Reflectance Spectroscopy

Kortüm, G.

doi:10.1007/978-3-642-88071-1

Cited by 1,128 publications

(460 citation statements)

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“…[30][31][32] The diffuse reflectance for infinitely thick samples (R ∞ ) is given by the reflectance of a sample of finite thickness (R sample ) divided by the reflectance of highly reflective standards (R reference ), such as MgO (the standard initially used here):…”

Section: Methodsmentioning

confidence: 99%

“…Thus, F(R ∞ ) provides a measure of absorbance throughout the experimental spectral range. 31 The reflectance relative to the fully oxidized sample (R ∞,rel ) was defined as This reflectance was used instead of that relative to MgO because fully oxidized samples provided a relevant standard spectrum measured in close temporal proximity to the reduction experiments. Spectra for fully oxidized samples were obtained before each experiment and provided a reliable internal reference.…”

Section: Methodsmentioning

confidence: 99%

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Extent of Reduction of Vanadium Oxides during Catalytic Oxidation of Alkanes Measured by in-Situ UV−Visible Spectroscopy

et al. 2004

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In-situ UV-visible spectroscopy was used to measure the extent of reduction of active centers in VO x /γ-Al 2 O 3 during oxidative dehydrogenation (ODH) of propane. Prevalent extents of reduction (0.062 to 0.30 e -/V) are much smaller than required for the formation of stoichiometric V 3+ or V 4+ suboxides. Surface oxygen atoms are the most abundant reactive intermediates during propane ODH, as previously suggested by kinetic and isotopic studies. These measurements involved the rigorous calibration of UV-visible intensities in the pre-edge region using quantitative reoxidation of a small number of centers reduced in H 2 . Transients observed during changes in C 3 H 8 and O 2 concentrations indicate that only a fraction of the prevalent reduced centers (∼30-40%) are active in catalytic turnovers, while the rest are reoxidized in time scales much longer than turnover times. The number of catalytically relevant reduced centers depends only on C 3 H 8 /O 2 ratios, and not on individual reactant concentrations, indicating that oxygen vacancies are the predominant reduced centers and that hydroxyls and alkoxides are present at much lower concentrations. The fraction of V-atoms that exist as catalytically reduced centers and the rate of propane ODH (per exposed V-atom) increase with increasing vanadia surface density and domain size up to surface densities typical of polyvanadate monolayers (∼7.5 V/nm 2 ) and then reach nearly constant values at higher surface densities. This relation between the extent of reduction during catalysis and the propene formation rates confirms the redox nature of catalytic cycles and the exclusive kinetic relevance of the reduction part of the cycle, in which C-H bonds are activated using lattice oxygen atoms. This method for measuring the extent of reduction during catalysis using preedge features in the UV-visible spectrum provides greater sensitivity and time resolution than X-ray absorption and UV-visible spectroscopic methods based on near-edge spectral features. The approach and initial results seem generally applicable to oxidation reactions using lattice oxygens as reactive intermediates.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Extent of Reduction of Vanadium Oxides during Catalytic Oxidation of Alkanes Measured by in-Situ UV−Visible Spectroscopy

et al. 2004

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“…BaSO 4 plate was used as a reference (100% reflectance), on which the finely ground powder of the samples were coated. The absorption spectrum was calculated from reflection spectra by the Kubelka-Munk function [20]: α/S = (1-R) 2 /2R, α is the absorption coefficient, S is the scattering coefficient which is practically wavelength independent when the particle size is larger than 5 m, and R is the reflectance. The fluorescence study was conducted at room temperature on a JY Fluorolog-322 fluorescence spectroscopy instrument.…”

Section: Materials and Measurementsmentioning

confidence: 99%

A novel samarium complex with interesting photoluminescence and semiconductive properties

Zhang¹,

Chen²,

F.Wang³

2018

Bull. Chem. Soc. Eth.

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ABSTRACT.[Sm(H2O)4(NO3)3](4,4'-Hbipy)2(NO3)2 (1) (bipy = bipyridine) has been synthesized via hydrothermal reaction and characterized by X-ray diffraction. The title complex features an isolated structure, based on discrete 4,4'-Hbipy moieties, isolated nitrates and [Sm(H2O)4(NO3)3] species. The samarium ion is in a distorted bicapped square antiprism environment, coordinated by three bidentate nitrates and four coordination water molecules. The 4,4'-Hbipy moieties, isolated nitrates and [Sm(H2O)4(NO3)3] species are held together via hydrogen bonds and … interactions to form a 3-D supramolecular framework. Luminescent investigation reveals a strong emission in blue region. Optical absorption spectrum of 1 reveals the presence of an optical gap of 3.60 eV.

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“…56 The DRS spectra of The intersection between the linear fit and photon energy axis gives the value of E g . The optical direct band-gap for the entire series of samples was determined ranging from 3.26(60.014) to 3.17(60.018) eV.…”

Section: Diffused Reflectance Spectroscopymentioning

confidence: 99%

Defects induced luminescence and tuning of bandgap energy narrowing in ZnO nanoparticles doped with Li ions

Awan¹,

Hasanain²,

Jaffari³

et al. 2014

Journal of Applied Physics

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Microstructural and optical properties of Zn 1Ày Li y O (0.00 y 0.10) nanoparticles are investigated. Li incorporation leads to substantial changes in the structural characterization. From micro-structural analysis, no secondary phases or clustering of Li was detected. Elemental maps confirmed homogeneous distribution of Li in ZnO. Sharp UV peak due to the recombination of free exciton and defects based luminescence broad visible band was observed. The transition from the conduction band to Zinc vacancy defect level in photoluminescence spectra is found at 518 6 2.5 nm. The yellow luminescence was observed and attributed to Li related defects in doped samples. With increasing Li doping, a decrease in energy bandgap was observed in the range 3.26 6 0.014 to 3.17 6 0.018 eV. The bandgap narrowing behavior is explained in terms of the band tailing effect due to structural disorder, carrier-impurities, carrier-carrier, and carrier-phonon interactions. Tuning of the bandgap energy in this class of wide bandgap semiconductor is very important for room temperature spintronics applications and optical devices. V C 2014 AIP Publishing LLC.[http://dx

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Reflectance Spectroscopy

Cited by 1,128 publications

References 0 publications

Extent of Reduction of Vanadium Oxides during Catalytic Oxidation of Alkanes Measured by in-Situ UV−Visible Spectroscopy

Extent of Reduction of Vanadium Oxides during Catalytic Oxidation of Alkanes Measured by in-Situ UV−Visible Spectroscopy

A novel samarium complex with interesting photoluminescence and semiconductive properties

Defects induced luminescence and tuning of bandgap energy narrowing in ZnO nanoparticles doped with Li ions

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