Pressure-induced Absorption Research Articles

Pressure-induced threshold optical pump intensity in a CdTe/ZnTe quantum dot

ABSTRACTPressure-induced binding energies of an exciton and a biexciton are studied taking into account the geometrical confinement effect in a CdTe/ZnTe quantum dot. Coulomb interaction energy is obtained using Hartree potential. The energy eigenvalue and wave functions of exciton and the biexciton are obtained using the self-consistent technique. The effective mass approximation and BenDaniel-Duke boundary conditions are used in the self-consistent calculations. The pressure-induced nonlinear optical absorption coefficients for the heavy hole exciton and the biexciton as a function of incident photon energy for CdTe/ZnTe quantum dot are investigated. The optical gain coefficient with the injection current density, in the presence of various hydrostatic pressure values, is studied in a CdTe/ZnTe spherical quantum dot. The pressure-induced threshold optical pump intensity with the dot radius is investigated. The results show that the pressure-induced electronic and optical properties strongly depend on the spatial confinement effect.

Measurement System for Study of Absorption Spectra of Gaseous Media at High Pressures

A system for measuring the absorption spectra of gaseous media at pressures of 0.01–150 atm in the 0.3–25 μm range is considered. Its suitability for studying pressure-induced absorption owing to intermolecular collisions and for measuring spectral absorption coefficients, integrated band intensities, and spectrum line profiles is discussed.

Mechanoelectric effect in O2− conducting cell: Relations to phase transformations and other lattice changes in YBa2Cu3O6 + x -like oxides

The origin of mechanoelectric voltage arising in an 2−-conducting solid-state cell O2,Pt|ZrO2|Pt, O2, YBCO due to the pressure applied on the YBCO sample is discussed. It is demonstrated that the mechanoelectric voltage is the sum of the electronic and ionic mechanoelectric contact potentials. The mechanoelectric contact potentials are determined by the work done by the load during an elementary ordering act or another elementary process taking place when the sample absorbs one oxygen atom. Effects related to oxygen atoms being ordered under the load, such as pressure-induced oxygen absorption, enhanced deformation, and change in the order parameter, are discovered.

High-pressure phase transition and behavior of protons in brucite Mg(OH) 2 : a high-pressure-temperature study using IR synchrotron radiation

Infrared absorption spectra of brucite Mg (OH)2 were measured under high pressure and high temperature from 0.1 MPa 25 °C to 16 GPa 360 °C using infrared synchrotron radiation at BL43IR of Spring-8 and a high-temperature diamond-anvil cell. Brucite originally has an absorption peak at 3700 cm−1, which is due to the OH dipole at ambient pressure. Over 3 GPa, brucite shows a pressure-induced absorption peak at 3650 cm−1. The pressure-induced peak can be assigned to a new OH dipole under pressure. The new peak indicates that brucite has a new proton site under pressure and undergoes a high-pressure phase transition. From observations of the pressure-induced peak under various P–T condition, a stable region of the high-pressure phase was determined. The original peak shifts to lower wavenumber at −0.25 cm−1 GPa−1, while the pressure-induced peak shifts at −5.1 cm−1 GPa−1. These negative dependences of original and pressure-induced peak shifts against pressure result from enhanced hydrogen bond by shortened O–H···O distance, and the two dependences must result from the differences of hydrogen bond types of the original and pressure-induced peaks, most likely from trifurcated and bent types, respectively. Under high pressure and high temperature, the pressure-induced peak disappears, but a broad absorption band between 3300 and 3500 cm−1 was observed. The broad absorption band may suggest free proton, and the possibility of proton conduction in brucite under high pressure and temperature.

Interlayer proton transfer in brucite under pressure by polarized IR spectroscopy to 5.3 GPa

In order to investigate the behaviour of proton in brucite under pressure, polarized IR absorption spectra and polarized absorbance distributions of (001) and (110) oriented single crystal of brucite under high pressure were measured by Fourier transform polarized infrared microspectroscopy with diamond anvil cell. A pressure-induced absorption peak at 3645 cm−1 observed under pressures over 2.9 GPa was confirmed to be due to a secondarily formed OH dipole. Polarized absorbance distribution measured under pressure of (110) suggests that the secondary OH dipole is oriented 136.0° to c-axis under 5.3 GPa. Isotropic absorbance distribution of (001) suggests that the secondary OH dipole is disorderly trifurcated. Abrupt onset of the secondary peak and its reverse pleochroism suggest that the process of secondary OH dipole formation is due to proton transfer between layers in brucite. The calculated orientation of the secondary OH dipole consistent with the O-H···O´ angle revealed by neutron diffraction supports the existence of proton transfer along H···O´. The secondary OH dipole implies a new site of proton in brucite under pressure.

Pressure-Induced Molecular Absorption in Stellar Atmospheres

Pressure-induced absorption arises in complexes of two or more inert atoms or molecules, due to dipole moments induced during the collisional interaction. The term “pressure-induced” still prevails in the astrophysical literature, yet “collision-induced” absorption (CIA), or “interaction-induced” absorption seems more appropriate and is commonly used elsewhere. Ordinary absorption processes in the infrared arise from individual, polar molecules interacting with electromagnetic radiation. As a consequence, the intensity of the allowed lines increases linearly with density. CIA, on the other hand, is most striking in gases composed of nonpolar, infrared-inactive molecules. Induced spectral lines are observed at rovibrational frequencies which are dipole-forbidden in single (i.e. non-interacting) molecules. Dipole transitions may, however, beinducedin the interacting pair. The new symmetry of the electronic cloud of a collisional complex may be very different from those of the isolated molecules and thus commonly allows for a transient dipole, which then interacts with radiation. Collision-induced absorption increases quadratically in the low density limit, thus reflecting the two-body origin of the basic absorption process. At higher gas densities, ternary interactions become significant and cubic and higher-order contributions to the observable absorption are then commonly seen.

Pressure-sensitive Optical Properties of Bis(1,2-dionedioximato)-Palladium (II) Complexes.

The absorption spectra of Pd(niox)2, Pd(dmg)2 and Pd(dpg)2 have been studied at high pressures. The absorption bands based on the 4dz2-5pz transition shifted rapidly to longer wavelengths with increasing pressure. The mean rates of the red shift with pressure were ca. -1170cm-1/GPa for Pd(niox)2, ca. -1300cm-1/GPa for Pd(dmg)2 and ca. -1990cm-1/GPa for Pd(dpg)2. A new pressure-induced absorption band at around 410nm was observed for Pd(niox)2 above 10GPa. The electronic states of the palladium complexes are discussed. The colors of the complexes in the diamond-anvil pressure cell were observed visually at various pressures. The colors of the complexes turn from yellow to orange and then to successive colors in the visible spectrum with increasing pressure. These materials can be utilized as a pressure indicator over the wide pressure range.

Insulator-to-Metal-to-Semiconductor Transitions of One-Dimensional Bis(1,2-dione dioximato)Pt(II) Complexes at High Pressures

Abstract The electrical resistivities and absorption spectra of one-dimensional bis(1,2-dione dioximato)Pt(II) have been studied at high pressures. The resistivities of needle crystals of Pt(dmg)2 and Pt(bqd)2 were measured in detail under a quasi-hydrostatic pressure of up to 7 GPa. Pt(dmg)2 is an insulator with a resistivity of 1015 Ω cm, and Pt(bqd)2 is a semiconductor with 103 Ω cm at atmospheric pressure. A pressure-induced insulator (semiconductor)-to-metal transition was observed for both complexes. This transition arises from a crossing of the 5dz2 valence and 6pz conduction bands. When the pressure was further increasued, a metal-to-semiconductor transition took place at around the pressure that showed a resistivity minimum. A new pressure-induced absorption band was found in the visible region for the Pt complexes. The new band did not shift with pressure; the intensity of the band, however, increased with pressure over a narrow pressure region. The pressure-induced band may be due to intramolecular d–d transitions. The metal-to-semiconductor transition may arise from a change in the electronic states at high pressure, since no anomaly in the strucutre was observed.

Far-infrared collision-induced absorption in some compressed gaseous polar molecules of atmospheric interest

The higher frequency part of the far-infrared pressure-induced absorption in gaseous polar molecules has its origin in binary collision-induced dipolar absorption. The lower frequency part of the band observed is due to the induced translational absorption. Detailed expressions for different possible contributions to the integrated intensities are reported for diatomics (CO, HCl), linear molecules (N2O, OCS) and symmetric top molecules (halogenated methanes such as CF3Cl, CF3H). From these calculated expressions and the moderately low pressure FIR data, new values of the quadrupole moment of N2O and CF3Cl (|Θ|N2O = 12.3 × 10×40C.m2, |Θ|CF3Cl = 22.0 × 10−40C.m2) are determined.

Pressure-induced absorption coefficients for radiative transfer calculations in Titan's atmosphere

For the purpose of calculating the far-infrared thermal radiation from Titan's atmosphere, the pressure-induced absorption in pure N2, CH4 and in N2Ar, N2CH4, and N2H2 mixtures has been modeled using recent laboratory measurements. The results are tabulated as a function of wavenumber and temperature, and gaseous absorption spectra are calculated for the composition and temperatures known to be typical of the troposphere of Titan.

Radiative equilibrium model of Titan's atmosphere

A simple global radiative equilibrium model is developed for Titan. It is restricted to the two-stream approximation, is vertically homogeneous in its scattering properties, and is spectrally divided into one thermal and two solar channels. A partially absorbing “violet” channel is responsible for heating in the stratosphere, while a conservatively scattering “red” channel permits heating at the surface. The optical thickness of the atmosphere in the red is 1 < τ 1 r < 3. Between 13 and 33% of the total incident solar radiation is absorbed at the planetary surface. The ratio of violet to thermal infrared absorption cross sections is between 30 and 60 in the stratosphere, leading to the large temperature inversion observed there. The observed and theoretically computed tropopause temperatures are 72 and 69°K, respectively, while their corresponding thermal optical depths are, respectively, ∼0.1 and ∼0.07. The spectrally integrated mass absorption coefficient at thermal wavelengths is approximately constant throughout the stratosphere and roughly linear with pressure in the troposphere. This in turn implies the presence of a uniformly mixed aerosol in the stratosphere, and suggests pressure-induced absorption by gaseous N 2CH 4H 2 in the troposphere. In addition there appear to be two regions of enhanced opacity near 30 and 500 mbar which may be due to C 2H 2C 2H 6C 3H 8 and CH 4 condensation clouds, respectively.

Pressure-induced absorption spectra change in alkali halide phosphors: mutual mixing between excited states

An apparatus has been developed which permits optical measurements up to 30 kbar at 1.5K using a piston-cylinder-type high-pressure cell. Using this apparatus, studies of the hydrostatic pressure effects of absorption spectra of KI and KBr doped with Tl+ or In+ have been made up to 10 kbar. Under high pressure, a mutual mixing occurs due to the electron-lattice interaction between the excited states corresponding to the A, B, C and D absorption bands, even at low temperatures, resulting in the give-and-take of the absorption intensity between these absorption bands. To explain the mutual mixing, the pressure dependence of the electron-lattice coupling is taken into account. The pressure variation of the A band shape is also discussed in connection with the pressure dependence of the electron-lattice coupling constants.

Stratospheric measurements of continuous absorption near 2400 cm^−1

Solar occultation spectra obtained with a balloon-borne interferometer have been used to study continuous absorption by N(2) and CO(2) near 2400 cm(-1) in the lower stratosphere. Synthetic continuum transmittances, calculated from published coefficients for far-wing absorption by CO(2) lines and for pressure-induced absorption by the fundamental band of N(2), are in fair agreement with the observed stratospheric values. The continuum close to the nu(3) R-branch band head of CO(2) is sensitive to the CO(2) far-wing line shape. Therefore, given highly accurate knowledge of the N(2) continuum from laboratory data, high-resolution stratospheric spectra provide a sensitive means for in situ testing of various air-broadened CO(2) line shapes at low temperatures.

Electrical and optical behavior of one-dimensional organic conductors at high pressures

Electrical and optical behavior of 10 one-dimensional organic conductors have been studied at high pressures. The electrical resistivity of the organic conductors decreases with increasing pressure in the low-pressure region and reaches each resistivity minimum. The lowest resistivity of TTF-TCNQ and TTF derivative salts at high pressures is much lower than that of other salts. For conducting TCNQ salts, a pressure-induced absorption band has been observed around 20 × 10 3 cm −1; it may be assigned to the new charge transfer band between TCNQ. A pressure-induced band is not found in TTF-TCNQ, but the change of spectra with pressure is observed around 12 × 10 3 cm −1. Above certain pressures the electrical resistivity of the organic conductors increases rapidly with increasing pressure and drifts upward with time. These phenomena arise from the solid phase reaction. The differences of the physicochemical properties of one-dimensional organic conductors will be discussed.

Atmospheric extinction in the four-micron region

view Abstract Citations (8) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atmospheric extinction in the four-micron region. Wing, R. F. ; Rinsland, C. P. Abstract Extinction by the terrestrial atmosphere, derived from scanner observations of stars, is found to be strongly wavelength-dependent between 3.98 and 4.07 microns. Synthetic extinction coefficients, generated by using absorption coefficients measured in the laboratory and a model terrestrial atmosphere, indicate that the dominant opacity source is pressure-induced absorption by the fundamental band of N2. Smaller contributors in this region are continuous absorption by H2O and CO2, discrete lines of N2O, and aerosol extinction. Publication: The Astronomical Journal Pub Date: August 1979 DOI: 10.1086/112534 Bibcode: 1979AJ.....84.1235W Keywords: Atmospheric Attenuation; Earth Atmosphere; Infrared Astronomy; Absorptivity; Carbon Dioxide; Nitrogen; Nitrous Oxides; Water; Astronomy; Earth Atmosphere:Extinction full text sources ADS |

Pressure Effects of Absorption Bands in NaBr: Cu+

Absorption spectra of NaBr: Cu + have been investigated over the pressure range from 1 bar to about 6 kbar at a low temperature. There occurs a critical pressure-induced local phase transition (off-center to on-center transition), accompanying appearance of new absorption. bands on the lower energy side of the known absorption bands. The above pressure-induced absorption bands are assigned to the A band (spin-forbidden transition) and the B band in order of increasing photon energy, refering to the absorption spectrum of an on-center system, NaCl: Cu + . The origin of the off-center is discussed in connection with the pressure effects.

Pressure-induced absorption of microwave radiation by the oxygen molecule

It has been known that microwave absorptions at 9, 23 and 60 GHz by high pressure oxygen gas are considerably greater than expected by conventional theory, except at 68.7 GHz. A reasonable explanation is the pressure-induced absorption, which enhances the well established magnetic dipole absorption at the 60 GHz region. A total of 4.3 p db/km ( p in atmosphere) of peak intensity is proposed to be due to the pressure-induced absorption in the 60 GHz region, compared to 145 db/km due to magnetic dipole absorption.

Pressure-induced polytypic transformations and edge absorption of GaSe

Jointly analyzing the absorption spectra and the interference patterns in the transmission spectra of GaSe at pressures between 1 and 5530 bar, further evidence is given relating to polytypic transformations in GaSe, namely: the intrapolytypic transformation when the pressure is increased from 2790 to 3350 bar and the interpolytypic transformation when the pressure is increased from 4340 to 4710 bar. This interpretation is confirmed by the analysis of the pressure dependence of the energy position of the exciton line. The possible mechanism of these transformations is discussed. Taking account of the intrapolytypic transformation, the pressure influence on the low-energy tail of the exciton lines is considered. [Russian text ignored]

Pressure-induced absorption in nonpolar gases containing tetrahedral molecules

The theory of pressure-induced absorption of far infrared radiation by gases is extended to include the contribution of the dipole moment induced in a molecule by the field gradient due to its neighbours. This dipole is nonzero when the molecule lacks a centre of inversion, as in a tetrahedron. In the collision of two tetrahedra, the dipole induced in molecule 2 by the electric field of the octopole moment Ω1 of the partner leads to transitions in which ΔJ(1) = 0, ± 1, ±2, ±3, and ΔJ(2) = 0. The dipole induced by the field gradient of Ω1 leads to ΔJ(1) = 0, ±1, ±2, ±3, and ΔJ(2) = 0, ±1, ±2, ±3, and therefore gives a required increase in absorption at higher frequencies. The field-gradient contribution vanishes in a collision involving a tetrahedral and a spherical molecule. General expressions are given for the field-gradient contributions to the integrated intensity and to the −2 spectral moment.

Theory of line shape in pressure-induced absorption

A quantum theory of line shape in pressure-induced absorption giving relatively simple results in closed form is developed. A flexible model correlation function satisfying certain general criteria is chosen and incorporated in a general quantum theory of absorption. Relations are derived for estimating the values of the time parameters in the correlation function in terms of known molecular parameters. The theory is applied to far infrared spectra: the translational spectrum of He–Ar, the well resolved S(0) rotational line of H2 at 77 K, and the unresolved rotational band of N2. In all cases, the theory fits the spectra and accounts for the spectral features.