Showing papers on "Absorption spectroscopy published in 1998"

WinXAS: a program for X-ray absorption spectroscopy data analysis under MS-Windows.

Abstract: WinXAS is a new X-ray absorption spectroscopy (XAS) data-analysis program. It runs under the operating system MS-Windows 95/NT and offers several unique features. It has a user-friendly graphical environment and is capable of reading a variety of data formats. It contains a number of useful numerical algorithms beyond those used in conventional XAS analysis and offers a simple interface to the ab-initio theoretical code FEFF. The availability of fast macros in WinXAS makes it particularly useful for on-line data examination at synchrotron radiation facilities during XAS experiments as well as for the analysis of multiple-scan data such as those from time-resolved experiments.

Surface Structures and Stability of Arsenic(III) on Goethite: Spectroscopic Evidence for Inner-Sphere Complexes

Abstract: The adsorption and stability of arsenite [As(III)] on goethite (α-FeOOH) was investigated using a combination of standard batch techniques and X-ray absorption spectroscopy (XAS). The reactivity of As(III) with α-FeOOH at varying pH and As(III) concentration provided macroscopic evidence for strong complexation on the α-FeOOH surface. Extended X-ray absorption fine structure (EXAFS) spectroscopy gave an average As(III)−Fe interatomic distance of 3.378 ± 0.014 A, which is indicative of bidentate binuclear bridging As(III) complexes on the α-FeOOH surface and which is similar to other oxyanions which adsorb on α-FeOOH by an inner-sphere mechanism. X-ray absorption near-edge structure (XANES) analysis indicated that the As(III)−α-FeOOH surface complex is stable toward heterogeneous oxidation to As(V), as determined by the energy position of the X-ray absorption edge. The structural information from EXAFS was included in the description of As(III) adsorption on the α-FeOOH surface using a surface complexation...

Infrared spectra of sodium phosphate glasses

Abstract: Infrared absorption spectra of sodium phosphate glasses, Na2O=30–50 mol%, have been studied in the region of 400–2000 cm−1. Spectra were analyzed to determine the relative intensity of the IR bands responsible for the different phosphate units. Spectral analyses has shown that the substitution of P2O5 by Na2O influences the intermediate range order of the glass matrix. Increasing Na2O content leads to a gradual degradation of the phosphate ring type structures, with consequent depolymerization causing compaction of the glass matrix. Analyses of IR spectra illustrates the reorganization effects of Na2O in the phosphate matrix.

Cavity ring-down spectroscopy

Abstract: Cavity ring-down spectroscopy (CRDS) is a laser-based absorption spectroscopy technique that is starting to find extensive application as a consequence of the very high sensitivity of the method compared with more traditional absorption spectroscopy techniques. We describe the experimental implementation of CRDS and its application to a number of areas of research including laser diagnostics of hostile environments, reaction kinetics and spectroscopy, with particular emphasis on our ongoing studies of the fast (sub-nanosecond) predissociation of electronically excited states of small molecules and radicals.

Silole-containing σ- and π-conjugated compounds

Abstract: Synthesis, properties, and application of new σ- and π-electron systems consisting of the silole rings are described. A series of 2,5- and 1,1-difunctionalized siloles have been prepared based on the intramolecular reductive cyclization of diethynylsilanes. Starting from these functionalized siloles, oligo(2,5-silole)s and oligo(1,1-silole)s have been synthesized as model compounds for poly(2,5-silole)s and poly(1,1-silole)s, respectively, which are still veiled target molecules in this field. Some silole-containing π-conjugated cooligomers and copolymers with thiophene, pyrrole, and acetylene π-electron systems have also been prepared. They all have unique photophysical properties such as long-wavelength absorption in the UV/VIS absorption spectra. Some silole-based π-conjugated compounds have also been found to work as new useful materials for organic electroluminescent devices.

The temperature‐dependent near‐infrared absorption spectrum of hexagonal H2O ice

Abstract: Transmission spectra were measured between 1.0 and 2.7 μm for monocrystalline samples of hexagonal water ice at temperatures between 20 and 270 K. Samples were crystallized from liquid water within closed cells, with thicknesses ranging from 100 μm to 1.0 cm. The absorption spectrum of ice changes with temperature in several ways. With higher temperature, the shapes of absorption bands become more smoothed, the strengths of some absorption bands decrease, the absorption in continuum wavelengths increases, and the band centers of some absorption bands shift to shorter wavelengths. In this paper we present the new absorption coefficient spectra along with an examination of the different temperature effects. These data should prove extremely valuable for analysis of near-infrared reflectance spectra of low-temperature icy surfaces, such as those of outer solar system satellites, Kuiper Belt objects, Pluto and Charon, comet nuclei, the polar caps of Mars, and terrestrial snow-and ice-covered regions. The data may also be of value in simulating radiative transfer in clouds of ice particles in the atmospheres of planets.

Visible Luminescence and Surface Properties of Nanosized ZnO Colloids Prepared by Hydrolyzing Zinc Acetate

Abstract: Luminescence properties of nanosized zinc oxide (ZnO) colloids greatly depend on their surface properties. These surface properties in turn are largely determined by the method of preparation. The procedure for producing ZnO colloids consists of two major steps: (1) preparing the precursor by reacting zinc acetate with ethanol and (2) hydrolyzing the precursor to form the colloid by using lithium hydroxide. The sample colloids in this study were prepared by hydrolyzing zinc acetate precursors containing various concentrations of Zn2+ with different concentrations of lithium hydroxide. The luminescence properties were evaluated by the energy difference, ΔE, between the band gap and the emission energy which were obtained from the onset of the absorption spectrum and the peak wavelength of the emission spectrum, respectively. The surface properties of ZnO particles were studied using thermal gravimetric and infrared techniques. ZnO particles produced via these procedures are not pure but have acetate (CH3C...

Characterization of Polyelectrolyte-Protein Multilayer Films by Atomic Force Microscopy, Scanning Electron Microscopy, and Fourier Transform Infrared Reflection-Absorption Spectroscopy.

Abstract: Protein-containing polyelectrolyte multilayer films of poly(styrenesulfonate) and poly(allylamine hydrochloride), fabricated by the sequential adsorption of polyelectrolyte and anti-immunoglobulin G (anti-IgG) on solid substrates, have been characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), and Fourier transform infrared reflection−absorption spectroscopy (FTIR-RAS). Visualization of the film structure on the nanometer scale, by AFM and SEM, showed that either layered or disordered films were formed depending on the number of polyelectrolyte layers separating each protein layer. For films where each anti-IgG layer was separated by one polyelectrolyte layer, an open, disordered film structure was observed and significant protein aggregation occurred. In contrast, for films in which the anti-IgG layers were separated by five polyelectrolyte layers, a layered structure with uniform protein layers was formed. Film thicknesses determined by SEM measurements were consistent w...

Excitonic Effects and the Optical Absorption Spectrum of Hydrogenated Si Clusters

Abstract: We calculate the optical absorption spectrum of hydrogen-terminated silicon clusters by solving the Bethe-Salpeter equation for the two-particle Green{close_quote}s function using an {ital ab initio} approach. The one-particle Green{close_quote}s function and the electron-hole interaction kernel are calculated within the GW approximation for the electron self-energy operator. Very large exciton binding energies are observed. Our results for the one-particle properties and the optical absorption spectra of the clusters are in very good agreement with available experimental data. {copyright} {ital 1998} {ital The American Physical Society}

Far-infrared photoconductivity in self-organized InAs quantum dots

Abstract: We report far-infrared photoconductivity in self-organized InAs/GaAs quantum dots grown by molecular beam epitaxy. Through use of a Fourier transform infrared spectrometer, a photoconductivity signal peaked at 17 μm is observed from a n–i–n detector structure with doped InAs quantum dots in the intrinsic region. Comparison of photoluminescence and band-to-band photocurrent absorption spectra suggests the far-infrared response is due to intersubband transitions in the quantum dots.

On the existence of positively charged single-substitutional nitrogen in diamond

Abstract: Infra-red (IR) absorption results on irradiated and annealed synthetic diamond are presented which confirm an earlier proposal that a component found in the defect-induced one-phonon region of some diamonds arises from positively charged single-substitutional nitrogen . The concentration ratio of to neutral substitutional nitrogen centres may be changed by shining light of various energies onto the examined samples. By correlating changes in absorption of the IR component associated with centres with changes in the component, and using a previously determined relation between the concentration of centres and peak absorption coefficient at 1130 , the relationship between peak absorption at 1332 and concentration of centres has been derived, namely 1 of absorption is produced by ppm centres. Other defects may also give rise to absorption at 1332 , but the component is uniquely identified by further peaks at 1046 and 950 . The significance of this component is demonstrated by the fact that some samples can contain in excess of 80 ppm centres, and this must consequently be accounted for when assaying the total nitrogen concentration in such samples. Using the above relationship useful parameters relating the concentration of neutral vacancies, negative vacancies and negatively charged nitrogen-vacancy centres to their respective zero-phonon line integrated absorptions have been derived.

Spectroscopic determination of the structure of amorphous nitrogenated carbon films

Abstract: Studies on structure and electronic properties of amorphous nitrogenated carbon films prepared in dual electron cyclotron resonance–radio frequency plasma from a mixture of methane and nitrogen are presently reported. These films are characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), electrical conductivity measurement, and optical absorption spectroscopy. Symmetry breaking of aromatic rings are at a very small amount of nitrogen incorporation is understood from FTIR spectra. The relative contribution of C=N and C–N bonds is found to change with the variation of the nitrogen content in the samples, which shows a similar trend with the shift of the G peak to a higher wave number and the increase of the ID/IG ratio. From decomposition of XPS C 1s and N 1s peaks a three-phase model of CN bonds is proposed. UPS valence band spectra obtained by using a Helium II source, are decomposed into p-...

Structural and Electronic Properties of Sol−Gel Titanium Oxides Studied by X-ray Absorption Spectroscopy

Abstract: X-ray absorption spectroscopy (XAS) has been used to study the local Ti environment in titania xerogel samples containing nanoparticles of different sizes. The xerogels were prepared by hydrolysis of titanium isopropoxide followed by peptization with HNO3 and size control was achieved through calcination in air at different temperatures. An amorphous precipitate obtained by hydrolysis of titanium isopropoxide prior to peptization with HNO3 has also been studied. The X-ray absorption near edge structure (XANES) of the precipitate possesses a characteristic preedge that is dominated by a transition designated as A2 at 4970.7 eV, and assigned to five coordinate Ti. This A2 component is detected in all of the studied xerogels. Its intensity decreases as the surface-to-volume ratio of the titania particles decreases, suggesting that it is associated with surface layers of the anatase particles. Other changes observed in the XANES of the xerogels as a function of particle size include broadening of 1s → np tran...

Anisotropy in the absorption and scattering spectra of chicken breast tissue.

Abstract: Oblique incidence reflectometry is a simple and accurate method for measuring the absorption and the reduced-scattering coefficients of turbid media. We used this technique to deduce absorption and reduced-scattering spectra from wavelength-resolved measurements of the relative diffuse reflectance profile of white light as a function of source–detector distance. In this study, we measured the absorption and the reduced-scattering coefficients of chicken breast tissue in the visible range (400–800 nm) with the oblique incidence probe oriented at 0° and 90° relative to the muscle fibers. We found that the deduced optical properties varied with the probe orientation. Measurements on homogenized chicken breast tissue yielded an absorption spectrum comparable with the average of the absorption spectra for 0° and 90° probe orientations measured on the unhomogenized tissue. The reduced-scattering spectrum for homogeneous tissue was greater than that acquired for unhomogenized tissue taken at either probe orientation. This experiment demonstrated the application of oblique-incidence, fiber-optic reflectometry to measurements on biological tissues and the effect of tissue structural anisotropy on optical properties.

Preparation and Stability of Template-Synthesized Metal Nanorod Sols in Organic Solvents

Abstract: Gold and silver nanorods of diameter 40 and 90 nm and having a variety of aspect ratios (length/diameter) were prepared using the template synthesis approach. After template synthesis, the nanorods were freed from the template membrane and dispersed in either hexafluoro-2-propanol (HFIP) or CHCl3. The stability of these nanorod sols was monitored using visible absorption spectroscopy. For both the Au and Ag nanorods (in both solvents), sols prepared from the 90-nm diameter nanorods were found to be less stable than sols prepared from the 40-nm diameter nanorods. The addition of the polymeric stabilizers poly(vinylpyridine) or poly(vinylpyrrolidone) did not enhance the stability of these nanorod sols. In addition to these studies of sol stability, UV−vis absorption spectroscopy was used to investigate the plasmon absorption band of these sols. The wavelength of maximum absorbance of the plasmon resonance band (λmax) for both Ag and Au sols was shifted to higher wavelengths when the nanorod diameter was inc...

Pre-edge fine structure of the 3d atom K x-ray absorption spectra and quantitative atomic structure determinations for ferroelectric perovskite structure crystals

Abstract: A complete interpretation is proposed for the pre-edge fine structure (PEFS) of the x-ray Ti K-absorption spectra for perovskite structure crystals. The interpretation is based on the results of numerous calculations performed by a modified full multiple scattering method which provides the theoretical spectra for the 3d transition metal oxides in fair agreement with experiment. It is shown that the three main peaks in the PEFS have quite different origin. The first long-wave side peak A is caused mainly by quadrupole transitions. The middle peak B is caused by the p-d mixture effect and the high intensity of it is considered to be a qualitative spectroscopic indication of ferroelectricity in the perovskite structure crystal. A simple formula is obtained which expresses the area under peak B through the lattice constants and mean-square displacement of the absorbing Ti atom from the instantaneous centre of the coordination polyhedron. The peak B area averaged over thermal atomic vibrations is determined by the three-particle atomic distribution function. The short-wave side peak C is caused by the Ti 1s electron transition to the unoccupied 3d states of the neighbouring transition metal atoms. We show that an additional peak on the short-wave side of peak C occurs if there are 4d atoms (for instance Zr atoms in the vicinity of the absorbing Ti atom in the (PZT) solid solution) within the oxygen atom octahedrons surrounding the absorbing 3d atom. The area under peak is directly determined by the average number of 4d atoms in the vicinity of the absorbing Ti one.

Electronic absorption by Ti 3+ ions and electron delocalization in synthetic blue rutile

Abstract: Polarized absorption spectra, σ and π, in the spectral range 30000–400 cm−1 (3.71–0.05 eV) were obtained on crystal slabs // [001] of deep blue rutile at various temperatures from 88 to 773 K. The rutile crystals were grown in Pt-capsules from carefully dried 99.999% TiO2 rutile powder at 50 kbar/1500 °C using graphite heating cells in a belt-type apparatus. Impurities were below the detection limits of the electron microprobe (about 0.005 wt% for elements with Z≥13). The spectra are characterized by an unpolarized absorption edge at 24300 cm−1, two weak and relatively narrow (Δν1/2≈3500–4000 cm−1), slightly σ-polarized bands ν1 at 23500 cm−1 and ν2 at 18500 cm−1, and a complex, strong band system in the NIR (near infra red) with sharp weak peaks in the region of the OH stretching fundamentals superimposed on the NIR system in the σ-spectra. The NIR band system and the UV edge produce an absorption minimum in both spectra, σ and π, at 21000 cm−1, i.e. in the blue, which explains the colour of the crystals. Bands ν1 and ν2 are assigned to dd transitions to the Jahn-Teller split upper Eg state of octahedral Ti3+. The NIR band system can be fitted as a sum of three components. Two of them are partly π-polarized, nearly Gaussian bands, both with large half widths 6000–7000 cm−1, ν3 at 12000 cm–1 and the most intense ν4 at 6500 cm−1. The third NIR band ν5 of a mixed Lorentz-Gaussian shape with a maximum at 3000 cm−1 forms a shoulder on the low-energy wing of ν4. Energy positions, half band widths and temperature behaviour of these bands are consistent with a small polaron type of Ti3+Ti4+ charge transfer (CT). Polarization dependence of CT bands can be explained on the basis of the structural model of defect rutile by Bursill and Blanchin (1983) involving interstitial titanium. Two OH bands at 3322 and 3279 cm−1 in σ-spectra show different stability during annealing, indicating two different positions of proton in the rutile structure, one of them probably connected with Ti3+ impurity. Total water concentration in blue rutile determined by IR spectroscopy is 0.10 wt-% OH. The EPR spectra measured in the temperature interval 20–295 K show the presence of an electron centre at temperatures above 100 K and Ti3+ ions in more than one structural position, but predominantly in compressed interstitial octahedral sites, at lower temperatures. These results are in good agreement with the conclusions based on the electronic absorption data.

Absorption Spectra Measurements for the Ozone Molecule in the 350-830 nm Region

Abstract: Absolute absorption cross-sections of ozone have been measured at ambient (295 K) and low temperature (218 K) in the visible region corresponding to the Chappuis bands. The temperature effect has been studied and found to be very small. The minimum of the absorption between the Hartley and the Chappuis bands is observed for the first time at 377,5 nm.

Poly((2,5-dialkoxy-p-phenylene)ethynylene-p-phenyleneethynylene)s and Their Model Compounds

Abstract: Poly((2,5-bis(n-hexyloxy)-p-phenylene)ethynylene-p-phenyleneethynylene) (1a), poly((2,5-bis(n-dodecyloxy)-p-phenylene)ethynylene-p-phenyleneethynylene) (1b), 1,4-diphenylethynylene-2,5-bis(n-hexyloxy)benzene (2a), and 1,4-diphenylethynylene-2,5-bis(n-dodecyloxy)benzene (2b) have been prepared by the Heck reaction. The X-ray crystal structures of 2a and 2b show that the overlap between aryl rings in neighboring molecules is small for 2a but large for 2b. 2a and 2b have similar electronic absorption spectra, and emission spectra in dilute solution, but the thin film emission of 2b is red shifted about 40 nm, perhaps due to excimer cluster formation or aggregation. Likewise, polymers 1a and 1b have similar absorption spectra and emission spectra in solution, but in the solid state the emission of 1b is significantly red shifted, also consistent with aggregation.

Structural characterization and thermal stability of MoS2 intercalation compounds

Abstract: The intercalation of MoS2 with Co and Fe complexes has been accomplished via exfoliation of LixMoS2 by reaction with water, followed by flocculation in the presence of cationic guest species. The resulting self-assembled compounds have been characterized by X-ray absorption spectroscopy, electron diffraction, powder X-ray diffraction, and magnetic measurements. The 2H-type (undistorted) MoS2 undergoes a structural distortion to 1T-type MoS2 during the Li intercalation, which is partially maintained upon exfoliation and flocculation. A structural model of 1T-MoS2 is proposed on the basis of X-ray absorption spectroscopy and electron diffraction, in which the unit cell has P3 symmetry with lattice parameters a = 6.52(5) A, c = 6.14 A. The Mo atoms are shifted approximately 0.5 A from their positions in 2H-MoS2 to form trigonal clusters in 1T-MoS2, with a concomitant change in coordination geometry from trigonal prismatic to distorted octahedral. Layers of Co(OH)2 were intercalated between the distorted and/...

Determination of the optical constants of zinc oxide thin films by spectroscopic ellipsometry

Abstract: Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions, e1(E)+ie2(E), of ZnO films on (0001) Al2O3 substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out with E⊥c at angles of incidence of 60° and 65° with respect to the surface normal. Below the band gap, the refractive index n is found to follow the first order Sellmeir dispersion relationship n2(λ)=1+1.881λ2/(λ2−0.05382). A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge.

X-ray absorption spectroscopy on layered photosystem II membrane particles suggests manganese-centered oxidation of the oxygen-evolving complex for the S0-S1, S1-S2, and S2-S3 transitions of the water oxidation cycle.

Abstract: By application of microsecond light flashes the oxygen-evolving complex (OEC) was driven through its functional cycle, the S-state cycle. The S-state population distribution obtained by the application of n flashes (n = 0. 6) was determined by analysis of EPR spectra; Mn K-edge X-ray absorption spectra were collected. Taking into consideration the likely statistical error in the data and the variability stemming from the use of three different approaches for the determination of edge positions, we obtained an upshift of the edge position by 0.8-1.5, 0.5-0.9, and 0.6-1.3 eV for the S0-S1, S1-S2, and S2-S3 transitions, respectively, and a downshift by 2.3-3.1 eV for the S3-S0 transition. These results are highly suggestive of Mn oxidation state changes for all four S-state transitions. In the S0-state spectrum, a clearly resolved shoulder in the X-ray spectrum around 6555 eV points toward the presence of Mn(II). We propose that photosynthetic oxygen evolution involves cycling of the photosystem II manganese complex through four distinct oxidation states of this tetranuclear complex: Mn(II)-Mn(III)-Mn(IV)2 in the S0-state, Mn(III)2-Mn(IV)2 in the S1-state, Mn(III)1-Mn(IV)3 in the S2-state, and Mn(IV)4 in the S3-state.

LiMn2 − x Cu x O 4 Spinels (0.1 ⩽ x ⩽ 0.5): A new Class of 5 V Cathode Materials for Li Batteries I. Electrochemical, Structural, and Spectroscopic Studies

Abstract: A series of electroactive spinel compounds, LiMn{sub 2{minus}x}Cu{sub x}O{sub 4} (0.1{le}x{le}0.5), has been studied by crystallographic, spectroscopic, and electrochemical methods and by electron microscopy. These spinels are nearly identical in structure to cubic LiMn{sub 2}O{sub 4} and successfully undergo reversible Li intercalation. The electrochemical data show a remarkable reversible electrochemical process at 4.9 V which is attributed to the oxidation of Cu{sup 2+} to Cu{sup 3+}. The inclusion of Cu in the spinel structure enhances the electrochemical stability of these materials upon cycling. The initial capacity of LiMn{sub 2{minus}x}Cu{sub x}O{sub 4} spinels decreases with increasing x from 130 mAh/g in LiMn{sub 2}O{sub 4} (x = 0) to 70 mAh/g in LiMn{sub 1.5}Cu{sub 0.5}O{sub 4} (x = 0.5). The data also show slight shifts to higher voltage for the delithiation reaction that normally occurs at 4.1 V in standard Li{sub 1{minus}x}Mn{sub 2}O{sub 4} electrodes (1{ge}x{ge}0) corresponding to the oxidation of Mn{sup 3+} to Mn{sup 4+}. Although the powder X-ray diffraction pattern of LiMn{sub 1.5}Cu{sub 0.5}O{sub 4} shows a single-phase spinel product, neutron diffraction data show a small but significant quantity of an impurity phase, the composition and structure of which could not be identified. X-ray absorption spectroscopy was used to gathermore » information about the oxidation states of the manganese and copper ions. The composition of the spinel component in the LiMn{sub 1.5}Cu{sub 0.5}O{sub 4} was determined from X-ray diffraction and X-ray absorption near-edge spectroscopy to be Li{sub 1.01}Mn{sub 1.67}Cu{sub 0.32}O{sub 4}, suggesting to a best approximation that the impurity in the sample was a lithium-copper-oxide phase. The substitution of manganese by copper enhances the reactivity of the spinel structure toward hydrogen: the compounds are more easily reduced at moderate temperature ({approximately} 200 C) than LiMn{sub 2}O{sub 4}.« less

Synthesis, Characterization, Absorption Spectra, and Luminescence Properties of Organometallic Platinum(II) Terpyridine Complexes

Abstract: A series of new organometallic platinum(II) complexes containing terdentate polypyridine ligands has been prepared and characterized. Their absorption spectra in 4:1 (v/v) MeOH/EtOH fluid solution at room temperature and luminescence in the same matrix at 77 K have been investigated. The new species are [Pt(terpy)Ph]Cl (3, terpy = 2,2‘:6‘,2‘‘-terpyridine, Ph = phenyl), [Pt(Ph-terpy)Cl]Cl (4, Ph-terpy = 4‘-phenyl-2,2‘:6‘,2‘‘-terpyridine), [Pt(Ph-terpy)Me]Cl (5), and [Pt(Ph-terpy)Ph]Cl (6). The results have been compared with those for [Pt(terpy)Cl]Cl (1) and [Pt(terpy)Me]Cl (2). NMR data evidence that all the complexes but 3 and 6 oligomerize in solution leading to stacked species. The absorption spectra are dominated by moderately intense metal-to-ligand charge-transfer (MLCT) bands in the visible region and by intense ligand-centered (LC) bands in the UV region. All the compounds are luminescent in a 4:1 (v/v) MeOH/EtOH rigid matrix at 77 K, exhibiting a structured emission within the range 460−600 nm. T...

Femtosecond laser-induced three-dimensional bright and long-lasting phosphorescence inside calcium aluminosilicate glasses doped with rare earth ions

Abstract: We report on a novel phenomenon in calcium aluminosilicate glasses doped with Ce3+, Tb3+, and Pr3+. After irradiation by an 800 nm femtosecond pulsed laser, the focused part of the laser in the glasses emits bright and long-lasting phosphorescence able to be clearly seen with the naked eye in the dark even one hour after the removal of the activating laser. Moreover, by selecting appropriate glass compositions and species of rare earth ions, optional three-dimensional image patterns emitting long-lasting phosphorescence in various colors, including blue, green, and red, can be formed within glass samples by moving the focal point of the laser. Based on absorption spectra, the long-lasting phosphorescence is considered to be due to the thermostimulated recombination of holes and electrons at traps induced by the laser irradiation, which leave holes or electrons in a metastable excited state at room temperature.

Strong hybridization in vanadium oxides: evidence from photoemission and absorption spectroscopy

Abstract: We present x-ray photoemission spectra of the vanadium oxides , and , and their analysis in terms of a simple cluster model based on the Anderson impurity Hamiltonian. The electronic structure of these materials is characterized by a strong V 3d-O 2p hybridization energy which exceeds the energy scales related to on-site Coulomb correlation and metal-ligand charge transfer. This result is at variance with the usual Mott-Hubbard picture, but agrees with recent studies of other early 3d transition metal compounds. The V 3d ground-state occupations obtained by the cluster-model analysis are considerably higher than the values derived from the formal valencies. Covalency also affects the exchange splitting observed in the V 3s core-hole spectra. X-ray absorption measurements and resonant photoemission spectroscopy at the V 2p-3d threshold provide further evidence for a strong V 3d-O 2p coupling.