Spectral Response (spectral + response)

Distribution by Scientific Domains


Selected Abstracts


Near IR Sensitization of Organic Bulk Heterojunction Solar Cells: Towards Optimization of the Spectral Response of Organic Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010
Markus Koppe
Abstract The spectroscopic response of a poly(3-hexylthiophene)/[6,6]-phenyl-C61 -butyric acid methyl ester (P3HT/PCBM)-based bulk heterojunction solar cell is extended into the near infrared region (NIR) of the spectrum by adding the low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H -cyclopenta[2,1- b;3,4- b´]-dithiophene)- alt -4,7-(2,1,3-benzothiadiazole)] [PCPDTBT] to the blend. The dominant mechanism behind the enhanced photosensitivity of the ternary blend is found to be a two-step process: first, an ultrafast and efficient photoinduced charge transfer generates positive charges on P3HT and PCPDTBT and a negative charge on PCBM. In a second step, the positive charge on PCPDTBT is transferred to P3HT. Thus, P3HT serves two purposes. On the one hand it is involved in the generation of charge carriers by the photoinduced electron transfer to PCBM, and, on the other hand, it forms the charge transport matrix for the positive carriers transferred from PCPDTBT. Other mechanisms, such as energy transfer or photoinduced charge transfer directly between the two polymers, are found to be absent or negligible. [source]


Polythiophene-Fullerene Based Photodetectors: Tuning of Spectral Response and Application in Photoluminescence Based (Bio)Chemical Sensors

ADVANCED MATERIALS, Issue 37 2010
Kanwar S. Nalwa
A photoluminescence (PL)-based oxygen and glucose sensor utilizing inorganic or organic light emitting diode as the light source, and polythiophene:fullerene type bulk-heterojunction devices as photodetectors, for both intensity and decay-time based monitoring of the sensing element's PL. The sensing element is based on the oxygen-sensitive dye Pt-octaethylporphyrin embedded in a polystyrene matrix. [source]


Spectral response and energy output of concentrator multijunction solar cells

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2009
Geoffrey S. Kinsey
Abstract The spectral response of concentrator multijunction solar cells has been measured over a temperature range of 25,75°C. These data are combined with reference spectra representing the AM1·5 standard as well as annual spectral irradiance at representative geographical locations. The results suggest that higher performance in the field may be obtained if multijunction cells are designed for an effective air mass higher than AM1·5. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Experimental Study and Modelling of Formation and Decay of Active Species in an Oxygen Discharge

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005
A.-M. Diamy
Abstract A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min,1) is studied by optical emission spectroscopy of O(5P) (line 777.4 nm) and of the atmospheric system of O2(head-line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(5P) and O2(b). The concentration of the O(5P) atoms is in the range 108,109 cm,3 and the concentration of the O2(b) molecules is in the range 1014 , 2 × 1014 cm,3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V-V and V-T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e-e collisions. V-V and V-T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O, and O2,, fundamental electronic neutral species O(3P), O2, O2(X,v), O3 and excited neutral species O2(a), O2(b), O2(A), O(1D), O(1S), O(5P), O(4d 5Do), O(5s 5So), O(3d 5Do) and O(4s 5So)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: , heterogeneous deactivation coefficient for O2(b) , = 2.6 × 10,2; , rate constant of reaction [O(1D) + O(3P) , 2 O(3P)] k34 = 1.4 × 10,11 cm3.s,1; , electron concentration in the range 1010 , 1011 cm,3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10,3 , 0.2 × 10,3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O2]initial) is about 33,50%. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Soil erosion assessment using geomorphological remote sensing techniques: an example from southern Italy

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2010
Sergio Lo Curzio
Abstract The aim of this study is to assess of the distribution and map the geomorphological effects of soil erosion at the basin scale identifying newly-formed erosional landsurfaces (NeFELs), by means of an integration of Landsat ETM 7+ remotely sensed data and field-surveyed geomorphological data. The study was performed on a 228·6,km2 -wide area, located in southern Italy. The study area was first characterized from a lithological, pedological, land-use and morpho-topographic point of view and thematic maps were created. Then, the georeferenced Landsat ETM 7+ satellite imagery was processed using the RSI ENVI 4.0 software. The processing consisted of contrast stretching, principal component analysis (PCA), decorrelation stretching and RGB false colour compositing. A field survey was conducted to characterize the features detected on the imagery. Particular attention was given to the NeFELs, which were located using a global positioning system (GPS). We then delimited the Regions of Interest (ROI) on the Landsat ETM 7+ imagery, i.e. polygons representing the ,ground-truth', discriminating the NeFELs from the other features occurring in the imagery. A simple statistical analysis was conducted on the digital number (DN) values of the pixels enclosed in the ROI of the NeFELs, with the aim to determine the spectral response pattern of such landsurfaces. The NeFELs were then classified in the entire image using a maximum likelihood classification algorithm. The results of the classification process were checked in the field. Finally, a spatial analysis was performed by converting the detected landsurfaces into vectorial format and importing them into the ESRI ArcViewGIS 9.0 software. Application of these procedures, together with the results of the field survey, highlighted that some ,objects' in the classified imagery, even if displaying the same spectral response of NeFELs, were not landsurfaces subject to intense soil erosion, thus confirming the strategic importance of the field-checking for the automatically produced data. During the production of the map of the NeFELs, which is the final result of the study, these ,objects' were eliminated by means of simple, geomorphologically-coherent intersection procedures in a geographic information system (GIS) environment. The overall surface of the NeFELs had an area of 22·9,km2, which was 10% of the total. The spatial analysis showed that the highest frequency of the NeFELs occurred on both south-facing and southwest-facing slopes, cut on clayey-marly deposits, on which fine-textured and carbonate-rich Inceptisols were present and displaying slope angle values ranging from 12° to 20°. The comparison of two satellite imageries of different periods highlighted that the NeFELs were most clearly evident immediately after summer tillage operations and not so evident before them, suggesting that these practices could have played an important role in inducing the erosional processes. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Perfluorinated Subphthalocyanine as a New Acceptor Material in a Small-Molecule Bilayer Organic Solar Cell

ADVANCED FUNCTIONAL MATERIALS, Issue 21 2009
Hans Gommans
Abstract The complex refractive index of fluorinated subphthalocyanines (SubPcs) deposited by vacuum sublimation is determined by spectral ellipsometry. Their performance as acceptor material is characterized in a range of donor/acceptor heterojunctions in organic photovoltaic cells (OPVCs) by current,voltage measurements under 1,sun AM 1.5D simulated solar illumination and spectral response. Both electron and hole transfer between donor and acceptor materials is demonstrated. Power conversion efficiencies of 0.96% are found with an open-circuit bias of 940,mV. Hence, it is shown that fluorinated SubPcs can be considered as an acceptor material in OPVCs with an absorption in the visible comparable to that of well-known metallophthalocyanines. [source]


A new land-cover map of Africa for the year 2000

JOURNAL OF BIOGEOGRAPHY, Issue 6 2004
Philippe Mayaux
Abstract Aim, In the framework of the Global Land Cover 2000 (GLC 2000), a land-cover map of Africa has been produced at a spatial resolution of 1 km using data from four sensors on-board four different Earth observing satellites. Location, The map documents the location and distribution of major vegetation types and non-vegetated land surface formations for the entire African continent plus Madagascar and the other surrounding islands. Methods, The bulk of these data were acquired on a daily basis throughout the year 2000 by the VEGETATION sensor on-board the SPOT-4 satellite. The map of vegetation cover has been produced based upon the spectral response and the temporal profile of the vegetation cover. Digital image processing and geographical information systems techniques were employed, together with local knowledge, high resolution imagery and expert consultation, to compile a cartographic map product. Radar data and thermal sensors were also used for specific land-cover classes. Results, A total of 27 land cover categories are documented, which has more thematic classes than previously published land cover maps of Africa contain. Systematic comparison with existing land cover data and 30-m resolution imagery from Landsat are presented, and the map is also compared with other pan-continental land cover maps. The map and digital data base are freely available for non-commercial uses from http://www.gvm.jrc.it/tem/africa/products.htm Main conclusions, The map improves our state of knowledge of the land-cover of Africa and presents the most spatially detailed view yet published at this scale. This first version of the map should provide an important input for regional stratification and planning purposes for natural resources, biodiversity and climate studies. Résumé Objet, Dans le cadre du projet Global Land Cover 2000 (GLC 2000), une carte d'Afrique d'occupation du sol a été produite à la résolution spatiale de 1 km à partir de données satellitales de 4 capteurs différents. Localisation, La carte représente la distribution des principaux types de végétation et des surfaces non-végétales du continent africain plus Madagascar et les autres îles voisines du continent. Méthodes, La plupart des données fut acquise durant l'année 2000 par le capteur VEGETATION, embarquéà bord du satellite SPOT-4. La réponse spectrale et le profil temporel des formations végétales ont permis la production de la carte d'occupation du sol. Des techniques de traitement d'image et de systèmes d'information géographique ont été combinées à la consultation d'experts locaux et à l'utilisation de cartes nationales et de données à haute résolution spatiale. Des images radar et thermiques ont servi à cartographier des classes spécifiques. Résultats, Un total de 27 classes est cartographié, ce qui est plus que les précédentes cartes basées sur l'imagerie satellitale. Une comparaison systématique avec les cartes publiées et des images Landsat à 30 m est présentée. Les données sont libres d'accès pour un usage non-commercial à l'adresse http://www.gvm.jrc.it/tem/africa/products.htm Conclusion, Cette carte accroît notre connaissance de l'occupation du sol de l'Afrique et présente la vue la plus détaillée jamais publiée à cette échelle. La première version de la carte devrait fournir une base importante pour une stratification régionale et pour la planification d'études sur les ressources naturelles, la biodiversité et le climat. [source]


The differentiation of biodegradable and non-biodegradable dissolved organic matter in wastewaters using fluorescence spectroscopy

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2002
M Reynolds
Abstract The chemical and biochemical oxygen demand values of a number of synthetic and wastewater samples were determined using fluorescence spectroscopy. Treated and untreated sewage samples were obtained from a local sewage treatment works while synthetic samples were analysed before, during, and after treatment via a rotating biodisc contactor. Fluorescence intensities were normalised using the water Raman signal as an internal standard and corrections applied to take into account the attenuation effects caused by the sample matrix. The fluorescence emission spectra (,exc,=,280,nm) of synthetic and sewage samples were very similar in that two main fluorescence bands centred around 350,nm and 440,nm were observed in all samples. Normalised fluorescence data, centred at 350,nm, correlate well with corresponding BOD, COD and TOC values (R2 values ranging between 0.93 and 0.98). Using BOD, COD and TOC data the fluorescence at 350,nm and 440,nm can be apportioned to biodegradable and non-biodegradable dissolved organic matter respectively. The findings of this research show that fluorescence data can be used to quantify oxygen demand values (chemical and biochemical) and total organic carbon values. Furthermore, the fluorescence spectral response can be apportioned to biodegradable (BOD) and non-biodegradable (COD,,,BOD) dissolved organic matter. The potential of using fluorescence spectroscopy as a possible tool for real-time monitoring of sewage wastes is discussed. © 2002 Society of Chemical Industry [source]


Standardization of line-scan NIR imaging systems

JOURNAL OF CHEMOMETRICS, Issue 3-4 2007
Zheng Liu
Abstract A simple and easy to use method is proposed for standardizing NIR imaging systems for differences among detectors in the charge-coupled device (CCD) array and illumination unevenness. The standardization equations are then used to pre-treat NIR image data to reduce the systematic errors introduced by a line-scan NIR imaging system. The method requires only easily available homogeneous standards with relatively uniform spectral response. The effectiveness of the standardization in reducing the pixel-to-pixel biases and other systematic effects is illustrated with examples, and the improved sensitivity in results obtained from a multivariate image analysis (MIA) based on multi-way principal component analysis (MPCA) is demonstrated. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Identification of chemical species of fluorescein isothiocyanate isomer,I (FITC) monolayers on platinum by doubly resonant sum-frequency generation spectroscopy

JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2008
Toshiki Maeda
Abstract Doubly resonant sum-frequency generation (DR-SFG) spectroscopy of fluorescein-4-isothiocyanate isomer-I (FITC) monolayers on platinum was performed. Vibrational spectra of the monolayers for the IR wavenumber of 1750,1450 cm,1 were measured with visible probes ranging from 431 to 582 nm. Two vibrational bands at 1643 and 1610 cm,1 were observed, and their DR-SFG excitation profiles displayed different shapes. By rinsing the monolayers with an alkaline solution, the smaller wavenumber band disappeared and the larger wavenumber band gained intensity. On the basis of the spectral response to the rinsing, we concluded that the FITC molecules existed on platinum as deprotonated and protonated forms; the former corresponds to the 1643 cm,1 band and the latter to the 1610 cm,1 band. The deprotonated form was assigned to an anionic surface species, and the protonated form to a neutral surface species by comparing the DR-SFG excitation profiles with electronic absorption spectra of the protolytic forms of fluorescein in an aqueous solution (Sjöback R et al., Spectrochimica Acta A 1995; 51: L7,L21). The results demonstrate that the measurement of DR-SFG excitation profiles is a useful technique to identify chemical species of monolayers on metal surfaces. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Fibre Bragg grating interrogation based on high-birefringence fibre loop mirror for strain temperature discrimination

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2006
O. Frazão
Abstract In this work, we present a fiber Bragg grating interrogation based on high-birefringence fiber loop mirror for strain,temperature discrimination. Due to spectral response of the optical filters it is possible to determine the variation of the wavelength and the optical power of the Bragg grating sensor when subject to strain or temperature. Maximum errors of ±0.4°C and ±12 ,, are reported over 80°C and 2000 ,, measurement ranges. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2326,2328, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21894 [source]


Novel structure of an arrayed-waveguide grating multiplexer with flat spectral response

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2004
Tsung-Hsin Lee
Abstract A novel structure of arrayed-waveguide grating (AWG) multiplexers with a graded-index free-propagation region (FPR) used to increase the wavelength pass band is presented. The 1-dB and 3-dB wavelength pass bands increase with the increase of the graded-index FPR length. Flat and broadened spectral responses are obtained by using this novel structure. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 444,445, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20165 [source]


The performance of AlGaN solar blind UV photodetectors: responsivity and decay time

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006
G. Cherkashinin
Abstract The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied. The photodetectors have shown a good spectral responsivity in a narrow spectral range (220 < , < 300 nm) and a short time response with the best estimated characteristic time constant of , , 30 ms measured at room temperature. Possible mechanisms responsible for the persistent photoconductivity (PPC) effect in AlxGa1,xN (x = 0.51) are analyzed. A shape of the spectral response as a function of the applied voltage is analyzed in the frameworks of the space-charge limited current model. It has been shown that the main source of PPC is traps above the Fermi level. PPC occurs when the density of free carriers equals the density of the traps. The model attributing PPC to the spatial separation of the photoexcited electrons and holes by the macroscopic potential barrier is not supported by our photocurrent studies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Ultra-thin silicon solar cell: Modelling and characterisation

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008
L. Danos
Abstract An ultra-thin crystalline silicon solar cell with an active silicon layer of 200 nm has been fabricated and fully characterised electrically (I-V characteristic, spectral response) and optically (Variable Angle Spectroscopic Ellipsometry). Interference effects were observed in the spectral response of the cell due to multiple reflections from the layers within the cell. A mathematical model was developed to account for the different reflections and transmission within the cell which reproduced excellently the essential features of the experimental spectral response. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Investigation to estimate the short circuit current by applying the solar spectrum

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2008
Jun Tsutsui
Abstract The influence of the solar spectrum is investigated to estimate the outdoor short circuit current (Isc) of various photovoltaic (PV) modules. It is well known that the solar spectrum always changes. Hence, it is rare to fit the standard solar spectrum AM1·5G defined in standard IEC 60904-3. In addition, the spectral response (SR) of PV module is different depending on the material. For example, crystal silicon (c-Si) has broad sensitivity that the wavelength range is between 350 and 1150,nm; meanwhile, amorphous silicon (a-Si) has relatively narrow sensitivity comparing to c-Si. Since Isc of the PV module decides by multiplying the solar spectrum and SR together, it is necessary to investigate the solar spectrum to estimate the outdoor Isc in addition to the solar irradiance and module temperature. In this study, the spectral mismatch is calculated and the outdoor Isc is estimated in the whole year. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Overcoming the poor short wavelength spectral response of CdS/CdTe photovoltaic modules via luminescence down-shifting: ray-tracing simulations

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2007
B.S. Richards
Abstract The short-wavelength response of cadmium sulfide/cadmium telluride (CdS/CdTe) photovoltaic (PV) modules can be improved by the application of a luminescent down-shifting (LDS) layer to the PV module. The LDS layer contains a mixture of fluorescent organic dyes that are able to absorb short-wavelength light of ,,<,540,nm, for which the PV module exhibited low external quantum efficiency (EQE), and re-emit it at a longer wavelength (,,>,540,nm), where the solar cell EQE is high. Ray-tracing simulations indicate that a mixed LDS layer containing three dyes could lead to an increase in the short-circuit current density from Jsc,=,19.8,mA/cm2 to Jsc,=,22.9,mA/cm2 for a CdS/CdTe PV module. This corresponds to an increase in conversion efficiency from 9.6% to 11.2%. This indicates that a relative increase in the performance of a production CdS/CdTe PV module of nearly 17% can be expected via the application of LDS layers, possibly without any making any alterations to the solar cell itself. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Highly-efficient Cd-free CuInS2 thin-film solar cells and mini-modules with Zn(S,O) buffer layers prepared by an alternative chemical bath process

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2006
A. Ennaoui
Abstract Recent progress in fabricating Cd- and Se-free wide-gap chalcopyrite thin-film solar devices with Zn(S,O) buffer layers prepared by an alternative chemical bath process (CBD) using thiourea as complexing agent is discussed. Zn(S,O) has a larger band gap (Eg,=,3·6,3·8,eV) than the conventional buffer material CdS (Eg,=,2·4,eV) currently used in chalcopyrite-based thin films solar cells. Thus, Zn(S,O) is a potential alternative buffer material, which already results in Cd-free solar cell devices with increased spectral response in the blue wavelength region if low-gap chalcopyrites are used. Suitable conditions for reproducible deposition of good-quality Zn(S,O) thin films on wide-gap CuInS2 (,CIS') absorbers have been identified for an alternative, low-temperature chemical route. The thickness of the different Zn(S,O) buffers and the coverage of the CIS absorber by those layers as well as their surface composition were controlled by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray excited Auger electron spectroscopy. The minimum thickness required for a complete coverage of the rough CIS absorber by a Zn(S,O) layer deposited by this CBD process was estimated to ,15,nm. The high transparency of this Zn(S,O) buffer layer in the short-wavelength region leads to an increase of ,1,mA/cm2 in the short-circuit current density of corresponding CIS-based solar cells. Active area efficiencies exceeding 11·0% (total area: 10·4%) have been achieved for the first time, with an open circuit voltage of 700·4,mV, a fill factor of 65·8% and a short-circuit current density of 24·5,mA/cm2 (total area: 22·5,mA/cm2). These results are comparable to the performance of CdS buffered reference cells. First integrated series interconnected mini-modules on 5,×,5,cm2 substrates have been prepared and already reach an efficiency (active area: 17·2,cm2) of above 8%. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Capturing the spectral response of solar cells with a quasi-steady-state, large-signal technique

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2006
Helmut Mäckel
Abstract A new approach to measure the spectral response of the short-circuit current of solar cells is presented in this investigation. The main innovative feature is the light source, which produces a broad range of intensities, up to 10 suns in a quasi-steady-state mode, thus making the use of a bias light redundant. This results in large, integral signals that can be recorded directly without resorting to lock-in amplification. Measurements of different solar cell structures with a conventional and the new measurement set-up resulted in good agreement. Copyright © 2005 John Wiley & Sons, Ltd. [source]


The use of acetone as a substitute for acetonitrile in analysis of peptides by liquid chromatography/electrospray ionization mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2010
Theodore R. Keppel
The recent worldwide shortage of acetonitrile has prompted interest in alternative solvents for liquid chromatography/mass spectrometry (LC/MS). In this work, acetone was substituted for acetonitrile in the separation of a peptide mixture by reversed-phase high-performance liquid chromatography (RP-HPLC) and in the positive electrospray ionization mass spectrometry (ESI-MS) of individual peptides. On both C12 and C18 stationary phases, the substitution of acetone for acetonitrile as the organic component of the mobile phase did not alter the gradient elution order of a five-peptide retention standard, but did increase peak width, shorten retention times, and increase peak tailing. Positive ESI mass spectra were obtained for angiotensin I, bradykinin, [Leu5]-enkephalin, and somatostatin 14 dissolved in both acetonitrile/water/formic acid (25%/75%/0.1%) and acetone/water/formic acid (25%/75%/0.1%). Under optimized ESI-MS conditions, the mass spectral response of [Leu5]-enkephalin was increased two-fold when the solvent contained acetone. The substitution of acetone for acetonitrile resulted in only slight changes in the responses of the remaining peptides. A higher capillary voltage was required for optimum response when acetone was used. Compared with acetonitrile/water/formic acid (50/50/0.1%), more interfering species below m/z,=,140 were found in the ESI-MS spectra of acetone/water/formic acid (50/50/0.1%). Copyright © 2009 John Wiley & Sons, Ltd. [source]


Clean and Flexible Modification Strategy for Carboxyl/Aldehyde-Functionalized Upconversion Nanoparticles and Their Optical Applications

ADVANCED FUNCTIONAL MATERIALS, Issue 24 2009
Huan-Ping Zhou
Abstract Rare-earth upconversion nanoparticles (UCNPs) exhibit great potential in luminescent biolabels and other multifunctional probes; however, their applications are limited by their low water solubility and the lack of binding groups. To address these problems, a clean and flexible strategy to modify hydrophobic monodisperse UCNPs into hydrophilic ones that are capped with functional groups is developed. The modification process is implemented by direct oxidation of oleic acid ligands with ozone under specific conditions, where the oleic acid (OA) ligands on the surface of the UCNPs can be converted into azelaic acid ligands (HOOC(CH2)7COOH) or azelaic aldehyde HOOC(CH2)7CHO, as is revealed by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) measurements. This oxidation process has no significant side-effects on the morphology, phase, composition, or luminescent properties of the UCNPs. Free carboxylic acid groups on the surface endow the UCNPs with good water solubility, while aldehyde groups at the surface provide binding sites for amino-containing molecules via Schiff-base condensation, such as 2-(4-aminophenylethylyl)-5-methoxy-2-(2-pyridyl)thiazole (MPTEA) and 2-aminoethanethiol hydrochloride (NH2CH2CH2SH·HCl, HEMA). A Ce4+ sensor is constructed based on the dual-emission arising from the different spectral responses of MPTEA and the UCNPs. Facilitated by the covalent linkage between the terminal aldehyde group on the UCNPs and the amino group in HEMA, a hybrid structure of UCNPs and Au NPs is fabricated. The effective coupling between the aldehyde group and the amino group suggests that these functionalized UCNPs have potential in combining other functional units for simultaneous biolabeling, or other optical applications. [source]


Novel structure of an arrayed-waveguide grating multiplexer with flat spectral response

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2004
Tsung-Hsin Lee
Abstract A novel structure of arrayed-waveguide grating (AWG) multiplexers with a graded-index free-propagation region (FPR) used to increase the wavelength pass band is presented. The 1-dB and 3-dB wavelength pass bands increase with the increase of the graded-index FPR length. Flat and broadened spectral responses are obtained by using this novel structure. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 444,445, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20165 [source]


The X-ray variability of the Seyfert 1 galaxy MCG,6-30-15 from long ASCA and RXTE observations

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2000
Julia C. Lee
We present an analysis of the long Rossi X-ray Timing Explorer (RXTE) observation of the Seyfert 1 galaxy MCG,6-30-15, taken in 1997 July. We have previously used the data to place constraints for the first time on the iron abundance,reflection fraction relationship, and now expand the analysis to investigate in detail the spectral X-ray variability of the object. Our results show that the behaviour is complicated. We find clear evidence from colour ratios and direct spectral fitting that changes to the intrinsic photon index are taking place. In general, spectral hardening is evident during periods of diminished intensity, and in particular, a general trend for harder spectra is seen in the period following the hardest RXTE flare. Flux-correlated studies further show that the 3,10 keV photon index ,3,10 steepens, while that in the 10,20 keV band, ,10,20, flattens with flux. The largest changes come from the spectral index below 10 keV; however, changes in the intrinsic power-law slope (shown by changes in ,3,10), and reflection (shown by changes in ,10,20) both contribute in varying degrees to the overall spectral variability. We find that the iron-line flux FK, is consistent with being constant over large time intervals on the order of days (although tentative evidence exists which show that FK, changes on shorter time intervals of order ,10 ks during time periods surrounding flare events), and has an equivalent width which anticorrelates with the continuum flux and reflection fraction. A possible interpretation for the iron-line flux constancy and the relative Compton reflection increase with flux from the flux-correlated data is an increasing ionization of the emitting disc surface, while spectral analysis of short time intervals surrounding flare events hints tentatively at observed spectral responses to the flare. We present a simple model for partial ionization where the bulk of the variability comes from within 6rg. Temporal analysis further provides evidence for possible time (,1000 s) and phase (,,0.6 rad) lags. Finally, we report an apparent break in the power density spectrum (,4,5×10,6 Hz) and a possible 33-hour period. Estimates for the mass of the black hole in MCG,6-30-15 are discussed in the context of spectral and temporal findings. [source]


Experimental solar spectral irradiance until 2500,nm: results and influence on the PV conversion of different materials

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 4 2007
J. J. Pérez-López
Abstract In this work, results are presented concerning solar spectral irradiance measurements performed in Madrid in the wavelength range 250,2500,nm, that is, extending the spectral range far away from the wavelengths where PV semiconductors are active. These data were obtained considering a horizontal receiver surface during selected clear days covering the four seasons of the year. PV materials having different spectral responses (m-Si, a-Si, CIGS, CdTe) have been considered to calculate spectral factors (SF) taking as reference the standard solar spectrum AM1.5 defined in standard IEC 60904-3. From these SFs, the influence of natural solar spectral variations in PV conversion has been established. It is shown, for example, that PV technologies based on a-Si are highly favored, from the spectral point of view, in spring,summer compared to other technologies having broader spectral responses, which are more favored in autumn,winter. From the experimental measured solar spectra, we have calculated Weighed Solar Spectra (WSS) corresponding to the four seasons of the year and also to the whole year. The WSS represents, for a certain period of time, the solar spectrum weighed over the irradiance level. SFs have been calculated for different WSSs showing spectral gains for the four PV materials during almost the full year. Otherwise, it is also shown in this work how the near-IR part of the solar spectrum affects the evaluation of the solar resource as a whole when reference solar cells made of different PV materials are used. For typical m-Si, a-Si, CIGS, and CdTe solar cells, the ratio of Isc over global irradiance is not constant along a given day showing variations that depend on the season and on the PV material considered. © 2006 John Wiley & Sons, Ltd. [source]


A new linear ion trap mass spectrometer

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2002
James W. Hager
Characteristics of mass selective axial ion ejection from a linear quadrupole ion trap in the presence of an auxiliary quadrupole field are described. Ion ejection is shown to occur through coupling of radial and axial motion in the exit fringing fields of the linear ion trap. The coupling is efficient and can result in extraction of as much as 20% of the trapped ions. This, together with the very high trapping efficiencies, can yield high sensitivity mass spectral responses. The experimental apparatus is based on the ion path of a triple quadrupole mass spectrometer allowing either the q2 collision cell or the final mass analysis quadrupole to be used as the linear trap. Space charge induced distortions of the mass resolved features while using the pressurized q2 linear ion trap occur at approximately the same ion density as reported for conventional three-dimensional ion traps. These distortions are, however, much reduced for the lower pressure linear trap possibly owing to the proposed axial ejection mechanism that leads to ion ejection only for ions of considerable radial amplitude. RF heating due to the high ejection q -value and the low collision frequency may also contribute. Two hybrid RF/DC quadrupole-linear ion trap instruments are described that provide high sensitivity product ion scanning while operated in the linear ion trap mode while also retaining all conventional triple quadrupole scan modes such as precursor ion and neutral loss scan modes. Copyright © 2002 John Wiley & Sons, Ltd. [source]