Search results for "absorption spectroscopy"
showing 10 items of 828 documents
Low temperature X-ray absorption spectroscopy study of $CuMoO_{4}$ and $CuMo_{0.90}W_{0.10}O_4$ using reverse Monte-Carlo method
2020
Radiation physics and chemistry 175, 108411 (2020). doi:10.1016/j.radphyschem.2019.108411
Direct determination of total mercury in phosphate rock using alkaline fusion digestion
2014
The aim of this work was to develop a new method to determine the mercury (Hg) concentrations in phosphate rock using a dedicated analytical instrument (the DMA80 Tricell by Milestone) that employs an integrated sequence of thermal decomposition followed by catalyst conversion, amalgamation and atomic absorption spectrophotometry. However, this instrument underestimates Hg concentrations when phosphorite and apatite rocks are investigated with a classic thermal decomposition treatment that complies with US EPA method 7473. Therefore, to improve the recovery of total Hg, we performed alkaline fusion digestion (AFD) directly inside the furnace of the instrument, using BCR(32) as a certified r…
Optical suppression of ferroelectricity in polysiloxane copolymers with chiral and photochromic side groups
1998
The ferroelectricity of surface-stabilized aligned films of polysiloxane copolymers containing chiral esters and photochromic azobenzene moieties within the side groups is suppressed on UV irradiation and is rebuilt on visible irradiation. The liquid crystalline polymer (Sc* 64 SA 80 i) shows ferroelectric behavior below 64°C. The photoinduced modification of supramolecular order and the corresponding changes in its dynamics are studied by polarized UV/vis spectroscopy and broad band dielectric spectroscopy (10−2–105 Hz). The dielectric measurements show that UV irradiation causes a loss of ferroelectricity within an interval of 10 K below the phase transition temperature. The photochemical…
Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy.
2015
International audience; We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (∼70 fs) relaxation preceding a slower (∼400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix
Carborane-stilbene dyads: influence of substituents and cluster isomers on the photoluminescence properties
2017
Two novel styrene-containing meta-carborane derivatives substituted at the second carbon cluster atom (Cc) with either a methyl (Me), or a phenyl (Ph) group, are introduced herein alongside with a new set of stilbene-containing ortho- (o-) and meta- (m-) carborane dyads. The latter set of compounds has been prepared from styrenecontaining carborane derivatives via Heck coupling reaction. High regioselectivity has been achieved for these compounds by using a combination of palladium complexes [Pd2(dba)3]/[Pd(t-Bu3P)2] as a catalytic system, yielding exclusively E isomers. All compounds have been fully characterized and the crystal structures of seven of them analyzed by X-ray diffraction. Th…
Experimental and theoretical studies of polaron optical properties in KNbO3 perovskite
2004
Time-resolved absorption and luminescence spectra have been measured in KNbO3 perovskite crystals after pulsed band-gap excitation by 200 fs laser pulses and 10 ns electron pulses. Quantum chemical calculations using the large unit cell periodic model support the interpretation of the observed transient absorption bands at 0.8 and 1.1 eV as the self-trapped electron polarons and bound hole polarons, respectively. The activation energy for the 2.2 eV green luminescence quenching is 0.05 eV. We suggest that the short lifetime (,15 ns) of the luminescence at RT is caused by the radiative recombination of nearest electron and hole polarons. q 2003 Elsevier Ltd. All rights reserved.
Photoluminescence activity in natural silica excited in the vacuum-UV range
1999
Abstract We report an experimental study on the optical absorption and photoluminescence detected in samples of natural silica. Our results show that the two emission bands, β (∼3.1 eV) and α E (∼4.3 eV), have an excitation profile in the vacuum ultraviolet region with a maximum at ∼7.5 eV. This excitation profile indicates that, in terms of energy levels of the luminescent defect, there is a transition from a ground state, S 0 , to a second excited state, S 2 , able to excite PL emission, in addition to the well known transition corresponding to the optical absorption band, B 2β . Our data are in a quantitative agreement with `ab initio' calculations carried out for a two-fold coordinated …
X‐ray and pulsed electron beam excited luminescence and optical absorption in KTaO 3 crystals
2005
Pulsed electron beam excited time-resolved transient absorption and luminescence have been studied in nominally pure and Li-doped KTaO3 single crystals. It is found that under electron beam excitation in nominally pure KTaO3 the absorption bands peaks at ∼0.8 eV, ∼1.1 eV and 1.7 eV whereas in KTaO3:Li at ∼1.1 eV and ∼1.7 eV. The transient absorption decay varies over the spectrum thus revealing several short-lived centers. The main luminescence peak is centred at ∼2.7 eV in all KTaO3 specimens. Luminescence decay kinetics observed for the two bands slightly differ indicating different kinds of excited states are involved. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Cathodoluminescence mechanism of crystalline Gd2SiO5:Ce
1993
Complex luminescence decay kinetics have been observed in Gd2SiO5:Ce crystals under electron beam irradiation. Absorption and photoluminescence excitation spectra, decay kinetics in various excitation bands over a wide range of photon energies from 3.6 to 7.0 eV in the temperature region from 80 to 400 K as well as the spectra of the glow curve creation efficiency at 80 K are examined. It is shown that the free electronic excitations produced, depending on the absorbed photon energy, have different recombination mechanisms finally leading to the radiative transitions between the 5d2E configuration and the 4f configuration of the Ce3+ ion. At hvexc < 6.1 eV a single exponential decay caused …
Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells
2016
A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-c…