Showing papers on "Absorption band published in 1974"

Atomic displacement and ionization effects on the optical absorption and structural properties of ion‐implanted Al2O3

Abstract: Ion‐induced lattice atom displacements in single‐crystal Al2O3 give rise to an optical absorption band at 204 nm as well as to expansion of the implanted volume. The 204‐nm absorption per unit energy into atomic processes is found to increase rapidly with decreasing incident ion mass. In contrast, light ions (H+, D+, He+) show less volume expansion per unit energy into atomic processes than do heavier ions. Furthermore, the volume expansion induced by heavy ion implantation can be completely relieved by H+‐ion implantation or by ionizing electron irradiation (8.16 keV). A simple model characterizes the results. The 204‐nm absorption is found to be proportional to the ion energy into electronic processes, and the expansion is proportional to the ion energy into atomic processes linearly reduced by the ion energy into electronic processes. The implications for defect production in CTR insulators are discussed.

Interionic vibrations and glass transitions in ionic oxide metaphosphate glasses

Abstract: The far infrared spectrum of each ionic metal‐metaphosphate glass, (MPO3)n (M = Li, Na, K, Rb, Cs) and [M(PO3)2]n (M = Ca, Sr, Ba), contains a broad absorption band whose peak frequency, ω0, and halfbandwidth, Δω1/2, are strongly dependent on the mass and charge of the glass‐modifying cation. Each such band, which appears as the envelope of the optical phonon spectrum of the crystalline form of the material, is assigned to a density of coupled oscillator pseudo phonon states, which assignment is shown to be consistent with experimental linear vibrations of ω0 with Δω1/2 and of ω02 with , the integrated absorbance, within the complete set of glasses. The net effect of coupling the oscillators in the vitreous (disordered) system is equivalently treated as a single damped harmonic oscillator. The damping coefficient, b = μΔω1/2, is constant in each series as is the complex part of the refractive index at ω0, κ(ω0), and the Lorentzian band is used to compute the force constant, F, b, and T, 0,...

Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS 2 . I. Absorption Spectra of CuFeS 2 and Fe-Doped CuAlS 2 and CuGaS 2

Abstract: Optical absorptions have been measured in chalcopyrite, CuFeS 2 , and Fe-doped CuAlS 2 and CuGaS 2 An extra absorption band with two peaks is observed at the low energy region of the absorption edge for Fe-doped CuAlS 2 and CuGaS 2 Energy positions of two absorption peaks are 13 eV and 20 eV for CuAlS 2 and 12 eV and 19 eV for CuGaS 2 , respectively The intensity of this absorption band increases with the increase of doped Fe ions and grows into the absorption edge of CuFeS 2 Its oscillator strength comes up to 7·10 -2 In chalcopyrite photoconductivity is observed and its maximum is just at the same energy region of the absorption edge By comparing our results with those of absorption measurements for Cu- or Fe-doped ZnS it is concluded that this absorption band originates from the charge transfer transitions relating to 3d electron of Fe ions and the absorption edge of CuFeS 2 rises from the band-to-band transition corresponding to this charge transfer transition

MoO3 layers — optical properties, colour centres, and holographic recording

Abstract: The spectral variations of optical absorption and refractive index are reported for thin layers of molybdenum trioxide prepared by evaporation in vacuum. These layers can be coloured by ultraviolet light and the absorption spectra of coloured layers show a single broad absorption band centred at 850 nm. The appearance of the colour centre absorption and the associated changes in the intrinsic edge have been used to record stable ‘thin’ holograms. A short discussion is given of the electronic structure of MoO3 and of the defects responsible for coloration. Le spectre d'absorption et l'indice de refraction ont ete mesure pour les couches minces de MoO3. Les couches minces ont ete colorees par UV et le spectre d'absorption des couches minces colorees a une bande d'absorption a la longeur d'onde λ = 850 nm. Le developpement de l'absorption des centres colores et le changement pres de l'absorption fondamentale ont ete utilises pour l'enregistrement holographique.

Disappearances of COOH infrared bands of benzoic acid

Abstract: Infrared spectra of benzoic acid and benzoic acid‐d were obtained in the range of temperatures from liquid nitrogen to liquid helium The C=O stretching band at 1688 cm−1, the strongest absorption band of this compound in the over‐all infrared region at room temperature, decreases in intensity with decreasing temperature and disappears near liquid‐helium temperatures Near this temperature, also lost was the band at 959 cm−1 which has been assigned to the OH out‐of‐plane vibration For the deuterated species both bands at 1689 and 1679 cm−1, which have been interpreted as splitting due to Fermi resonance of the C=O stretching vibration, were lost Close to the positions of these lost bands, alternative bands, which are assignable to the same modes and increase in intensity with decreasing temperature, are found The results support the postulate proposed in our earlier work that two distinct equilibrium configurations of benzoic acid dimer coexist in the crystal

Infrared absorption in low-loss KCl single crystals near 10.6 μm

Abstract: The infrared absorption in KCl single crystals near 10.6 μm has been studied using calorimetric techniques with fixed‐frequency and tunable CO2 laser sources. By use of crystals grown in a reactive CCl4 atmosphere, with surfaces carefully prepared by chemical polishing, it is possible to obtain absorption coefficients of 0.0002 cm−1 or less in samples several centimeters thick. This residual absorption is composed of a surface and a bulk part. It is possible to show that the bulk absorption approaches the estimated intrinsic limit of 0.00008 cm−1. An absorption band near 9.8 μm is present in all samples examined and appears to be largely associated with the surface.

Jahn-Teller effect in the 3T1(P) absorption band of Ni2+ in ZnS and ZnO

Abstract: The 3T1(P) absorption band of Ni2+ in cubic ZnS hexagonal ZnS and ZnO has been measured. The sharp zero-phonon structure of the low-energy edge of the spectra is found to be consistent with the predictions of static crystal field theory. A Jahn-Teller model is proposed, which accounts not only for the zero-phonon lines, but also for those phonon assisted lines, which cannot be explained as simple unshifted phonon sidebands. For ZnS the data indicate a weak to moderate Jahn-Teller coupling with acoustical phonons having E and T2 symmetry. For ZnO, coupling with a 100 cm-1 T2 mode suffices to explain the experimental results. On the basis of the Jahn-Teller model proposed for ZnS a reinterpretation of the 3T1(P) absorption band of GaP:Ni2+ is suggested.

Effect of solvent on the absorption spectra and Stokes’ shift of absorption and fluorescence of chlorophylls

Abstract: The absorption and fluorescence spectra of chlorophyll-a and chlorophyll-b solutions in a concentration of 6 · 10−6 M were determined in 22 solvents. The positions and the molar extinction coefficients of the red absorption band, the positions of the fluorescence bands, the oscillator strengths of the red bands and the Stokes’ shifts are tabulated. The results can be summarized as follows: The changes in the oscillator strength and the Stokes’ shifts obey roughly the theory of “internal field effect”. An evaluation of this effect yields 0.34 and 0.50 for the ratios of the polarizability of the chlorophylls and the Onsager radius of the solvents, for chlorophyll-a and chlorophyll-b, respectively. The results indicate that chlorophyll-b is more sensitive to environmental effects than chlorophyll-a.

On the excited‐state geometry of the adenine residue as revealed by a preresonance Raman effect

Abstract: The Raman specrum of β-adenosine-5′-phosphoric acid has been observed in its aqueous solution with 6471, 5145, 4880, 4579, 4579, and 3511 A excitation. An examination of the manner of increase of the intensities of the Raman lines at 1580 and 1484 cm−1 of the adenine residue indicated that the electronic excited state corresponding to a weak absorption band at 276 nm is responsible for these Raman scatterings. This idea has been supported by a similar examination of the Raman spectrum of β-adenosine-3′,5′-cyclic phosphoric acid and an examination of the effect of temperature on the Raman spectra of poly rA and poly(rA-rU). A discussion is included of the geometrical structure of the adenine residue in its lowest-singlet electronic excited state, based on the vibrational structure of the fluorescence spectrum, the result of a normal coordinate treatment, and the result of a semiempirical Pariser-Parr-Pople calculation, as well as the Raman data.

Absorption of OH in the 1200 Å region

Abstract: A strong absorption band of OH has been observed near 1221 A. From the analysis of high resolution spectra, it has been determined that the upper state is a 2Σ− Rydberg state and the constants of the OH and the corresponding OD state have been obtained. It is shown that the new absorption band will give interstellar absorption lines of OH at 1221.166, 1222.071, and 1222.524 A. New constants have also been determined for the A2Σ+ and X2Π states of OD.

Kinetics and Temperature Dependences of Polarized Emission of Anisotropic Tin Centres in Alkali Halides

Abstract: Temperature and time dependences of the polarized A emission of tetragonal Sn2+v centres in alkali halides have been investigated under excitation in the A absorption band. The change of polarization during the relaxation time, low-temperature depolarization due to the tunnel transitions between the minima of the lowest excited states, evidence of the metastable state in emission processes, and high-temperature depolarization due to the jumps of cation vacancy (v) around Sn2+, have been observed. A model is proposed for the excited states of Sn2+, in which the electron-lattice interaction is considered to be the main interaction, while the Spin–orbit interaction is taken into account as an additive correction. The formulae have been obtained for temperature and time dependences of polarization and decay time. Some parameters of Sn2+v centres in KCl:Sn have been found from comparison of the formulae with experimental data. [Russian Text Ignored]

A Study of Na 2 O-TiO 2 -SiO 2 Glasses by Infrared Spectroscopy

Abstract: The infrared absorption spectra of six Na2O-TiO2-SiO2 glasses in the frequency range of 1600 to 200 cm−1 are reported. These glasses, having a SiO2/Na2O molar ratio of 1.67 to 3.54, and containing 20 or 25 mole % TiO2, demonstrate two main absorptions at ~950 cm−1 and at ~450 cm−1. A weak absorption at ~790 cm−1 becomes progressively weaker in intensity, and a weak shoulder at 1050 cm−1 appears with increasing Na2O content. The frequency of the absorption band at ~950 cm−1 is found to decrease markedly and systematically with a decrease in the SiO2/Na2O molar ratio, whereas the frequency of the band at ~450 cm−1 shows a slight increase. The infrared results may be interpreted in terms of a lowering of symmetry occurring for the SiO4 units. The effect of TiO2 content on the relationship between vibrational frequency is discussed. The frequency composition curves for glasses containing 20 and 25 mole % of TiO2 intersect at SiO2/Na2O ratio ~2. A reversal in the frequency vs SiO2/Na2O ratio relation was also found at SiO2/Na2O ~2 for the sodium silicate glasses.

The 10.6-μm absorption of KCl

Abstract: The 10.6‐μm absorption in most KCl is shown to be dominated by a broad absorption band near 9.7 μm. The integrated absorption of this band decreases with increasing temperature. The temperature dependence is consistent with that to be expected from the dissociation of an absorbing pair. A KCl crystal has been measured whose 10.6‐μm absorption, 6.6±2×10−5 cm−1, is at the intrinsic multiphonon level.

Donor-acceptor complexes formed by perfluoro-organo bromides and iodides wlth nitrogenous and other bases. V. Comparison of liquid phase complexes of CFI3, C2F5I or C3F7I with Nme3, NEt3 or NPr3; infrared, far-infrared and N.M.R. spectra

Abstract: Equimolar liquid mixtures of CF3I, C2F5I or C3F7I and NMe3, Net3 or NPr3 were examined by infrared, far-infrared and N.M.R. spectroscopy. In the liquid mixtures of the halides with NMe3 or Net3 a broad absorption band at respectively c. 100 cm-l or c.75 cm-1 was observed, which is assigned to the N-I stretching mode of the intermolecular complex, analogous to the complexes described in Parts 111 and IV. The fluorine resonances in CF3I and in the ?CF3I groups are shifted markedly upfield in the equimolar liquid mixture compared to the liquid halide. Upfield shifts caused by the amines are in the order NMe3 > Net3 > NPr3. Infrared frequency shifts suggest that NMe3 forms stronger complexes with these halides than does NEt3.

Infrared absorption of mixed silicon isotope pairs in gallium arsenide

Abstract: The infrared absorption of GaAs doped with 28Si, 30Si, or 28Si + 30Si and compensated by 6Li diffusion or electron irradiation is reported. Isotopic shifts close to those predicted from local‐mode theory are observed for all the silicon defect bands in 30Si‐doped GaAs from frequencies previously reported for 28Si‐doped material. a new band is observed at 456 cm−1 for the sample containing both 28Si and 30Si, and is attributed to (28Si–30Si) pairs. The frequency of the new band is in accord with simple theory, and its presence confirms the observation of the nearest‐neighbor silicon pairs. The results indicate, however, that the indentification of one of the three absorption bands previously attributed to the 28Si pairs is questionable. The experimental result also indicates that an absorption band at 369 cm−1 previously observed in electron‐irradiated samples in indeed due to a silicon‐related defect.

Observations of "forbidden" soft-x-ray transitions: Li K absorption in LiF

Abstract: A weak absorption band at 53.5-60 eV, associated with transitions from the $\mathrm{Li} 1s$ core level to the $s$-like conduction band of LiF, has been detected, confirming the results of recent band calculations.

Absorption, transmission, and reflection spectra of mono‐ and bimolecular layers

Abstract: A microscopic theory of the optical properties of mono‐ and bimolecular layers is described. Intermolecular interactions are assumed to be of the point dipole type. It is shown how the refractive index of a mono‐ or bilayer may be defined and connections to the refractive index of a three dimensional crystal are established. At frequencies close to an absorption band, strong exciton‐photon coupling is shown to result in excited states with very short radiative lifetimes.

Absorption, Excitation, and Fluorescence Spectra of Thallium‐Activated Ammonium Chloride

Abstract: Absorption and fluorescence spectra of ammonium chloride activated by varied amount of thallium have been investigated at various temperatures in order to study the nature of electronic states involved in the luminescence centres. Absorption bands at 6.05, 5.84, 5.63, 5.38, 5.17, 5.00, and 4.86 eV and emission bands at 3.45, 2.70, and 2.30 eV have been observed. The disappearance of visible bands, the shift of the ultraviolet band from 3.45 to 3.65 eV, and the shift of the A absorption band (1A1g → 3T1u) towards longer wavelengths at about the transition temperature (184°C) have been correlated to the change in the crystal structure of the host lattice from b.c.c. to f.c.c. The excitation and emission spectra have been recorded at liquid nitrogen temperature to ascertain the electronic transitions of different emission bands. The absorption and fluorescence bands have been attributed to the electronic transitions in monomer and dimer centres having cubic and tetragonal site symmetries.

Excitation and luminescence spectra of dipotassium hexafluoromanganate(IV)

Abstract: Measurement of the excitation and luminescence spectra of the salt K2[MnF6] prepared by different methods shows that the intense emission observed at low temperatures between 14 700 and 13 500 cm–1 is caused by a MnIV species present as impurity. The 2E state of the impurity is populated by energy transfer from the 2E state of the [MnF6]2– ion thereby almost quenching the emission from the latter. The nature of this impurity is discussed. The previously reported absorption band at 19 300 cm–1 is not present in the excitation spectrum and is attributed to another impurity. All the expected electronic and vibronic origins of the 4A2→2E and 4A2→2T1 transitions of the [MnF6]2– ion have been identified.