)(MeCN)n]m+ (n = 1–3, m = 1–2) were generated from these ligands on solid phase, then cleaved from resin for photochemical analysis. Data indicate a wide range of spectral tuning and reactivity with visible light. Three complexes that showed strong absorbance in the visible range were synthesized by solution phase for comparison. Photochemical behavior of solution- and solid-phase complexes was in good agreement, confirming that the library approach is useful in identifying candidates with desired photoreactivity in short order, avoiding time consuming chromatography and compound purification. PMID:25611351

  8. Photothermally tunable silicon-microring-based optical add-drop filter through integrated light absorber.

    PubMed

    Chen, Xi; Shi, Yuechun; Lou, Fei; Chen, Yiting; Yan, Min; Wosinski, Lech; Qiu, Min

    2014-10-20

    An optically pumped thermo-optic (TO) silicon ring add-drop filter with fast thermal response is experimentally demonstrated. We propose that metal-insulator-metal (MIM) light absorber can be integrated into silicon TO devices, acting as a localized heat source which can be activated remotely by a pump beam. The MIM absorber design introduces less thermal capacity to the device, compared to conventional electrically-driven approaches. Experimentally, the absorber-integrated add-drop filter shows an optical response time of 13.7 μs following the 10%-90% rule (equivalent to a exponential time constant of 5 μs) and a wavelength shift over pump power of 60 pm/mW. The photothermally tunable add-drop filter may provide new perspectives for all-optical routing and switching in integrated Si photonic circuits. PMID:25401557

  9. Fabrication of chalcopyrite light-absorbing layers based on nanoparticle and nanowire networks

    NASA Astrophysics Data System (ADS)

    Ren, Yuhang; Luo, Paifeng; Gao, Bo; Cevher, Zehra; Sun, Chivin

    2013-03-01

    We report on a method of preparing chalcopyrite, CuInGaSe2 (CIGS) light-absorbing layers using low cost air stable ink based on semiconductor nanoparticle and nanowires. The nanoparticles and nanowires are prepared from metal salts such as metal chloride and acetate at room temperature without inert gas protection. A uniform and non-aggregation CIGS precursor layer is fabricated with the formation of nanoparticle and nanowire networks utilizing ultrasonic spaying technique. We obtain a high quality CIGS absorber by cleaning the residue salts and carbon agents at an increased temperature and through selenizing the pretreated CIGS precursors. Our results offer an opportunity for the low-cost deposition of chalcopyrite absorber materials at large scale with high throughput. This work was partially sponsored by Sun Harmonics Ltd. and by NYSTAR through the Photonics Center for Applied Technology at the City University of New York.

  10. Ab initio studies of Nb-N-S tri-doped TiO2 with enhanced visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Ren, Dahua; Cheng, Junxia; Cheng, Xinlu

    2016-06-01

    The electronic and optical properties of Nb-N-S tri-doped anatase TiO2 were investigated within the frame of the density functional theory (DFT) plus U method. Results show that a significant red-shift effect and improvement of visible-light absorption for Nb-N-S tri-doped TiO2 are observed with respect to pure TiO2 and S-N codoped TiO2. At the same time, the enhanced visible-light photocatalytic activity of tri-doped TiO2 is derived from the narrowing band gap, the appearance of Nb 4d state at the bottom of conduction band and the mixture of N 2p, S 3p states forming new defect levels at the top of valance band, which is excellently consistent with the previous experiment. Moreover, S ion leads to the lattice distortion and promotes the visible-light photocatalytic activity. Furthermore, the absorbance of 1.39NbNS-TiO2 accords well with the experimental result in the visible region. It is also found that the 2.78NbNS-TiO2 can be easily grown under O-rich condition and have the strongest absorbance from 2.0 to 4.2 eV among four models.

  11. Visible-light photoconductivity of Zn1-xCoxO and its dependence on Co2+ concentration

    SciTech Connect

    Johnson, Claire A.; Cohn, Alicia; Kaspar, Tiffany C.; Chambers, Scott A.; Salley, G. Mackay; Gamelin, Daniel R.

    2011-09-06

    Many metal oxides investigated for solar photocatalysis or photoelectrochemistry have band gaps that are too wide to absorb a sufficient portion of the solar spectrum. Doping with impurity ions has been extensively explored as a strategy to sensitize such oxides to visible light, but the electronic structures of the resulting materials are frequently complex and poorly understood. Here, we report a detailed photoconductivity investigation of the wide-gap II-VI semiconductor ZnO doped with Co2+ (Zn1-xCoxO), which responds to visible light in photoelectrochemical and photoconductivity experiments and thus represents a well-defined model system for understanding dopant-sensitized oxides. Variable-temperature scanning photoconductivity measurements have been performed on high-structural-quality Zn1-xCoxO epitaxial films to examine the relationship between dopant concentration (x) and visible-light photoconductivity, with particular focus on mid-gap d-d photoactivity. Excitation into the intense 4T1(P) d-d band at ~2.0 eV (620 nm) leads to Co2+/3+ ionization with a quantum efficiency that increases with decreasing cobalt concentration and increasing sample temperature. Both spontaneous and thermally assisted ionization from the Co2+ d-d excited state are found to become less effective as x is increased, attributed to an increasing conduction-band-edge potential. These trends counter the increasing light absorption with increasing x, explaining the experimental maximum in external photon-to-current conversion efficiencies at values well below the solid solubility of Co2+ in ZnO.

  12. Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes.

    PubMed

    Byun, Jinwoo; Cho, Himchan; Wolf, Christoph; Jang, Mi; Sadhanala, Aditya; Friend, Richard H; Yang, Hoichang; Lee, Tae-Woo

    2016-09-01

    Efficient quasi-2D-structure perovskite light-emitting diodes (4.90 cd A(-1) ) are demonstrated by mixing a 3D-structured perovskite material (methyl ammonium lead bromide) and a 2D-structured perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density. PMID:27334788

  13. Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes.

    PubMed

    Byun, Jinwoo; Cho, Himchan; Wolf, Christoph; Jang, Mi; Sadhanala, Aditya; Friend, Richard H; Yang, Hoichang; Lee, Tae-Woo

    2016-09-01

    Efficient quasi-2D-structure perovskite light-emitting diodes (4.90 cd A(-1) ) are demonstrated by mixing a 3D-structured perovskite material (methyl ammonium lead bromide) and a 2D-structured perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density.

  14. 33 CFR 83.22 - Visibility of lights (Rule 22).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... at the following minimum ranges: (a) Vessel of 50 meters or more in length. In a vessel of 50 meters... special flashing light, 2 miles. (b) Vessels of 12 meters or more in length but less than 50 meters in length. In a vessel of 12 meters or more in length but less than 50 meters in length: (1) A...

  15. Gain dispersion in Visible Light Photon Counters as a function of counting rate

    SciTech Connect

    Bross, A.; Buscher, V.; Estrada, J.; Ginther, G.; Molina, J.; /Rio de Janeiro State U.

    2005-03-01

    We present measurements of light signals using Visible Light Photon Counters (VLPC), that indicate an increase in gain dispersion as the counting rate increases. We show that this dispersion can be understood on the basis of a recent observation of localized field reduction in VLPCs at high input rates.

  16. Stratocumulus to Cumulus Transition Capped by a Light-Absorbing Smoke Layer

    NASA Astrophysics Data System (ADS)

    Yamaguchi, T.; Feingold, G.; Kazil, J.; McComiskey, A. C.

    2015-12-01

    Biomass burning aerosol emitted from Africa seasonally advects over the eastern Atlantic and forms a layer of light-absorbing smoke above stratocumulus clouds, which influences heating profiles, dynamics, and cloud microphysics. In this study, large-eddy simulation is used to investigate the effect of the absorbing smoke layer on the stratocumulus to cumulus transition (SCT). A prognostic absorbing smoke model incorporates humidity effects on optical properties, and is coupled with a two-moment bulk microphysics scheme and an interactive radiation code. Smoke both absorbs shortwave radiation and acts as cloud condensation nuclei (CCN). Simulations are of three day duration. The simulations assess sensitivity of the SCT to distance of the smoke layer from the cloud top, aerosol optical thickness and single scattering albedo, and precipitation. Our simulations show that 1) As a shortwave absorber, the smoke stabilizes the free atmosphere and strengthens the temperature jump at the boundary layer top, which limits entrainment; 2) Smoke helps evaporate cloud during daytime, which amplifies the diurnal cycle of cloud cover; 3) As a source of CCN, the entrained smoke suppresses rain formation, which inhibits precipitation-generated cloud breakup. The net effect of smoke is modification of heating profiles to limit the deepening of the planetary boundary layer, and suppression of precipitation. This leads to enhancement of the diurnal cycle of cloudiness but a delay in the SCT.

  17. Environmental remediation and superhydrophilicity of ultrafine antibacterial tungsten oxide-based nanofibers under visible light source

    NASA Astrophysics Data System (ADS)

    Srisitthiratkul, Chutima; Yaipimai, Wittaya; Intasanta, Varol

    2012-10-01

    Fabrication of nanosilver-decorated WO3 nanofibers was successfully performed. First, deposition of nanosilver onto electrospun WO3 nanofibers' surface was done via photoreduction of silver ion under visible or UV light. The resulting hybrid nanofibers not only revealed antibacterial characteristics but also maintained their photocatalytic performance towards methylene blue decomposition. Unexpectedly, the nanofibrous layers prepared from these nanofibers showed superhydrophilicity under a visible light source. The nanofibers might be advantageous in environmental and hygienic nanofiltration under natural light sources, where the self-cleaning characteristics could be valuable in maintenance processes.

  18. Strong visible light emission from well-aligned multiwalled carbon nanotube films under infrared laser irradiation

    SciTech Connect

    Zhang Yong; Gong Tao; Liu Wenjin; Zhang Xianfeng; Chang Jianguo; Wang Kunlin; Wu Dehai

    2005-10-24

    We report strong and brilliant visible light emission from well-aligned multiwalled carbon nanotube (AMWNT) films under infrared (IR) laser irradiation with wavelength at 1.06 and 10.6 {mu}m, respectively. The AMWNT film shows a high durability against laser irradiation and achieved a conversion from IR laser to visible light. It is a good candidate for optical converter. Light emission spectra versus different wavelengths and various powers were found to have similar line shapes. It could be explained as combination of laser-induced photoluminescence and resistive heating.

  19. Visible light inactivation of bacteria and fungi by modified titanium dioxide.

    PubMed

    Mitoraj, Dariusz; Jańczyk, Agnieszka; Strus, Magdalena; Kisch, Horst; Stochel, Grazyna; Heczko, Piotr B; Macyk, Wojciech

    2007-06-01

    Visible light induced photocatalytic inactivation of bacteria (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis) and fungi (Candida albicans, Aspergillus niger) was tested. Carbon-doped titanium dioxide and TiO2 modified with platinum(IV) chloride complexes were used as suspension or immobilised at the surface of plastic plates. A biocidal effect was observed under visible light irradiation in the case of E. coli in the presence of both photocatalysts. The platinum(IV) modified titania exhibited a higher inactivation effect, also in the absence of light. The mechanism of visible light induced photoinactivation is briefly discussed. The observed detrimental effect of photocatalysts on various microorganism groups decreases in the order: E. coli > S. aureus approximately E. faecalis>C. albicans approximately A. niger. This sequence results most probably from differences in cell wall or cell membrane structures in these microorganisms and is not related to the ability of catalase production. PMID:17549266

  20. Automatic illumination compensation device based on a photoelectrochemical biofuel cell driven by visible light.

    PubMed

    Yu, You; Han, Yanchao; Xu, Miao; Zhang, Lingling; Dong, Shaojun

    2016-04-28

    Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm(-2) and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications. PMID:27076202

  1. Three-visible-light wave combiner based on photonic crystal waveguides.

    PubMed

    Liu, Dingwen; Sun, Yiling; Ouyang, Zhengbiao

    2014-07-20

    We present a three-visible-light wave combiner based on two-dimensional photonic crystal waveguides whose widths are not integral multiples of the lattice period. The proposed device consists of two cascaded directional couplers. It combines three visible light waves with different wavelengths from three input ports into a single output port. As an example, a combiner for combining light waves of 635, 532, and 488 nm, which are commonly used as the three primary colors in laser display systems, is designed and demonstrated through the finite-difference time-domain method. The results show that the proposed device can perform efficient synthesis for three visible light waves with transmittance exceeding 89% for each wavelength and high ability in preventing the backward coupling of waves from different waveguides. The method for designing the combiner is useful for designing other waveguide couplers based on photonic crystals made of dispersion materials.

  2. Visible supercontinuum radiation of light bullets in the femtosecond filamentation of IR pulses in fused silica

    NASA Astrophysics Data System (ADS)

    Chekalin, S. V.; Kompanets, V. O.; Dokukina, A. E.; Dormidonov, A. E.; Smetanina, E. O.; Kandidov, V. P.

    2015-05-01

    We report experimental and theoretical investigations of visible supercontinuum generation in the formation of light bullets in a filament produced by IR pulses. In the filamentation of a 1700 - 2200 nm pulse in fused silica, bright tracks are recorded resulting from the recombination glow of carriers in the laser plasma produced by a sequence of light bullets and from the scattering in silica of the visible supercontinuum generated by the light bullets. It is found that the formation of a light bullet is attended with an outburst of a certain portion of supercontinuum energy in the visible range. The energy outburst is the same for all bullets in the sequence and becomes smaller with increasing pulse wavelength.

  3. Lighting factors affecting the visibility of a moving display.

    NASA Technical Reports Server (NTRS)

    Gilson, R. D.

    1971-01-01

    Compensatory tracking performance was shown to be substantially degraded by oscillation of the visual display at both 1.0 and 2.0 Hz. The severity of this decrement was altered significantly by changes in both the color and the intensity of the display illumination. Performance was significantly better with red light illuminating the display at 0.05 mL than with blue light at the equivalent luminance. This improvement in performance was similar in magnitude to that found for an increase in broad-band illumination of the display where luminance was increased from 1/2 log unit below to 1/2 log unit above 0.05 mL. Visual mechanisms that may have been responsible for these findings are suggested.

  4. Automatic illumination compensation device based on a photoelectrochemical biofuel cell driven by visible light

    NASA Astrophysics Data System (ADS)

    Yu, You; Han, Yanchao; Xu, Miao; Zhang, Lingling; Dong, Shaojun

    2016-04-01

    Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm-2 and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications.Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm-2 and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00759g

  5. Erbium and nitrogen co-doped SrTiO{sub 3} with highly visible light photocatalytic activity and stability by solvothermal synthesis

    SciTech Connect

    Xu, Jing; Wei, Yuelin; Huang, Yunfang; Wang, Jing; Zheng, Xuanqing; Sun, Zhixian; Wu, Ying; Tao, Xinling; Fan, Leqing; Wu, Jihuai

    2015-10-15

    Highlights: • Er/N co-doped SrTiO{sub 3} was prepared by a solvothermal process at low temperature. • The co-doping induces the band gap narrowing and prominent absorbance in visible light region. • The samples show excellent catalytic activity and stability under visible light irradiation. - Abstract: Erbium–nitrogen co-doped SrTiO{sub 3} photocatalysts have been synthesized by a facile solvothermal method. The resulting samples were analyzed by FE-SEM, XRD, BET-surface area and UV–vis. The UV–vis absorption spectra of these powders indicated that erbium–nitrogen co-doped SrTiO{sub 3} possessed stronger absorption bands in the visible light region in comparison with that of pure SrTiO{sub 3}. The occurrence of the erbium–nitrogen co-doped cubic SrTiO{sub 3} induced the higher photocatalytic activities for the degradation of methyl orange (MO) under irradiation by ultraviolet light and visible light, respectively, being superior to that of pure SrTiO{sub 3} and commercial TiO{sub 2} (P-25) powders. In addition, the Er–N co-doped SrTiO{sub 3} (initial molar ratios of Sr/Er/N = 1:0.015:0.1, designated as S5) sample showed the best photocatalytic activity with the degradation rate as high as 98% after 30 min under the visible light irradiation. After five cycles, the photocatalytic activity of the S5 catalyst showed no significant decrease, which indicated that the photocatalysts were stable under visible light irradiation.

  6. Phototoxic effect of visible light on Porphyromonas gingivalis and Fusobacterium nucleatum: an in vitro study.

    PubMed

    Feuerstein, Osnat; Persman, Nir; Weiss, Ervin I

    2004-01-01

    The antibacterial effect of visible light irradiation combined with photosensitizers has been reported. The objective of this was to test the effect of visible light irradiation without photosensitizers on the viability of oral microorganisms. Strains of Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus mutans and Streptococcus faecalis in suspension or grown on agar were exposed to visible light at wavelengths of 400-500 nm. These wavelengths are used to photopolymerize composite resins widely used for dental restoration. Three photocuring light sources, quartz-tungsten-halogen lamp, light-emitting diode and plasma-arc, at power densities between 260 and 1300 mW/cm2 were used for up to 3 min. Bacterial samples were also exposed to a near-infrared diode laser (wavelength, 830 nm), using identical irradiation parameters for comparison. The results show that blue light sources exert a phototoxic effect on P. gingivalis and F. nucleatum. The minimal inhibitory dose for P. gingivalis and F. nucleatum was 16-62 J/cm2, a value significantly lower than that for S. mutans and S. faecalis (159-212 J/cm2). Near-infrared diode laser irradiation did not affect any of the bacteria tested. Our results suggest that visible light sources without exogenous photosensitizers have a phototoxic effect mainly on Gram-negative periodontal pathogens. PMID:15623322

  7. Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light

    NASA Astrophysics Data System (ADS)

    Wong, Ming-Show; Chen, Chun-Wei; Hsieh, Chia-Chun; Hung, Shih-Che; Sun, Der-Shan; Chang, Hsin-Hou

    2015-07-01

    Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet-visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

  8. Layered double hydroxides as highly efficient photocatalysts for visible light oxygen generation from water.

    PubMed

    Gomes Silva, Cláudia; Bouizi, Younès; Fornés, Vicente; García, Hermenegildo

    2009-09-30

    Oxygen generation through photocatalytic water splitting under visible light irradiation is a challenging process. In this work we have synthesized a series of Zn/Ti, Zn/Ce, and Zn/Cr layered double hydroxides (LDH) at different Zn/metal atomic ratio (from 4:2 to 4:0.25) and tested them for the visible light photocatalytic oxygen generation. The most active material was found to be (Zn/Cr)LDH with an atomic ratio of 4:2 that exhibits two absorption bands in the visible region at lambda(max) of 410 and 570 nm. It was found that the efficiency of these chromium layered double oxides for oxygen generation increases asymptotically with the Cr content. Using iron oxalate as chemical actinometer we have determined that the apparent quantum yields for oxygen generation (Phi apparent = 4 x mol oxygen/mol incident photons) are of 60.9% and 12.2% at 410 and 570 nm, respectively. These quantum yields are among the highest values ever determined with visible light for solid materials in the absence of light harvesting dye. The overall efficiency of (Zn/Cr)LDH for visible light oxygen generation was found to be 1.6 times higher than that of WO(3) under the same conditions.

  9. Indoor visible light communication: modeling and analysis of multi-state modulation

    NASA Astrophysics Data System (ADS)

    Koudelka, Petr; Latal, Jan; Siska, Petr; Vitasek, Jan; Liner, Andrej; Martinek, Radek; Vasinek, Vladimir

    2014-10-01

    The new dynamic direction of wireless networks development is based on the idea of networks utilizing the optical radiation in the visible spectrum VLC (Visible Light Communications). The impulse of this development direction was improvement in the semiconductor lighting technologies, namely the white power LEDs (Light Emitting Diode). These types of wireless networks are denoted as the optical wireless networks for indoor spaces utilizing optical radiation in the visible spectrum. The paper deals with the issue of deployment of multi-state modulations into the indoor visible light communications in LOS (Line of Sight) configuration. The first part of the paper focuses on design of modulation element (SMD LED matrix 3 × 3) and problems connected to deployment of multi-state modulation M-QAM (subcarrier intensity modulation) through this modulation element into the indoor visible light communications (MER). The second part deals with the irradiation distribution in dark room in comparison with real room during used multi-state modulation scheme in both simulation and real measurement.

  10. Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light

    PubMed Central

    Wong, Ming-Show; Chen, Chun-Wei; Hsieh, Chia-Chun; Hung, Shih-Che; Sun, Der-Shan; Chang, Hsin-Hou

    2015-01-01

    Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet–visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films. PMID:26156001

  11. Visible light photocatalytic activity of TiO2 nanoparticles hybridized by conjugated derivative of polybutadiene

    NASA Astrophysics Data System (ADS)

    Liu, Guoquan; Liu, Longchen; Song, Jinran; Liang, Jiudi; Luo, Qingzhi; Wang, Desong

    2014-05-01

    A series of conjugated polymer/TiO2 (CP/TiO2) nanocomposites were prepared from TiO2 and commercial polybutadiene. The as-prepared CP/TiO2 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman Spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of CP/TiO2 nanocomposites were investigated by monitoring the degradation of methyl orange aqueous solution under visible light irradiation. The effects of preparation conditions (such as the mass ratio of PB to TiO2 in suspensions for PB/TiO2 preparation, heat-treatment temperature and time) of CP/TiO2 nanocomposites on their visible light photocatalytic activity were investigated. The results show that the CP/TiO2 nanocomposites have excellent visible light photocatalytic activity. As the content of conjugated polymer on the TiO2 surface, heat-treatment temperature and time increase, the visible light photocatalytic activity increases at first and then decreases. The visible light photocatalytic mechanism of the CP/TiO2 nanocomposites has been discussed.

  12. Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light.

    PubMed

    Wong, Ming-Show; Chen, Chun-Wei; Hsieh, Chia-Chun; Hung, Shih-Che; Sun, Der-Shan; Chang, Hsin-Hou

    2015-07-09

    Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet-visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

  13. Improving visible light sensitization of luminescent europium complexes.

    PubMed

    Kadjane, Pascal; Charbonnière, Loïc; Camerel, Franck; Lainé, Philippe P; Ziessel, Raymond

    2008-01-01

    The synthesis and characterization of the new ligands L(1), L(2) and L(4) are described with the series of four europium complexes of formula [EuL(n)(TTA)(3)] in which TTA refers to 2-thenoyltrifluoroacetonate and L(n) to tridentate ligands with nitrogen containing heterocyclic structure, such as a 2,6-bis(3-methyl-pyrazolyl)-4-(p-toluyl-ethynyl)-triazine for L(1), or terpyridines functionalized at the 4' position by a phenyl-vinylene for L(2), a p-dimethylamino-phenylene for L(3), or a p-aminophenyl-ethynylene for L(4). The spectroscopic properties of the ligands and of the complexes are studied by means of UV-Vis absorption spectroscopy, as well as steady-state and time-resolved luminescence spectroscopy. All complexes display europium centred luminescence upon ligand excitation. Careful examination of the excitation spectra revealed differences in the ligand based sensitization efficiencies. For complexes of L(1) and L(2), excitation of europium is mainly achieved through the TTA moieties and the photo-physical studies on [EuL(1)(TTA)(3)] evidenced a weaker coordination of the bispyrazolyltriazine tridentate ligand, resulting from a partial decomplexation upon dilution. Complexes of L(3) and L(4) display intense excitation through the tridentate units, which extend down to 460 nm in the visible region. In the case of L(3), selective excitation reveals the presence of a ligand-centred emission band at 520 nm which is likely ascribed to a L(3) centred charge transfer state. PMID:17909952

  14. Superposed pulse amplitude modulation for visible light communication.

    PubMed

    Li, J F; Huang, Z T; Zhang, R Q; Zeng, F X; Jiang, M; Ji, Y F

    2013-12-16

    We propose and experimentally demonstrate a novel modulation scheme called superposed pulse amplitude modulation (SPAM) which is low-cost, insensitive to non-linearity of light emitting diode (LED). Multiple optical pulses transmit parallelly from different spatial position in the LED array and overlap linearly in free space to realize SPAM. With LED arrangement, the experimental results show that using the modulation we proposed the data rate of 120 Mbit/s with BER 1 × 10(-3) can be achieved with an optical blue filter and RC post-equalization. PMID:24514674

  15. Volume-scalable high-brightness three-dimensional visible light source

    SciTech Connect

    Subramania, Ganapathi; Fischer, Arthur J; Wang, George T; Li, Qiming

    2014-02-18

    A volume-scalable, high-brightness, electrically driven visible light source comprises a three-dimensional photonic crystal (3DPC) comprising one or more direct bandgap semiconductors. The improved light emission performance of the invention is achieved based on the enhancement of radiative emission of light emitters placed inside a 3DPC due to the strong modification of the photonic density-of-states engendered by the 3DPC.

  16. Efficient ZnO-based visible-light-driven photocatalyst for antibacterial applications.

    PubMed

    Kumar, Raju; Anandan, Srinivasan; Hembram, Kaliyan; Rao, Tata Narasinga

    2014-08-13

    Herein, we report the development of a ZnO-based visible-light-driven photocatalyst by interfacial charge transfer process for the inactivation of pathogens under visible-light illumination. Surface modification by a cocatalyst on ZnO, prepared by flame spray pyrolysis process is carried out to induce the visible-light absorption in ZnO. Optical studies showed that surface modification of Cu(2+) induces the visible-light absorption in ZnO by interfacial charge transfer between ZnO and surface Cu(2+) ions upon light irradiation. The photocatalytic efficiency of pure and modified ZnO is evaluated for the inactivation of pathogens and the decomposition of methylene blue under visible-light illumination. The antibacterial activity of Cu(2+)-ZnO is several orders higher than pure ZnO and commercial Degussa-P25 and comparable with Cu(2+)-TiO2. Cu(2+)-ZnO nanorods show better photocatalytic activity than Cu(2+)-ZnO nanosphere, which is attributed to high surface area to volume ratio of former than later. The holes generated in the valence band and the Cu(1+) species generated during the interfacial charge transfer process may attribute for the inactivation of bacteria, whereas the strong oxidation power of hole is responsible for the decomposition of methylene blue. Besides the advantage of Cu(2+)-modified ZnO for visible-light-assisted photocatalytic applications, the method (FSP) used for the synthesis of ZnO in the present study is attractive for commercial application because the process has potential for the production of large quantities (2-3 kg/h) of semiconductors. PMID:25029041

  17. Electrodeposition synthesis of MnO{sub 2}/TiO{sub 2} nanotube arrays nanocomposites and their visible light photocatalytic activity

    SciTech Connect

    Xu, Xuyao; Zhou, Xiaosong; Li, Xiaoyu; Yang, Fei; Jin, Bei; Xu, Tan; Li, Guosheng; Li, Manyi

    2014-11-15

    Highlights: • MnO{sub 2}/TiO{sub 2} nanotube arrays nanocomposites are prepared by electrodeposition. • MnO{sub 2}/TiO{sub 2} exhibits high visible light photocatalytic activity. • The results of XRD show the depositions are attributed to α-MnO{sub 2}. • A photocatalytic mechanism is discussed under visible light irradiation. - Abstract: MnO{sub 2}/TiO{sub 2} nanotube arrays nanocomposite photocatalysts have been synthesized through an electrodeposition method. X-ray powder diffraction analysis and X-ray photoelectron spectroscopy measurements reveal that the products of electrodeposition method are MnO{sub 2}. Scanning electron microscopy measurements suggest that the depositions are deposited on the surface or internal of the nanotube. UV–vis light absorbance spectra demonstrate the excellent adsorption properties of MnO{sub 2}/TiO{sub 2} over the whole region of visible light, which enables this novel photocatalytic material to possess remarkable activity in the photocatalytic degradation of acid Orange II under visible light radiation. Moreover, a possible photocatalytic mechanism is discussed.

  18. Mussel-inspired green synthesis of polydopamine-Ag-AgCl composites with efficient visible-light-driven photocatalytic activity.

    PubMed

    Cai, Aijun; Wang, Xiuping; Guo, Aiying; Chang, Yongfang

    2016-09-01

    Polydopamine-Ag-AgCl composites (PDA-Ag-AgCl) were synthesized using a mussel-inspired method at room temperature, where PDA acts as a reducing agent to obtain the noble Ag nanoparticles from a precursor. The morphologies and structures of the as-prepared PDA-Ag-AgCl were characterized by several techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (SEM), Raman spectra, and X-Ray photoelectron spectrum (XPS). The morphological observation depicts formation of nanoparticles with various micrometer size diameters and surface XPS analysis shows presence of various elements including Ag, N, Cl, and O. The enhanced absorbance of the PDA-Ag-AgCl particles in the visible light region is confirmed through UV-Vis diffuse reflectance spectra (DRS), and the charge transfer is demonstrated by photoluminescence (PL) and photocurrent response. The synthesized PDA-Ag-AgCl composites could be used as visible-light-driven photocatalysts for the degradation of Rhodamine B. The elevated photocatalytic activity is ascribed to the effective charge transfer from plasmon-excited Ag to AgCl that can improve the efficiency of the charge separation during the photocatalytic reaction. Furthermore, differences in the photocatalytic performance among the different PDA-Ag-AgCl composites are noticed that could be attributed to the Brunauer-Emmett-Teller (BET) specific surface area, which benefits to capture the visible light efficiently. The PDA-Ag-AgCl exhibits excellent stability without a significant loss in activity after 5cycles. The proposed method is low-cost and environmentally friendly, hence a promising new way to fabricate plasmon photocatalysts. PMID:27450302

  19. Mussel-inspired green synthesis of polydopamine-Ag-AgCl composites with efficient visible-light-driven photocatalytic activity.

    PubMed

    Cai, Aijun; Wang, Xiuping; Guo, Aiying; Chang, Yongfang

    2016-09-01

    Polydopamine-Ag-AgCl composites (PDA-Ag-AgCl) were synthesized using a mussel-inspired method at room temperature, where PDA acts as a reducing agent to obtain the noble Ag nanoparticles from a precursor. The morphologies and structures of the as-prepared PDA-Ag-AgCl were characterized by several techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (SEM), Raman spectra, and X-Ray photoelectron spectrum (XPS). The morphological observation depicts formation of nanoparticles with various micrometer size diameters and surface XPS analysis shows presence of various elements including Ag, N, Cl, and O. The enhanced absorbance of the PDA-Ag-AgCl particles in the visible light region is confirmed through UV-Vis diffuse reflectance spectra (DRS), and the charge transfer is demonstrated by photoluminescence (PL) and photocurrent response. The synthesized PDA-Ag-AgCl composites could be used as visible-light-driven photocatalysts for the degradation of Rhodamine B. The elevated photocatalytic activity is ascribed to the effective charge transfer from plasmon-excited Ag to AgCl that can improve the efficiency of the charge separation during the photocatalytic reaction. Furthermore, differences in the photocatalytic performance among the different PDA-Ag-AgCl composites are noticed that could be attributed to the Brunauer-Emmett-Teller (BET) specific surface area, which benefits to capture the visible light efficiently. The PDA-Ag-AgCl exhibits excellent stability without a significant loss in activity after 5cycles. The proposed method is low-cost and environmentally friendly, hence a promising new way to fabricate plasmon photocatalysts.

  20. Robust sensor for turbidity measurement from light scattering and absorbing liquids.

    PubMed

    Kontturi, Ville; Turunen, Petri; Uozumi, Jun; Peiponen, Kai-Erik

    2009-12-01

    Internationally standardized turbidity measurements for probing solid particles in liquid are problematic in the case of simultaneous light scattering and absorption. A method and a sensor to determine the turbidity in the presence of light absorption are presented. The developed sensor makes use of the total internal reflection of a laser beam at the liquid-prism interface, and the turbidity is assessed using the concept of laser speckle pattern. Using average filtering in speckle data analyzing the observed dynamic speckle pattern, which is due to light scattering from particles and the static speckle due to stray light of the sensor, can be separated from each other. Good correlation between the standard deviation of dynamic speckle and turbidity value for nonabsorbing and for absorbing liquids was observed. The sensor is suggested, for instance, for the measurement of ill-behaved as well as small-volume turbid liquids in both medicine and process industry.

  1. 9nm node wafer defect inspection using visible light

    NASA Astrophysics Data System (ADS)

    Zhou, Renjie; Edwards, Chris; Popescu, Gabriel; Goddard, Lynford L.

    2014-04-01

    Over the past 2 years, we have developed a common optical-path, 532 nm laser epi-illumination diffraction phase microscope (epi-DPM) and successfully applied it to detect different types of defects down to 20 by 100 nm in a 22nm node intentional defect array (IDA) wafer. An image post-processing method called 2DISC, using image frame 2nd order differential, image stitching, and convolution, was used to significantly improve sensitivity of the measured images. To address 9nm node IDA wafer inspection, we updated our system with a highly stable 405 nm diode laser. By using the 2DISC method, we detected parallel bridge defects in the 9nm node wafer. To further enhance detectability, we are exploring 3D wafer scanning, white-light illumination, and dark-field inspection.

  2. Phototoxic reaction to xanthene dyes induced by visible light.

    PubMed

    Morikawa, F; Fukuda, M; Naganuma, M; Nakayama, Y

    1976-04-01

    Many dyes, for instance methylene blue, rose bengal, and eosin, are known as photosensitizers, and in the presence of molecular oxygen they induce cell lethality and skin photosensitivity (1-4). Several dyes are used in cosmetic products, particularly in lipsticks. Human lip skin is therefore exposed to potential danger from dye-sensitized phototoxic reactions. Using an in vivo system of mammalian skin, such as the abdominal skin of rabbits, we established screening tests for the phototoxic potential of synthetic dyes in two ways: (a) intracutaneous injection; (b) topical application with and without damaging the barrier property of the stratum corneum. In the intracutaneous injection assay, distinct phototoxic reactions were induced by rose bengal, eosin Y.S., and dibromofluorescein. When these dyes were applied topically to intact skin, no phototoxic reactions were observed. Phototoxic reactions were, however, elicited when the dye solutions were applied to abraded or scratched skin. The intensity of phototoxic reaction was found to be influenced by the vehicle in which the dyes were suspended. Phototoxic reaction to the dyes was induced by artificial light as well as by sunlight. By using commercially available fluorescent lamps with different spectral emissions, the action spectra for the phototoxic reaction to these dyes were investigated and it was found that the maximum phototoxicities of the dyes were manifested by light within a spectral range of 400-600 nm. Further studies on action spectra, using a monochromatic irradiation system, revealed a high correlation between the action spectra of the dyes and their absorption spectra. Maximum effective wavelength for the phototoxic reaction of eosin Y.S. was 525 nm. This topical as well as intradermal assay for assesing phototoxic reaction to synthetic dyes in living skin will be a practical and useful measure for studying the phototoxicity of the dyes.

  3. Sb(2)O(3) nanobelt networks for excellent visible-light-range photodetectors.

    PubMed

    Li, L; Zhang, Y X; Fang, X S; Zhai, T Y; Liao, M Y; Wang, H Q; Li, G H; Koide, Y; Bando, Y; Golberg, D

    2011-04-22

    Excellent photoconductive properties have been found in Sb(2)O(3) nanobelts synthesized by a surfactant-assisted solvothermal method. Visible-light photodetectors have been designed from Sb(2)O(3) nanobelt networks using micrometer-wide gold wires as masks. Photodetectors show high sensitivity to visible light, high stability, and reproducibility. Fast response and decay times (<0.3 s) are comparable or even better than these parameters in many other metal oxide nanoscale photodetectors. The dominant mechanism of excellent photoconductivity is attributed to the barrier height modulations in the nanobelt-to-nanobelt contact regions. These results demonstrate that Sb(2)O(3) nanobelt networks can indeed serve as high-performance photodetectors in the visible light range.

  4. Enhanced visible-light activity of titania via confinement inside carbon nanotubes.

    PubMed

    Chen, Wei; Fan, Zhongli; Zhang, Bei; Ma, Guijun; Takanabe, Kazuhiro; Zhang, Xixiang; Lai, Zhiping

    2011-09-28

    Titania confined inside carbon nanotubes (CNTs) was synthesized using a restrained hydrolysis method. Raman spectra and magnetic measurements using a SQUID magnetometer suggested the formation of remarkable oxygen vacancies over the encapsulated TiO(2) in comparison with nanoparticles dispersed on the outer surface of CNTs, extending the photoresponse of TiO(2) from the UV to the visible-light region. The CNT-confined TiO(2) exhibited improved visible-light activity in the degradation of methylene blue (MB) relative to the outside titania and commercial P25, which is attributed to the modification of the electronic structure of TiO(2) induced by the unique confinement inside CNTs. These results provide further insight into the effect of confinement within CNTs, and the composites are expected to be promising for applications in visible-light photocatalysis.

  5. Photoinduced reactions between Pb3O4 and organic dyes in aqueous solution under visible light.

    PubMed

    Zhou, Yangen; Long, Jinlin; Gu, Quan; Lin, Huaxiang; Lin, Huan; Wang, Xuxu

    2012-12-01

    Pb(3)O(4) could react with organic dyes in aqueous solution under visible light irradiation, in which Pb(3)O(4) was transformed into Pb(3)(CO(3))(2)(OH)(2) along with oxidation of the organic dyes. Cu(2+) has considerable effect on the reaction. In the presence of Cu(2+), MO (20 ppm) and RhB (10(-5) mol L(-1)) were completely degraded under visible light within 6 and 20 min, respectively, while both Pb(3)O(4) and Cu(2+) keep almost stable during photodegradation. The mechanisms of the reactions with and without Cu(2+) ions were studied. The photochemical system of Pb(3)O(4) cooperating with Cu(2+) ions is probably used for the treatment of organic pollutants in water under visible light.

  6. Visible-Light-Responsive Catalyst Development for Volatile Organic Carbon Remediation Project

    NASA Technical Reports Server (NTRS)

    Zeitlin, Nancy; Hintze, Paul E.; Coutts, Janelle

    2015-01-01

    Photocatalysis is a process in which light energy is used to 'activate' oxidation/reduction reactions. Unmodified titanium dioxide (TiO2), a common photocatalyst, requires high-energy UV light for activation due to its large band gap (3.2 eV). Modification of TiO2 can reduce this band gap, leading to visible-light-responsive (VLR) photocatalysts. These catalysts can utilize solar and/or visible wavelength LED lamps as an activation source, replacing mercury-containing UV lamps, to create a "greener," more energy-efficient means for air and water revitalization. Recently, KSC developed several VLR catalysts that, on preliminary evaluation, possessed high catalytic activity within the visible spectrum; these samples out-performed existing commercial VLR catalysts.

  7. Indoor anti-occlusion visible light positioning systems based on particle filtering

    NASA Astrophysics Data System (ADS)

    Jiang, Meng; Huang, Zhitong; Li, Jianfeng; Zhang, Ruqi; Ji, Yuefeng

    2015-04-01

    As one of the most popular categories of mobile services, a rapid growth of indoor location-based services has been witnessed over the past decades. Indoor positioning methods based on Wi-Fi, radio-frequency identification or Bluetooth are widely commercialized; however, they have disadvantages such as low accuracy or high cost. An emerging method using visible light is under research recently. The existed visible light positioning (VLP) schemes using carrier allocation, time allocation and multiple receivers all have limitations. This paper presents a novel mechanism using particle filtering in VLP system. By this method no additional devices are needed and the occlusion problem in visible light would be alleviated which will effectively enhance the flexibility for indoor positioning.

  8. Differences in visible and near-infrared light reflectance between orange fruit and leaves

    NASA Technical Reports Server (NTRS)

    Gausman, H. W.; Escobar, D. E.; Berumen, A.

    1975-01-01

    The objective was to find the best time during the season (April 26, 1972 to January 8, 1973) to distinguish orange fruit from leaves by spectrophotometrically determining at 10-day intervals when the difference in visible (550- and 650-nm wavelengths) and near-infrared (850-nm wavelength) light reflectance between fruit and nearby leaves was largest. December 5 to January 8 was the best time to distinguish fruit from leaves. During this period the fruit's color was rapidly changing from green to yellow, and the difference in visible light reflectance between fruit and leaves was largest. The difference in near-infrared reflectance between leaves and fruit remained essentially constant during ripening when the difference in visible light reflectance between leaves and fruit was largest.

  9. Visible-Light-Sensitive Photocatalysts: Nanocluster-Grafted Titanium Dioxide for Indoor Environmental Remediation.

    PubMed

    Miyauchi, Masahiro; Irie, Hiroshi; Liu, Min; Qiu, Xiaoqing; Yu, Huogen; Sunada, Kayano; Hashimoto, Kazuhito

    2016-01-01

    Photocatalytic degradation of organic compounds requires photoexcited holes with strong oxidative power in the valence band (VB) of semiconductors. Although numerous types of doped semiconductors, such as nitrogen-doped TiO2, have been studied as visible-light-sensitive photocatalysts, the quantum yields of these materials were very low because of the limited oxidation power of holes in the nitrogen level above the VB. Recently, we developed visible-light-sensitive Cu(II) and Fe(III) nanocluster-grafted TiO2 using a facile impregnation method and demonstrated that visible-light absorption occurs at the interface between the nanoclusters and TiO2, as electrons in the VB of TiO2 are excited to the nanoclusters under visible-light irradiation. In addition, photogenerated holes in the VB of TiO2 efficiently oxidize organic contaminants, and the excited electrons that accumulate in nanoclusters facilitate the multielectron reduction of oxygen. Notably, Cu(II) and Fe(III) nanocluster-grafted TiO2 photocatalyst has the highest quantum yield among reported photocatalysts and has antiviral, self-cleaning, and air purification properties under illumination by indoor light fixtures equipped with white fluorescent bulbs or white light-emitting diodes. PMID:26654353

  10. Sequential growth of zinc oxide nanorod arrays at room temperature via a corrosion process: application in visible light photocatalysis.

    PubMed

    Iqbal, Danish; Kostka, Aleksander; Bashir, Asif; Sarfraz, Adnan; Chen, Ying; Wieck, Andreas D; Erbe, Andreas

    2014-11-12

    Many photocatalyst systems catalyze chemical reactions under ultraviolet (UV) illumination, because of its high photon energies. Activating inexpensive, widely available materials as photocatalyst using the intense visible part of the solar spectrum is more challenging. Here, nanorod arrays of the wide-band-gap semiconductor zinc oxide have been shown to act as photocatalysts for the aerobic photo-oxidation of organic dye Methyl Orange under illumination with red light, which is normally accessible only to narrow-band semiconductors. The homogeneous, 800-1000-nm-thick ZnO nanorod arrays show substantial light absorption (absorbances >1) throughout the visible spectral range. This absorption is caused by defect levels inside the band gap. Multiple scattering processes by the rods make the nanorods appear black. The dominantly crystalline ZnO nanorod structures grow in the (0001) direction, i.e., with the c-axis perpendicular to the surface of polycrystalline zinc. The room-temperature preparation route relies on controlled cathodic delamination of a weakly bound polymer coating from metallic zinc, an industrially produced and cheaply available substrate. Cathodic delamination is a sequential synthesis process, because it involves the propagation of a delamination front over the base material. Consequently, arbitrarily large sample surfaces can be nanostructured using this approach.

  11. Atomic-layer molybdenum sulfide optical modulator for visible coherent light

    PubMed Central

    Zhang, Yuxia; Wang, Shuxian; Yu, Haohai; Zhang, Huaijin; Chen, Yanxue; Mei, Liangmo; Di Lieto, Alberto; Tonelli, Mauro; Wang, Jiyang

    2015-01-01

    Coherent light sources in the visible range are playing important roles in our daily life and modern technology, since about 50% of the capability of the our human brains is devoted to processing visual information. Visible lasers can be achieved by nonlinear optical process of infrared lasers and direct lasing of gain materials, and the latter has advantages in the aspects of compactness, efficiency, simplicity, etc. However, due to lack of visible optical modulators, the directly generated visible lasers with only a gain material are constrained in continuous-wave operation. Here, we demonstrated the fabrication of a visible optical modulator and pulsed visible lasers based on atomic-layer molybdenum sulfide (MoS2), a ultrathin two-dimensional material with about 9–10 layers. By employing the nonlinear absorption of the modulator, the pulsed orange, red and deep red lasers were directly generated. Besides, the present atomic-layer MoS2 optical modulator has broadband modulating properties and advantages in the simple preparation process. The present results experimentally verify the theoretical prediction for the low-dimensional optoelectronic modulating devices in the visible wavelength region and may open an attractive avenue for removing a stumbling block for the further development of pulsed visible lasers. PMID:26067821

  12. Achieving significantly enhanced visible-light photocatalytic efficiency using a polyelectrolyte: the composites of exfoliated titania nanosheets, graphene, and poly(diallyl-dimethyl-ammonium chloride)

    NASA Astrophysics Data System (ADS)

    Zhang, Qian; An, Qi; Luan, Xinglong; Huang, Hongwei; Li, Xiaowei; Meng, Zilin; Tong, Wangshu; Chen, Xiaodong; Chu, Paul K.; Zhang, Yihe

    2015-08-01

    A high-performance visible-light-active photocatalyst is prepared using the polyelectrolyte/exfoliated titania nanosheet/graphene oxide (GO) precursor by flocculation followed by calcination. The polyelectrolyte poly(diallyl-dimethyl-ammonium chloride) serves not only as an effective binder to precipitate GO and titania nanosheets, but also boosts the overall performance of the catalyst significantly. Unlike most titania nanosheet-based catalysts reported in the literature, the composite absorbs light in the UV-Vis-NIR range. Its decomposition rate of methylene blue is 98% under visible light. This novel strategy of using a polymer to enhance the catalytic performance of titania nanosheet-based catalysts affords immense potential in designing and fabricating next-generation photocatalysts with high efficiency.A high-performance visible-light-active photocatalyst is prepared using the polyelectrolyte/exfoliated titania nanosheet/graphene oxide (GO) precursor by flocculation followed by calcination. The polyelectrolyte poly(diallyl-dimethyl-ammonium chloride) serves not only as an effective binder to precipitate GO and titania nanosheets, but also boosts the overall performance of the catalyst significantly. Unlike most titania nanosheet-based catalysts reported in the literature, the composite absorbs light in the UV-Vis-NIR range. Its decomposition rate of methylene blue is 98% under visible light. This novel strategy of using a polymer to enhance the catalytic performance of titania nanosheet-based catalysts affords immense potential in designing and fabricating next-generation photocatalysts with high efficiency. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03256c

  13. Impact of different visible light spectra on oxygen absorption and surface discoloration of bologna sausage.

    PubMed

    Böhner, Nadine; Rieblinger, Klaus

    2016-11-01

    The objective of this study was to evaluate the influence of several visible light spectra in various intensities on the oxygen absorption and surface color of sliced bologna. Sausage samples were stored in a gastight model packaging system and illuminated at 5°C with six single-colored LEDs covering the main part of the visible light spectrum. The initial oxygen level was set at 0.5% in order to simulate common residual oxygen amounts in conventional packaging. The oxygen absorption and the discoloration measured as changes in CIE a*-value were dependent from the applied light intensity. The color stability of bologna was differently affected by light of various wavelengths. The results show that the use of suitable LEDs with specific spectra for display illumination can help to reduce the light induced deterioration of cured sausages in retail markets. PMID:27343458

  14. Impact of different visible light spectra on oxygen absorption and surface discoloration of bologna sausage.

    PubMed

    Böhner, Nadine; Rieblinger, Klaus

    2016-11-01

    The objective of this study was to evaluate the influence of several visible light spectra in various intensities on the oxygen absorption and surface color of sliced bologna. Sausage samples were stored in a gastight model packaging system and illuminated at 5°C with six single-colored LEDs covering the main part of the visible light spectrum. The initial oxygen level was set at 0.5% in order to simulate common residual oxygen amounts in conventional packaging. The oxygen absorption and the discoloration measured as changes in CIE a*-value were dependent from the applied light intensity. The color stability of bologna was differently affected by light of various wavelengths. The results show that the use of suitable LEDs with specific spectra for display illumination can help to reduce the light induced deterioration of cured sausages in retail markets.

  15. Development and Progress in Enabling the Photocatalyst Ti02 Visible-Light-Active

    NASA Technical Reports Server (NTRS)

    Levine, Lanfang H.; Coutts, Janelle L.; Clausen, Christian A.

    2011-01-01

    Photocatalytic oxidation (PCO) of organic contaminants is a promising air and water quality management approach which offers energy and cost savings compared to thermal catalytic oxidation (TCO). The most widely used photocatalyst, anatase TiO2, has a wide band gap (3.2 eV) and is activated by UV photons. Since solar radiation consists of less than 4% UV, but contains 45% visible light, catalysts capable of utilizing these visible photons need to be developed to make peo approaches more efficient, economical, and safe. Researchers have attempted various approaches to enable TiO2 to be visible-light-active with varied degrees of success'. Strategies attempted thus far fall into three categories based on their electrochemical' mechanisms: 1) narrowing the band gap of TiO2 by implantation of transition metal elements or nonmetal elements such as N, S, and C, 2) modifying electron-transfer processes during PCO by adsorbing sensitizing dyes, and 3) employing light-induced interfacial electron transfer in the heteronanojunction systems consisting of narrow band gap semiconductors represented by metal sulfides and TiO2. There are diverse technical approaches to implement each of these strategies. This paper presents a review of these approaches and results of the photocatalytic activity and photonic efficiency of the end .products under visible light. Although resulting visible-light-active (VLA) photocatalysts show promise, there is often no comparison with unmodified TiO2 under UV. In a limited number of studies where such comparison was provided, the UV-induced catalytic activity of bare TiO2 is much greater than the visible-light-induced catalytic activity of the VLA catalyst. Furthermore, VLA-catalysts have much lower quantum efficiency compared to the approx.50% quantum efficiency of UV-catalysts. This stresses the need for continuing research in this area.

  16. The action spectrum of Photosystem II photoinactivation in visible light.

    PubMed

    Zavafer, Alonso; Chow, Wah Soon; Cheah, Mun Hon

    2015-11-01

    Photosynthesis is always accompanied by light induced damage to the Photosystem II (PSII) which is compensated by its subsequent repair. Photoinhibition of PSII is a complex process, balancing between photoinactivation, protective and repair mechanisms. Current understanding of photoinactivation is limited with competing hypotheses where the photosensitiser is either photosynthetic pigments or the Mn4CaO5 cluster itself, with little consensus on the mechanisms and consequences of PSII photoinactivation. The mechanism of photoinactivation should be reflected in the action spectrum of PSII photoinactivation, but there is a great diversity of the action spectra reported thus far. The only consensus is that PSII photoinactivation is greatest in the UV region of the electromagnetic spectrum. In this review, the authors revisit the methods, technical constraints and the different action spectra of PSII photoinactivation reported to date and compare them against the diverse mechanisms proposed. Upon critical examination of the reported action spectra, a hybrid mechanism of photoinactivation, sensitised by both photosynthetic pigments and the Mn4CaO5 appears to be the most plausible rationalisation.

  17. The action spectrum of Photosystem II photoinactivation in visible light.

    PubMed

    Zavafer, Alonso; Chow, Wah Soon; Cheah, Mun Hon

    2015-11-01

    Photosynthesis is always accompanied by light induced damage to the Photosystem II (PSII) which is compensated by its subsequent repair. Photoinhibition of PSII is a complex process, balancing between photoinactivation, protective and repair mechanisms. Current understanding of photoinactivation is limited with competing hypotheses where the photosensitiser is either photosynthetic pigments or the Mn4CaO5 cluster itself, with little consensus on the mechanisms and consequences of PSII photoinactivation. The mechanism of photoinactivation should be reflected in the action spectrum of PSII photoinactivation, but there is a great diversity of the action spectra reported thus far. The only consensus is that PSII photoinactivation is greatest in the UV region of the electromagnetic spectrum. In this review, the authors revisit the methods, technical constraints and the different action spectra of PSII photoinactivation reported to date and compare them against the diverse mechanisms proposed. Upon critical examination of the reported action spectra, a hybrid mechanism of photoinactivation, sensitised by both photosynthetic pigments and the Mn4CaO5 appears to be the most plausible rationalisation. PMID:26298696

  18. Visible light may directly induce nuclear DNA damage triggering the death pathway in RGC-5 cells

    PubMed Central

    Fan, Bin; Ma, Tong-Hui

    2011-01-01

    Purpose Visible light has been previously demonstrated to induce retinal ganglion cell (RGC)-5 cell death through the mitochondrial pathway. The present study was designed to determine whether visible light might also directly trigger the death pathway by damaging nuclear DNA. Methods RGC-5 cells were exposed to various intensities and durations of visible light exposure. Cell viability and death were monitored with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and propidium iodide staining. Nuclear DNA damage caused by light was determined with the plasmid assay, genome DNA assay, and in situ terminal deoxynucleotidyl transferase dUTP nick end labeling. The subsequent activation of nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) was measured with western blot, and PARP-1’s role in the death pathway was assessed by using specific inhibitors. Poly (ADP-ribose) glycohydrolase and apoptosis-inducing factor (AIF) inhibitors were used to show their influence on light-induced cell death. Calcium influx was examined with the fura-2 assay and calcium channel blocker. Results We found that visible light induced RGC-5 cell death in a time- and intensity-dependent manner. After the light intensity was increased to 2,600 lx, activation of the death pathway in RGC-5 cells was clearly observed by detecting double-strand DNA breaks and nuclear DNA damage in vitro. Nuclear enzyme PARP-1 was promptly activated after exposure to 2,600 lx of light for 2 days, and specific inhibitors of PARP-1 had significant neuroprotective effects. The poly(ADP-ribose) glycohydrolase inhibitor tannic acid and AIF inhibitor N-phenylmaleimide partially protected RGC-5 cells from light injury. A massive calcium influx was detected after 2 days of light exposure, and a calcium channel blocker partially protected cells against light injury. Conclusions These results suggest that visible light exposure may directly cause nuclear DNA damage, which consequently activates

  19. The chemistry of amine radical cations produced by visible light photoredox catalysis

    PubMed Central

    Hu, Jie; Wang, Jiang; Nguyen, Theresa H

    2013-01-01

    Summary Amine radical cations are highly useful reactive intermediates in amine synthesis. They have displayed several modes of reactivity leading to some highly sought-after synthetic intermediates including iminium ions, α-amino radicals, and distonic ions. One appealing method to access amine radical cations is through one-electron oxidation of the corresponding amines under visible light photoredox conditions. This approach and subsequent chemistries are emerging as a powerful tool in amine synthesis. This article reviews synthetic applications of amine radical cations produced by visible light photocatalysis. PMID:24204409

  20. Photometry in the dark: time dependent visibility of low intensity light sources.

    PubMed

    Poelman, Dirk; Smet, Philippe F

    2010-12-01

    This paper aims at describing the perceived brightness of persistent luminescent materials for emergency signage. In case of emergency, typically, a fully light adapted person is left in the dark, except for the emergency sign. The available photometric models cannot describe visibility of such light source, as they do not consider the slow dark adaptation of the human eye. The model proposed here fully takes into account the shift from photopic to scotopic vision, the related shift in spectral sensitivity and the dark adaptation. The resulting metric is a 'visibility index' and preliminary tests show that it more realistically describes the perceived brightness of persistent luminescent materials than the common photometric standards.

  1. Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity.

    PubMed

    Panomsuwan, Gasidit; Watthanaphanit, Anyarat; Ishizaki, Takahiro; Saito, Nagahiro

    2015-06-01

    Black titania spheres (H-TiO2-x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO2-x, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO2-x can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti(3+) sites. PMID:25946395

  2. Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity.

    PubMed

    Panomsuwan, Gasidit; Watthanaphanit, Anyarat; Ishizaki, Takahiro; Saito, Nagahiro

    2015-06-01

    Black titania spheres (H-TiO2-x) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO2-x, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO2-x can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti(3+) sites.

  3. Nitrogen-sensitized dual phase titanate/titania for visible-light driven phenol degradation

    SciTech Connect

    Cheng, Yu Hua; Subramaniam, Vishnu P.; Gong, Dangguo; Tang, Yuxin; Highfield, James; Pehkonen, Simo O.; Pichat, Pierre; Chen, Zhong

    2012-12-15

    A dual-phase material (DP-160) comprising hydrated titanate (H{sub 2}Ti{sub 3}O{sub 7}{center_dot}xH{sub 2}O) and anatase (TiO{sub 2}) was synthesized in a low-temperature one-pot process in the presence of triethylamine (TEA) as the N-source. The unique structure exhibits strong visible light absorption. The chromophore is linked to Ti-N bonds derived from both surface sensitization and sub-surface (bulk) doping. From transmission electron microscope (TEM) and textural studies by N{sub 2} physisorption, the composite exists as mesoporous particles with a grain size of {approx}20 nm and mean pore diameter of 3.5 nm, responsible for the high surface area ({approx}180 m{sup 2}/g). DP-160 demonstrated photocatalytic activity in the degradation of phenol under visible light ({lambda}>420 nm). The activity of the composite was further enhanced by a small addition (0.001 M) of H{sub 2}O{sub 2}, which also gave rise to some visible light activity in the control samples. This effect is believed to be associated with the surface peroxo-titanate complex. GC-MS analyses showed that the intermediate products of phenol degradation induced by visible light irradiation of DP-160 did not differ from those obtained by UV (band-gap) irradiation of TiO{sub 2}. The overall performance of the composite is attributed to efficient excitation via inter-band states (due to N-doping), surface sensitization, improved adsorptive properties of aromatic compounds due to the N-carbonaceous overlayer, and the presence of heterojunctions that are known to promote directional charge transfer in other mixed-phase titanias like Degussa P25. - graphical abstract: Nitrogen-sensitized dual phase titanate/titania photocatalyst showing extended visible light absorption and efficient photocatalytic degradation of phenol. Highlights: Black-Right-Pointing-Pointer Low temperature one-pot synthesis of visible light active dual phase photocatalyst. Black-Right-Pointing-Pointer The dual phase consists of

  4. Iron(III)-oxo centers on TiO{sub 2} for visible light photocatalysis.

    SciTech Connect

    Libera, J. A.; Elam, J. W.; Sather, N. F.; Rajh, T.; Dimitrijevic, N. M.

    2009-01-01

    Isolated iron(III)-oxo clusters were synthesized onto TiO{sub 2} using atomic layer deposition. The Fe{sub x}O{sub y}/TiO{sub 2} nanocomposites have unique properties that enable not only absorption of visible light, but efficient photocatalysis as demonstrated by methylene blue degradation. The localization of photogenerated electrons in core TiO{sub 2} nanocrystallites upon visible light excitation demonstrates coupling of conduction bands of mixed oxides. The redox properties of photogenerated charges in nanocomposites were studied using in situ electron paramagnetic resonance spectroscopy.

  5. Photocatalytic water treatment over WO 3 under visible light irradiation combined with ozonation

    NASA Astrophysics Data System (ADS)

    Nishimoto, Shunsuke; Mano, Takayuki; Kameshima, Yoshikazu; Miyake, Michihiro

    2010-11-01

    Photocatalytic water treatment over bare WO 3 under visible light irradiation combined with ozonation (O 3/vis/WO 3) was investigated using an aqueous phenol solution as model wastewater. The O 3/vis/WO 3 treatment exhibited a much higher total organic carbon removal than ozonation alone. Bare WO 3 was found to function as an active visible-light-responsive photocatalyst for decomposition of organic compounds in the presence of ozone, which readily reacts with photoexcited electrons in the conduction band of WO 3.

  6. Characterization of internal geometry / covered surface defects with a visible light sensing system

    NASA Astrophysics Data System (ADS)

    Straub, Jeremy

    2016-05-01

    Previous work has used visible light scanning to detect and characterize defects in 3D printed objects. This paper focuses on assessing the internal structures and external surfaces (that will be later hidden) of complex objects. These features make in-process defect detection far more important than it would be with an object that can be fully assessed with a post-completion scan, as it is required both for in-process correction and end-product quality assurance. This paper presents work on the use of a multi-camera visible light 3D scanning system to identify defects with printed objects' interior and covered / obscured exterior surfaces.

  7. High bandwidth based on a tapped delay line equalization in visible light communications

    NASA Astrophysics Data System (ADS)

    Zhang, Minglun; Guo, Xujing; Zhu, Hetian; Wang, Chao; Bai, Xiaonan; Zhai, Xiangwen

    2015-08-01

    In the visible light communication, the white LED bandwidth severely limits the transmission rate of information. This paper presents an analog pre-equalization technology to compensate for the bandwidth of white LED. The technology not only can debug according to the actual channel changing, but also avoid the high costs of using FPGA technology. The pre-equalization technology is implemented by an analog circuit of tapped-delay-line, in the circuit we select an appropriate delay line and a digital to analog converter. In our LED visible light communication system, we can achieve a bandwidth of 150MHz which was proved theoretically in the paper.

  8. Carbon quantum dots with photo-generated proton property as efficient visible light controlled acid catalyst

    NASA Astrophysics Data System (ADS)

    Li, Haitao; Liu, Ruihua; Kong, Weiqian; Liu, Juan; Liu, Yang; Zhou, Lei; Zhang, Xing; Lee, Shuit-Tong; Kang, Zhenhui

    2013-12-01

    Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34

  9. Experimental Study of Red-, Green-, and Blue-Based Light Emitting Diodes Visible Light Communications for Micro-Projector Application

    NASA Astrophysics Data System (ADS)

    Chou, H.-H.; Liaw, S.-K.; Jiang, J.-S.; Teng, C.

    2016-05-01

    In this research, an experimental short-range visible light communication link using red-, green-, and blue-based light-emitting diodes (LEDs) for portable micro-projector applications is presented. A Reconfigurable design of a post-equalizer aimed to improve the inherent narrow modulation bandwidth of red-, green-, and blue-based LEDs has been experimentally implemented, and its effectiveness with optical filters at the receiver is investigated. Reflective liquid-crystal-on-silicon-based micro-projection architecture, widely used in portable micro-projectors, was set up to evaluate the proposed visible light communication system. The measurement results demonstrated that a significant aggregative bandwidth improvement of 162 MHz as well as an aggregative data transmission rate of nearly 400 Mb/s can be achieved by using a non-return-to-zero-on-off keying (NRZ-OOK) modulation scheme based on only one polarization state of incident light without any offline signal processing.

  10. Measurements of the light-absorbing material inside cloud droplets and its effect on cloud albedo

    NASA Technical Reports Server (NTRS)

    Twohy, C. H.; Clarke, A. D.; Warren, Stephen G.; Radke, L. F.; Charleson, R. J.

    1990-01-01

    Most of the measurements of light-absorbing aerosol particles made previously have been in non-cloudy air and therefore provide no insight into aerosol effects on cloud properties. Here, researchers describe an experiment designed to measure light absorption exclusively due to substances inside cloud droplets, compare the results to related light absorption measurements, and evaluate possible effects on the albedo of clouds. The results of this study validate those of Twomey and Cocks and show that the measured levels of light-absorbing material are negligible for the radiative properties of realistic clouds. For the measured clouds, which appear to have been moderately polluted, the amount of elemental carbon (EC) present was insufficient to affect albedo. Much higher contaminant levels or much larger droplets than those measured would be necessary to significantly alter the radiative properties. The effect of the concentrations of EC actually measured on the albedo of snow, however, would be much more pronounced since, in contrast to clouds, snowpacks are usually optically semi-infinite and have large particle sizes.

  11. Aerosol impacts on visible light extinction in the atmosphere of Mexico City.

    PubMed

    Eidels-Dubovoi, Silvia

    2002-03-27

    Eleven diurnal aerosol visible light absorption and scattering patterns were obtained from measurements done with an aethalometer and an integrating nephelometer during 28 February-10 March 1997 at two different sites in the Mexico City basin. Both measurement sites, the Merced site affected by regional and urban-scale aerosol and the Pedregal site dominated by regional-scale aerosol, showed a variety of diurnal light absorption and scattering patterns. For the majority of the 11 studied days, the highest absorption peaks appeared in the early morning, 07.00-09.30 h while those of scattering appeared later, 09.30-11.00 h. The earlier absorption peaks could be attributed to the elevated elemental carbon vehicular emissions during the heavy traffic hours whereas the later scattering peaks could be attributed to secondary aerosols formed photochemically in the atmosphere. During the period examined, the Pedregal site exhibited on the average a lower aerosol scattering and a higher aerosol absorption contribution to the total aerosol visible light extinction and a better visibility than that of the Merced site. Hence, the impact of aerosol absorption on the visibility degradation due to aerosols was greater at the less hazy Pedregal site. The overall 11-day aerosol visibility average of 20.9 km found at La Merced site, was only 9.4 km lower than that of 30.3 km found at the Pedregal site. This small aerosol visibility difference, of the order of the standard deviation, led to the conclusion that besides the regional-scale aerosol impact, the urban-scale aerosol impact on aerosol visible light extinction is very similar at La Merced and Pedregal sites.

  12. White-Light-Induced Collective Heating of Gold Nanocomposite/Bombyx mori Silk Thin Films with Ultrahigh Broadband Absorbance.

    PubMed

    Tsao, Shao Hsuan; Wan, Dehui; Lai, Yu-Sheng; Chang, Ho-Ming; Yu, Chen-Chieh; Lin, Keng-Te; Chen, Hsuen-Li

    2015-12-22

    This paper describes a systematic investigation of the phenomenon of white-light-induced heating in silk fibroin films embedded with gold nanoparticles (Au NPs). The Au NPs functioned to develop an ultrahigh broadband absorber, allowing white light to be used as a source for photothermal generation. With an increase of the Au content in the composite films, the absorbance was enhanced significantly around the localized surface plasmon resonance (LSPR) wavelength, while non-LSPR wavelengths were also increased dramatically. The greater amount of absorbed light increased the rate of photoheating. The optimized composite film exhibited ultrahigh absorbances of approximately 95% over the spectral range from 350 to 750 nm, with moderate absorbances (>60%) at longer wavelengths (750-1000 nm). As a result, the composite film absorbed almost all of the incident light and, accordingly, converted this optical energy to local heat. Therefore, significant temperature increases (ca. 100 °C) were readily obtained when we irradiated the composite film under a light-emitting diode or halogen lamp. Moreover, such composite films displayed linear light-to-heat responses with respect to the light intensity, as well as great photothermal stability. A broadband absorptive film coated on a simple Al/Si Schottky diode displayed a linear, significant, stable photo-thermo-electronic effect in response to varying the light intensity.

  13. [UV, visible and infrared light. Which wavelengths produce oxidative stress in human skin?].

    PubMed

    Zastrow, L; Groth, N; Klein, F; Kockott, D; Lademann, J; Ferrero, L

    2009-04-01

    Experimental evidence suggests that the creation of free radicals--mainly reactive oxygen species (ROS)--is the common photobiological answer to the skin-sunlight interaction. The free radical action spectrum (wavelength dependency) for ultraviolet and visible light (280-700 nm) has been determined by quantitative ESR spectroscopy. Visible light produces around 50% of the total oxidative stress caused by sunlight. Reactive species like *O(-)(2), *OH and *CHR are generated by visible light. The amount of ROS correlates with the visible light intensity (illuminance). We demonstrated the creation of excess free radicals by near-infrared light (NIR, 700-1600 nm). Free radical generation does not depend exclusively on the NIR irradiance, but also on the NIR initiated skin temperature increase. The temperature dependence follows the physiological fever curve. Our results indicate that the complex biological system skin creates the same type of free radicals over the entire active solar spectrum. This general response will make it possible to define the beneficial or deleterious action of sunlight on human skin by introduction of a free radical threshold value.

  14. Polymer nanoparticles for controlled release stimulated by visible light and pH.

    PubMed

    Dong, Jie; Zhang, Ruichen; Wu, Hao; Zhan, Xiaowei; Yang, Huai; Zhu, Siquan; Wang, Guojie

    2014-07-01

    Polymer nanoparticles are prepared by self-assembly of visible light and pH sensitive perylene-functionalized copolymers which are synthesized by quaternization between 1-(bromomethyl)perylene and the dimethylaminoethyl units of poly(dimethylaminoethyl methacrylate) (PDMAEMA). The perylene-containing polymethacrylate segments afford the system visible light responsiveness and the unquaternized PDMAEMA segments afford the system pH responsiveness. The self-assembled nanoparticles exhibit a unique dual stimuli response. They can be photocleaved under visible light irradiation, shrunken to smaller nanoparticles at high pH, and swollen at low pH. The structural change endows the nanoparticle with great potential as a sensitive nanocarrier for controlled release of Nile Red and lysozyme under this stimulation. The visible light responsiveness and synergistic effect on the release of loaded molecules with the dual stimulation may obviate the need for harsh conditions such as UV light or extreme pH stimulation, rendering the system more applicable under mild conditions. PMID:24719021

  15. Highly Active TiO2-Based Visible-Light Photocatalyst with Nonmetal Doping and Plasmonic Metal Decoration

    SciTech Connect

    Zhang, Qiao; Lima, Diana Q.; Chi, Miaofang; Yin, Yadong

    2011-01-01

    A sandwich-structured photocatalyst shows an excellent performance in degradation reactions of a number of organic compounds under UV, visible light, and direct sunlight (see picture). The catalyst was synthesized by a combination of nonmetal doping and plasmonic metal decoration of TiO2 nanocrystals, which improves visible-light activity and enhances light harvesting and charge separation, respectively.

  16. Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility

    PubMed Central

    Aubé, Martin; Roby, Johanne; Kocifaj, Miroslav

    2013-01-01

    Artificial light at night can be harmful to the environment, and interferes with fauna and flora, star visibility, and human health. To estimate the relative impact of a lighting device, its radiant power, angular photometry and detailed spectral power distribution have to be considered. In this paper we focus on the spectral power distribution. While specific spectral characteristics can be considered harmful during the night, they can be considered advantageous during the day. As an example, while blue-rich Metal Halide lamps can be problematic for human health, star visibility and vegetation photosynthesis during the night, they can be highly appropriate during the day for plant growth and light therapy. In this paper we propose three new indices to characterize lamp spectra. These indices have been designed to allow a quick estimation of the potential impact of a lamp spectrum on melatonin suppression, photosynthesis, and star visibility. We used these new indices to compare various lighting technologies objectively. We also considered the transformation of such indices according to the propagation of light into the atmosphere as a function of distance to the observer. Among other results, we found that low pressure sodium, phosphor-converted amber light emitting diodes (LED) and LED 2700 K lamps filtered with the new Ledtech’s Equilib filter showed a lower or equivalent potential impact on melatonin suppression and star visibility in comparison to high pressure sodium lamps. Low pressure sodium, LED 5000 K-filtered and LED 2700 K-filtered lamps had a lower impact on photosynthesis than did high pressure sodium lamps. Finally, we propose these indices as new standards for the lighting industry to be used in characterizing their lighting technologies. We hope that their use will favor the design of new environmentally and health-friendly lighting technologies. PMID:23861808

  17. Effective visible light-active boron and europium co-doped BiVO4 synthesized by sol-gel method for photodegradion of methyl orange.

    PubMed

    Wang, Min; Che, Yinsheng; Niu, Chao; Dang, Mingyan; Dong, Duo

    2013-11-15

    Eu-B co-doped BiVO4 visible-light-driven photocatalysts have been synthesized using the sol-gel method. The resulting materials were characterized by a series of joint techniques, including XPS, XRD, SEM, BET, and UV-vis DRS analyses. Compared with BiVO4 and B-BiVO4 photocatalysts, the Eu-B-BiVO4 photocatalysts exhibited much higher photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. The optimal Eu doping content is 0.8 mol%. It was revealed that boron and europium were doped into the lattice of BiVO4 and this led to more surface oxygen vacancies, high specific surface areas, small crystallite size, a narrower band gap and intense light absorbance in the visible region. The doped Eu(III) cations can help in the separation of photogenerated electrons. The synergistic effects of boron and europium in doped BiVO4 were the main reason for improving visible light photocatalytic activity.

  18. Coupled Heterojunction Sn₂Ta₂O₇@SnO₂: Cooperative Promotion of Effective Electron-Hole Separation and Superior Visible-light Absorption.

    PubMed

    Lang, Junyu; Li, Congyan; Wang, Shuwei; Lv, Juanjuan; Su, Yiguo; Wang, Xiaojing; Li, Guangshe

    2015-07-01

    In this work, a novel heterostructure integrated by two wide-band gap semiconductors, SnO2 and Sn2Ta2O7, is successfully prepared via a hydrothermal approach. Hollow Sn2Ta2O7 spheres were first formed, and small SnO2 particles were then well-dispersed onto the outside surface of the spheres, forming a p-n heterostructure. This heterostructure exhibits a higher potential edge that yielded enhanced photoredox ability. Further, the heterostructure is of Z-type with a consistent internal electric field direction, which effectively separates the photogenerated electron-hole pairs. Although both component semiconductors do not absorb visible light, the resulted p-n heterostructure is surprisingly observed to show an outstanding photocatalytic performance under visible light illumination. Such a visible light response is concluded to be the consequence of the impurity band formed by Sn(2+) doped in SnO2 and Sn(4+) in Sn2Ta2O7 via in situ redox. The existence of coupled Sn(2+) and Sn(4+) ions in p-n heterostructure is responsible for the absence of defects and the regenerated catalytic activities. The findings reported here may provide an approach to fabricate the new types of photocatalysts with a synergetic promotion for visible light absorption and sustained photocatalytic activities by coupling different wide-band semiconductors.

  19. Investigation of optical intensity in indoor visible light communication with different LEDs array

    NASA Astrophysics Data System (ADS)

    Chen, Hsi-Chao; Liou, Cheng-Jyun; Chou, Yang; Siao, Syuan-Ruei; Liu, I.-Ju; Lai, Wei-Cheng

    2014-09-01

    The purpose of this study was look for the optimized design of light source array applied in indoor lighting combined with visible light communication. The design of different light source arrays: circle, radiation, and rectangle were simulated and experimental for lighting, and then actually be used in visible light communication. The simulation results showed the rectangle array has the largest illumination flux than other arrays. And its total flux was 2662.3 lm; maximum illumination was 338 lx, and the effective illumination area of above 200 lx with a cover area of 2090 mm2. The measurement results also exhibited the rectangle array has the largest illumination flux than other arrays. Its total luminous flux is 2538.95 lm, and the effective illumination area of above 200 lx with a cover area of 2078 mm2. The measurement and simulation results have the same trend and the curve similarity was more than 99% by normalized cross correlation. Finally, combined with the signal transfer analysis of visible light communication, a measurement system was built with the input signal frequency of 1k Hz and the transmission distance of 1.8m. The receive waveform of rectangle array was best in the transport of free space to other arrays and the divergence angle could reaches to 85°.

  20. Synthesis and photophysics of a red-light absorbing supramolecular chromophore system.

    PubMed

    Rombouts, Jeroen A; Ravensbergen, Janneke; Frese, Raoul N; Kennis, John T M; Ehlers, Andreas W; Slootweg, J Chris; Ruijter, Eelco; Lammertsma, Koop; Orru, Romano V A

    2014-08-11

    In search of supramolecular antenna systems for light-harvesting applications, we report on a short and effective synthesis of a fused NDI-zinc-salphen-based chromophore (salphen = bis-salicylimide phenylene) and its photophysical properties. A supramolecular recognition motif is embedded into the chromophoric π-system of this compound. The fused π-chromophore behaves as one pigment, absorbs light between 600 and 750 nm and displays a modest Stokes shift. Upon binding pyridines, the compound (DATZnS) does not change its redox potentials, does not undergo any internal excited state quenching and does not appreciably alter its excited state lifetime. These notable properties define DATZnS as an alternative to porphyrin-based components used in supramolecular light-harvesting architectures.

  1. Synthesis and photophysics of a red-light absorbing supramolecular chromophore system.

    PubMed

    Rombouts, Jeroen A; Ravensbergen, Janneke; Frese, Raoul N; Kennis, John T M; Ehlers, Andreas W; Slootweg, J Chris; Ruijter, Eelco; Lammertsma, Koop; Orru, Romano V A

    2014-08-11

    In search of supramolecular antenna systems for light-harvesting applications, we report on a short and effective synthesis of a fused NDI-zinc-salphen-based chromophore (salphen = bis-salicylimide phenylene) and its photophysical properties. A supramolecular recognition motif is embedded into the chromophoric π-system of this compound. The fused π-chromophore behaves as one pigment, absorbs light between 600 and 750 nm and displays a modest Stokes shift. Upon binding pyridines, the compound (DATZnS) does not change its redox potentials, does not undergo any internal excited state quenching and does not appreciably alter its excited state lifetime. These notable properties define DATZnS as an alternative to porphyrin-based components used in supramolecular light-harvesting architectures. PMID:24965936

  2. Visible light photocatalytic antibacterial activity of Ni-doped and N-doped TiO2 on Staphylococcus aureus and Escherichia coli bacteria.

    PubMed

    Ananpattarachai, Jirapat; Boonto, Yuphada; Kajitvichyanukul, Puangrat

    2016-03-01

    The Ni-doped and N-doped TiO2 nanoparticles were investigated for their antibacterial activities on Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria. Their morphological features and characteristics such as particle size, surface area, and visible light absorbing capacity were compared and discussed. Scanning electron microscopy, X-ray diffraction, and UV-visible spectrophotometry were used to characterize both materials. The inactivation of E. coli (as an example of Gram-negative bacteria) and S. aureus (as an example of Gram-positive bacteria) with Ni-doped and N-doped TiO2 was investigated in the absence and presence of visible light. Antibacterial activity tests were conducted using undoped, Ni-doped, and N-doped TiO2. The N-doped TiO2 nanoparticles show higher antibacterial activity than Ni-doped TiO2. The band gap narrowing of N-doped TiO2 can induce more visible light absorption and leads to the superb antibacterial properties of this material. The complete inactivation time for E. coli at an initial cell concentration of 2.7 × 10(4) CFU/mL was 420 min which is longer than the 360 min required for S. aureus inactivation. The rate of inactivation of S. aureus using the doped TiO2 nanoparticles in the presence of visible light is greater than that of E. coli. The median lethal dose (LD50) values of S. aureus and E. coli by antibacterial activity under an 18-W visible light intensity were 80 and 350 mg/ml for N-doped TiO2, respectively.

  3. BODIPY star-shaped molecules as solid state colour converters for visible light communications

    NASA Astrophysics Data System (ADS)

    Vithanage, D. A.; Manousiadis, P. P.; Sajjad, M. T.; Rajbhandari, S.; Chun, H.; Orofino, C.; Cortizo-Lacalle, D.; Kanibolotsky, A. L.; Faulkner, G.; Findlay, N. J.; O'Brien, D. C.; Skabara, P. J.; Samuel, I. D. W.; Turnbull, G. A.

    2016-07-01

    In this paper, we study a family of solid-state, organic semiconductors for visible light communications. The star-shaped molecules have a boron-dipyrromethene (BODIPY) core with a range of side arm lengths which control the photophysical properties. The molecules emit red light with photoluminescence quantum yields ranging from 22% to 56%. Thin films of the most promising BODIPY molecules were used as a red colour converter for visible light communications. The film enabled colour conversion with a modulation bandwidth of 73 MHz, which is 16 times higher than that of a typical phosphor used in LED lighting systems. A data rate of 370 Mbit/s was demonstrated using On-Off keying modulation in a free space link with a distance of ˜15 cm.

  4. Tuning laccase catalytic activity with phosphate functionalized carbon dots by visible light.

    PubMed

    Li, Hao; Guo, Sijie; Li, Chuanxi; Huang, Hui; Liu, Yang; Kang, Zhenhui

    2015-05-13

    The phosphate functionalized carbon dots (PCDs) with high biocompatibility and low toxicity can be used as efficient additives for the construction of laccase/PCDs hybrids catalyst. A series of experiments indicated that the activity of laccase/PCDs was higher than that of free laccase (increased by 47.7%). When laccase/PCDs hybrids catalyst was irradiated with visible light (laccase/PCDs-Light), its activity was higher than that of laccase/PCDs hybrids without light irradiation (increased by 92.1%). In the present system, the T1 Cu in laccase was combined with the phosphate group on PCDs, which can increase binding capacity of laccase/PCDs hybrids and substrate. Further, the visible light irradiation increased the donating and accepting electronic capability of the laccase/PCDs hybrids, improving their catalytic activity.

  5. Synthesis of visible light-activated TiO 2 photocatalyst via surface organic modification

    NASA Astrophysics Data System (ADS)

    Jiang, Dong; Xu, Yao; Hou, Bo; Wu, Dong; Sun, Yuhan

    2007-05-01

    A visible light-activated TiO 2 photocatalyst was successfully synthesized by the surface organic modification to sol-gel-hydrothermal synthesized TiO 2. The surface hydroxyls of TiO 2 nanoparticles reacted with the active -NCO groups of tolylene diisocyanate (TDI) to form a surface complex that was confirmed by the FT-IR and XPS spectra. Due to the existence of surface complex, the absorption edge of as-prepared TDI-modified TiO 2 nanomaterial extended well into visible region. Compared with unmodified TiO 2 and Degussa P25, the TDI-modified TiO 2 photocatalysts showed higher activity for the photocatalytic degradation of methylene blue under visible light irradiation.

  6. High-confinement photonic structures for light propagation in the visible range

    NASA Astrophysics Data System (ADS)

    Turner, Amy C.; Almeida, Vilson R.; Lipson, Michal F.

    2004-10-01

    Planar integrated photonic devices are typically designed for telecommunications wavelengths in the 1.55 micron range. For strong mode-confinement at these wavelengths, very high index contrasts are required and semiconductor materials are often used for the waveguide core. Recently, planar devices designed for the visible range were demonstrated with relatively large dimensions on the order of 0.5 - 5 mm. Here in contrast we demonstrate micron-size photonic devices with single-mode operation in the visible range. Devices made for light propagation in the visible range are designed for tapping specific wavelengths of light vertically out of the plane of integration. The structures are based on high confinement waveguides with an effective mode size on the order of 0.5 μm2.

  7. Selective Release of Aromatic Heterocycles from Ruthenium Tris(2-pyridylmethyl)amine with Visible Light

    PubMed Central

    Li, Ao; White, Jessica K.; Arora, Karan; Herroon, Mackenzie K.; Martin, Philip D.; Schlegel, H. Bernhard; Podgorski, Izabela; Turro, Claudia; Kodanko, Jeremy J.

    2016-01-01

    Three complexes of the general formula [Ru(TPA)L2](PF6)2 [TPA = tris(2-pyridylmethyl)amine], where L = pyridine (1), nicotinamide (2), and imidazole (3), were prepared and characterized spectroscopically. X-ray crystallographic data were obtained for 1 and 3. Complexes 1–3 show strong absorption in the visible region and selective release of heterocycles upon irradiation with visible light. Time-dependent density functional theory calculations are consistent with the presence of singlet metal-to-ligand charge-transfer bands in the visible region in 1–3. Caged heterocycles 1–3 are highly stable in solution in the dark, including in cell growth media. Cell viability data show no signs of toxicity of 1–3 against PC-3 cells at concentrations up to 100 μM under light and dark conditions, consistent with Ru(TPA) acting as a nontoxic and effective photocaging group for aromatic heterocycles. PMID:26670781

  8. Visible light assisted degradation of organic dye using Ag3PO4

    NASA Astrophysics Data System (ADS)

    Dhanabal, R.; Velmathi, S.; Bose, A. Chandra

    2015-06-01

    The study of visible light photodegradation of organic dye Methylene Blue (MB) have been investigated using silver phosphate (Ag3PO4) as a photocatalyst which is good efficient material for photocatalytic reaction. The simple ion-exchange method is used to prepare Ag3PO4. The structure of the material have been confirmed using X-ray diffraction which shows cubic structure of Ag3PO4. The functional group of the Ag3PO4 has been verified by Fourier transform infrared spectroscopy. The bandgap of Ag3PO4 is calculated using kubelka-munk function from the ultra violet-visible diffuse reflectance spectroscopy, the absorption of Ag3PO4 starts from 470 nm. Under simulated visible light irradiation, Ag3PO4 catalyst exhibits good catalytic ability for degrading MB dye.

  9. Cu-doped TiO(2) nanoparticles for photocatalytic disinfection of bacteria under visible light.

    PubMed

    Karunakaran, C; Abiramasundari, G; Gomathisankar, P; Manikandan, G; Anandi, V

    2010-12-01

    Two percent Cu-doped TiO(2) nanoparticles were prepared by a modified ammonia-evaporation-induced synthetic method, calcined at 450°C, and characterized by powder X-ray diffraction, energy dispersive X-ray analysis, ESR spectroscopy, scanning electron microscopy, UV-visible diffuse reflectance spectrum, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Doping shifts the optical absorption edge to the visible region but increases the charge-transfer resistance and decreases the capacitance. Under visible light, the composite nanoparticles very efficiently catalyze the disinfection of Escherichia coli. The prepared oxide is selective in photocatalysis; under UV light, its photocatalytic activity to degrade sunset yellow, rhodamine B, and methylene blue dyes is less than that of the undoped one. PMID:20832079

  10. Fast visible light photoelectric switch based on ultralong single crystalline V₂O₅ nanobelt.

    PubMed

    Lu, Jianing; Hu, Ming; Tian, Ye; Guo, Chuanfei; Wang, Chuang; Guo, Shengming; Liu, Qian

    2012-03-26

    A photoelectric switch with fast response to visible light (<200 μs), suitable photosensitivity and excellent repeatability is proposed based on the ultralong single crystalline V₂O₅ nanobelt, which are synthesized by chemical vapor deposition and its photoconductive mechanism can well be explained by small polaron hopping theory. Our results reveal that the switch has a great potential in next generation photodetectors and light-wave communications.

  11. Light-absorbing Aerosol Properties in the Kathmandu Valley during SusKat-ABC Field Campaign

    NASA Astrophysics Data System (ADS)

    Kim, S.; Yoon, S.; Kim, J.; Cho, C.; Jung, J.

    2013-12-01

    Light-absorbing aerosols, such as black carbon (BC), are major contributors to the atmospheric heating and the reduction of solar radiation reaching at the earth's surface. In this study, we investigate light-absorption and scattering properties of aerosols (i.e., BC mass concentration, aerosol solar-absorption/scattering efficiency) in the Kathmandu valley during Sustainable atmosphere for the Kathmandu valley (SusKat)-ABC campaign, from December 2012 to February 2013. Kathmandu City is among the most polluted cities in the world. However, there are only few past studies that provide basic understanding of air pollution in the Kathmandu Valley, which is not sufficient for designing effective mitigation measures (e.g., technological, financial, regulatory, legal and political measures, planning strategies). A distinct diurnal variation of BC mass concentration with two high peaks observed during wintertime dry monsoon period. BC mass concentration was found to be maximum around 09:00 and 20:00 local standard time (LST). Increased cars and cooking activities including substantial burning of wood and other biomass in the morning and in the evening contributed to high BC concentration. Low BC concentrations during the daytime can be explain by reduced vehicular movement and cooking activities. Also, the developmements of the boundary layer height and mountain-valley winds in the Kathmandu Valley paly a crucial role in the temproal variation of BC mass concentrations. Detailed radiative effects of light-absorbing aerosols will be presented.

  12. Inherent visible light signature of an intense underwater ultraviolet light source due to combined Raman and fluorescence effects

    NASA Astrophysics Data System (ADS)

    Mazel, Charles H.; Kalata-Olson, Jody; Pham, Chuong N.

    2000-07-01

    We investigated the utility of a portable, intense source of ultraviolet light for diver use in support of Very Shallow Water operations. The working hypothesis was that the light would be of use to divers at short-to-medium ranges (up to several meters) while remaining invisible to surface observers due to the incoherent insensitivity of the human eye to ultraviolet light. The light source contained an arc discharge lamp rich in short wavelengths and was fitted with a filter that transmitted only the near ultraviolet portion of the spectrum. In-water tests were made in darkness using Navy divers both in a natural coastal environment and in a test tank. It was found that the light was of limited utility to the divers. In addition, the light was not covert because of a bluish-white glow associated with the ultraviolet beam. Subsequent measurements demonstrated that the visible glow was produced by a combination of fluorescence of dissolved organic matter in the water and Raman scatter from the water itself. The relative importance of the two factors varied with water type. These two effects that transform light from the invisible to the visible impose inherent limitations on the use of ultraviolet light for covert operations.

  13. A visible-light-promoted aerobic metal-free C-3 thiocyanation of indoles.

    PubMed

    Fan, Weigang; Yang, Qi; Xu, Fengshan; Li, Pixu

    2014-11-01

    A simple and efficient visible-light-promoted method for the C-3 thiocyanation of indoles has been developed. The transformation uses Rose Bengal as the photocatalyst and air as the terminal oxidant. The reaction is mild, high-yielding, and environmentally benign.

  14. Visible-light-mediated chan-lam coupling reactions of aryl boronic acids and aniline derivatives.

    PubMed

    Yoo, Woo-Jin; Tsukamoto, Tatsuhiro; Kobayashi, Shū

    2015-05-26

    The copper(II)-catalyzed aerobic oxidative coupling reaction between aryl boronic acids and aniline derivatives was found to be improved significantly under visible-light-mediated photoredox catalysis. The substrate scope of this oxidative Chan-Lam reaction was thus expanded to include electron-deficient aryl boronic acids as viable starting materials.

  15. Effects of ultraviolet radiation, visible light, and infrared radiation on erythema and pigmentation: a review.

    PubMed

    Sklar, Lindsay R; Almutawa, Fahad; Lim, Henry W; Hamzavi, Iltefat

    2013-01-01

    The effects of ultraviolet radiation, visible light, and infrared radiation on cutaneous erythema, immediate pigment darkening, persistent pigment darkening, and delayed tanning are affected by a variety of factors. Some of these factors include the depth of cutaneous penetration of the specific wavelength, the individual skin type, and the absorption spectra of the different chromophores in the skin. UVB is an effective spectrum to induce erythema, which is followed by delayed tanning. UVA induces immediate pigment darkening, persistent pigment darkening, and delayed tanning. At high doses, UVA (primarily UVA2) can also induce erythema in individuals with skin types I-II. Visible light has been shown to induce erythema and a tanning response in dark skin, but not in fair skinned individuals. Infrared radiation produces erythema, which is probably a thermal effect. In this article we reviewed the available literature on the effects of ultraviolet radiation, visible light, and infrared radiation on the skin in regards to erythema and pigmentation. Much remains to be learned on the cutaneous effects of visible light and infrared radiation.

  16. Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle.

    PubMed

    Kumar, Dinesh; Lee, Ah-Reum; Kaur, Sandeep; Lim, Dong-Kwon

    2015-09-22

    Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

  17. Visible light induced photobleaching of methylene blue over melamine-doped TiO2 nanocatalyst

    EPA Science Inventory

    TiO2 doping with N-rich melamine produced a stable, active and visible light sentisized nanocatalyst that showed a remarkable efficiency towards the photobleaching of a model compound – methylene blue (MB) in aqueous solution. The photobleaching followed a mixed reaction order ki...

  18. Visible light photon counters (VLPCs) for high rate tracking medical imaging and particle astrophysics

    SciTech Connect

    Atac, M.

    1998-02-01

    This paper is on the operation principles of the Visible Light Photon Counters (VLPCs), application to high luminosity-high multiplicity tracking for High Energy Charged Particle Physics, and application to Medical Imaging and Particle Astrophysics. The VLPCs as Solid State Photomultipliers (SSPMS) with high quantum efficiency can detect down to single photons very efficiently with excellent time resolution and high avalanche gains.

  19. Regioselective 2,2,2-Trifluoroethylation of Imidazopyridines by Visible Light Photoredox Catalysis.

    PubMed

    Zhu, Mei; Han, Xin; Fu, Weijun; Wang, Zhiqiang; Ji, Baoming; Hao, Xin-Qi; Song, Mao-Ping; Xu, Chen

    2016-08-19

    A visible-light-induced C-3 selective trifluoroethylation of imidazoheterocycles using 1,1,1-trifluoro-2-iodoethane as trifluoroethyl radical sources was developed. The methodology enables the introduction of a trifluoroethyl group in a fast and efficient reaction under mild conditions with excellent regioselectivities and high functional group tolerance. PMID:27328667

  20. Visible-Light-Induced Bactericidal Activity of Titanium Dioxide Co-doped with Nitrogen and Silver

    PubMed Central

    Wu, Pinggui; Xie, Rongcai; Imlay, Kari; Shang, Jian-Ku

    2011-01-01

    Titanium dioxide nanoparticles co-doped with nitrogen and silver (Ag2O/TiON) were synthesized by the sol-gel process and found to be an effective visible light driven photocatalyst. The catalyst showed strong bactericidal activity against Escherichia coli (E. coli) under visible light irradiation (λ> 400 nm). In x-ray photoelectron spectroscopy and x-ray diffraction characterization of the samples, the as-added Ag species mainly exist as Ag2O. Spin trapping EPR study showed Ag addition greatly enhanced the production of hydroxyl radicals (•OH) under visible light irradiation. The results indicate that the Ag2O species trapped eCB− in the process of Ag2O/TiON photocatalytic reaction, thus inhibiting the recombination of eCB− and hVB+ in agreement with the stronger photocatalytic bactericidal activity of Ag2O/TiON. The killing mechanism of Ag2O/TiON under visible light irradiation is shown to be related to oxidative damages in the forms of cell wall thinning and cell disconfiguration. PMID:20726520

  1. Visible-Light-Driven Photocatalytic Initiation of Radical Thiol-Ene Reactions Using Bismuth Oxide.

    PubMed

    Fadeyi, Olugbeminiyi O; Mousseau, James J; Feng, Yiqing; Allais, Christophe; Nuhant, Philippe; Chen, Ming Z; Pierce, Betsy; Robinson, Ralph

    2015-12-01

    A nontoxic and inexpensive photocatalytic initiation of anti-Markovnikov hydrothiolation of olefins using visible light is reported. This method is characterized by low catalyst loading, thereby enabling a mild and selective method for radical initiation in thiol-ene reactions between a wide scope of olefins and thiols. PMID:26572219

  2. Selective Breaking of Hydrogen Bonds of Layered Carbon Nitride for Visible Light Photocatalysis.

    PubMed

    Kang, Yuyang; Yang, Yongqiang; Yin, Li-Chang; Kang, Xiangdong; Wang, Lianzhou; Liu, Gang; Cheng, Hui-Ming

    2016-08-01

    Selective breaking of the hydrogen bonds of graphitic carbon nitride can introduce favorable features, including increased band tails close to the band edges and the creation of abundant pores. These features can simultaneously improve the three basic processes of photocatalysis. As a consequence, the photocatalytic hydrogen-generation activity of carbon nitride under visible light is drastically increased by tens of times.

  3. Electrically tunable selective reflection of light from ultraviolet to visible and infrared by heliconical cholesterics.

    PubMed

    Xiang, Jie; Li, Yannian; Li, Quan; Paterson, Daniel A; Storey, John M D; Imrie, Corrie T; Lavrentovich, Oleg D

    2015-05-20

    Electrical tuning of selective reflection of light is achieved in a very broad spectral range from ultraviolet to visible and infrared by an oblique helicoidal state of a cholesteric liquid crystal in a wide temperature range (including room temperature). The phenomenon offers potential applications in tunable smart windows, lasers, optical filters and limiters, as well as in displays. PMID:25821155

  4. Intermolecular C-H Quaternary Alkylation of Aniline Derivatives Induced by Visible-Light Photoredox Catalysis.

    PubMed

    Cheng, Jie; Deng, Xia; Wang, Guoqiang; Li, Ying; Cheng, Xu; Li, Guigen

    2016-09-16

    The intermolecular direct C-H alkylation of aniline derivatives with α-bromo ketones to build a quaternary carbon center was reported with a visible-light catalysis procedure. The reaction covers a variety of functional groups with good to excellent yields. A regioselectivity favoring the ortho position for the amine group was observed and investigated with Fukui indices and spectral methods.

  5. Synthesis of novel photocatalytic RGO-InVO{sub 4} nanocomposites with visible light photoactivity

    SciTech Connect

    Shen, Jianfeng; Li, Xianfu; Huang, Weishi; Li, Na; Ye, Mingxin

    2013-09-01

    Graphical abstract: A facile method for preparation of reduced graphene oxide (RGO) sheets supported indium vanadate (InVO{sub 4}) photocatalysts is reported. The visible light response and adsorption ability of RGO-InVO{sub 4} nanocomposites is greatly improved, which can effectively remove methyl orange and Cr (VI) from water. - Highlights: • Supramolecular photocatalyst of RGO-InVO{sub 4} was achieved. • Reduction of GO and preparation of RGO-InVO{sub 4} was simultaneous. • The prepared RGO-InVO{sub 4} shows high photocatalytic activity and adsorption capacity under visible light. • In situ growth of uniform InVO{sub 4} particles on RGO sheets is facile and efficient - Abstract: In this study, we report a facile method for preparation of reduced graphene oxide (RGO) sheets supported indium vanadate (InVO{sub 4}) photocatalysts. A wide range of characterization techniques, such as Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, Thermogravimetric analysis and Transmission electron microscopy were applied to characterize the obtained composites. The results indicated that the composites consist of uniformly dispersed InVO{sub 4} nanocrystals on RGO sheets. Visible light responses of RGO-InVO{sub 4} nanocomposites are greatly improved as compared with the bulk InVO{sub 4}. The as-prepared RGO-InVO{sub 4} nanocomposites can effectively remove methyl orange and Cr (VI) from water under visible light irradiation, which can be used as novel photocatalysts for environmental protection.

  6. Do Tengmalm's owls see vole scent marks visible in ultraviolet light?

    PubMed

    Koivula; Korpimäki; Viitala

    1997-10-01

    Scent markings (urine and faeces) of small mammals are visible in ultraviolet (UV) light. Diurnal kestrels, Falco tinnunculususe them as a cue to find areas of food abundance. We studied whether vole-eating, nocturnal Tengmalm's owls, Aegolius funereuscan see vole scent marks using UV-vision. In a laboratory experiment, 14 young (less than 6 months old) and 14 adult (more than 6 months old) owls were individually given a choice between four adjacent arenas: (1) an arena with vole urine and faeces in UV light; (2) an arena with vole urine and faeces in visible light; (3) a clean arena in UV light; and (4) a clean arena in visible light. Owls did not prefer any of the four arenas. Our results suggest that Tengmalm's owls probably do not use UV light as a cue to detect vole scent marks.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour PMID:9344440

  7. Visible Light Driven Photoelectrodes Made of Earth Abundant Elements for Water Photoelectrolysis

    NASA Astrophysics Data System (ADS)

    Huang, Qiang

    With the aim of creating a clean and sustainable energy supply, the direct use of solar energy to produce chemical energy has been pursued for many years. Particularly, the photoelectrolysis of water to generate hydrogen by semiconductor photoelectrodes has attracted great attention because of its advantage of using only water and sunlight, both of which are widely distributed, as raw materials. The earth abundant and visible light absorbing materials are promising for this application for the advantages of easy access and high theoretical solar to hydrogen conversion efficiency. In this thesis, the cadmium sulfide based and copper oxide based photoelectrodes were fabricated and characterized to determine their potential for photoelectrolysis. As one of the semiconductors with relatively narrow band gap, CdS (2.4eV) has a conduction band edge more negative than the water reduction potential level and a valence band edge more positive than the water oxidation potential level, enabling n-type CdS and p-type CdS as good candidates for photoanode and photocathode respectively. CdS thin film with thickness around 2mum was deposited onto Mo back contact on glass, which formed ohmic contact with CdS. The as-prepared CdS was intrinsic n-type due to the easy formation of sulfur vacancies and it was converted to p-type by the controlled thermal diffusion of copper atoms which substituted cadmium to produce acceptor state. The optimal Cu doping level for the interest of water photoelectrolysis was found to be at 5.4% concentration. Cu2O with band gap of 2.0eV is another attracting competitor for the photoelectrode among the metal-oxide semiconductors. Both thin film and highly aligned nanowire arrays Cu2O were prepared by thermal oxidation of Cu film and Cu nanowires on Au substrates synthesized by electrodeposition. Cu2O was found to be p-type because of the copper vacancies. The photocurrent of the Cu2O nanowires photocathode was found to be twice that of the Cu2O film, and

  8. Once the Light Touch to the Brain: Cytotoxic Effects of Low-Dose Gamma-Ray, Laser Light, and Visible Light on Rat Neuronal Cell Culture

    PubMed Central

    Cakir, Murteza; Colak, Abdullah; Calikoglu, Cagatay; Taspinar, Numan; Sagsoz, Mustafa Erdem; Kadioglu, Hakan Hadi; Hacimuftuoglu, Ahmet; Seven, Sabriye

    2016-01-01

    Objective: We aimed to evaluate the effects of gamma-ray, laser light, and visible light, which neurons are commonly exposed to during treatment of various cranial diseases, on the viability of neurons. Materials and Methods: Neuronal cell culture was prepared from the frontal cortex of 9 newborn rats. Cultured cells were irradiated with gamma-ray for 1–10 min by 152Eu, 241Am, and 132Ba isotopes, visible light for 1–160 min, and laser light for 0.2–2 seconds. The MTT tetrazolium reduction assay was used to assess the number of viable cells in the neuronal cell cultures. Wavelength dispersive X-ray fluorescence spectrometer was used to determine Na, K, and Ca levels in cellular fluid obtained from neuronal cell culture plaques. Results: Under low-dose radiation with 152Eu, 241Am, and 132Ba isotopes, cell viability insignificantly decreased with time (p>0.05). On the other hand, exposure to visible light produced statistically significant decrease in cell viability at both short- (1–10 min) and long-term (20–160 min). Cell viability did not change with 2 seconds of laser exposure. Na, K, and Ca levels significantly decreased with gamma-ray and visible light. The level of oxidative stress markers significantly changed with gamma-ray. Conclusion: In conclusion, while low dose gamma-ray has slight to moderate apoptotic effect in neuronal cell cultures by oxidative stress, long-term visible light induces remarkable apoptosis and cell death. Laser light has no significant effect on neurons. Further genetic studies are needed to clarify the chronic effect of visible light on neuronal development and functions. PMID:27551168

  9. Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis.

    PubMed

    Sun, Bo; Reddy, Ettireddy P; Smirniotis, Panagiotis G

    2005-08-15

    Here we report the simultaneous Cr(VI) reduction and 4-chlorophenol (4-CP) oxidation in water under visible light (wavelength > 400 nm) using commercial Degussa P25 TiO2. This remarkable observation was attributed to a synergistic effect among TiO2, Cr(VI), and 4-CP. It is well known that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interaction between Cr(VI) and 4-CP is minimal if not negligible. However, we found that the combination of TiO2, Cr(VI), and 4-CP together can enable efficient Cr(VI) reduction and 4-CP oxidation under visible light. The specific roles of the three ingredients in the synergistic system were studied parametrically. It was found that optimal concentrations of Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CP oxidation. Cr(VI) was compared experimentally with other metals such as Cu(ll), Fe(lll), Mn(IV), Ce(IV), and V(V). Among all these metal ions, only Cr(VI) promotes the photocatalytic oxidation of 4-CP. The amount of 4-CP removed was directly related to the initial concentration of Cr(VI). The system was also tested with four other chemicals (aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurred for organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicals being oxidized during photoreaction under visible light. The synergistic effect was also found with pure anatase TiO2 and rutile TiO2. This study demonstrates a possible economical way for environmental cleanup under visible light.

  10. [TiO2-Induced Photodegradation of Levofloxacin by Visible Light and Its Mechanism].

    PubMed

    Guo, Hong-sheng; Liu, Ya-nan; Qiao, Qi; Wei, Hong; Dong, Cheng-xing; Xue, Jie; Li, Ke-bin

    2015-05-01

    Levofloxacin is an emerging pollutant. Single levofloxacin and TiO2 have no visible-light activity. However, photodegradation of levofloxacin dramatically enhanced in the presence of TiO2 under visible light irradiation. Considering this finding, he photodegradation of levofloxacin over TiO2 was investigated under visible light irradiation. Effects of TiO2 dosage, levofloxacin concentration, and solution pH on levofloxacin photodegradation were examined by monitoring its concentration decay with time. The results showed that levofloxacin photodegradation fitted the Langmuir-Hinshelwood kinetic model. Solution pH, TiO2 dose, and levofloxacin concentration had significant effects on the photodegradation rates. In addition, batch adsorption experiments revealed that adsorption of levofloxacin on TiO2 conformed to the pseudo-second-order kinetics and the Langmuir isotherm. DRS spectrum of levofloxacin-adsorbed TiO2 suggested that a surface complex was formed between levofloxacin and TiO2. Addition of radical scavengers and N2-degassing affecting levofloxacin photodegradation indicated that the superoxide ion radical was mainly active species. UV-Vis spectra of a deaerated TiO2 and levofloxacin suspensions further confirmed that the electron injection into TiO2 conduction band took place under visible light irradiation. Based on these results, a charge-transfer mechanism initiated by photoexcitation of TiO2/ levofloxacin surface complex was proposed for levofloxacin photocatalytic degradation over TiO2 under visible light. This study indicates that the charge-transfer-complex-mediated photocatalytic technique has promising applications in the removal of colorless organic pollutants.

  11. Property Characterization and Photocatalytic Activity Evaluation of BiGdO₃ Nanoparticles under Visible Light Irradiation.

    PubMed

    Luan, Jingfei; Shen, Yue; Zhang, Lingyan; Guo, Ningbin

    2016-01-01

    BiGdO₃ nanoparticles were prepared by a solid-state reaction method and applied in photocatalytic degradation of dyes in this study. BiGdO₃ was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, UV-Vis diffuse reflectance spectroscopy and transmission electron microscopy. The results showed that BiGdO₃ crystallized well with the fluorite-type structure, a face-centered cubic crystal system and a space group Fm3m 225. The lattice parameter of BiGdO₃ was 5.465 angstrom. The band gap of BiGdO₃ was estimated to be 2.25 eV. BiGdO₃ showed a strong optical absorption during the visible light region. Moreover, the photocatalytic activity of BiGdO₃ was evaluated by photocatalytic degradation of direct dyes in aqueous solution under visible light irradiation. BiGdO₃ demonstrated excellent photocatalytic activity in degrading Direct Orange 26 (DO-26) or Direct Red 23 (DR-23) under visible light irradiation. The photocatalytic degradation of DO-26 or DR-23 followed the first-order reaction kinetics, and the first-order rate constant was 0.0046 or 0.0023 min(-1) with BiGdO₃ as catalyst. The degradation intermediates of DO-26 were observed and the possible photocatalytic degradation pathway of DO-26 under visible light irradiation was provided. The effect of various operational parameters on the photocatalytic activity and the stability of BiGdO₃ particles were also discussed in detail. BiGdO₃/(visible light) photocatalysis system was confirmed to be suitable for textile industry wastewater treatment. PMID:27618018

  12. Visible light curing of Epon SU-8 based superparamagnetic polymer composites with random and ordered particle configurations.

    PubMed

    Peters, Christian; Ergeneman, Olgaç; Sotiriou, Georgios A; Choi, Hongsoo; Nelson, Bradley J; Hierold, Christofer

    2015-01-14

    The performance of superparamagnetic polymer composite microdevices is highly dependent on the magnetic particle content. While high loading levels are desired for many applications, the UV absorption of these nanoparticles limits the overall thickness of the fabricated microstructures and subsequently their capability of magnetic interaction. The combination of a visible-light-sensitive photoinitiator and particle self-organization is proposed to extend the exposure depth limitation in Epon SU-8 based superparamagnetic polymer composites. While superparamagnetic iron oxide particles strongly absorb i-line radiation required to cross-link the Epon SU-8 polymer matrix, we propose the utilization of H-Nu 470 photoinitiator to expand the photosensitivity of the composite toward the visible spectrum, where the dispersed nanoparticles are more transparent. The novel photoinitiator preserves the composite's superparamagnetic properties as well as a homogeneous particle distribution. As a result, particle load or resist thickness can be more than doubled while maintaining exposure time. The self-organization of ordered magnetic structures allows for an additional increase in exposure depth of up to 40%, resulting in a 2.5-fold saturation magnetization.

  13. Photodynamic Approach for Teratoma-Free Pluripotent Stem Cell Therapy Using CDy1 and Visible Light

    PubMed Central

    2016-01-01

    Pluripotent stem cells (PSC) are promising resources for regeneration therapy, but teratoma formation is one of the critical problems for safe clinical application. After differentiation, the precise detection and subsequent elimination of undifferentiated PSC is essential for teratoma-free stem cell therapy, but a practical procedure is yet to be developed. CDy1, a PSC specific fluorescent probe, was investigated for the generation of reactive oxygen species (ROS) and demonstrated to induce selective death of PSC upon visible light irradiation. Importantly, the CDy1 and/or light irradiation did not negatively affect differentiated endothelial cells. The photodynamic treatment of PSC with CDy1 and visible light irradiation confirmed the inhibition of teratoma formation in mice, and suggests a promising new approach to safe PSC-based cell therapy. PMID:27725957

  14. Visible Light Image-Based Method for Sugar Content Classification of Citrus.

    PubMed

    Wang, Xuefeng; Wu, Chunyan; Hirafuji, Masayuki

    2016-01-01

    Visible light imaging of citrus fruit from Mie Prefecture of Japan was performed to determine whether an algorithm could be developed to predict the sugar content. This nondestructive classification showed that the accurate segmentation of different images can be realized by a correlation analysis based on the threshold value of the coefficient of determination. There is an obvious correlation between the sugar content of citrus fruit and certain parameters of the color images. The selected image parameters were connected by addition algorithm. The sugar content of citrus fruit can be predicted by the dummy variable method. The results showed that the small but orange citrus fruits often have a high sugar content. The study shows that it is possible to predict the sugar content of citrus fruit and to perform a classification of the sugar content using light in the visible spectrum and without the need for an additional light source.

  15. Versatile Micropatterning of Plasmonic Nanostructures by Visible Light Induced Electroless Silver Plating on Gold Nanoseeds.

    PubMed

    Yoshikawa, Hiroyuki; Hironou, Asami; Shen, ZhengJun; Tamiya, Eiichi

    2016-09-14

    A versatile fabrication technique for plasmonic silver (Ag) nanostructures that uses visible light exposure for micropatterning and plasmon resonance tuning is presented. The surface of a glass substrate modified with gold (Au) nanoseeds by a thermal dewetting process was used as a Ag plating platform. When a solution containing silver nitrate and sodium citrate was dropped on the Au nanoseeds under visible light exposure, the plasmon-mediated reduction of Ag ions was induced on the Au nanoseeds to form Ag nanostructures. The plasmon resonance spectra of Ag nanostructures were examined by an absorption spectral measurement and a finite-difference time-domain (FDTD) simulation. Some examples of Ag nanostructure patterning were demonstrated by means of light exposure through a photomask, direct writing with a focused laser beam, and the interference between two laser beams. Surface enhanced Raman spectroscopy (SERS) of 4-aminothiophenol (4-ATP) was conducted with fabricated Ag nanostructures.

  16. Vehicle-mounted real-time digital voice communication system based on visible light communication

    NASA Astrophysics Data System (ADS)

    Yan, Qiurong; Gu, Xiuxiu; Chen, Du; Wang, Hui; Huang, Hua; Chen, Xuxin; Cao, Qingshan; Liu, Hongqing

    2015-11-01

    Based on the phenomenon that more and more cars use LED for lighting and the current rise of visible light communication technology, this paper proposes a vehicle real-time voice communication system with high reliability on the basis of visible light communication for verification. The paper introduces the design of digital audio collection and output module, On-Off Keying (OOK) modulation and demodulation, Reed-Solomon encoding and decoding module, array LEDs emission and the module of PIN receiving signals. The LED lamp frequency response, communication distance, error rate and other parameters are tested and calibrated. The digital audio real-time communication system's receiving speed is 500Kbps when the communication distance is 3.9 meters.

  17. An adaptive scaling and biasing scheme for OFDM-based visible light communication systems.

    PubMed

    Wang, Zhaocheng; Wang, Qi; Chen, Sheng; Hanzo, Lajos

    2014-05-19

    Orthogonal frequency-division multiplexing (OFDM) has been widely used in visible light communication systems to achieve high-rate data transmission. Due to the nonlinear transfer characteristics of light emitting diodes (LEDs) and owing the high peak-to-average-power ratio of OFDM signals, the transmitted signal has to be scaled and biased before modulating the LEDs. In this contribution, an adaptive scaling and biasing scheme is proposed for OFDM-based visible light communication systems, which fully exploits the dynamic range of the LEDs and improves the achievable system performance. Specifically, the proposed scheme calculates near-optimal scaling and biasing factors for each specific OFDM symbol according to the distribution of the signals, which strikes an attractive trade-off between the effective signal power and the clipping-distortion power. Our simulation results demonstrate that the proposed scheme significantly improves the performance without changing the LED's emitted power, while maintaining the same receiver structure. PMID:24921387

  18. [Development of low-concentration hydrogen peroxide whitening agent using visible light-responsive titania photocatalyst].

    PubMed

    Arai, Hiroshi

    2010-06-01

    Although highly concentrated hydrogen peroxide (HP) has been used to bleach vital discolored teeth during office whitening, low-concentration HP was recognized to have insufficient whitening ability. We demonstrated that using a visible light-responsive titania photocatalyst (VLRTP) and a vis-Nd : YAG laser, 3 wt% HP-bleached oxytetracycline (OTC)-stained teeth models were more efficient than 30 wt% HP. The stained samples were prepared by soaking synthetic hydroxyapatite ceramic disks in OTC aqueous solutions. Color images of the OTC-stained models before and after whitening were taken with a conventional flatbed scanner and calibrated using a photocell colorimeter. By VLRTP treatment with vis-Nd : YAG laser irradiation, the lightness value (L*) significantly increased and the yellowness index (b*) significantly approached zero. This suggests that a diluted HP agent with VLRTP can more efficiently decolorize stained teeth by visible light irradiation.

  19. Versatile Micropatterning of Plasmonic Nanostructures by Visible Light Induced Electroless Silver Plating on Gold Nanoseeds.

    PubMed

    Yoshikawa, Hiroyuki; Hironou, Asami; Shen, ZhengJun; Tamiya, Eiichi

    2016-09-14

    A versatile fabrication technique for plasmonic silver (Ag) nanostructures that uses visible light exposure for micropatterning and plasmon resonance tuning is presented. The surface of a glass substrate modified with gold (Au) nanoseeds by a thermal dewetting process was used as a Ag plating platform. When a solution containing silver nitrate and sodium citrate was dropped on the Au nanoseeds under visible light exposure, the plasmon-mediated reduction of Ag ions was induced on the Au nanoseeds to form Ag nanostructures. The plasmon resonance spectra of Ag nanostructures were examined by an absorption spectral measurement and a finite-difference time-domain (FDTD) simulation. Some examples of Ag nanostructure patterning were demonstrated by means of light exposure through a photomask, direct writing with a focused laser beam, and the interference between two laser beams. Surface enhanced Raman spectroscopy (SERS) of 4-aminothiophenol (4-ATP) was conducted with fabricated Ag nanostructures. PMID:27564976

  20. Effect of interferences on indoor visible light car-to-car communication systems

    NASA Astrophysics Data System (ADS)

    Kim, Jong-Young; Park, Bong-Seok; Choi, Hyun-Sik; Kim, So Eun; Moon, Inkyu; Lee, Chung Ghiu

    2016-04-01

    We report the effect of interferences on visible light car-to-car communication system. The interferences from floor reflections and fluorescent lamps are taken into account for indoor car-to-car visible light communication (VLC) systems. The system is composed of a white LED lamp as a VLC transmitter and a photo-receiver with an appropriate optical filter as a VLC receiver. The signal power distribution patterns are measured and analyzed at a transmission distance, considering the positions of the transmitter and receiver. Generally, the light from fluorescent lamps in indoor environment affects the DC level of the received signal power, which is more significant at higher receiver positions. The measurements show that the indoor VLC communication performance can be varied depending on floor reflections. Also, the fluorescent ceiling illuminations affect the DC level change of the received VLC signal waveforms.

  1. Synthesis of nanoplate bismuth oxychloride—a visible light active material

    NASA Astrophysics Data System (ADS)

    Tripathi, Gagan Kant; Saini, K. K.; Kurchania, Rajnish

    2015-10-01

    We have synthesized bismuth oxychloride (BiOCl) by wet chemical route. Characterization of the synthesized samples has been carried out using XRD, SEM with EDAX, HRTEM, FT-IR, Raman Spectroscopy, PL and UV. XRD and SEM analysis confirms crystallite size varying from 20-40 nm. FTIR spectrum indicates that the prepared material is highly pure and there is no water molecule present. Raman and photoluminescence spectrum of the bismuth oxychloridenanoplate demonstrated strong blue light emission which brings them in a special class of materials which work under visible light exposure. UV-Vis spectroscopy shows very less charge carriers transit time under visible light thus confirming excellent photocatalytic properties of material.

  2. Visible Light Image-Based Method for Sugar Content Classification of Citrus

    PubMed Central

    Wang, Xuefeng; Wu, Chunyan; Hirafuji, Masayuki

    2016-01-01

    Visible light imaging of citrus fruit from Mie Prefecture of Japan was performed to determine whether an algorithm could be developed to predict the sugar content. This nondestructive classification showed that the accurate segmentation of different images can be realized by a correlation analysis based on the threshold value of the coefficient of determination. There is an obvious correlation between the sugar content of citrus fruit and certain parameters of the color images. The selected image parameters were connected by addition algorithm. The sugar content of citrus fruit can be predicted by the dummy variable method. The results showed that the small but orange citrus fruits often have a high sugar content. The study shows that it is possible to predict the sugar content of citrus fruit and to perform a classification of the sugar content using light in the visible spectrum and without the need for an additional light source. PMID:26811935

  3. Fungal photobiology: visible light as a signal for stress, space and time

    PubMed Central

    Fuller, Kevin K.; Loros, Jennifer J.; Dunlap, Jay C.

    2014-01-01

    Visible light is an important source of energy and information for much of life on this planet. Though fungi are neither photosynthetic nor capable of observing adjacent objects, it is estimated that the majority of fungal species display some form of light response, ranging from developmental decision making to metabolic reprogramming to pathogenesis. As such, advances in our understanding of fungal photobiology will likely reach the broad fields impacted by these organisms, including agriculture, industry and medicine. In this review, we will first describe the mechanisms by which fungi sense light and then discuss the selective advantages likely imparted by their ability to do so. PMID:25323429

  4. Is it effective to harvest visible light by decreasing the band gap of photocatalytic materials?

    SciTech Connect

    Fu Ning; Tang Xinhu; Li Dongyang

    2012-02-27

    In situ variations in the electron work function and photo-current of TiO{sub 2} nanotubes demonstrate that long-wavelength illumination only has a minor effect on the excitation of electrons in the nanotubes after being exposed to short-wavelength light or when the short-wavelength light coexisted, indicating that the solar spectrum may not be utilized as efficiently as expected by extending the absorption spectrum of the photocatalytic material to visible light range with decreased band gaps.

  5. Fungal photobiology: visible light as a signal for stress, space and time.

    PubMed

    Fuller, Kevin K; Loros, Jennifer J; Dunlap, Jay C

    2015-08-01

    Visible light is an important source of energy and information for much of life on this planet. Though fungi are neither photosynthetic nor capable of observing adjacent objects, it is estimated that the majority of fungal species display some form of light response, ranging from developmental decision-making to metabolic reprogramming to pathogenesis. As such, advances in our understanding of fungal photobiology will likely reach the broad fields impacted by these organisms, including agriculture, industry and medicine. In this review, we will first describe the mechanisms by which fungi sense light and then discuss the selective advantages likely imparted by their ability to do so.

  6. Synthesis of supported silver nano-spheres on zinc oxide nanorods for visible light photocatalytic applications

    SciTech Connect

    Saoud, Khaled; Alsoubaihi, Rola; Bensalah, Nasr; Bora, Tanujjal; Bertino, Massimo; Dutta, Joydeep

    2015-03-15

    Highlights: • Synthesis of supported Ag NPs on ZnO nanorods using open vessel microwave reactor. • Use of the Ag/ZnO NPs as an efficient visible light photocatalyst. • Complete degradation of methylene blue in 1 h with 0.5 g/L Ag/ZnO NPs. - Abstract: We report the synthesis of silver (Ag) nano-spheres (NS) supported on zinc oxide (ZnO) nanorods through two step mechanism, using open vessel microwave reactor. Direct reduction of ZnO from zinc nitrates was followed by deposition precipitation of the silver on the ZnO nanorods. The supported Ag/ZnO nanoparticles were then characterized by electron microscopy, X-ray diffraction, FTIR, photoluminescence and UV–vis spectroscopy. The visible light photocatalytic activity of Ag/ZnO system was investigated using a test contaminant, methylene blue (MB). Almost complete removal of MB in about 60 min for doses higher than 0.5 g/L of the Ag/ZnO photocatalyst was achieved. This significant improvement in the photocatalytic efficiency of Ag/ZnO photocatalyst under visible light irradiation can be attributed to the presence of Ag nanoparticles on the ZnO nanoparticles which greatly enhances absorption in the visible range of solar spectrum enabled by surface plasmon resonance effect from Ag nanoparticles.

  7. Visible-light-induced degradation of rhodamine B by nanosized Bi2WO6.

    PubMed

    Fu, Hongbo; Pan, Chengshi; Yao, Wenqing; Zhu, Yongfa

    2005-12-01

    Visible-light-induced photodegradation of rhodamine B over nanosized Bi2WO6 has been observed. Bi2WO6 exhibited a high photoactivity to photodegrade rhodamine B in the central pH solution under visible irradiation (lambda > 420 nm). After five recycles for the photodegradation of rhodamine B, the catalyst did not exhibit any significant loss of activity, confirming the photocatalyst is essentially stable. The total organic carbon measurement displayed that a high degree of mineralization was achieved in the present photochemical system. The results of density functional theory calculation illuminated that the visible-light absorption band in the Bi2WO6 catalyst is attributed to the band transition from the hybrid orbitals of Bi6s and O2p to the W5d orbitals. The Bi2WO6-assisted photocatalytic degradation of rhodamine occurs via two competitive processes: a photocatalytic process and a photosensitized process. The transformation of rhodamine is mainly via the photocatalytic process. Kinetic studies by using electron spin resonance and the radical scavenger technologies suggest that *OH is not the dominant photooxidant. Direct hole transfers and O2*- could take part in Bi2WO6 photocatalysis. This study provided a possible treatment approach for organic pollutants by using visible light in aqueous ecosystems.

  8. Far Ultraviolet and Visible Light Scatter Measurements for CVD Silicon Carbide Mirrors for SOHO

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.; Gardner, Larry D.

    1998-01-01

    Chemically-vapor-deposited (CVD) silicon carbide (SiC) has become a popular mirror material for spaceborne solar instrumentation for the vacuum ultraviolet wavelength range due to its appreciable broadband reflectance and favorable thermal and opto-mechanical properties. Scatter from surfaces of mirrors operating in this wavelength range can destroy otherwise good image contrast especially for extended targets such as the sun. While visible light scatter measurements are relatively easy to conduct, far ultraviolet (FUV) scatter measurements are not so easy. Visible light (633 nm) scatter measurements were performed on CVD SiC telescope mirrors (from the same vendor) for two instruments on the Solar and Heliospheric Observatory (SOHO) -- Ultraviolet Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurement of Emitted Radiation (SUMER). Additionally, extensive FUV scatter measurements were made for SUMER telescope mirrors. We attempt to correlate the results for those visible light scatter measurements and to explore the usefulness of visible scatter measurements to predictions of FUV scatter for this important material.

  9. The interplay between assumed morphology and the direct radiative effect of light-absorbing organic aerosol

    NASA Astrophysics Data System (ADS)

    Saleh, Rawad; Adams, Peter J.; Donahue, Neil M.; Robinson, Allen L.

    2016-08-01

    Mie theory is widely employed in aerosol top-of-the-atmosphere direct radiative effect (DRE) calculations and to retrieve the absorptivity of light-absorbing organic aerosol (OA) from measurements. However, when OA is internally mixed with black carbon, it may exhibit complex morphologies whose optical behavior is imperfectly predicted by Mie theory, introducing bias in the retrieved absorptivities. We performed numerical experiments and global radiative transfer modeling (RTM) to investigate the effect of this bias on the calculated absorption and thus the DRE. We show that using true OA absorptivity, retrieved with a realistic representation of the complex morphology, leads to significant errors in DRE when the RTM employs the simplified Mie theory. On the other hand, when Mie theory is consistently applied in both OA absorptivity retrieval and the RTM, the errors largely cancel out, yielding accurate DRE. As long as global RTMs use Mie theory, they should implement parametrizations of light-absorbing OA derived from retrievals based on Mie theory.

  10. Light absorbing organic aerosols (brown carbon) over the tropical Indian Ocean: impact of biomass burning emissions

    NASA Astrophysics Data System (ADS)

    Srinivas, Bikkina; Sarin, M. M.

    2013-12-01

    The first field measurements of light absorbing water-soluble organic carbon (WSOC), referred as brown carbon (BrC), have been made in the marine atmospheric boundary layer (MABL) during the continental outflow to the Bay of Bengal (BoB) and the Arabian Sea (ARS). The absorption signal measured at 365 nm in aqueous extracts of aerosols shows a systematic linear increase with WSOC concentration, suggesting a significant contribution from BrC to the absorption properties of organic aerosols. The mass absorption coefficient (babs) of BrC shows an inverse hyperbolic relation with wavelength (from ˜300 to 700 nm), providing an estimate of the Angstrom exponent (αP, range: 3-19 Av: 9 ± 3). The mass absorption efficiency of brown carbon (σabs-BrC) in the MABL varies from 0.17 to 0.72 m2 g-1 (Av: 0.45 ± 0.14 m2 g-1). The αP and σabs-BrC over the BoB are quite similar to that studied from a sampling site in the Indo-Gangetic Plain (IGP), suggesting the dominant impact of organic aerosols associated with the continental outflow. A comparison of the mass absorption efficiency of BrC and elemental carbon (EC) brings to focus the significant role of light absorbing organic aerosols (from biomass burning emissions) in atmospheric radiative forcing over oceanic regions located downwind of the pollution sources.

  11. Visible Light Generation and Its Influence on Supercontinuum in Chalcogenide As2S3 Microstructured Optical Fiber

    NASA Astrophysics Data System (ADS)

    Gao, Weiqing; Liao, Meisong; Yan, Xin; Kito, Chihiro; Kohoutek, Tomas; Suzuki, Takenobu; El-Amraoui, Mohammed; Jules, Jean-Charles; Gadret, Grégory; Désévédavy, Frédéric; Smektala, Frédéric; Ohishi, Yasutake

    2011-10-01

    We demonstrate visible light generation in chalcogenide As2S3 microstructured optical fiber. The generated visible light causes irreversible damage to the fiber core because of the high absorption coefficient of chalcogenide glasses in the visible band. The SCs (supercontinua) are measured in both untapered and tapered As2S3 fibers, no wider SC is obtained in the tapered one. The SC growth is prevented by the visible light generation since the damage to the fiber core decreases the fiber transmission substantially. This effect can be avoided by designing the fiber to enable the pump source to work in single-mode operation.

  12. Metal free earth abundant elemental red phosphorus: a new class of visible light photocatalyst and photoelectrode materials.

    PubMed

    Ansari, Sajid Ali; Ansari, Mohammad Shahnawaze; Cho, Moo Hwan

    2016-02-01

    Developing a high-performance photocatalyst and a photoelectrode with enhanced visible light harvesting properties is essential for practical visible light photocatalytic applications. Noble metal-free, highly visible light-active, elemental red phosphorus (RP) was prepared by a facile mechanical ball milling method, which is a reproducible, low cost and controllable synthesis process. The synthesis used inexpensive and abundant raw materials because most RP hybrids are based on expensive noble-metals. The novel milled RP showed significantly enhanced photocatalytic and photoelectrochemical performances with a lower charge transfer resistance compared to commercial RP under wide visible photoirradiation, making it a feasible alternative for photocatalytic applications. PMID:26765211

  13. Visible light and near-infrared-responsive chromophores for drug delivery-on-demand applications.

    PubMed

    Linsley, Chase S; Quach, Viola Y; Agrawal, Gaurav; Hartnett, Elyse; Wu, Benjamin M

    2015-12-01

    The need for temporal-spatial control over the release of biologically active molecules has motivated efforts to engineer novel drug delivery-on-demand strategies actuated via light irradiation. Many systems, however, have been limited to in vitro proof-of-concept due to biocompatibility issues with the photo-responsive moieties or the light wavelength, intensity, and duration. To overcome these limitations, this paper describes a light actuated drug delivery-on-demand strategy that uses visible and near-infrared (NIR) light and biocompatible chromophores: cardiogreen, methylene blue, and riboflavin. All three chromophores are capable of significant photothermal reaction upon exposure to NIR and visible light, and the amount of temperature change is dependent upon light intensity, wavelength as well as chromophore concentration. Pulsatile release of bovine serum albumin (BSA) from thermally responsive hydrogels was achieved over 4 days. These findings have the potential to translate light-actuated drug delivery-on-demand systems from the bench to clinical applications that require explicit control over the presentation of biologically active molecules.

  14. Visible light and near infrared-responsive chromophores for drug delivery-on-demand applications

    PubMed Central

    Linsley, Chase S.; Quach, Viola Y.; Agrawal, Gaurav; Hartnett, Elyse; Wu, Benjamin M.

    2016-01-01

    The need for temporal-spatial control over the release of biologically active molecules has motivated efforts to engineer novel drug delivery-on-demand strategies actuated via light irradiation. Many systems, however, have been limited to in vitro proof-of-concept due to biocompatibility issues with the photo-responsive moieties or the light wavelength, intensity and duration. To overcome these limitations, this paper describes a light actuated drug delivery-on-demand strategy that uses visible and near infrared (NIR) light and biocompatible chromophores: cardiogreen, methylene blue and riboflavin. All 3 chromophores are capable of significant photothermal reaction upon exposure to NIR and visible light, and the amount of temperature change is dependent upon light intensity, wavelength as well as chromophore concentration. Pulsatile release of bovine serum albumin (BSA) from thermally-responsive hydrogels was achieved over 4 days. These findings have the potential to translate light actuated drug delivery-on-demand systems from the bench to clinical applications that require explicit control over the presentation of biologically active molecules. PMID:26423655

  15. Microfluidic reactors for visible-light photocatalytic water purification assisted with thermolysis

    PubMed Central

    Wang, Ning; Tan, Furui; Wan, Li; Wu, Mengchun

    2014-01-01

    Photocatalytic water purification using visible light is under intense research in the hope to use sunlight efficiently, but the conventional bulk reactors are slow and complicated. This paper presents an integrated microfluidic planar reactor for visible-light photocatalysis with the merits of fine flow control, short reaction time, small sample volume, and long photocatalyst durability. One additional feature is that it enables one to use both the light and the heat energy of the light source simultaneously. The reactor consists of a BiVO4-coated glass as the substrate, a blank glass slide as the cover, and a UV-curable adhesive layer as the spacer and sealant. A blue light emitting diode panel (footprint 10 mm × 10 mm) is mounted on the microreactor to provide uniform irradiation over the whole reactor chamber, ensuring optimal utilization of the photons and easy adjustments of the light intensity and the reaction temperature. This microreactor may provide a versatile platform for studying the photocatalysis under combined conditions such as different temperatures, different light intensities, and different flow rates. Moreover, the microreactor demonstrates significant photodegradation with a reaction time of about 10 s, much shorter than typically a few hours using the bulk reactors, showing its potential as a rapid kit for characterization of photocatalyst performance. PMID:25584117

  16. The effect of visible light on gold nanoparticles and some bioeffects on environmental fungi.

    PubMed

    Andries, Maria; Pricop, Daniela; Oprica, Lacramioara; Creanga, Dorina-Emilia; Iacomi, Felicia

    2016-05-30

    The oxidative stress induced by light exposed gold nanoparticles in some microorganism cells was investigated. Gold nanoparticles are currently used in biomedical and pharmaceutical research. For this study citrate-gold nanoparticles were synthesized in alkaline conditions at constant temperature of 85°C under magnetic stirring. Equal volumes of such prepared colloidal solution, were exposed to visible light at different wavelengths for 90min at room temperature. The spectra in the visible and ultraviolet range have revealed an increase in the intensity of the absorption band for gold nanoparticles exposed to light, due to the effect of surface plasmon resonance. Versatility of gold nanoparticles photocatalytic action was shown by means of manipulating wavelengths of incident light, which evidenced differences in the bioeffects induced in cellulolytic fungi - known for their environmental role but also for other applications such as in cosmetics industry. The comparative analysis of fungal response to gold nanoparticle stressors has revealed different enzyme activity and lipid peroxidation when fungi were supplied with gold nanoparticles exposed to different wavelength lights. The activity of catalase and superoxide dismutase were remarkably increased for green light exposure of gold nanoparticles suggesting fungi adaption to increased oxidative stress induced by irradiated particles; increased level of lipid peroxidation was showed by high concentration of malondialdehyde for white light exposed gold particles since antioxidant enzymes were less active. PMID:27063667

  17. High performance Au-Cu alloy for enhanced visible-light water splitting driven by coinage metals.

    PubMed

    Liu, Mingyang; Zhou, Wei; Wang, Ting; Wang, Defa; Liu, Lequan; Ye, Jinhua

    2016-03-28

    A Au-Cu alloy strategy is, for the first time, demonstrated to be effective in enhancing visible-light photocatalytic H2 evolution via promoting metal interband transitions. Au3Cu/SrTiO3, in which oxidation of Cu was successfully restrained, showed the highest visible-light H2 evolution activity.

  18. High performance Au-Cu alloy for enhanced visible-light water splitting driven by coinage metals.

    PubMed

    Liu, Mingyang; Zhou, Wei; Wang, Ting; Wang, Defa; Liu, Lequan; Ye, Jinhua

    2016-03-28

    A Au-Cu alloy strategy is, for the first time, demonstrated to be effective in enhancing visible-light photocatalytic H2 evolution via promoting metal interband transitions. Au3Cu/SrTiO3, in which oxidation of Cu was successfully restrained, showed the highest visible-light H2 evolution activity. PMID:26952932

  19. An Amorphous Carbon Nitride Photocatalyst with Greatly Extended Visible-Light-Responsive Range for Photocatalytic Hydrogen Generation.

    PubMed

    Kang, Yuyang; Yang, Yongqiang; Yin, Li-Chang; Kang, Xiangdong; Liu, Gang; Cheng, Hui-Ming

    2015-08-19

    Amorphous carbon nitride (ACN) with a bandgap of 1.90 eV shows an order of magnitude higher photocatalytic activity in hydrogen evolution under visible light than partially crystalline graphitic carbon nitride with a bandgap of 2.82 eV. ACN is photocatalytically active under visible light at a wavelength beyond 600 nm.

  20. Oxygen deficient ZnO1-x nanosheets with high visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Guo, Hong-Li; Zhu, Qing; Wu, Xi-Lin; Jiang, Yi-Fan; Xie, Xiao; Xu, An-Wu

    2015-04-01

    Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO1-x. The incorporation of oxygen defects could effectively extend the light absorption of ZnO1-x into the visible-light region due to the fact that the energy of the localized state is located in the forbidden gap. Thus, our obtained ZnO1-x shows a higher photodegradation of methyl orange (MO) compared to defect-free ZnO under visible light illumination. Additionally, the high content of &z.rad;OH radicals with a strong photo-oxidation capability over the ZnO1-x nanosheets significantly contributes to the improvement in the photocatalytic performance. Our oxygen deficient ZnO1-x sample shows a very high photocatalytic activity for the degradation of MO even after 5 cycles without any obvious decline. The results demonstrate that defect engineering is a powerful tool to enhance the optoelectronic and photocatalytic performances of nanomaterials.Zinc oxide is one of the most important wide-band-gap (3.2 eV) materials with versatile properties, however, it can not be excited by visible light. In this work, we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1-x nanosheets with a gray-colored appearance and excellent visible light photocatalytic activity. Detailed analysis based on UV-Vis absorption spectra, X-band electron paramagnetic resonance (EPR) spectra, and photoluminescence (PL) spectra confirms the existence of oxygen vacancies in ZnO1-x. The incorporation of oxygen defects could effectively extend the light

  1. Electronic Reconstruction of α-Ag2WO4 Nanorods for Visible-Light Photocatalysis.

    PubMed

    Lin, Zhaoyong; Li, Jiling; Zheng, Zhaoqiang; Yan, Jiahao; Liu, Pu; Wang, Chengxin; Yang, Guowei

    2015-07-28

    α-Ag2WO4 (AWO) has been studied extensively due to its H2 evolution and organic pollution degradation ability under the irradiation of UV light. However, the band gap of AWO is theoretically calculated to be 3.55 eV, resulting in its sluggish reaction to visible light. Herein, we demonstrated that, by using the electronic reconstruction of AWO nanorods upon a unique process of laser irradiation in liquid, these nanorods performed good visible-light photocatalytic organics degradation and H2 evolution. Using commercial AWO powders as the starting materials, we achieved the electronic reconstruction of AWO by a recrystallization of the starting powders upon laser irradiation in liquid and synthesized AWO nanorods. Due to the weak bond energy of AWO and the far from thermodynamic equilibrium process created by laser irradiation in liquid, abundant cluster distortions, especially [WO6] cluster distortions, are introduced into the crystal lattice, the defect density increases by a factor of 2.75, and uneven intermediate energy levels are inset into the band gap, resulting in a 0.44 eV decrease of the band gap, which modified the AWO itself by electronic reconstruction to be sensitive to visible light without the addition of others. Further, the first-principles calculation was carried out to clarify the electronic reconstruction of AWO, and the theoretical results confirmed the deduction based on the experimental measurements.

  2. Efficient chemical and visible-light-driven water oxidation using nickel complexes and salts as precatalysts.

    PubMed

    Chen, Gui; Chen, Lingjing; Ng, Siu-Mui; Lau, Tai-Chu

    2014-01-01

    Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7-9 in borate buffer. For chemical oxidation, [Ru(bpy)3](3+) (bpy = 2,2'-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s(-1). Notably, simple Ni salts such as Ni(NO3 )2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3](2+) as the photosensitizer and S2 O8 (2-) as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced β-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.

  3. CdS-graphene Nanocomposite for Efficient Visible-light-driven Photocatalytic and Photoelectrochemical Applications.

    PubMed

    Khan, Mohammad Ehtisham; Khan, Mohammad Mansoob; Cho, Moo Hwan

    2016-11-15

    This paper reports cadmium sulphide nanoparticles-(CdS NPs)-graphene nanocomposite (CdS-Graphene), prepared by a simple method, in which CdS NPs were anchored/decorated successfully onto graphene sheets. The as-synthesized nanocomposite was characterized using standard characterization techniques. A combination of CdS NPs with the optimal amount of two-dimensional graphene sheets had a profound influence on the properties of the resulting hybrid nanocomposite, such as enhanced optical, photocatalytic, and photo-electronic properties. The photocatalytic degradation ability of the CdS-Graphene nanocomposite was evaluated by degrading different types of dyes in the dark and under visible light irradiation. Furthermore, the photoelectrode performance of the nanocomposite was evaluated by different electrochemical techniques. The results showed that the CdS-Graphene nanocomposite can serve as an efficient visible-light-driven photocatalyst as well as photoelectrochemical performance for optoelectronic applications. The significantly enhanced photocatalytic and photoelectrochemical performance of the CdS-Graphene nanocomposite was attributed to the synergistic effects of the enhanced light absorption behaviour and high electron conductivity of the CdS NPs and graphene sheets, which facilitates charge separation and lengthens the lifetime of photogenerated electron-hole pairs by reducing the recombination rate. The as-synthesized narrow band gap CdS-Graphene nanocomposite can be used for wide range of visible light-induced photocatalytic and photoelectrochemical based applications. PMID:27505275

  4. Photocatalysis using zero-valent nano-copper for degrading methyl orange under visible light irradiation

    NASA Astrophysics Data System (ADS)

    Liú, Dan; Wang, Guoqiang; Liŭ, Dan; Lin, Junhong; He, Yingqiao; Li, Xiangru; Li, Ziheng

    2016-03-01

    As one of zero-valent transition metals, nano-copper was synthesized by a simple chemical reduction route and its photocatalytic activity was appraised by the degradation rate of methyl orange (MO) in aqueous solution under irradiation of a three-band fluorescent lamp. The results showed that nano-copper possessed visible-light photocatalytic activity. The finite-difference time-domain (FDTD) method was used to simulate the electric field distribution of nano-copper. From the results of simulation, it found that there was an enhancement electric field in course of light absorption on the surface of nano-copper, different morphology resulted in a diverse electric field distribution. Enhancement electric field intensity decided the visible-light photocatalytic activity of nano-copper. So the activity was affected by the morphology of nano-copper, as the size reduced and surface roughness increased, could be enhanced. It did be worth noting that the nanoscale of copper played the fatal decisive role for whether copper has the ability to degrade MO. So As-prepared nano-copper may be a novel visible-light photocatalytic material to treat organic pollution.

  5. Photodegradation of aniline by goethite doped with boron under ultraviolet and visible light irradiation

    SciTech Connect

    Liu, Guanglong; Liao, Shuijiao; Zhu, Duanwei; Liu, Linghua; Cheng, Dongsheng; Zhou, Huaidong

    2011-08-15

    Highlights: {yields} Goethite modified by boron was prepared by sol-gel method in presence of boron acid at the low temperature. {yields} B-goethite has slight red shift in the band gap transition beside their stronger light absorption compared with pristine goethite. {yields} The results showed that semiconductor photocatalytic reaction mechanism should exist in the process of aniline degradation with goethite and B-goethite as photocatalyst. -- Abstract: In the present study, goethite and goethite doped with boron (B-goethite) were employed to detect the presence or absence of semiconductor photocatalytic reaction mechanism in the reaction systems. B-goethite was prepared by sol-gel method in presence of boron acid in order to improve its photocatalystic efficiency under the ultraviolet and visible light irradiation. The optical properties of goethite and B-goethite were characterized by ultraviolet and visible absorption spectra and the result indicated that B-goethite has slight red shift in the band gap transition beside their stronger light absorption compared with pristine goethite. Degradation of aniline was investigated in presence of goethite and B-goethite in aqueous solution. It was found that the B-goethite photocatalyst exhibited enhanced ultraviolet and visible light photocatalytic activity in degradation of aniline compared with the pristine goethite. The photocatalytic degradation mechanism of B-goethite was discussed.

  6. Tungsten trioxide as a visible light photocatalyst for volatile organic carbon removal.

    PubMed

    Wicaksana, Yossy; Liu, Sanly; Scott, Jason; Amal, Rose

    2014-10-31

    Tungsten trioxide (WO3) has been demonstrated to possess visible light photoactivity and presents a means of overcoming the UV-light dependence of photocatalysts, such as titanium dioxide. In this study, WO3 nanostructures have been synthesised by a hydrothermal method using sodium tungstate (Na2WO4·2H2O), sulphate precursors and pH as structure-directing agents and parameters, respectively. By altering the concentration of the sulphate precursors and pH, it was shown that different morphologies and phases of WO3 can be achieved. The effect of the morphology of the final WO3 product on the visible light photoactivity of ethylene degradation in the gas phase was investigated. In addition, platinum (Pt) was photodeposited on the WO3 structures with various morphologies to enhance the photocatalytic properties. It was found that the photocatalytic properties of the WO3 samples greatly depend on their morphology, chemical composition and surface modification. WO3 with a cuboid morphology exhibited the highest visible light photoactivity compared to other morphologies, while adding Pt to the surface improved the performance of certain WO3 structures.

  7. Enhanced visible light photocatalytic performance of polyaniline modified mesoporous single crystal TiO2 microsphere

    NASA Astrophysics Data System (ADS)

    Deng, Yaocheng; Tang, Lin; Zeng, Guangming; Dong, Haoran; Yan, Ming; Wang, Jingjing; Hu, Wei; Wang, Jiajia; Zhou, Yaoyu; Tang, Jing

    2016-11-01

    Polyaniline (PANI) modified mesoporous single crystal TiO2 microsphere (PANI/MS-TiO2) with excellent photocatalytic activity was successfully prepared by a simple method of solution evaporation and chemisorption. The X-ray diffraction characterization demonstrated that the whole MS-TiO2 kept the crystal type of anatase. The nitrogen adsorption-desorption characterization coupled with scanning electron microscopy indicated that the MS-TiO2 possessed a unique mesoporous structure with high specific surface area, which resulted in the increased load of PANI on the surface of MS-TiO2 and multiple light reflection in the photocatalyst. The UV-vis diffuse reflectance spectra confirmed that PANI/MS-TiO2 presented more absorption ability in the visible light range than that of the pristine MS-TiO2. The transient photocurrent responses and electrochemical impedance spectroscopy (EIS) indicated the high photo responses and fast photogenerated charge separation efficiency of PANI/MS-TiO2. The photocatalytic activity of the PANI/MS-TiO2 was evaluated by the photodegradation of RhB and MB under visible light irradiation. MS-TiO2 photocatalyst with different molar ration of PANI had been prepared, and the results showed that the optimal photocatalyst (PANI/MS-TiO2 (1:40)) exhibited the highest photocatalytic efficiency which is nearly three times as great as that of pristine MS-TiO2 for the degradation of the RhB and MB under visible light irradiation. The remarkable performance of the PANI/MS-TiO2 under visible light was attributed to its mesoporous single crystal structure with large surface, conductivity, as well as the synergistic effect between PANI and MS-TiO2.

  8. Visible-Light-Triggered Drug Release from TiO2 Nanotube Arrays: A Controllable Antibacterial Platform.

    PubMed

    Xu, Jingwen; Zhou, Xuemei; Gao, Zhida; Song, Yan-Yan; Schmuki, Patrik

    2016-01-11

    In this work, we use a double-layered stack of TiO2 nanotubes (TiNTs) to construct a visible-light-triggered drug delivery system. The key for visible light drug release is a hydrophobic cap on the nanotubes containing Au nanoparticles (AuNPs). The AuNPs allow for a photocatalytic scission of the hydrophobic chain under visible light. To demonstrate this principle, we loaded ampicillin (AMP) into the lower part of the TiO2 nanotube stack, triggered visible-light-induced release, and carried out antibacterial studies. The release from the platform becomes most controllable if the drug is silane-grafted in the hydrophilic bottom layer for drug storage. Thus, visible light photocatalysis can also determine the release kinetics of the active drug from the nanotube wall.

  9. Effects of polychromatic visible and infrared light on biological liquid media.

    PubMed

    Zilov, V G; Khadartsev, A A; Bitsoev, V D

    2014-08-01

    Experimental study of the effects of polychromatic visible and infrared light on biological fluids was carried out in order to validate the new approaches to phototherapy. Polychromatic light generated by Bioptron device at different modes and frequencies was released through the fiberoptic cable, including the exposure paralleled by CO2 saturation of water and exposure from a device placed 10 cm above the water surface, which ensured maximum light absorption. The effects of irradiation were recorded in 26 and 15 min, while the increase of light absorption by blood plasma in vivo was recorded 1 h after a bath with water pre-exposed to polarized light. Absorption bands corresponding to those for immunomodulatory, anti-inflammatory, and antiviral drugs, were detected. Changes in the spectra of valency oscillations, depending on the oscillation anharmonism values, were detected.

  10. Annual Patterns and Sources of Light-Absorbing Aerosols over Central Greenland

    NASA Astrophysics Data System (ADS)

    Hu, J.; Bergin, M. H.; Dibb, J. E.; Sheridan, P. J.; Ogren, J. A.

    2014-12-01

    The Arctic region has proven to be more responsive to recent changes in climate than other parts of the Earth. A key component of the Arctic climate is the Greenland ice sheet (GIS), which has the potential to dramatically influence sea level, depending on the amount of melting that occurs, as well as climate, through shifts in the regional radiation balance. Light-absorbing aerosols from biomass burning, fossil fuel combustion, and dust sources can potentially have a significant impact on the radiation balance of the GIS; however, in order to better understand their impact, it is important to first understand the annual trends of light-absorbing aerosols and their sources over the ice sheet. With this in mind, aerosol properties including the wavelength dependent aerosol light scattering and absorption coefficients have been continuously measured at Summit, Greenland since the spring of 2011. These measurements will be used to calculate the multi-wavelength single-scattering albedo (ω0) and absorption Ångström exponent, identify annual patterns of aerosols over the GIS and how they vary from year to year, detect events of high absorption, and determine the sources of the aerosols. Preliminary findings indicate that the aerosols have an absorption Ångström exponent of approximately 1, which is characteristic of black carbon (BC). Absorption and scattering coefficients are higher in the spring and summer (March-September) and consequently lower in the fall and winter (September-March). Absorption and single-scattering albedo are averaged over the sunlit months of April-August and are found to be highest and lowest, respectively, in the year of 2012, corresponding to the year of record melt extent over the GIS.

  11. On the interrelations between ultraviolet and visible light during their simultaneous action on the cell.

    PubMed

    Zaar, E I

    1968-01-01

    Beyond the Earth's atmosphere, ultraviolet (UV) light that is a component of the Sun's spectrum appears as one of the limiting factors to life in space and on the planets which have no ozone layer in their atmosphere. At early stages in the evolution of life, the Earth's atmosphere contained neither free oxygen nor the layers serving as a screen for short-wave UV light. Under such conditions, the UV radiation lasted for 8-10 hours a day. Similar radiation conditions may be found on Mars. Still, we do not know to what extent the photo-reactivating region of sun radiation (3000-5490 angstroms) can protect cells from the action of short UV light. Therefore, it will be of interest to study a prolonged action of UV radiation on living systems (protozoa, bacteria, fungi, animal and plant cells) in the presence of visible rays capable of reactivating UV damage. We subjected infusoria (Paramecium caudatum) to prolonged action of UV light (2537 angstroms). The cells were irradiated daily for 8-16 hours with doses of 1.5-40 and 120 mkvt. A sharp reduction in the rate of division and the lethality to the infusoria were observed from the second to the fifth day of experimentation. In the light variant, UV radiation was performed simultaneously with the application of visible light (2800-15000 lux). In such conditions, the cells kept their normal rate of division for 12 days. In the next 30 days without irradiation, no deviation from the normal rate was noted. The experimental results permit the conclusion that under certain conditions of interaction between visible and UV light, UV does not produce a deleterious effect on cell division.

  12. Is blue optical filter necessary in high speed phosphor-based white light LED visible light communications?

    PubMed

    Sung, Jiun-Yu; Chow, Chi-Wai; Yeh, Chien-Hung

    2014-08-25

    Optical blue filter is usually regarded as a critical optical component for high speed phosphor-based white light emitting diode (LED) visible-light-communication (VLC). However, the optical blue filter plays different roles in VLC when using modulations of on-off keying (OOK) or discrete multi-tone (DMT). We show that in the DMT VLC system, the blue optical filter may be unnecessary, and even degrade the transmission performance (by reducing the optical signal-to-noise ratio (SNR)). Analyses and verifications by experiments are performed. To the best of our knowledge, this is the first time the function of blue filters in VLC is explicitly analyzed.

  13. Visible Light Crosslinking of Methacrylated Hyaluronan Hydrogels for Injectable Tissue Repair

    PubMed Central

    Fenn, Spencer L.; Oldinski, Rachael A.

    2015-01-01

    Tissue engineering hydrogels are primarily cured in situ using ultraviolet (UV) radiation which limits the use of hydrogels as drug or cell carriers. Visible green light activated crosslinking systems are presented as a safe alternative to UV photocrosslinked hydrogels, without compromising material properties such as viscosity and stiffness. The objective of this study was to fabricate and characterize photocrosslinked hydrogels with well-regulated gelation kinetics and mechanical properties for the repair or replacement of soft tissue. An anhydrous methacrylation of hyaluronan (HA) was performed to control the degree of modification (DOM) of HA, verified by 1H-NMR spectroscopy. UV activated crosslinking was compared to visible green light activated crosslinking. While the different photocrosslinking techniques resulted in varied crosslinking times, comparable mechanical properties of UV and green light activated crosslinked hydrogels were achieved using each photocrosslinking method by adjusting time of light exposure. Methacrylated HA (HA-MA) hydrogels of varying molecular weight, DOM and concentration exhibited compressive moduli ranging from 1 kPa to 116 kPa, for UV crosslinking, and 3 kPa to 146 kPa, for green light crosslinking. HA-MA molecular weight and concentration were found to significantly influence moduli values. HA-MA hydrogels did not exhibit any significant cytotoxic affects towards human mesenchymal stem cells. Green light activated crosslinking systems are presented as a viable method to form natural-based hydrogels in situ. PMID:26097172

  14. Characteristics of dissolved organic carbon revealed by ultraviolet/visible absorbance and fluorescence spectroscopy: The current status and future exploration

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dissolved organic carbon (DOC) is an important research subject for various disciplines. The objectives of this chapter are to review and summarize recent advancement in characterization of DOC by ultraviolet/visible (UV/Vis) and fluorescence spectroscopies and to identify the information gaps for ...

  15. Preparation and efficient visible light-induced photocatalytic activity of m-BiVO4 with different morphologies

    NASA Astrophysics Data System (ADS)

    Lu, Yanjie; Shang, Huishan; Shi, Fengjuan; Chao, Cong; Zhang, Xiang; Zhang, Bing

    2015-10-01

    The monoclinic scheelite BiVO4 crystals with peanut-like, oval, twin-quadrangle and twin-four-pointed star morphologies were synthesized via a facile one step hydrothermal method by using sodium citrate as the chelating agent. The X-ray diffraction and scanning electron microscopy were employed to elucidate the structures and mophologies of the as-prepared BiVO4 samples. The results showed that the formation of m-BiVO4 with different morphologies relied on the pH value of the precursor solution. The band gaps values (Eg) of all the BiVO4 samples were around 2.37-2.45 eV according to the UV-vis diffuse reflectance spectrum, which indicated that samples could strongly absorb in the visible light region. The photocatalytic activities of BiVO4 crystals were evaluated by degradation of MB in aqueous solution under artificial solar-light. The BiVO4 samples obtained at different pH values showed different photocatalytic activities during the sunlight-driven photodegradation of methylene blue (MB). The sample with peanut-like-shape prepared at pH=1 exhibited the highest activity, and the photocatalytic conversion could reach above 90% after 3 h of irradiation. The result suggested that m-BiVO4 with peanut-like-shape could be used as an effective photocatalyst in practical application for organic pollutants degradation.

  16. Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors.

    PubMed

    Straathof, Natan J W; Su, Yuanhai; Hessel, Volker; Noël, Timothy

    2016-01-01

    In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime. PMID:26633128

  17. In Vivo Visible Light-Triggered Drug Release From an Implanted Depot

    PubMed Central

    Carling, Carl-Johan; Viger, Mathieu L.; Huu, Viet Anh Nguyen; Garcia, Arnold V.; Almutairi, Adah

    2014-01-01

    Controlling chemistry in space and time has offered scientists and engineers powerful tools for research and technology. For example, on-demand photo-triggered activation of neurotransmitters has revolutionized neuroscience. Non-invasive control of the availability of bioactive molecules in living organisms will undoubtedly lead to major advances; however, this requires the development of photosystems that efficiently respond to regions of the electromagnetic spectrum that innocuously penetrate tissue. To this end, we have developed a polymer that photochemically degrades upon absorption of one photon of visible light and demonstrated its potential for medical applications. Particles formulated from this polymer release molecular cargo in vitro and in vivo upon irradiation with blue visible light through a photoexpansile swelling mechanism. PMID:25598962

  18. Superhydrophilicity-assisted preparation of transparent and visible light activated N-doped titania film.

    PubMed

    Xu, Qing Chi; Wellia, Diana V; Amal, Rose; Liao, Dai Wei; Loo, Say Chye Joachim; Tan, Timothy Thatt Yang

    2010-07-01

    A novel and environmental friendly method was developed to prepare transparent, uniform, crack-free and visible light activated nitrogen doped (N-doped) titania thin films without the use of organic Ti precursors and organic solvents. The N-doped titania films were prepared from heating aqueous peroxotitanate thin films deposited uniformly on superhydrophilic uncoated glass substrates. The pure glass substrates were superhydrophilic after being heated at 500 degrees C for 1 h. Nitrogen concentrations in the titania films were adjusted by changing the amount of ammonia solution. The optimal photocatalytic activity of the N-doped titania films was about 14 times higher than that of a commercial self-cleaning glass under the same visible light illumination. The current reported preparative technique is generally applicable for the preparation of other thin films.

  19. Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors.

    PubMed

    Straathof, Natan J W; Su, Yuanhai; Hessel, Volker; Noël, Timothy

    2016-01-01

    In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime.

  20. Measurement of temperature generated by visible-light-cure lamps in an in vitro model.

    PubMed

    Goodis, H E; White, J M; Andrews, J; Watanabe, L G

    1989-07-01

    The dental pulp is vulnerable to cavity preparation and restoration procedures. This vulnerability may be a result of the temperature rise generated by those procedures. When visible-light-cure lamps are used to place composite restorations, they cause the temperature in the pulp to rise. This study measured the temperature rise recorded when six visible-light-cure lamps were tested for 20- and 60-second exposure times. They were also tested in conjunction with an air current passed along the face of the lens in order to lower the temperature. Analysis of the data indicates that the lamps do cause a temperature rise within the pulp chamber--a higher rise the longer the lamp is used. Dentin thickness is important, and air lowers the temperature generated.

  1. Study of Visible Light Reactive Photocatalyst TIO2 Prepared with Thiourea

    NASA Astrophysics Data System (ADS)

    Murai, Kei-Ichiro; Endo, Kazuki; Nakagawa, Taisuke; Yamahata, Akiko; Moriga, Toshihiro

    Visible light reactive N-doped TiO2 samples were prepared with thiourea in the sol-gel method. They had the single anatase-type crystal structure. N-doped TiO2 synthesized with thiourea (T-TiO2) had a higher catalytic activity than that synthesized with urea (U-TiO2). The S2p peak observed on the surface of T-TiO2 was assigned to S6+ by XPS measurement. It was estimated that sulfuric acid species exist on the surface of T-TiO2. However, it was concluded that sulfuric acid species do not have the catalytic activity directly, but depress the crystallinity, the decrease of specific surface area and the decrease of visible light absorption.

  2. Dye-sensitized polyoxometalate for visible-light-driven photoelectrochemical cells.

    PubMed

    Gao, Junkuo; Miao, Jianwei; Li, Yongxin; Ganguly, Rakesh; Zhao, Yang; Lev, Ovadia; Liu, Bin; Zhang, Qichun

    2015-08-28

    A simple and facile one-step method for the synthesis of an organic dye-functionalized polyoxometalate (POM) hybrid with visible-light photo-response was reported. The POM hybrid was fully characterized via single crystal XRD, powder XRD, FTIR and elemental analysis. The reaction of the organic dye with inorganic salts gave the dye-functionalized POM (MoBB3), in which the POM cluster was formed in situ. The electronic absorption peak of this hybrid was successfully extended beyond 680 nm. Photoelectrochemical measurement indicated that MoBB3 was photoresponsive under visible-light illumination, suggesting that it is an n-type (electron conductive) semiconducting material. This result might offer a method for the design of novel organic dye-functionalized POMs for photoelectric applications.

  3. Polarization-independent and high-efficiency dielectric metasurfaces for visible light.

    PubMed

    Li, Qi-Tong; Dong, Fengliang; Wang, Bong; Gan, Fengyuan; Chen, Jianjun; Song, Zhiwei; Xu, Lixua; Chu, Weiguo; Xiao, Yun-Feng; Gong, Qihuang; Li, Yan

    2016-07-25

    Dielectric metasurfaces are capable of completely manipulating the phase, amplitude, and polarization of light with high spatial resolutions. The emerging design based on high-index and low-loss dielectrics has led to the realization of novel metasurfaces with high transmissions, but these devices usually operate at the limited bandwidth, and are sensitive to the incident polarization. Here, we report the realization of the polarization-independent and high-efficiency silicon metasurfaces spanning the visible wavelengths about 200 nm. The fabricated computer-generated meta-holograms exhibit a 90% diffraction efficiency, which are verified by gradient metasurfaces with measured efficiencies up to 93% at 670 nm, and exceeding 75% at the wavelengths from 600 to 800 nm for the two orthogonally polarized incidences. These dielectric metasurfaces effectively decouple the phase modulation from the polarization states and frequencies for visible light, which hold great potential for novel flat optical devices operating over a broad spectrum. PMID:27464084

  4. Synthesis of Bi2WO6 Microspheres with Visible-Light Photocatalytic Properties

    NASA Astrophysics Data System (ADS)

    Wan, Gengping; Wang, Guizhen

    2013-12-01

    Bi2WO6 microspheres constructed from nanosheets have been synthesized by a controllable solvothermal route in a large scale. The structure characterizations of the microspheres were investigated in detail by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). On the basis of XRD analysis and SEM observation of the products at different reaction time periods, a growth mechanism of Bi2WO6 microspheres was proposed. UV-Visible diffuse reflectance (DR) spectrum of the prepared Bi2WO6 microspheres demonstrates that they have absorption in the visible light region. The photocatalytic activity of Bi2WO6 microspheres toward Rhodamine-B (RhB) degradation was investigated and the as-prepared products exhibited good photocatalytic activity in degradation of RhB under 300 W Xe lamp light irradiation.

  5. Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide

    PubMed Central

    Kong, Xingang; Zeng, Chaobin; Wang, Xing; Huang, Jianfeng; Li, Cuiyan; Fei, Jie; Li, Jiayin; Feng, Qi

    2016-01-01

    The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating. PMID:27350285

  6. Construction of carbon nanodots/tungsten trioxide and their visible-light sensitive photocatalytic activity.

    PubMed

    Yan, Fanyong; Kong, Depeng; Fu, Yang; Ye, Qianghua; Wang, Yinyin; Chen, Li

    2016-03-15

    Herein we designed a simple and effective method for synthesizing carbon nanodots/tungsten trioxide nanocomposite with high photocatalytic activity. The as-prepared carbon nanodots/ tungsten trioxide has strong photoabsorption under visible light irradiation. Then, carbon nanodots/tungsten trioxide was successfully applied to the degradation of methylene blue. The photodegradation efficiency of methylene blue can be reached as high as 100% after 0.5 h visible light illumination. In addition, carbon nanodots/tungsten trioxide could also be used to degrade rhodamine B and methyl orange. Most importantly, the photocatalytic activity of carbon nanodots/tungsten trioxide did not exhibit obvious changes after five cycles. The results indicate that carbon nanodots/tungsten trioxide has potential applications in the degradation of organic pollutants in industrial waste water.

  7. Polarization-independent and high-efficiency dielectric metasurfaces for visible light.

    PubMed

    Li, Qi-Tong; Dong, Fengliang; Wang, Bong; Gan, Fengyuan; Chen, Jianjun; Song, Zhiwei; Xu, Lixua; Chu, Weiguo; Xiao, Yun-Feng; Gong, Qihuang; Li, Yan

    2016-07-25

    Dielectric metasurfaces are capable of completely manipulating the phase, amplitude, and polarization of light with high spatial resolutions. The emerging design based on high-index and low-loss dielectrics has led to the realization of novel metasurfaces with high transmissions, but these devices usually operate at the limited bandwidth, and are sensitive to the incident polarization. Here, we report the realization of the polarization-independent and high-efficiency silicon metasurfaces spanning the visible wavelengths about 200 nm. The fabricated computer-generated meta-holograms exhibit a 90% diffraction efficiency, which are verified by gradient metasurfaces with measured efficiencies up to 93% at 670 nm, and exceeding 75% at the wavelengths from 600 to 800 nm for the two orthogonally polarized incidences. These dielectric metasurfaces effectively decouple the phase modulation from the polarization states and frequencies for visible light, which hold great potential for novel flat optical devices operating over a broad spectrum.

  8. Visible-light-driven hydrogen production in a dye sensitized polyoxometalate system without noble metals

    NASA Astrophysics Data System (ADS)

    Liu, Xing; Li, Yuexiang; Peng, Shaoqin; Lai, Hua; Yi, Zhengji

    2016-05-01

    In this work, a noble-metal-free homogeneous system was constructed in one step with Keggin-type polyoxometalate (POM) SiW12O404- as a catalyst, Eosin Y as a photosensitizer, and triethanolamine (TEOA) as a sacrificial electron donor for water splitting to produce hydrogen under visible-light irradiation. A two-electron reduced heteropoly blue SiW12O406- is produced by photosensitization under visible-light irradiation. The effect of various component concentrations and POMs with different central atoms (PW12O403-, GeW12O404-, etc.) on hydrogen production was discussed. This simple system made of earth-abundant elements is expected to contribute toward the development of functional and efficient artificial photosynthetic system.

  9. Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide

    NASA Astrophysics Data System (ADS)

    Kong, Xingang; Zeng, Chaobin; Wang, Xing; Huang, Jianfeng; Li, Cuiyan; Fei, Jie; Li, Jiayin; Feng, Qi

    2016-06-01

    The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

  10. Batch and Flow Synthesis of Disulfides by Visible-Light-Induced TiO2 Photocatalysis.

    PubMed

    Bottecchia, Cecilia; Erdmann, Nico; Tijssen, Patricia M A; Milroy, Lech-Gustav; Brunsveld, Luc; Hessel, Volker; Noël, Timothy

    2016-07-21

    A mild and practical method for the preparation of disulfides through visible-light-induced photocatalytic aerobic oxidation of thiols has been developed. The method involves the use of TiO2 as a heterogeneous photocatalyst. The catalyst's high stability and recyclability makes this method highly practical. The reaction can be substantially accelerated in a continuous-flow packed-bed reactor, which enables a safe and reliable scale-up of the reaction conditions. The batch and flow protocol described herein can be applied to a diverse set of thiol substrates for the preparation of homo- and hetero-dimerized disulfides. Furthermore, biocompatible reaction conditions (i.e., room temperature, visible light, neutral buffer solution, and no additional base) have been developed, which permits the rapid and chemoselective modification of densely functionalized peptide substrates without recourse to complex purification steps.

  11. Dye-sensitized polyoxometalate for visible-light-driven photoelectrochemical cells.

    PubMed

    Gao, Junkuo; Miao, Jianwei; Li, Yongxin; Ganguly, Rakesh; Zhao, Yang; Lev, Ovadia; Liu, Bin; Zhang, Qichun

    2015-08-28

    A simple and facile one-step method for the synthesis of an organic dye-functionalized polyoxometalate (POM) hybrid with visible-light photo-response was reported. The POM hybrid was fully characterized via single crystal XRD, powder XRD, FTIR and elemental analysis. The reaction of the organic dye with inorganic salts gave the dye-functionalized POM (MoBB3), in which the POM cluster was formed in situ. The electronic absorption peak of this hybrid was successfully extended beyond 680 nm. Photoelectrochemical measurement indicated that MoBB3 was photoresponsive under visible-light illumination, suggesting that it is an n-type (electron conductive) semiconducting material. This result might offer a method for the design of novel organic dye-functionalized POMs for photoelectric applications. PMID:26200796

  12. Decoding mobile-phone image sensor rolling shutter effect for visible light communications

    NASA Astrophysics Data System (ADS)

    Liu, Yang

    2016-01-01

    Optical wireless communication (OWC) using visible lights, also known as visible light communication (VLC), has attracted significant attention recently. As the traditional OWC and VLC receivers (Rxs) are based on PIN photo-diode or avalanche photo-diode, deploying the complementary metal-oxide-semiconductor (CMOS) image sensor as the VLC Rx is attractive since nowadays nearly every person has a smart phone with embedded CMOS image sensor. However, deploying the CMOS image sensor as the VLC Rx is challenging. In this work, we propose and demonstrate two simple contrast ratio (CR) enhancement schemes to improve the contrast of the rolling shutter pattern. Then we describe their processing algorithms one by one. The experimental results show that both the proposed CR enhancement schemes can significantly mitigate the high-intensity fluctuations of the rolling shutter pattern and improve the bit-error-rate performance.

  13. Facile synthesis and enhanced visible-light photocatalysis of graphitic carbon nitride composite semiconductors.

    PubMed

    Li, Huiquan; Liu, Yuxing; Gao, Xing; Fu, Cong; Wang, Xinchen

    2015-04-13

    The semiconductor heterojunction has been an effective architecture to enhance photocatalytic activity by promoting photogenerated charge separation. Here, graphitic carbon nitride (CN) and B-modified graphitic carbon nitride (CNB) composite semiconductors were fabricated by a facile calcination process using cheap, sustainable, and easily available sodium tetraphenylboron and urea as precursors. The synthetic CN-CNB-25 semiconductor with a suitable CNB content showed the highest visible-light activity. Its degradation ratio for methyl orange and phenol was more than twice that of CN and CNB and its H2 evolution rate was ∼3.4 and ∼1.8 times higher than that of CN and CNB, respectively. It also displayed excellent stability and reusability. The enhanced activity of CN-CNB-25 was attributed predominantly to the efficient separation of photoinduced electrons and holes. This paper describes a visible-light-responsive CN composite semiconductor with great potential in environmental and energy applications.

  14. Self-Sensitized Carbon Nitride Microspheres for Long-Lasting Visible-Light-Driven Hydrogen Generation.

    PubMed

    Gu, Quan; Gao, Ziwei; Xue, Can

    2016-07-01

    A new type of metal-free photocatalyst is reported having a microsphere core of oxygen-containing carbon nitride and self-sensitized surfaces by covalently linked polymeric triazine dyes. These self-sensitized carbon nitride microspheres exhibit high visible-light activities in photocatalytic H2 generation with excellent stability for more than 100 h reaction. Comparing to the traditional g-C3 N4 with activities terminated at 450 nm, the polymeric triazine dyes on the carbon nitride microsphere surface allow for effective wide-range visible-light harvesting and extend the H2 generation activities up to 600 nm. It is believed that this new type of highly stable self-sensitized metal-free structure opens a new direction of future development of low-cost photocatalysts for efficient and long-term solar fuels production.

  15. Batch and Flow Synthesis of Disulfides by Visible-Light-Induced TiO2 Photocatalysis.

    PubMed

    Bottecchia, Cecilia; Erdmann, Nico; Tijssen, Patricia M A; Milroy, Lech-Gustav; Brunsveld, Luc; Hessel, Volker; Noël, Timothy

    2016-07-21

    A mild and practical method for the preparation of disulfides through visible-light-induced photocatalytic aerobic oxidation of thiols has been developed. The method involves the use of TiO2 as a heterogeneous photocatalyst. The catalyst's high stability and recyclability makes this method highly practical. The reaction can be substantially accelerated in a continuous-flow packed-bed reactor, which enables a safe and reliable scale-up of the reaction conditions. The batch and flow protocol described herein can be applied to a diverse set of thiol substrates for the preparation of homo- and hetero-dimerized disulfides. Furthermore, biocompatible reaction conditions (i.e., room temperature, visible light, neutral buffer solution, and no additional base) have been developed, which permits the rapid and chemoselective modification of densely functionalized peptide substrates without recourse to complex purification steps. PMID:27329945

  16. A comparison study of rhodamine B photodegradation over nitrogen-doped lamellar niobic acid and titanic acid under visible-light irradiation.

    PubMed

    Li, Xiukai; Kikugawa, Naoki; Ye, Jinhua

    2009-01-01

    A solid-state reaction method with urea as a nitrogen precursor was used to prepare nitrogen-doped lamellar niobic and titanic solid acids (i.e., HNb(3)O(8) and H(2)Ti(4)O(9)) with different acidities for visible-light photocatalysis. The photocatalytic activities of the nitrogen-doped solid acids were evaluated for rhodamine B (RhB) degradation and the results were compared with those obtained over the corresponding nitrogen-doped potassium salts. Techniques such as XRD, BET, SEM, X-ray photoelectron spectroscopy, and UV-visible diffuse reflectance spectroscopy were adopted to explore the nature of the materials as well as the characteristics of the doped nitrogen species. It was found that the intercalation of the urea precursor helped to stabilize the layered structures of both lamellar solid acids and enabled easier nitrogen doping. The effects of urea intercalation were more significant for the more acidic HNb(3)O(8) sample than for the less acidic H(2)Ti(4)O(9). Compared with the nitrogen-doped KNb(3)O(8) and K(2)Ti(4)O(9) samples, the nitrogen-doped HNb(3)O(8) and H(2)Ti(4)O(9) solid acids absorb more visible light and exhibit a superior activity for RhB photodegradation under visible-light irradiation. The nitrogen-doped HNb(3)O(8) sample performed the best among all the samples. The results of the current study suggest that the protonic acidity of the lamellar solid-acid sample is a key factor that influences nitrogen doping and the resultant visible-light photocatalysis.

  17. Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light.

    PubMed

    Lin, Jheng-Cyuan; Tra, Vu Thanh; Tsai, Dung-Sheng; Lin, Tai-Te; Huang, Po-Cheng; Hsu, Wei-Lun; Wu, Hui Jun; Huang, Rong; Van Chien, Nguyen; Yoshida, Ryuji; Lin, Jiunn-Yuan; Ikuhara, Yuichi; Chiu, Ya-Ping; Gwo, Shangjr; Tsai, Din Ping; He, Jr-Hau; Chu, Ying-Hao

    2016-01-27

    The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3 /SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.

  18. Intermolecular C-H Quaternary Alkylation of Aniline Derivatives Induced by Visible-Light Photoredox Catalysis.

    PubMed

    Cheng, Jie; Deng, Xia; Wang, Guoqiang; Li, Ying; Cheng, Xu; Li, Guigen

    2016-09-16

    The intermolecular direct C-H alkylation of aniline derivatives with α-bromo ketones to build a quaternary carbon center was reported with a visible-light catalysis procedure. The reaction covers a variety of functional groups with good to excellent yields. A regioselectivity favoring the ortho position for the amine group was observed and investigated with Fukui indices and spectral methods. PMID:27571116

  19. N-Iodosuccinimide-Promoted Hofmann-Löffler Reactions of Sulfonimides under Visible Light.

    PubMed

    O'Broin, Calvin Q; Fernández, Patricia; Martínez, Claudio; Muñiz, Kilian

    2016-02-01

    Conditions for an attractive and productive protocol for the position-selective intramolecular C-H amination of aliphatic groups (Hofmann-Löffler reaction) are reported employing sulfonimides as nitrogen sources. N-Iodosuccinimide is the only required promoter for this transformation, which is conveniently initiated by visible light. The overall transformation provides pyrrolidines under mild and selective conditions as demonstrated for 17 different substrates.

  20. Controlled trifluoromethylation reactions of alkynes through visible-light photoredox catalysis.

    PubMed

    Iqbal, Naeem; Jung, Jaehun; Park, Sehyun; Cho, Eun Jin

    2014-01-01

    The control of a reaction that can form multiple products is a highly attractive and challenging concept in synthetic chemistry. A set of valuable CF3 -containing molecules, namely trifluoromethylated alkenyl iodides, alkenes, and alkynes, were selectively generated from alkynes and CF3 I by environmentally benign and efficient visible-light photoredox catalysis. Subtle differences in the combination of catalyst, base, and solvent enabled the control of reactivity and selectivity for the reaction between an alkyne and CF3 I.

  1. Photoinduced Cleavage of N–N Bonds of Aromatic Hydrazines and Hydrazides by Visible Light

    PubMed Central

    Zhu, Mingzhao

    2012-01-01

    A photocatalytic system involving [Ru(bpyrz)3](PF6)2·2H2O, visible light, and air has been developed for cleavage of the N–N bonds of hydrazines and hydrazides. This catalytic system is generally effective for N,N-disubstituted hydrazine and hydrazide derivatives, including arylhydrazides, N-alkyl-N-arylhydrazines, and N,N-diarylhydrazines. The utility of this cleavage reaction has been demonstrated by synthesizing a variety of secondary aromatic amines. PMID:23543799

  2. Local Measurement of Flap Oxygen Saturation: An Application of Visible Light Spectroscopy.

    PubMed

    Nasseri, Nassim; Kleiser, Stefan; Reidt, Sascha; Wolf, Martin

    2016-01-01

    The aim was to develop and test a new device (OxyVLS) to measure tissue oxygen saturation by visible light spectroscopy independently of the optical pathlength and scattering. Its local applicability provides the possibility of real time application in flap reconstruction surgery. We tested OxyVLS in a liquid phantom with optical properties similar to human tissue. Our results were in good agreement with a conventional near infrared spectroscopy device.

  3. Organic Photocatalytic Cyclization of Polyenes: A Visible-Light-Mediated Radical Cascade Approach.

    PubMed

    Yang, Zhongbo; Li, Han; Zhang, Long; Zhang, Ming-Tian; Cheng, Jin-Pei; Luo, Sanzhong

    2015-10-12

    A visible-light-mediated, organic photocatalytic stereoselective radical cascade cyclization of polyprenoids is described. The desired cascade cyclization products are achieved in good yields and high stereoselectivities with eosin Y as photocatalyst in hexafluoro-2-propanol. The catalyst system is also suitable for 1,3-dicarbonyl compounds, which require only catalytic amounts of LiBr to promote the formation of the corresponding enols.

  4. Visible-Light-Promoted Oxidative [4 + 2] Cycloadditions of Aryl Silyl Enol Ethers.

    PubMed

    Yang, Bo; Lu, Zhan

    2016-08-19

    Visible-light-promoted oxidative [4 + 2] cycloadditions of ε,3-unsaturated silyl enol ethers have been developed to efficiently and diastereoselectively construct polycyclic skeletons under mild conditions. The diastereoselectivities were dependent on the stereoconfiguration of silyl enol ether, substitutions on the link, as well as electric properties of substitutions on aryl rings. The intermediates could be trapped by TEMPO, oxygen or methanol. Mechanistic studies indicated the reaction was initiated by one-electron oxidation of the silyl enol ether. PMID:27391768

  5. The Uranyl Cation as a Visible-Light Photocatalyst for C(sp(3) )-H Fluorination.

    PubMed

    West, Julian G; Bedell, T Aaron; Sorensen, Erik J

    2016-07-25

    The fluorination of unactivated C(sp(3) )-H bonds remains a desirable and challenging transformation for pharmaceutical, agricultural, and materials scientists. Previous methods for this transformation have used bench-stable fluorine atom sources; however, many still rely on the use of UV-active photocatalysts for the requisite high-energy hydrogen atom abstraction event. Uranyl nitrate hexahydrate is described as a convenient, hydrogen atom abstraction catalyst that can mediate fluorinations of certain alkanes upon activation with visible light. PMID:27320442

  6. Significantly Enhanced Visible Light Photoelectrochemical Activity in TiO₂ Nanowire Arrays by Nitrogen Implantation.

    PubMed

    Wang, Gongming; Xiao, Xiangheng; Li, Wenqing; Lin, Zhaoyang; Zhao, Zipeng; Chen, Chi; Wang, Chen; Li, Yongjia; Huang, Xiaoqing; Miao, Ling; Jiang, Changzhong; Huang, Yu; Duan, Xiangfeng

    2015-07-01

    Titanium oxide (TiO2) represents one of most widely studied materials for photoelectrochemical (PEC) water splitting but is severely limited by its poor efficiency in the visible light range. Here, we report a significant enhancement of visible light photoactivity in nitrogen-implanted TiO2 (N-TiO2) nanowire arrays. Our systematic studies show that a post-implantation thermal annealing treatment can selectively enrich the substitutional nitrogen dopants, which is essential for activating the nitrogen implanted TiO2 to achieve greatly enhanced visible light photoactivity. An incident photon to electron conversion efficiency (IPCE) of ∼10% is achieved at 450 nm in N-TiO2 without any other cocatalyst, far exceeding that in pristine TiO2 nanowires (∼0.2%). The integration of oxygen evolution reaction (OER) cocatalyst with N-TiO2 can further increase the IPCE at 450 nm to ∼17% and deliver an unprecedented overall photocurrent density of 1.9 mA/cm(2), by integrating the IPCE spectrum with standard AM 1.5G solar spectrum. Systematic photoelectrochemical and electrochemical studies demonstrated that the enhanced PEC performance can be attributed to the significantly improved visible light absorption and more efficient charge separation. Our studies demonstrate the implantation approach can be used to reliably dope TiO2 to achieve the best performed N-TiO2 photoelectrodes to date and may be extended to fundamentally modify other semiconductor materials for PEC water splitting.

  7. Functionally Diverse Nucleophilic Trapping of Iminium Intermediates Generated Utilizing Visible Light

    PubMed Central

    Freeman, David B.; Furst, Laura; Condie, Allison G.

    2011-01-01

    Our previous studies into visible light-mediated aza-Henry reactions demonstrated that molecular oxygen played a vital role in catalyst turnover as well as the production of base to facilitate the nucleophilic addition of nitroalkanes. Herein, improved conditions for the generation of iminium ions from tetrahydroisoquinolines that allow for versatile nucleophilic trapping are reported. The new conditions provide access to a diverse range of functionality under mild, anaerobic reaction conditions as well as mechanistic insights into the photoredox cycle. PMID:22148974

  8. Potential climatic effects of light absorbing particles over the Third Pole regions

    NASA Astrophysics Data System (ADS)

    Ji, Zhenming; Kang, Shichang

    2016-04-01

    Light absorbing particles (LAPs) have important impact on regional climate over the Third Pole regions. Carbonaceous and mineral aerosols, which are considered as the anthropogenic and natural sources respectively, can absorb and scatter incident solar radiation in the atmosphere. Meanwhile, LAPs deposition in snow/ice can also change the surface albedo, resulting in perturbations in the surface radiation balance. However, most studies that have made quantitative assessments of the climatic effect of LAPs over the Third Pole regions did not consider the impact of dust on snow/ice at the surface. In this study, a regional climate model RegCM4.3.4 (Regional Climate Model version 4.3.4) coupled with an aerosol-snow/ice feedback module was used to investigate the emission, distribution, and deposition of carbonaceous and dust aerosols. The study was focused on the two issues: 1) the evaluation of model performance; 2) the assessment of climatic effects induced by carbonaceous and mineral dust aerosols, respectively.

  9. Modeling of light absorbing particles in atmosphere, snow and ice in the Arctic

    NASA Astrophysics Data System (ADS)

    Sobhani, N.; Kulkarni, S.; Carmichael, G. R.

    2015-12-01

    Long-range transport of atmospheric particles from mid-latitude sources to the Arctic is the main contributor to the Arctic aerosol loadings and deposition. Black Carbon (BC), Brown Carbon (BrC) and dust are considered of great climatic importance and are the main absorbers of sunlight in the atmosphere. Furthermore, wet and dry deposition of light absorbing particles (LAPs) on snow and ice cause reduction of snow and ice albedo. LAPs have significant radiative forcing and effect on snow albedo. There are high uncertainties in estimating radiative forcing of LAPs. We studied the potential effect of LAPs from different emission source regions and sectors on snow albedo in the Arctic. The transport pathway of LAPs to the Arctic is studies for different high pollution episodes. In this study a modeling framework including Weather Research and Forecasting Model (WRF) and the University of Iowa's Sulfur Transport and dEpostion model(STEM) is used to predict the transport of LAPs from different geographical sources and sectors (i.e. transportation, residential, industry, biomass burning and power) to the Arctic. For assessing the effect of LAP deposition on snow single-layer simulator of the SNow, Ice, and Aerosol Radiation (SNICAR-Online) model was used to derive snow albedo values for snow albedo reduction causes by BC deposition. To evaluate the simulated values we compared the BC concentration in snow with observed values from previous studies including Doherty et al. 2010.

  10. Enhancement of absorption of visible light in forest canopies caused by snowy backgrounds

    NASA Astrophysics Data System (ADS)

    Pinty, B.; Widlowski, J.; Andredakis, I.; Verstraete, M. M.; Arino, O.; Clerici, M.; Kaminski, T.; Taberner, M.

    2010-12-01

    The fraction of radiation absorbed in forest canopies depends on the amount and angular distribution of the solar irradiance reaching the top of the canopy as well as the fraction of this irradiance that is transmitted through the canopy gaps and reflected back to the vegetation by the background. We show that the presence of snow on the forest floor systematically enhances the fraction of absorbed Photosynthetically Active Radiation (PAR) radiation. This observation derives from results of the application of an inversion method conducted using both MODIS and MISR broadband visible and near-infrared surface albedo products available during a full seasonal cycle. The core of the inversion method that relates the observed albedos with a radiative transfer flux model capitalizes a Bayesian approach. The inversion package generates Probability Density Functions (PDFs) of the flux model process parameters as well as PDFs of the scattered, transmitted and absorbed fluxes by the vegetation and the background layers, respectively. The current investigation addresses complex geophysical scenarios involving snow occurrence in mid and high-latitude evergreen and deciduous forest canopy systems mapped from the ESA-MERIS Globcover project . It reveals that this absorption enhancement affects evergreen and deciduous forests of the boreal zone, wherever and whenever snow covers the forest floor. Theoretical investigations based on 3-D modelling of radiation transfer in realistic forest scenarios support these observations and indicate that the absorbed fraction of PAR can even exceeds the fraction of downwelling radiation from the Sun that is intercepted by the trees. The radiative responses of evergreen needleleaf forests to sudden and drastic changes in ambient conditions in particular those imposed by the occurrence and melting of snow will then be illustrated.

  11. Indium oxide thin film as potential photoanodes for corrosion protection of stainless steel under visible light

    SciTech Connect

    Zhang, Yan; Yu, Jianqiang; Sun, Kai; Zhu, Yukun; Bu, Yuyu; Chen, Zhuoyuan

    2014-05-01

    Graphical abstract: If the conduction band potential of In{sub 2}O{sub 3} is more negative than the corrosion potential of stainless steel, photo-induced electrons will be transferred from In{sub 2}O{sub 3} to the steel, thus shifting the potential of the steel into a corrosion immunity region and preventing the steel from the corrosion. - Highlights: • Indium oxide performed novel application under visible light. • Indium oxide by sol–gel method behaved better photoelectrochemical properties. • Electrons were transferred to stainless steel from indium oxide once light on. - Abstract: This paper reports the photoelectrochemical cathodic protection of 304 stainless steel by In{sub 2}O{sub 3} thin-film under visible-light. The films were fabricated with In{sub 2}O{sub 3} powders, synthesized by both sol–gel (In{sub 2}O{sub 3}-sg) and solid-state (In{sub 2}O{sub 3}-ss) processes. The photo-induced open circuit potential and the photo-to-current efficiency measurements suggested that In{sub 2}O{sub 3} could be a promising candidate material for photoelectrochemical cathodic protection of metallic alloys under visible light. Moreover, the polarization curve experimental results indicated that In{sub 2}O{sub 3}-sg thin-film can mitigate the corrosion potential of 304 stainless steel to much more negative values with a higher photocurrent density than the In{sub 2}O{sub 3}-ss film under visible-light illumination. All the results demonstrated that the In{sub 2}O{sub 3}-sg thin-film provides a better photoelectrochemical cathodic protection for 304 stainless steel than In{sub 2}O{sub 3}-ss thin-film under visible-light illumination. The higher photoelectrochemical efficiency is possibly due to the uniform thin films produced with the smaller particle size of In{sub 2}O{sub 3}-sg, which facilitates the transfer of the photo-induced electrons from bulk to the surface and suppresses the charge recombination of the electrons and holes.

  12. The high frequency characteristics of laser reflection and visible light during solid state disk laser welding

    NASA Astrophysics Data System (ADS)

    Gao, Xiangdong; You, Deyong; Katayama, Seiji

    2015-07-01

    Optical properties are related to weld quality during laser welding. Visible light radiation generated from optical-induced plasma and laser reflection is considered a key element reflecting weld quality. An in-depth analysis of the high-frequency component of optical signals is conducted. A combination of a photoelectric sensor and an optical filter helped to obtain visible light reflection and laser reflection in the welding process. Two groups of optical signals were sampled at a high sampling rate (250 kHz) using an oscilloscope. Frequencies in the ranges 1-10 kHz and 10-125 kHz were investigated respectively. Experimental results showed that there was an obvious correlation between the high-frequency signal and the laser power, while the high-frequency signal was not sensitive to changes in welding speed. In particular, when the defocus position was changed, only a high frequency of the visible light signal was observed, while the high frequency of the laser reflection signal remained unchanged. The basic correlation between optical features and welding status during the laser welding process is specified, which helps to provide a new research focus for investigating the stability of welding status.

  13. Visible-Light Photoexcited Electron Dynamics of Scandium Endohedral Metallofullerenes: The Cage Symmetry and Substituent Effects.

    PubMed

    Wu, Bo; Hu, Jiahua; Cui, Peng; Jiang, Li; Chen, Zongwei; Zhang, Qun; Wang, Chunru; Luo, Yi

    2015-07-15

    Endohedral metallofullerenes (EMFs) have become an important class of molecular materials for optoelectronic applications. The performance of EMFs is known to be dependent on their symmetries and characters of the substituents, but the underlying electron dynamics remain unclear. Here we report a systematic study on several scandium EMFs and representative derivatives to examine the cage symmetry and substituent effects on their photoexcited electron dynamics using ultrafast transient absorption spectroscopy. Our attention is focused on the visible-light (530 nm as a demonstration) photoexcited electron dynamics, which is of broad interest to visible-light solar energy harvesting but is considered to be quite complicated as the visible-light photons would promote the system to a high-lying energy region where dense manifolds of electronic states locate. Our ultrafast spectroscopy study enables a full mapping of the photoinduced deactivation channels involved and reveals that the long-lived triplet exciton plays a decisive role in controlling the photoexcited electron dynamics under certain conditions. More importantly, it is found that the opening of the triplet channels is highly correlated to the fullerene cage symmetry as well as the electronic character of the substituents.

  14. Visible-light sensitized luminescent europium(III)-β-diketonate complexes: bioprobes for cellular imaging.

    PubMed

    Reddy, M L P; Divya, V; Pavithran, Rani

    2013-11-21

    Visible-light sensitized luminescent europium(III) molecular materials are of considerable importance because their outstanding photophysical properties make them well suited as labels in fluorescence-based bioassays and low-voltage driven pure red-emitters in optoelectronic technology. One challenge in this field is development of visible-light sensitizing ligands that can form highly emissive europium(III) complexes with sufficient stability and aqueous solubility for practical applications. Indeed, some of the recent reports have demonstrated that the excitation-window can be shifted to longer-wavelengths in europium(III)-β-diketonate complexes by appropriate molecular engineering and suitably expanded π-conjugation in the complex molecules. In this review, attention is focused on the latest innovations in the syntheses and photophysical properties of visible-light sensitized europium(III)-β-diketonate complexes and their application as bioprobes for cellular imaging. Furthermore, luminescent nanomaterials derived from long-wavelength sensitized europium(III)-β-diketonate complexes and their application in life sciences are also highlighted.

  15. Visible-Light Photoexcited Electron Dynamics of Scandium Endohedral Metallofullerenes: The Cage Symmetry and Substituent Effects.

    PubMed

    Wu, Bo; Hu, Jiahua; Cui, Peng; Jiang, Li; Chen, Zongwei; Zhang, Qun; Wang, Chunru; Luo, Yi

    2015-07-15

    Endohedral metallofullerenes (EMFs) have become an important class of molecular materials for optoelectronic applications. The performance of EMFs is known to be dependent on their symmetries and characters of the substituents, but the underlying electron dynamics remain unclear. Here we report a systematic study on several scandium EMFs and representative derivatives to examine the cage symmetry and substituent effects on their photoexcited electron dynamics using ultrafast transient absorption spectroscopy. Our attention is focused on the visible-light (530 nm as a demonstration) photoexcited electron dynamics, which is of broad interest to visible-light solar energy harvesting but is considered to be quite complicated as the visible-light photons would promote the system to a high-lying energy region where dense manifolds of electronic states locate. Our ultrafast spectroscopy study enables a full mapping of the photoinduced deactivation channels involved and reveals that the long-lived triplet exciton plays a decisive role in controlling the photoexcited electron dynamics under certain conditions. More importantly, it is found that the opening of the triplet channels is highly correlated to the fullerene cage symmetry as well as the electronic character of the substituents. PMID:26097975

  16. Black lead molybdate nanoparticles: Facile synthesis and photocatalytic properties responding to visible light

    NASA Astrophysics Data System (ADS)

    Du, Weimin; Liu, Lixin; Zhou, Keke; Ma, Xiaodan; Hao, Yaming; Qian, Xuefeng

    2015-02-01

    Black lead molybdate (PbMoO4) nanoparticles were first synthesized by the glycol-solvothermal method. Phase, morphology, crystal lattice, and specific surface of products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller nitrogen adsorption-desorption, respectively. Results revealed that the as-synthesized PbMoO4 nanoparticles are the scheelite-type tetragonal structure with 30-50 nm in size. Also, glycol played a dual function in present synthetic system: solvent and surface modification agent. Optical properties reveal glycol-modification on the surface of PbMoO4 nanoparticles can generate new energy level between the original conduction band and valence band, leading to better absorption of visible light and the black appearance. Photocatalytic experimental results demonstrate that black PbMoO4 nanoparticles synthesized in glycol medium have pretty visible-light-responsive photocatalytic degradation performance on methylene blue and phenol solution. Reaction mechanism investigations show that the excellent photocatalytic activities of black PbMoO4 nanoparticles derive from the novel energy band structure, smaller size, and larger specific surface area. Hence one can see that black PbMoO4 nanoparticles are a type of visible-light-responsive photocatalysts with excellent photocatalytic activities and potentially applied prospects in dye wastewater treatment and environmental protection. Meanwhile, the present work provides an innovative strategy for adjusting the energy band structure of wide band-gap semiconductors.

  17. Recognizing Banknote Fitness with a Visible Light One Dimensional Line Image Sensor

    PubMed Central

    Pham, Tuyen Danh; Park, Young Ho; Kwon, Seung Yong; Nguyen, Dat Tien; Vokhidov, Husan; Park, Kang Ryoung; Jeong, Dae Sik; Yoon, Sungsoo

    2015-01-01

    In general, dirty banknotes that have creases or soiled surfaces should be replaced by new banknotes, whereas clean banknotes should be recirculated. Therefore, the accurate classification of banknote fitness when sorting paper currency is an important and challenging task. Most previous research has focused on sensors that used visible, infrared, and ultraviolet light. Furthermore, there was little previous research on the fitness classification for Indian paper currency. Therefore, we propose a new method for classifying the fitness of Indian banknotes, with a one-dimensional line image sensor that uses only visible light. The fitness of banknotes is usually determined by various factors such as soiling, creases, and tears, etc. although we just consider banknote soiling in our research. This research is novel in the following four ways: first, there has been little research conducted on fitness classification for the Indian Rupee using visible-light images. Second, the classification is conducted based on the features extracted from the regions of interest (ROIs), which contain little texture. Third, 1-level discrete wavelet transformation (DWT) is used to extract the features for discriminating between fit and unfit banknotes. Fourth, the optimal DWT features that represent the fitness and unfitness of banknotes are selected based on linear regression analysis with ground-truth data measured by densitometer. In addition, the selected features are used as the inputs to a support vector machine (SVM) for the final classification of banknote fitness. Experimental results showed that our method outperforms other methods. PMID:26343654

  18. PbO-modified TiO2 thin films: a route to visible light photocatalysts.

    PubMed

    Bhachu, Davinder S; Sathasivam, Sanjayan; Carmalt, Claire J; Parkin, Ivan P

    2014-01-21

    PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface.

  19. Efficient visible-light photocatalytic performance of cuprous oxide porous nanosheet arrays

    SciTech Connect

    Li, Xianghua; Wang, Jianqiang; Cao, Minhua

    2015-10-15

    Graphical Abstract: We demonstrated a facile and efficient process for fabricating Cu{sub 2}O porous nanosheet arrays on Cu mesh. Benefiting from the 1D array structure and porous structure, the as-prepared Cu{sub 2}O sample exhibited significantly improved photocatalytic activity for methyl orange degradation under visible light irradiation. - Highlights: • Cu{sub 2}O porous nanosheet arrays on Cu mesh were synthesized via the facile and efficient process. • The Cu{sub 2}O sample exhibited the 1D array structure and porous nanosheet morphology. • The as-prepared Cu{sub 2}O porous nanosheet arrays exhibited significantly improved photocatalytic activity. - Abstract: One-dimensional nanostructures are of great interest for a wide range of applications. In this work, we demonstrated the fabrication of visible-light-responsive Cu{sub 2}O porous nanosheet arrays. The synthesis involved the growth of Cu(OH){sub 2} nanosheet arrays on Cu mesh by solution-based corrosion and thermal transformation of Cu(OH){sub 2} nanosheet to Cu{sub 2}O porous nanosheets on Cu mesh. Benefiting from the one dimensional array structure and porous structure, the as-prepared Cu{sub 2}O porous nanosheet arrays exhibited significantly improved photocatalytic activity for methyl orange degradation under visible light irradiation.

  20. Growth of Au capped GeO2 nanowires for visible-light photodetection

    NASA Astrophysics Data System (ADS)

    Ghosh, Arnab; Guha, Puspendu; Mukherjee, Subhrajit; Bar, Rajshekhar; Ray, Samit K.; Satyam, Parlapalli V.

    2016-09-01

    A single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported. Without the external source supply, the growth of the Au-GeO2 nanowires on the Ge substrate is addressed with possible mechanism. Despite high band gap, application of GeO2 as a possible new material for visible light photodetection is presented. The as-grown samples were found to have a photo-response of ≥102 with 17% external quantum efficiency at -2.0 V applied bias upon visible-light illumination (λ = 540 nm, 0.2 mW/cm2). This visible-light detection can be attributed to the oxygen vacancy related defect states as well as localized surface plasmon resonance induced absorption and subsequent hot electron injection from Au to conduction band of GeO2. The photodetection performance of the devices has been understood by the proposed energy band diagrams. In addition, ≈4 times enhancement in the efficiency has been achieved by further decoration of the Au nanoparticles on the as-grown nanowire surfaces.

  1. Silver bromide in montmorillonite as visible light-driven photocatalyst and the role of montmorillonite

    NASA Astrophysics Data System (ADS)

    Sohrabnezhad, Sh.; Pourahmad, A.; Razavi, M.

    2016-09-01

    In this study, novel plasmonic photocatalyst, Ag/AgBr-montmorillonite (MMT) nanocomposite, was prepared by dispersion method and light irradiation. The structure, composition and optical properties of such material was investigated by transmission electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The powder X-ray diffraction showed intercalation of Ag/AgBr nanoparticles into the clay interlayer space. The results showed that the prepared sample has a similar phase composition. However, their photocatalytic activity varied significantly. The photocatalytic testing result showed that the Ag/AgBr-MMT nanocomposite was more efficient photocatalyst in the discoloration of methylene blue under visible light illumination. The Ag/AgBr-MMT nanocomposite in pH = 2 and under visible light degraded 92 % of dye at the irradiation time of 20 min. MMT as matrix showed excellent role in separation efficiency of electron-hole pairs. The mechanism of separation of the photogenerated electrons and holes at the Ag/AgBr-MMT nanocomposite was discussed.

  2. Recognizing Banknote Fitness with a Visible Light One Dimensional Line Image Sensor.

    PubMed

    Pham, Tuyen Danh; Park, Young Ho; Kwon, Seung Yong; Nguyen, Dat Tien; Vokhidov, Husan; Park, Kang Ryoung; Jeong, Dae Sik; Yoon, Sungsoo

    2015-08-27

    In general, dirty banknotes that have creases or soiled surfaces should be replaced by new banknotes, whereas clean banknotes should be recirculated. Therefore, the accurate classification of banknote fitness when sorting paper currency is an important and challenging task. Most previous research has focused on sensors that used visible, infrared, and ultraviolet light. Furthermore, there was little previous research on the fitness classification for Indian paper currency. Therefore, we propose a new method for classifying the fitness of Indian banknotes, with a one-dimensional line image sensor that uses only visible light. The fitness of banknotes is usually determined by various factors such as soiling, creases, and tears, etc. although we just consider banknote soiling in our research. This research is novel in the following four ways: first, there has been little research conducted on fitness classification for the Indian Rupee using visible-light images. Second, the classification is conducted based on the features extracted from the regions of interest (ROIs), which contain little texture. Third, 1-level discrete wavelet transformation (DWT) is used to extract the features for discriminating between fit and unfit banknotes. Fourth, the optimal DWT features that represent the fitness and unfitness of banknotes are selected based on linear regression analysis with ground-truth data measured by densitometer. In addition, the selected features are used as the inputs to a support vector machine (SVM) for the final classification of banknote fitness. Experimental results showed that our method outperforms other methods.

  3. Visible-light-induced instability in amorphous metal-oxide based TFTs for transparent electronics

    SciTech Connect

    Ha, Tae-Jun

    2014-10-15

    We investigate the origin of visible-light-induced instability in amorphous metal-oxide based thin film transistors (oxide-TFTs) for transparent electronics by exploring the shift in threshold voltage (V{sub th}). A large hysteresis window in amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs possessing large optical band-gap (≈3 eV) was observed in a visible-light illuminated condition whereas no hysteresis window was shown in a dark measuring condition. We also report the instability caused by photo irradiation and prolonged gate bias stress in oxide-TFTs. Larger V{sub th} shift was observed after photo-induced stress combined with a negative gate bias than the sum of that after only illumination stress and only negative gate bias stress. Such results can be explained by trapped charges at the interface of semiconductor/dielectric and/or in the gate dielectric which play a role in a screen effect on the electric field applied by gate voltage, for which we propose that the localized-states-assisted transitions by visible-light absorption can be responsible.

  4. The study of visible light active bismuth modified nitrogen doped titanium dioxide photocatlysts: Role of bismuth

    NASA Astrophysics Data System (ADS)

    Bagwasi, Segomotso; Niu, Yuxiao; Nasir, Muhammad; Tian, Baozhu; Zhang, Jinlong

    2013-01-01

    Bismuth modified nitrogen doped TiO2 nanoparticles have been successfully prepared by two steps synthesis route which includes hydrothermal and impregnation hydrolysis method. Samples were characterized using X-ray diffraction (XRD), N2 physical adsorption, Transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Fourier Transmission Infrared (FTIR), Raman, X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PLS) technologies. The preparatory method afforded the production of well crystallized spherical Bi modified N-doped TiO2 nanoparticles with varied amounts of Bi content. XRD analysis results reveal that Bi exists as rare metastable Bi20TiO32 which started to surface at Bi loading content of 7 mol% in relation to Ti ions. All Bi modified N-TiO2 samples exhibited higher photocatalytic activity toward degradation of 2,4-DCP over N-TiO2 under visible light irradiation. The sample with 10% composition of the Bi20TiO32 exhibited the highest activity. The superior photocatalytic performance of 10%Bi/N-TiO2 is attributed to high visible light absorption as well as effective charge carrier separation. Therefore, the role of Bi species in the N-TiO2 is improvement of visible light harvesting and facilitation of charge carrier separation hence alleviating electron-hole recombination.

  5. PbO-modified TiO2 thin films: a route to visible light photocatalysts.

    PubMed

    Bhachu, Davinder S; Sathasivam, Sanjayan; Carmalt, Claire J; Parkin, Ivan P

    2014-01-21

    PbO clusters were deposited onto polycrystalline titanium dioxide (anatase) films on glass substrates by aerosol-assisted chemical vapor deposition (AACVD). The as-deposited PbO/TiO2 films were then tested for visible light photocatalysis. This was monitored by the photodegradation of stearic acid under visible light conditions. PbO/TiO2 composite films were able to degrade stearic acid at a rate of 2.28 × 10(15) molecules cm(-2) h(-1), which is 2 orders of magnitude greater than what has previously been reported. The PbO/TiO2 composite film demonstrated UVA degradation of resazurin redox dye, with the formal quantum yield (FQY) and formal quantum efficiency (FQE) exceeding that of a TiO2 film grown under the same conditions and Pilkington Activ, a commercially available self-cleaning glass. This work correlates with computational studies that predicted PbO nanoclusters on TiO2 form active visible light photocatalysts through new electronic states through PbO/TiO2 interfacial bonds resulting in new electronic states above the valence band maximum in TiO2, shifting the valence band upward as well as more efficient electron/hole separation with hole localization on PbO particles and electron on the TiO2 surface. PMID:24354409

  6. A dye-sensitized visible light photocatalyst-Bi24O31Cl10

    PubMed Central

    Wang, Liang; Shang, Jun; Hao, Weichang; Jiang, Shiqi; Huang, Shiheng; Wang, Tianmin; Sun, Ziqi; Du, Yi; Dou, Shixue; Xie, Tengfeng; Wang, Dejun; Wang, Jiaou

    2014-01-01

    The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi24O31Cl10 by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi24O31Cl10. Bi24O31Cl10 exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi24O31Cl10 is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%. PMID:25488704

  7. A dye-sensitized visible light photocatalyst-Bi24O31Cl10.

    PubMed

    Wang, Liang; Shang, Jun; Hao, Weichang; Jiang, Shiqi; Huang, Shiheng; Wang, Tianmin; Sun, Ziqi; Du, Yi; Dou, Shixue; Xie, Tengfeng; Wang, Dejun; Wang, Jiaou

    2014-01-01

    The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi24O31Cl10 by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi24O31Cl10. Bi24O31Cl10 exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi24O31Cl10 is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%. PMID:25488704

  8. Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

    SciTech Connect

    Song, Peng; Zhang, Xiaoyan; Sun, Mingxuan; Cui, Xiaoli; Lin, Yuehe

    2012-01-01

    Novel nanocomposite films based on graphene oxide (GO) and TiO2 nanotube arrays were synthesized by assembling GO on the surface of self-organized TiO2 nanotube arrays through a simple assembling method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV-vis diffuse reflectance spectroscopy. Photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO2 nanotube composite electrode compared with pristine TiO2 nanotube arrays. Sensitizing effect of GO on the photoelectrochemical response of TiO2 nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. Enhanced photocatalytic activity of TiO2 nanotube arrays towards degradation of methyl blue was also demonstrated after modification of GO. The results presented here demonstrate GO to be efficient for the improvement of utilization of visible light for TiO2 nanotube arrays.

  9. Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

    NASA Astrophysics Data System (ADS)

    Song, Peng; Zhang, Xiaoyan; Sun, Mingxuan; Cui, Xiaoli; Lin, Yuehe

    2012-02-01

    Novel nanocomposite films, based on graphene oxide (GO) and TiO2 nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO2 nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO2 nanotube composite electrode compared with pristine TiO2 nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO2 nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO2 nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO2 nanotube arrays.

  10. Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties.

    PubMed

    Song, Peng; Zhang, Xiaoyan; Sun, Mingxuan; Cui, Xiaoli; Lin, Yuehe

    2012-03-01

    Novel nanocomposite films, based on graphene oxide (GO) and TiO(2) nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO(2) nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO(2) nanotube composite electrode compared with pristine TiO(2) nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO(2) nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO(2) nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO(2) nanotube arrays. PMID:22297577

  11. Multiple-wavelength spectroscopic quantitation of light-absorbing species in scattering media

    DOEpatents

    Nathel, Howard; Cartland, Harry E.; Colston, Jr., Billy W.; Everett, Matthew J.; Roe, Jeffery N.

    2000-01-01

    An oxygen concentration measurement system for blood hemoglobin comprises a multiple-wavelength low-coherence optical light source that is coupled by single mode fibers through a splitter and combiner and focused on both a target tissue sample and a reference mirror. Reflections from both the reference mirror and from the depths of the target tissue sample are carried back and mixed to produce interference fringes in the splitter and combiner. The reference mirror is set such that the distance traversed in the reference path is the same as the distance traversed into and back from the target tissue sample at some depth in the sample that will provide light attenuation information that is dependent on the oxygen in blood hemoglobin in the target tissue sample. Two wavelengths of light are used to obtain concentrations. The method can be used to measure total hemoglobin concentration [Hb.sub.deoxy +Hb.sub.oxy ] or total blood volume in tissue and in conjunction with oxygen saturation measurements from pulse oximetry can be used to absolutely quantify oxyhemoglobin [HbO.sub.2 ] in tissue. The apparatus and method provide a general means for absolute quantitation of an absorber dispersed in a highly scattering medium.

  12. Visible-light sensitization of boron-doped nanocrystalline diamond through non-covalent surface modification.

    PubMed

    Krysova, Hana; Vlckova-Zivcova, Zuzana; Barton, Jan; Petrak, Vaclav; Nesladek, Milos; Cigler, Petr; Kavan, Ladislav

    2015-01-14

    A novel simple and versatile synthetic strategy is developed for the surface modification of boron-doped diamond. In a two-step procedure, polyethyleneimine is adsorbed on the hydrogenated diamond surface and subsequently modified with a model light-harvesting donor-π-bridge-acceptor molecule (coded P1). The sensitized diamond exhibits stable cathodic photocurrents under visible-light illumination in aqueous electrolyte solution with dimethylviologen serving as an electron mediator. In spite of the simplicity of the surface sensitization protocol, the photoelectrochemical performance is similar to or better than that of other sensitized diamond electrodes which were reported in previous studies (2008-2014). PMID:25418375

  13. Visible light-promoted metal-free sp(3)-C-H fluorination.

    PubMed

    Xia, Ji-Bao; Zhu, Chen; Chen, Chuo

    2014-10-11

    Photoexcited acetophenone can catalyze the fluorination of unactivated C(sp(3))-H groups. While acetophenone, a colorless oil, only has a trace amount of absorption in the visible light region, its photoexcitation can be achieved by irradiation with light generated by a household compact fluorescent lamp (CFL). This operational simple method provides improved substrate scope for the direct incorporation of a fluorine atom into simple organic molecules. CFL-irradiation can also be used to promote certain classic UV-promoted photoreactions of colorless monoarylketones and enones/enals. PMID:25143256

  14. QPSK modulation for AC-power-signal-biased visible light communication system

    NASA Astrophysics Data System (ADS)

    Liu, Yu-Feng; Yeh, Chien-Hung; Chow, Chi-Wai; Liu, Yang

    2013-01-01

    With the integration of light emitting diode (LED), visible light communication (VLC) can provide wireless communication link using the lightning system. Due to the consideration of power efficiency, AC-LED has the design of reducing energy waste with alternating current from the power outlet. In this work, we propose an AC-power-signalbiased system that provides communication on both DC-LED and AC-LED. The bias circuit is designed to combine ACpower signal and the message signal with QPSK format. This driving scheme needs no AC-to-DC converters and it is suitable for driving AC LED. Synchronization is completed to avoid threshold effect of LED.

  15. The effects of narrowbands of visible light upon some skin disorders: a review.

    PubMed

    Greaves, A J

    2016-08-01

    This review article focuses on clinical studies published in the fields of (i) photorejuvenation and anti-ageing, (ii) oily or acne-prone skin and related imperfections, (iii) skin pigmentation and lightening, (iv) dandruff and other Malassezia-related skin disorders and (v) prevention and reversal of hair loss using non-thermal, non-ablative devices (principally light-emitting diodes). It mainly focuses on clinical proof of performance and also on in vitro studies that support the clinical findings. The mode of action of narrowbands of visible light upon the skin is only briefly discussed since their biological effects have been previously reviewed. PMID:26708128

  16. Visible-Light-Promoted Trifluoromethylthiolation of Styrenes by Dual Photoredox/Halide Catalysis.

    PubMed

    Honeker, Roman; Garza-Sanchez, R Aleyda; Hopkinson, Matthew N; Glorius, Frank

    2016-03-18

    Herein, we report a new visible-light-promoted strategy to access radical trifluoromethylthiolation reactions by combining halide and photoredox catalysis. This approach allows for the synthesis of vinyl-SCF3 compounds of relevance in pharmaceutical chemistry directly from alkenes under mild conditions with irradiation from household light sources. Furthermore, alkyl-SCF3-containing cyclic ketone and oxindole derivatives can be accessed by radical-polar crossover semi-pinacol and cyclization processes. Inexpensive halide salts play a crucial role in activating the trifluoromethylthiolating reagent towards photoredox catalysis and aid the formation of the SCF3 radical.

  17. Effects of darkening processes on surfaces of airless bodies. [light-absorbing coatings on lunar soil

    NASA Technical Reports Server (NTRS)

    Cassidy, W.; Hapke, B.

    1975-01-01

    We find the lunar darkening process could be due neither to simple addition of impact-melted glass nor to addition of devitrified glass to crushed lunar rock. There is evidence that lunar soil grains have thin, very light-absorbing coatings that mask absorption bands, seen in the reflection spectra of freshly crushed lunar rock, in the same manner as they are masked in the spectra of lunar soils. We believe the processes that produce these coatings are (1) deposition of atoms sputtered from lunar soil grains by solar wind particles and (2) deposition of vapor species vaporized from lunar soil grains by micrometeoritic impacts. We describe an apparent new type of fractionation that occurs during deposition of sputtered atoms. This fractionation favors retention of higher mass atoms over lower mass atoms, and appears to be a linear function of mass.

  18. Zinc oxide nanorod mediated visible light photoinactivation of model microbes in water

    NASA Astrophysics Data System (ADS)

    Sapkota, Ajaya; Anceno, Alfredo J.; Baruah, Sunandan; Shipin, Oleg V.; Dutta, Joydeep

    2011-05-01

    The inactivation of model microbes in aqueous matrix by visible light photocatalysis as mediated by ZnO nanorods was investigated. ZnO nanorods were grown on glass substrate following a hydrothermal route and employed in the inactivation of gram-negative Escherichia coli and gram-positive Bacillus subtilis in MilliQ water. The concentration of Zn2 + ions in the aqueous matrix, bacterial cell membrane damage, and DNA degradation at post-exposure were also studied. The inactivation efficiencies for both organisms under light conditions were about two times higher than under dark conditions across the cell concentrations assayed. Anomalies in supernatant Zn2 + concentration were observed under both conditions as compared to control treatments, while cell membrane damage and DNA degradation were observed only under light conditions. Inactivation under dark conditions was hence attributed to the bactericidal effect of Zn2 + ions, while inactivation under light conditions was due to the combined effects of Zn2 + ions and photocatalytically mediated electron injection. The reduction of pathogenic bacterial densities by the photocatalytically active ZnO nanorods in the presence of visible light implies potential ex situ application in water decontamination at ambient conditions under sunlight.

  19. Structural Effects in Visible-Light-Responsive Metal-Organic Frameworks Incorporating ortho-Fluoroazobenzenes.

    PubMed

    Castellanos, Sonia; Goulet-Hanssens, Alexis; Zhao, Fangli; Dikhtiarenko, Alla; Pustovarenko, Alexey; Hecht, Stefan; Gascon, Jorge; Kapteijn, Freek; Bléger, David

    2016-01-11

    The ability to control the interplay of materials with low-energy photons is important as visible light offers several appealing features compared to ultraviolet radiation (less damaging, more selective, predominant in the solar spectrum, possibility to increase the penetration depth). Two different metal-organic frameworks (MOFs) were synthesized from the same linker bearing all-visible ortho-fluoroazobenzene photoswitches as pendant groups. The MOFs exhibit different architectures that strongly influence the ability of the azobenzenes to isomerize inside the voids. The framework built with Al-based nodes has congested 1D channels that preclude efficient isomerization. As a result, local light-heat conversion can be used to alter the CO2 adsorption capacity of the material on exposure to green light. The second framework, built with Zr nodes, provides enough room for the photoswitches to isomerize, which leads to a unique bistable photochromic MOF that readily responds to blue and green light. The superiority of green over UV irradiation was additionally demonstrated by reflectance spectroscopy and analysis of digested samples. This material offers promising perspectives for liquid-phase applications such as light-controlled catalysis and adsorptive separation.

  20. The Influence of Light Absorbing Aerosols on the Radiation Balance Over Central Greenland

    NASA Astrophysics Data System (ADS)

    Strellis, B.; Bergin, M. H.; Sokolik, I. N.; Dibb, J. E.; Sheridan, P. J.; Ogren, J. A.

    2011-12-01

    The Arctic region has proven to be more responsive to recent changes in climate than other parts of the Earth. A key component of the Arctic climate is the Greenland Ice Sheet, which has the potential to dramatically influence both sea level, depending on the amount of melting that occurs, and climate, through shifts in the regional radiation balance. Light absorbing aerosols from biomass burning, fossil fuel combustion, and dust sources can potentially have a significant impact on the radiation balance of the ice sheet, although at this time we lack the key measurements needed to accurately quantify aerosol forcing over the ice sheet. For this reason a field study was conducted at Summit, Greenland, from May-July of 2012. Our efforts included real-time measurements of aerosol physical and optical properties including size distribution, multi-wavelength scattering (σsp) and backscattering (σbsp) coefficients, and multi-wavelength absorption coefficient (σap), as well as measurements of wavelength dependent aerosol optical depth and spectral snow albedo. The measurements serve as inputs to a radiative transfer model to estimate the direct aerosol radiative forcing at both the surface and top of the atmosphere. Preliminary results indicate that the direct aerosol radiative forcing is often several Wm-2 and is at times greater than 10 Wm-2. The aerosol chemical composition (major ions, elements, and organic and elemental carbon compounds) was also determined through filter sampling and will be discussed in terms of the sources of light absorbing aerosols over central Greenland.

  1. Spatiotemporal variability of light-absorbing carbon concentration in a residential area impacted by woodsmoke.

    PubMed

    Krecl, Patricia; Johansson, Christer; Ström, Johan

    2010-03-01

    Residential wood combustion (RWC) is responsible for 33% of the total carbon mass emitted in Europe. With the new European targets to increase the use of renewable energy, there is a growing concern that the population exposure to woodsmoke will also increase. This study investigates observed and simulated light-absorbing carbon mass (MLAC) concentrations in a residential neighborhood (Lycksele, Sweden) where RWC is a major air pollution source during winter. The measurement analysis included descriptive statistics, correlation coefficient, coefficient of divergence, linear regression, concentration roses, diurnal pattern, and weekend versus weekday concentration ratios. Hourly RWC and road traffic contributions to MLAC were simulated with a Gaussian dispersion model to assess whether the model was able to mimic the observations. Hourly mean and standard deviation concentrations measured at six sites ranged from 0.58 to 0.74 microg m(-3) and from 0.59 to 0.79 microg m(-3), respectively. The temporal and spatial variability decreased with increasing averaging time. Low-wind periods with relatively high MLAC concentrations correlated more strongly than high-wind periods with low concentrations. On average, the model overestimated the observations by 3- to 5-fold and explained less than 10% of the measured hourly variability at all sites. Large residual concentrations were associated with weak winds and relatively high MLAC loadings. The explanation of the observed variability increased to 31-45% when daily mean concentrations were compared. When the contribution from the boilers within the neighborhood was excluded from the simulations, the model overestimation decreased to 16-71%. When assessing the exposure to light-absorbing carbon particles using this type of model, the authors suggest using a longer averaging period (i.e., daily concentrations) in a larger area with an updated and very detailed emission inventory. PMID:20397565

  2. Spatiotemporal variability of light-absorbing carbon concentration in a residential area impacted by woodsmoke.

    PubMed

    Krecl, Patricia; Johansson, Christer; Ström, Johan

    2010-03-01

    Residential wood combustion (RWC) is responsible for 33% of the total carbon mass emitted in Europe. With the new European targets to increase the use of renewable energy, there is a growing concern that the population exposure to woodsmoke will also increase. This study investigates observed and simulated light-absorbing carbon mass (MLAC) concentrations in a residential neighborhood (Lycksele, Sweden) where RWC is a major air pollution source during winter. The measurement analysis included descriptive statistics, correlation coefficient, coefficient of divergence, linear regression, concentration roses, diurnal pattern, and weekend versus weekday concentration ratios. Hourly RWC and road traffic contributions to MLAC were simulated with a Gaussian dispersion model to assess whether the model was able to mimic the observations. Hourly mean and standard deviation concentrations measured at six sites ranged from 0.58 to 0.74 microg m(-3) and from 0.59 to 0.79 microg m(-3), respectively. The temporal and spatial variability decreased with increasing averaging time. Low-wind periods with relatively high MLAC concentrations correlated more strongly than high-wind periods with low concentrations. On average, the model overestimated the observations by 3- to 5-fold and explained less than 10% of the measured hourly variability at all sites. Large residual concentrations were associated with weak winds and relatively high MLAC loadings. The explanation of the observed variability increased to 31-45% when daily mean concentrations were compared. When the contribution from the boilers within the neighborhood was excluded from the simulations, the model overestimation decreased to 16-71%. When assessing the exposure to light-absorbing carbon particles using this type of model, the authors suggest using a longer averaging period (i.e., daily concentrations) in a larger area with an updated and very detailed emission inventory.

  3. Transmission of UV/visible light through model human epidermis at varying ambient humidity

    NASA Astrophysics Data System (ADS)

    Farley, Carlton W.; Sadate, Sandra; Kassu, Aschalew; Sharma, Anup

    2014-09-01

    Model human epidermal samples are used for transmission measurements at varying ambient humidity. Light is used from four different light emitting diodes (LEDs), of UVA wavelength of 365nm, and three visible wavelengths of 460nm, 500nm, and 595nm. A humidity-controlled chamber was used to house the samples while transmission measurements were taken. Many different types of measurements were taken, including raising ambient humidity from 20% to 75% then adding 0.5mL of water to the sample; lowering humidity from near 100% to 60%; and alternately raising and lowering of the ambient humidity. The results show higher transmission of light through the samples at very high ambient humidity, about 100%; whereas the transmission is much lower at lower ambient humidity. A simple model of epidermis as a turbid medium and reduced light scattering by refractive index matching is used to explain the results. Implications of these results are discussed.

  4. Cu2O nanoparticles decorated BiVO4 as an effective visible-light-driven p-n heterojunction photocatalyst for methylene blue degradation

    NASA Astrophysics Data System (ADS)

    Min, Shixiong; Wang, Fang; Jin, Zhiliang; Xu, Jing

    2014-10-01

    Bismuth vanadate (BiVO4) is a chemically stable and nontoxic semiconductor (SC) photocatalyst that can absorb visible light to degrade most of pollutants in aqueous solution due to suitable band-gap energy (ca. 2.4 eV), but it usually shows a low activity in its pristine form owing to poor charge-separation characteristics and the weak surface adsorption properties. In this paper, we demonstrated that the photocatalytic activity of BiVO4 can be greatly enhanced by surface modification with Cu2O nanoparticles through polyol reduction method. The modified photocatalysts (Cu2O/BiVO4) with proper loading amount of Cu2O (0.75 wt%) showed the highest photocatalytic degradation activity for methylene blue (MB) degradation with the pseudo-first-order rate constant kapp and degradation efficiency two times higher than pristine BiVO4 under visible light and solar light irradiation. The characterizations of resulting photocatalysts revealed that decoration of Cu2O nanoparticles led to the formation of a p-n heterojunction at the contact interface of Cu2O and BiVO4, which narrowed the band gap of BiVO4 for extending the absorption range of visible light and promoted the charge transfer across interface for suppressing the recombination of photogenerated electron-hole pairs, thus improving the catalytic performance of photocatalysts. This work demonstrates that the structural integration of p-type Cu2O SC with n-type BiVO4 SC will be a new promising strategy to develop a high-efficient heterojunction photocatalyst for visible-light-driven degradation of pollutants.

  5. Solution-processed PCDTBT capped low-voltage InGaZnO{sub x} thin film phototransistors for visible-light detection

    SciTech Connect

    Wang, Han; Xiao, Yubin; Chen, Zefeng; Xu, Wangying; Long, Mingzhu; Xu, Jian-Bin

    2015-06-15

    The effects of visible-light detection based on solution processed poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′, 3′benzothiadiazole) (PCDTBT) capped InGaZnOx (IGZO) phototransistors with Al{sub 2}O{sub x} serving as gate dielectric are investigated in this paper. The high-k dielectric is used to lower the device operating voltage down to 2 V. Photons emitted from laser sources with the wavelengths (λ) of 532 nm and 635 nm are absorbed through the layer of PCDTBT to generate electron-hole-pairs (EHPs). After the separation of EHPs, electrons are injected into IGZO layer through the p-n junction formed between the IGZO (n-type semiconductor) and the PCDTBT (p-type semiconductor). The photo-generated carriers boost the drain current of the transistors as well as bring about the negative threshold voltage shift. Significant enhanced detection performance is achieved under the laser wavelength of 532 nm. The highest photoresponsivity reaches up to 20 A/W, while the photoresponse rise time comes to 10 ms and the fall time comes to approximate 76 ms, which is much faster than trap assisted IGZO visible light detection. The fabricated phototransistors favor the application of visible-light detectors and/or optical switches.

  6. Synthesis, characterization and degradation of Bisphenol A using Pr, N co-doped TiO 2 with highly visible light activity

    NASA Astrophysics Data System (ADS)

    Yang, Juan; Dai, Jun; Li, Jiantong

    2011-08-01

    Praseodymium and nitrogen co-doped titania (Pr/N-TiO 2) photocatalysts, which could degrade Bisphenol A (BPA) under visible light irradiation, were prepared by the modified sol-gel process. Tetrabutyl titanate, urea and praseodymium nitrate were used as the sources of titanium, nitrogen and praseodymium, respectively. The resulting materials were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), N 2 adsorption-desorption isotherm and Fourier transform infrared spectra (FTIR). It was found that Pr doping inhibited the growth of crystalline size and the transformation from anatase to rutile. The degradation of BPA under visible light illumination was taken as probe reaction to evaluate the photo-activity of the co-doped photocatalyst. In our experiments, the optimal dopant amount of Pr was 1.2 mol% and the calcination temperature was 500 °C for the best photocatalytic activity. Pr/N-TiO 2 samples exhibited enhanced visible-light photocatalytic activity compared to N-TiO 2, undoped TiO 2 and commercial P25. The nitrogen atoms were incorporated into the crystal of titania and could narrow the band gap energy. Pr doping could slow the radiative recombination of photogenerated electrons and holes in TiO 2. The improvement of photocatalytic activity was ascribed to the synergistic effects of nitrogen and Pr co-doping.

  7. Palladium nanoparticles anchored to anatase TiO2 for enhanced surface plasmon resonance-stimulated, visible-light-driven photocatalytic activity

    PubMed Central

    Leong, Kah Hon; Chu, Hong Ye; Ibrahim, Shaliza

    2015-01-01

    Summary Freely assembled palladium nanoparticles (Pd NPs) on titania (TiO2) nano photocatalysts were successfully synthesized through a photodeposition method using natural sunlight. This synthesized heterogeneous photocatalyst (Pd/TiO2) was characterized through field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), BET surface area, UV–vis diffuse reflectance spectra (UV-DRS), Raman and photoluminescence (PL) analyses. The simple and smart synthesis anchored well the deposition with controlled Pd NPs size ranging between 17 and 29 nm onto the surface of TiO2. Thus, it gives the characteristic for Pd NPs to absorb light in the visible region obtained through localized surface plasmon resonance (LSPRs). Apparently, the photocatalytic activity of the prepared photocatalysts was evaluated by degrading the endocrine disrupting compound (EDC) amoxicillin (AMX) excited under an artificial visible light source. In the preliminary run, almost complete degradation (97.5%) was achieved in 5 h with 0.5 wt % Pd loading and the degradation followed pseudo-first-order kinetics. The reusability trend proved the photostability of the prepared photocatalysts. Hence, the study provides a new insight about the modification of TiO2 with noble metals in order to enhance the absorption in the visible-light region for superior photocatalytic performance. PMID:25821683

  8. Photocatalytic oxidation of organic dyes with visible-light-driven codoped TiO2 photocatalysts

    NASA Astrophysics Data System (ADS)

    Zhang, Dongfang; Zeng, Fanbin

    2011-06-01

    A novel copper (II) and zinc (II) codoped TiO2 photocatalyst was synthesized by a modified sol-gel method using titanium (IV) isopropoxide, Zn(NO3)2 · 6H2O and copper(Il) nitrate as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and photo-luminescence spectra (PL). The XRD results showed undoped and Zn, Cu-codoped TiO2 nanoparticles mainly including anatase phase and a tiny amount of Zn- and Cu-oxides exist in the mixed system, which is attributed to the decomposition of copper and zinc nitrates in the TiO2 gel to form CuO and ZnO and randomly dispersed on the TiO2 surface. On the basis of the optical characterization results, we found that the codoping of copper (II) and zinc (II) resulted a red shift of adsorption and lower recombination probability between electrons and holes, which were the reasons for high photocatalytic activity of Zn, Cu-codoped TiO2 nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of samples was tested for degradation of methyl orange (MO) in solutions. The results indicated that the visible-light driven capability of the codoped catalyst were much higher than that of the pure TiO2 catalyst under visible irradiation. Because of the synergetic effect of copper (II) and zinc (II) element, the Zn, Cu-codoped TiO2 catalyst will show higher quantum yield and enhance absorption of visible light. In the end, a key mechanism was proposed in order to account for the enhanced activity.

  9. Visible Light Responsive Catalysts Using Quantum Dot-Modified Ti02 for Air and Water Purification

    NASA Technical Reports Server (NTRS)

    Coutts, Janelle L.; Levine, Lanfang H.; Richards, Jeffrey T.; Hintze, paul; Clausen, Christian

    2012-01-01

    The method of photocatalysis utilizing titanium dioxide, TiO2, as the catalyst has been widely studied for trace contaminant control for both air and water applications because of its low energy consumption and use of a regenerable catalyst. Titanium dioxide requires ultraviolet light for activation due to its band gap energy of 3.2 eV. Traditionally, Hg-vapor fluorescent light sources are used in PCO reactors and are a setback for the technology for space application due to the possibility of Hg contamination. The development of a visible light responsive (VLR) TiO2-based catalyst could lead to the use of solar energy in the visible region (approx.45% of the solar spectrum lies in the visible region; > 400 nm) or highly efficient LEDs (with wavelengths > 400 nm) to make PCO approaches more efficient, economical, and safe. Though VLR catalyst development has been an active area of research for the past two decades, there are few commercially available VLR catalysts; those that are available still have poor activity in the visible region compared to that in the UV region. Thus, this study was aimed at the further development of VLR catalysts by a new method - coupling of quantum dots (QD) of a narrow band gap semiconductor (e.g., CdS, CdSe, PbS, ZnSe, etc.) to the TiO2 by two preparation methods: 1) photodeposition and 2) mechanical alloying using a high-speed ball mill. A library of catalysts was developed and screened for gas and aqueous phase applications, using ethanol and 4-chlorophenol as the target contaminants, respectively. Both target compounds are well studied in photocatalytic systems serve as model contaminants for this research. Synthesized catalysts were compared in terms of preparation method, type of quantum dots, and dosage of quantum dots.

  10. Observations of Light-Absorbing Carbonaceous Aerosols in East and South Asia

    NASA Astrophysics Data System (ADS)

    Yoon, S.; Kim, S.; Choi, W.

    2013-05-01

    Light-absorbing aerosols, such as black carbon (BC), brown carbon and mineral dust, typically constitute a small fraction of ambient particle mass but can contribute to solar radiative forcing through absorption of solar radiation and heating of the absorbing aerosol layer. Besides the direct radiative effect, the heating can evaporate clouds and change the atmospheric dynamics. In this study, we investigate the optical and radiative properties of light-absorbing aerosols from ground-based and aircraft measurements in East and South Asia within the framework of UNEP Atmospheric Brown Cloud-Asia (ABC-Asia) project and Sustainable Atmosphere for the Kathmandu Valley (SusKat) campaign (December 2012 ~ February 2013). BC mass concentration, aerosol scattering and absorption coefficients measurements and radiative forcing calculations were performed at four sites: Gosan (Korea), Anmyeon (Korea), Hanimaadhoo (Maldives) and Pyramid (Nepal). No significant seasonal variations of aerosol properties, except for summer due to wet scavenging by rainfall, were observed in East Asia, whereas dramatic changes of light-absorbing aerosol properties were observed in South Asia between dry and wet monsoon periods. Although BC mass concentration in East Asia is generally higher than that observed in South Asia, BC mass concentration at Hanimaadhoo during winter dry monsoon is similar to that of East Asia. The observed solar absorption efficiency (absorption coefficient/extinction coefficient) at 550 nm at Gosan and Anmyeon is higher than that in Hanimaadhoo due to large portions of BC emission from fossil fuel combustion. Interestingly, solar absorption efficiency at Pyramid is 0.14, which is two times great than that in Hanimaadhoo and is about 40% higher than that in East Asia, though BC mass concentration at Pyramid is the lowest among four sites. Throughout the unmanned aerial vehicle experiment in Jeju, Korea during August-September 2008, long-range transport of aerosols from

  11. Nitrogen allocation and the fate of absorbed light in 21-year-old Pinus radiata.

    PubMed

    Posch, Sabine; Warren, Charles R; Kruse, Jörg; Guttenberger, Helmut; Adams, Mark A

    2008-03-01

    We investigated effects of nitrogen (N) fertilizer and canopy position on the allocation of N to Rubisco and chlorophyll as well as the distribution of absorbed light among thermal energy dissipation, photochemistry, net CO2 assimilation and alternative electron sinks such as the Mehler reaction and photorespiration. The relative reduction state of the primary quinone receptor of photosystem II (QA) was used as a surrogate for photosystem II (PSII) vulnerability to photoinactivation. Measurements were made on needles from the lower, mid and upper canopy of 21-year-old Pinus radiata D. Don trees grown with (N+) and without (N0) added N fertilizer. Rubisco was 45 to 60% higher in needles of N+ trees than in needles of N0 trees at all canopy positions. Chlorophyll was approximately 80% higher in lower- and mid-canopy needles of N+ trees than of N0 trees, but only approximately 20% higher in upper-canopy needles. Physiological differences between N+ and N0 trees were found only in the lower- and mid- canopy positions. Needles of N+ trees dissipated up to 30% less light energy as heat than needles of N0 trees and had correspondingly more reduced QA. Net CO2 assimilation and the proportions of electrons used by alternative electron sinks such as the Mehler reaction and photorespiration were unaffected by N treatment regardless of canopy position. We conclude that the application of N fertilizer mainly affected the biochemistry and light-use physiology in lower- and mid-canopy needles by increasing the amount of chlorophyll and hence the amount of light harvested. This, however, did not improve photochemistry or safe dissipation, but increased PSII vulnerability to photoinactivation, an effect with likely significant consequences during sunflecks or sudden gap formation. PMID:18171661

  12. Self-assembly based plasmonic arrays tuned by atomic layer deposition for extreme visible light absorption.

    PubMed

    Hägglund, Carl; Zeltzer, Gabriel; Ruiz, Ricardo; Thomann, Isabell; Lee, Han-Bo-Ram; Brongersma, Mark L; Bent, Stacey F

    2013-07-10

    Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems. PMID:23805835

  13. Fullerene C70 decorated TiO2 nanowires for visible-light-responsive photocatalyst

    NASA Astrophysics Data System (ADS)

    Cho, Er-Chieh; Ciou, Jing-Hao; Zheng, Jia-Huei; Pan, Job; Hsiao, Yu-Sheng; Lee, Kuen-Chan; Huang, Jen-Hsien

    2015-11-01

    In this study, we have synthesized C60 and C70-modified TiO2 nanowire (NW) through interfacial chemical bonding. The results indicate that the fullerenes (C60 and C70 derivatives) can act as sinks for photogenerated electrons in TiO2, while the fullerene/TiO2 is illuminated under ultraviolet (UV) light. Therefore, in comparison to the pure TiO2 NWs, the modified TiO2 NWs display a higher photocatalytic activity under UV irradiation. Moreover, the fullerenes also can function as a sensitizer to TiO2 which expand the utilization of solar light from UV to visible light. The results reveal that the C70/TiO2 NWs show a significant photocatalytic activity for degradation of methylene blue (MB) in visible light region. To better understand the mechanism responsible for the effect of fullerenes on the photocatalytic properties of TiO2, the electron only devices and photoelectrochemical cells based on fullerenes/TiO2 are also fabricated and evaluated.

  14. Visible and Near-infrared Light Curves of SN 2009nr

    NASA Astrophysics Data System (ADS)

    Heath, Jonathan; Bryngelson, Ginger

    2014-03-01

    This study explores the behavior of SN 2009nr, an apparently normal type Ia supernova (SN Ia). A plot of this object's brightness over time is known as a light curve. Because of the uniformity of their light curves, SNe Ia are valuable markers for determining the expansion of the universe and other cosmological parameters. Understanding the properties of these supernovae is vital in order to build our confidence in their use as standard candles. A small, but increasing number of SN Ia late-time observations have been made in the near-infrared (NIR). Most exhibit a flattening of the NIR power even as the visible light declines at a steady rate. It is still unclear as to why they exhibit this behavior and how typical this is. In order to characterize the late behavior of SNe Ia, images of SN 2009nr were analyzed using the Image Reduction and Analysis Facility (IRAF). NIR (J, H, K) images were taken with the 4m Mayall Telescope at Kitt Peak National-Observatory using the FLAMINGOS IR Imaging Spectrometer while visible (B, V, R, I) images used the Mosaic 1 imager. The supernova's apparent magnitude for each night of observation (by filter) was found by using reference stars. We present preliminary light curves of SN 2009nr and a comparison to another SN observed at similar epochs.

  15. Self-assembly based plasmonic arrays tuned by atomic layer deposition for extreme visible light absorption.

    PubMed

    Hägglund, Carl; Zeltzer, Gabriel; Ruiz, Ricardo; Thomann, Isabell; Lee, Han-Bo-Ram; Brongersma, Mark L; Bent, Stacey F

    2013-07-10

    Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity, where benefits in conversion efficiency and economy can be obtained. On a fundamental level, it is of great interest to explore whether the ultimate limits in light absorption per unit volume can be achieved by capitalizing on the advances in metamaterial science and nanosynthesis. Here, we combine block copolymer lithography and atomic layer deposition to tune the effective optical properties of a plasmonic array at the atomic scale. Critical coupling to the resulting nanocomposite layer is accomplished through guidance by a simple analytical model and measurements by spectroscopic ellipsometry. Thereby, a maximized absorption of light exceeding 99% is accomplished, of which up to about 93% occurs in a volume-equivalent thickness of gold of only 1.6 nm. This corresponds to a record effective absorption coefficient of 1.7 × 10(7) cm(-1) in the visible region, far exceeding those of solid metals, graphene, dye monolayers, and thin film solar cell materials. It is more than a factor of 2 higher than that previously obtained using a critically coupled dye J-aggregate, with a peak width exceeding the latter by 1 order of magnitude. These results thereby substantially push the limits for light harvesting in ultrathin, nanoengineered systems.

  16. Three-visible-light wave combiner based on photonic crystal microcavities.

    PubMed

    Zhou, Xiaoyi; Liu, Dingwen; Sun, Yiling; Ouyang, Zhengbiao

    2015-08-01

    We propose a three-visible-light wave combiner based on two-dimensional square-lattice photonic crystal (PhC) microcavities. A coupled-cavity waveguide is introduced to reduce the insertion losses for the three waves in the combiner. The transmission characteristic of light waves in PhCs with point defects is analyzed. As an example, a combiner for combining light waves of 488, 532, and 635 nm, which are commonly used as the three primary colors in laser display systems, is designed and demonstrated through the finite-difference time-domain method. The three visible light waves of 488, 532, and 635 nm are output at the same output port with transmittances of 97.6%, 98.1%, and 90.0%, respectively. The results show that the proposed device can perform efficient synthesis and the designing method can be applied in building other combiners based on PhCs made of dispersion materials.

  17. Maximum likelihood estimation of vehicle position for outdoor image sensor-based visible light positioning system

    NASA Astrophysics Data System (ADS)

    Zhao, Xiang; Lin, Jiming

    2016-04-01

    Image sensor-based visible light positioning can be applied not only to indoor environments but also to outdoor environments. To determine the performance bounds of the positioning accuracy from the view of statistical optimization for an outdoor image sensor-based visible light positioning system, we analyze and derive the maximum likelihood estimation and corresponding Cramér-Rao lower bounds of vehicle position, under the condition that the observation values of the light-emitting diode (LED) imaging points are affected by white Gaussian noise. For typical parameters of an LED traffic light and in-vehicle camera image sensor, simulation results show that accurate estimates are available, with positioning error generally less than 0.1 m at a communication distance of 30 m between the LED array transmitter and the camera receiver. With the communication distance being constant, the positioning accuracy depends on the number of LEDs used, the focal length of the lens, the pixel size, and the frame rate of the camera receiver.

  18. A novel screen design for anti-ambient light front projection display with angle-selective absorber

    NASA Astrophysics Data System (ADS)

    Liao, Tianju; Chen, Weigang; He, Kebo; Zhang, Zhaoyu

    2016-03-01

    Ambient light is destructive to the reflective type projection system's contrast ratio which has great influence on the image quality. In contrast to the conventional front projection, short-throw projection has its advantage to reject the ambient light. Fresnel lens-shaped reflection layer is adapted to direct light from a large angle due to the low lens throw ratio to the viewing area. The structure separates the path of the ambient light and projection light, creating the chance to solve the problem that ambient light is mixed with projection light. However, with solely the lens-shaped reflection layer is not good enough to improve the contrast ratio due to the scattering layer, which contributes a necessarily wide viewing angle, could interfere with both light paths before hitting the layer. So we propose a new design that sets the draft angle surface with absorption layer and adds an angle-selective absorber to separate these two kinds of light. The absorber is designed to fit the direction of the projection light, leading to a small absorption cross section for the projection light and respectfully big absorption cross section for the ambient light. We have calculated the design with Tracepro, a ray tracing program and find a nearly 8 times contrast ratio improvement against the current design in theory. This design can hopefully provide efficient display in bright lit situation with better viewer satisfaction.

  19. A new class of homogeneous visible-light photocatalysts: molecular cerium vanadium oxide clusters.

    PubMed

    Seliverstov, Andrey; Streb, Carsten

    2014-07-28

    The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di-cerium-functionalized vanadium oxide clusters and their use as visible-light-driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu4 N)2 [(Ce(dmso)3 )2 V12 O33 Cl]⋅2 DMSO (1), two new di-cerium-containing vanadium oxide clusters [(Ce(dmso)4 )2 V11 O30 Cl]⋅DMSO (2) and [(Ce(nmp)4 )2 V12 O32 Cl]⋅NMP⋅Me2 CO (3; NMP=N-methyl-2-pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M5 } (M=V, Ce) reminiscent of "Müller-type" pentagons are observed in 2 and 3. Compounds 1-3 feature high visible-light photooxidative activity, and quantum efficiencies >10 % for indigo photooxidation are observed. Photocatalytic performance increases in the order 1<3<2. Mechanistic studies show that the irradiation wavelength and the presence of oxygen strongly affect photoreactivity. Initial findings suggest that the photooxidation mechanism proceeds by intermediate formation of hydroxyl radicals. The findings open new avenues for the bottom-up design of sunlight-driven photocatalysts.

  20. Microwave-assisted synthesis of bismuth oxybromochloride nanoflakes for visible light photodegradation of pollutants

    NASA Astrophysics Data System (ADS)

    Bijanzad, Keyvan; Tadjarodi, Azadeh; Moghaddasi Khiavi, Mohammad; Akhavan, Omid

    2015-10-01

    BiOBrxCl1-x (0visible diffuse reflectance and photoluminescence (PL) spectroscopies revealed the indirect band gap of ~2.82 eV for the bismuth oxybromochloride nanoflakes. Visible light-assisted photocatalytic studies showed that the degradation efficiency of the as-prepared BiOBrxCl1-x for (100 mL of 10 mg L-1) Rhodamine B (RhB), Natural Red 4 (N-Red) dye solutions was 98.14% and for the colorless organic pentachlorophenol (PCP) solution was 91.09% over 150 min. The possible mechanisms involved in the visible light photodegradation of the pollutants by BiOBrxCl1-x photocatalyst were also discussed.