Search results for "absorption spectroscopy"
showing 10 items of 828 documents
Local structure relaxation in nanosized tungstates
2014
Abstract The atomic structure of nanosized and microcrystalline tungstates MeWO 4 (Me=Co, Ni, Cu, Zn), synthesized by co-precipitation technique, has been studied by x-ray absorption spectroscopy at the W L 3 -edge and Co/Ni/Cu/Zn K-edges, x-ray diffraction, Raman and Fourier transform infrared spectroscopies. The distortion of metal–oxygen octahedra is caused by the electron–lattice coupling and is further enhanced in nanosized tungstates due to formation of the double tungsten–oxygen bonds at the nanoparticle surface.
Experimental and theoretical study to explain the morphology of CaMoO4 crystals
2018
Abstract CaMoO 4 crystals were prepared by a controlled co-precipitation method and processed in a domestic microwave-assisted hydrothermal system with two different surfactants (ethyl 4-dimethylaminobenzoate and 1,2,4,5-benzenetetracarboxylic dianhydride). The corresponding structures were characterized by X-ray diffraction and Rietveld refinement techniques, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy, and photoluminescence measurements. Field emission scanning electron microscopy was used to investigate the morphology of the as-synthesized aggregates. The structure, the surface stability of the (001), (112), (100), (110), (101), and (111) surfaces…
Electronic properties and high-pressure behavior of wolframite-type CoWO4
2021
In this work we characterize wolframite-type CoWO4 under ambient conditions and under compression up to 10 GPa, with emphasis on its electronic structure. X-Ray diffraction and vibrational experiments, supported by ab initio calculations, show that CoWO4 is stable under high-pressure conditions, as no structural changes are detected in the studied pressure range. Interesting findings come from optical absorption spectroscopy. On the one hand, CoWO4 is confirmed to have one of the lowest band gaps among similar wolframites, around 2.25 eV. This makes CoWO4 suitable for use in applications such as the photocatalysis of organic pollutants and water splitting. Additionally, a monotonic decrease…
Influence of hydrogen intercalation on the local structure around Re ions in perovskite‐type ReO 3
2005
octahedra with the Re-O-Re angle equal to 169° and the Re-O distance of about 1.90 A [9]. More accurate information on the local atomic and electronic structure of the bronzes can be ob-tained using XAS, which is a structural method complimentary to diffraction. To our knowledge, no such works have been performed until now. In this work, we present the first results of the in-situ XAS study of hydrogen intercalation into ReO
Dynamic Diglyme-Mediated Self-Assembly of Gold Nanoclusters
2015
We report the assembly of gold nanoclusters by the nonthiolate ligand diglyme into discrete and dynamic assemblies. To understand this surprising phenomenon, the assembly of Au20(SC2H4Ph)15-diglyme into Au20(SC2H4Ph)15-diglyme-Au20(SC2H4Ph)15 is explored in detail. The assembly is examined by high-angle annular dark field scanning transmission electron microscopy, size exclusion chromatography, mass spectrometry, IR spectroscopy, and calorimetry. We establish a dissociation constant for dimer to monomer conversion of 20.4 μM. Theoretical models validated by transient absorption spectroscopy predict a low-spin monomer and a high-spin dimer, with assembly enabled through weak diglyme oxygen-g…
Charge transfer states of C2 in Kr clusters
2004
Abstract Ab initio and diatomics-in-ionic-systems (DIIS) calculations are carried out for the C 2 –Kr pair and C 2 –Kr n clusters, respectively. Energetics and transition dipole moments between the ground and excited states are obtained from the calculations. This data is then used to predict the UV charge transfer absorption spectrum of C 2 embedded in Kr n clusters with n = 1, 12, and 224. The results reveal discrete structure in the computed UV spectrum, which is mainly related to the spin–orbit splitting of Kr + .
Use of the red-edge excitation effect for investigation of dielectric interactions in biomembranes
1999
Dipole moments of the fluorescent probes 1-phenylnaphthylamine (1-AN) and 1-anilinonaphthalene-8-sulfonate (1,8-ANS) are measured using electro-optical absorption and emission methods. Dipole moments in the ground and excited states were measured in cyclohexane and dioxane. It is shown that the charge distributions in the 1-AN and 1,8-ANS molecules differ substantially. The spectral dependence of the electro-optical coefficients suggests that the absorption spectrum of 1,8-ANS is due to a superposition of (at least two) electronic transitions. It is found that spectra of 1-AN in erythocyte ghosts are inhomogeneously broadened. The above effect makes it possible to selectively excite probe m…
Tunable dual-wavelength thulium-doped fiber laser in the range from 2067 to 2073.5 nm
2017
A tunable dual-wavelength lineal cavity Tm-doped fiber laser is presented. The generation of the laser lines is based on the use of cascaded fiber Bragg gratings and a Hi-Bi fiber optic loop mirror.
4W continuous-wave narrow-linewidth tunable solid-state laser source at 546nm by externally frequency doubling a ytterbium-doped single-mode fiber la…
2009
A high-power continuous-wave coherent light source at 545.5nm is described. We use 8.3W from a solid-state ytterbium-doped single-mode fiber oscillator/amplifier system as input into an external frequency doubling stage. This system produces up to 4.1 W of stable green single-frequency laser radiation. We characterize the light source by performing absorption spectroscopy on iodine across the full tuning range of the fiber laser and saturation spectroscopy on one strong iodine line of the doppler-broadened spectrum.
Urbach absorption edge of silica: reduction of glassy disorder by fluorine doping
2004
Abstract The vacuum-ultraviolet fundamental absorption edge (‘Urbach edge’) of four types of synthetic silica glasses, ‘wet’, ‘dry’, and doped by 570 and 6010 ppm wt. fluorine, was studied in the absorption coefficient range (1 cm−1–500 cm−1) at room temperature. The absorption edge has exponential form in agreement with the Urbach’s rule. The well-documented increase of vacuum-ultraviolet transparency upon fluorine doping is due to a steeper absorption edge (shorter ‘Urbach tail’) as compared to undoped silicas. The increase of the edge slope in F-doped silica occurs already the lower dopant concentration (570 ppm), the slope does not increase further in the 6010 ppm doped glass. These fin…