Search results for "Absorption band"
showing 10 items of 143 documents
Developments for vegetation fluorescence retrieval from spaceborne high-resolution spectrometry in the O2-A and O2-B absorption bands
2010
Solar-induced chlorophyll fluorescence is a weak electromagnetic signal emitted in the red and far-red spectral regions by vegetation chlorophyll under excitation by solar radiation. Chlorophyll fluorescence has been demonstrated to be a close proxy to vegetation physiological functioning. The basis for fluorescence retrieval from passive space measurements is the exploitation of the O2-A and O2-B atmospheric absorption features to isolate the fluorescence signal from the solar radiation reflected by the surface and the atmosphere. High spectral resolution measurements and a precise modeling of the atmospheric radiative transfer in the visible and near-infrared regions are mandatory. Recent…
Structural symmetry breaking in octupolar tetrastyrylpyrazines and their dipole moments in equilibrium ground and Franck-Condon excited state
2018
Abstract From electrooptical absorption measurements (EOAM) follows that the dipole moment of octupolar tetrastyrylpyrazines in the equilibrium ground state is large and that the change of dipole moments upon transition to the excited Franck–Condon state is significant. Obtained results unambiguously testify to structural symmetry breaking in the studied octupolar tetrastyrylpyrazines. Molecular mechanics and semi-empirical calculations evidence that tetrastyrylpyrazines have non-planar configurations. The non-planar geometry of the molecules causes large μg values and significant change of dipole moment Δaμ after excitation. Due to large μg and Δaμ values the maxima of the first absorption…
Electrochromic absorbance changes in the chlorophyll-c-containing alga Pleurochloris meiringensis (Xanthophyceae)
1994
Flash-induced absorbance changes were measured in the Chl-c-containing alga Pleurochloris meiringensis (Xanthophyceae) between 430 and 570 nm. In addition to the bands originating from redox changes of cytochromes, three major positive and tow negative transient bands were observed both 0.7 and 20 ms after the exciting flash. These transient bands peaking at 520, 480 and 451 nm and 497 and 465 nm, respectively, could be assigned to an almost homogeneous shift of the absorbance bands with maxima at 506, 473 and 444 nm, respectively. The shape of the absorbance transients elicited from PS I or PS II was identical, and the two photosystems contributed nearly equally to the absorbance changes. …
Experimental evidence of E’_gamma centers generation from oxygen vacancies in a-SiO2
2007
Abstract We report on the thermal treatment effects in a γ-ray irradiated oxygen deficient amorphous silicon dioxide (a-SiO2) containing Al impurities. We observed that by thermal treatments the intensity of the 7.6 eV optical absorption band, associated to an oxygen deficient center, and the EPR signal amplitude of irradiation induced [AlO4]0 centers gradually decrease. During these thermal treatments, the E γ ′ centers concentration is found to increase in a correlated way to the decrease of the 7.6 eV absorption amplitude. These results are interpreted assuming an hole-transfer process from the [AlO4]0 centers to the diamagnetic oxygen vacancies, resulting in the generation of E γ ′ cent…
Oxygen influence on luminescence properties of rare-earth doped NaLaF 4
2016
Abstract Luminescence properties of erbium and europium doped NaLaF4 with different oxygen content have been studied. Vacuum ultraviolet (VUV) excitation luminescence spectroscopy technique has been applied by using synchrotron radiation excitation. It was found that oxygen impurity leads to significant degradation of Er3+ or Eu3+ emission under VUV excitation. The intensive O2−–Er3+ charge transfer excitation band has been detected from oxygen abundant NaLaF4 in the 150–165 nm spectral range. This band reveals a competing absorption mechanism in oxygen containing NaLaF4. It is clearly demonstrated that one reason for the Er3+ emission degradation in oxygen abundant NaLaF4 is strong suppres…
Electro-optical and laser spectrofluorimetry study of coumarins 7 and 30: evidence for the existence of the close-lying electronic states and conform…
1997
Our experiments and calculations reveal a set of anomalous and interesting properties of coumarin 7 (CU7) and coumarin 30 (CU30) in solution. The spectral dependence of electro-optical coefficients and, consequently, dipole moments indicates that the absorption band is a superposition of several (at least two) electronic transitions. Probably, there are two close-lying π,π* singlet electronic excited states which contribute to the first absorption band. The calculations using the MM2 program show that both dyes in the ground state have two stable plane anti conformers. From time-resolved spectrofluorimetric measurements we obtained evidence for the existence of conformers in paraffin oil so…
Electron paramagnetic resonance and magnetic circular dichroism of Gd3+ ions in oxyfluoride glass–ceramics containing CaF2 nanocrystals
2015
Abstract Magnetic resonance investigations of the Gd3 + centre structure in the oxyfluoride glass and glass–ceramics (GCs) have been carried out. The electron paramagnetic resonance (EPR) measurements showed the presence of low symmetry Gd3 + centres in the glass sample. The cubic Gd3 + centre appeared in the glass–ceramics after heat treatment of the samples at temperatures above 650 °C. The magnetic circular dichroism (MCD) measurements of both glass and glass–ceramics showed wide absorption band around 310 nm. In the GC samples MCD–EPR of the cubic Gd3 + centre has been detected.
Time-resolved luminescence and induced absorption in PbWO4
1997
Abstract Luminescence and short-lived induced absorption are studied for two undoped PbWO4 crystals. Luminescence decay at LNT is delayed relative to irradiation pulse. The delay observed is either due to reabsorption of luminescence or due to creation of luminescence center excited states via energy or/and charge transfer after irradiation pulse. Short-lived absorption is observed within 1.1–3.6 eV spectral region at LNT as well as at RT. It is proposed that the short-lived absorption band peaking at ~ 3.5 eV is intrinsic.
Dyes That Bear Thiazolylazo Groups as Chromogenic Chemosensors for Metal Cations
2011
A family of dyes (L 1-L 6) that contain a thiazolylazo group as signalling subunit and several macrocyclic cavities with different ring sizes and type and number of heteroatoms as binding sites has been synthesized and characterized. Solutions of L 1-L 6 in acetonitrile show broad and structureless absorption bands in the 554-577 nm range with typicalmolar absorption coefficients that range from 20000 to 32000 M -1 cm -1. A detailed protonation study was carried out with solutions of L 1, L 2 and L 5 in acetonitrile. Addition of one equivalent of protons to L 1 and L 2 resulted in the development of a new band at 425 and 370 nm, respectively, which was ascribed to protonation in the aniline…
Circular and linear dichroism of aggregates of chlorophyll a and chlorophyll b in 3-methylpentane and paraffin oil.
1996
A circular (CD) and linear dichroism (LD) study of the water adducts of the green plant chlorophylls a (Chl a) and b (Chl b) in hydrocarbon solvents 3-methylpentane and paraffin oil is presented. A strong red shift of the Qy-absorption band from 663 to 746 nm (1678 cm−1) is observed as the water adduct of Chl a is formed. The Chl a-water adduct shows a strong, nonconservative CD signal, which is characterized by a positive peak at 748 nm and two negative peaks at 720 and 771 nm. The maximum CD (AL - AR) is only one order of magnitude smaller than the isotropic absorption maximum. We propose that this exceptionally strong signal is the so-called psi-type CD. The LD spectrum was measured in a…