Urbach's rule in impurity absorption

1969 ◽  
Vol 47 (16) ◽  
pp. 1703-1708 ◽  
Author(s):  
Dennis Dunn
Keyword(s):  
Absorption Spectrum ◽  
Absorption Coefficient ◽  
Photon Energy ◽  
Valence Electron ◽  
Impurity State ◽  
Function Technique ◽  
Absorption Process ◽  
Impurity Absorption ◽  
Long Wavelength ◽  
State Electron

We have investigated theoretically the shape of the long-wavelength edge of the impurity absorption spectrum in an insulator (or semiconductor) by means of a Green's function technique. The absorption process is assumed to be the excitation of a valence electron into a previously unoccupied impurity state. We have shown that Urbach's rule is obeyed, that is the absorption coefficient depends exponentially upon the photon energy, if either the valence electron or the impurity state electron is coupled strongly to monoenergetic phonons.

Quantitative Ausmessung des Fluor-Affinitätskontinuums

1967 ◽  
Vol 22 (2) ◽  
pp. 254-259 ◽  
Author(s):  
Hanns-Peter Popp
Keyword(s):  
Absorption Coefficient ◽  
Cross Section ◽  
Photon Energy ◽  
Temperature Measurements ◽  
Total Absorption ◽  
Long Wavelength ◽  
Continuous Background ◽  
Total Absorption Coefficient ◽  
The Continuum ◽  
Kirchhoff's Law

The radiation emitted from a cylindric arc burning in SF6-gas at low currents shows the affinitycontinuum of fluorine with a long wavelength threshold of 3646 A. By means of spectroscopic temperature measurements and using KIRCHHOFF’s law the total absorption coefficient for the continuum in the range from 6800 to 2600 A is obtained. Isolating the F-affinity-continuum from the continuous background, the detachment cross section of the negative fluorine ion is obtained as a function of the photon energy.

THE PRESSURE-INDUCED ROTATIONAL ABSORPTION SPECTRUM OF HYDROGEN: I. A STUDY OF THE ABSORPTION INTENSITIES

1959 ◽  
Vol 37 (3) ◽  
pp. 362-376 ◽  
Author(s):  
Z. J. Kiss ◽  
H. P. Gush ◽  
H. L. Welsh
Keyword(s):  
Absorption Spectrum ◽  
Kinetic Energy ◽  
Infrared Spectrum ◽  
Absorption Coefficient ◽  
Quadrupole Interaction ◽  
Vibrational Band ◽  
Absorption Process ◽  
Relative Kinetic ◽  
Good Agreement ◽  
Gas Pressures

The pressure-induced infrared spectrum of H2 and mixtures of H2 with N2, He, Ne, A, Kr, and Xe was measured in the region 300–1400 cm−1 at total gas pressures up to 250 atm at 300° K and, where possible, at 195° K and 85° K. The spectrum shows greatly broadened S lines (ΔJ = + 2) with half widths which decrease as the temperature is lowered. The integrated absorption coefficient of the band is of the form [Formula: see text], where ρƒ is the density of the perturbing gas, except in the case of Xe for which a cubic term, [Formula: see text], is also necessary. The binary coefficient α1 increases by a factor of 28 in going from He to Xe. The theoretical band intensity, calculated on the basis of quadrupole interaction alone, is in good agreement with the experimental value only for Xe as perturbing gas; in other cases the calculated value is appreciably less than the observed value. The shape of the absorption contours suggests that the S lines are overlaid by a continuum increasing in intensity towards lower frequencies. This continuum is interpreted as the counterpart of the QR component in the vibrational band, that is, a collision-induced absorption due to overlap interaction in which the relative kinetic energy of the collision partners changes in the absorption process.

Effective Dielectric Function of Porous Silicon: the Transverse Component

1994 ◽  
Vol 358 ◽  
Author(s):  
G. Gumbs
Keyword(s):  
Absorption Spectrum ◽  
Absorption Coefficient ◽  
Electron Density ◽  
Quantum Wires ◽  
Interband Transition ◽  
Incident Light ◽  
Transverse Component ◽  
Effect Of Temperature ◽  
High Electron ◽  
Confining Potential

ABSTRACTA self-consistent many-body theory is developed to study the effect of temperature and electron density on the interband absorption coefficient and the frequency-dependent refractive index for an array of isolated quantum wires. The peaks in the absorption coefficient correspond to interband transitions resulting in the resonant absorption of light. The oscillations in the derivative spectrum are due to the quantization of the energy levels related to the in-plane confining potential for such reduced dimensional systems. There are appreciable changes in the absorption spectrum when the electron density or temperature is increased. One interband transition peak is suppressed in the high electron density limit and the thermal depopulation effect on the electron subbands can be easily seen when the temperature is high. We also find that the exciton coupling weakens the shoulder features in the absorption spectrum. This study is relevant to optical characterization of the confining potential and the areal density of electrons using photoreflectance. By using incident light with tunable frequencies in the interband excitation regime, contactless photoreflectance measurements may be carried out and the data compared with our calculations. By fitting the numerical results to the peak positions of the photoreflectance spectrum, the number of electrons in each wire may be extracted.

scholarly journals The absorption spectrum and fluorescence of mercury vapour

1905 ◽  
Vol 76 (512) ◽  
pp. 428-430 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Absorption Coefficient ◽  
Absorption Spectra ◽  
Quartz Glass ◽  
Mercury Vapour ◽  
Blue Colour ◽  
Water Jacket ◽  
Side Tube ◽  
Quartz Spectrograph

Having undertaken the investigation of the absorption spectra of metals in a state of vapour, the first substance examined was mercury, and as the results are interesting I have deemed it advisable to make them a separate communication to the Society. F. P. le Roux describes the vapour of mercury as having a bluish colour, and according to R. J. Strutt, it transmits a feeble steel-blue colour, but the absorption coefficient is small. Experimental.—The substance to be volatilised was contained in a flask of Heraeus’ quartz-glass, with a side tube to the neck from which the metal may be distilled and condensed. To the side tube a water-jacket is fitted through which a constant stream of water may be passed if necessary. The rays from the condensed spark of a pair of lead-cadmium and tin-cadmium electrodes were passed through the flask and on to a cylindrical condensing lens of quartz which focussed the rays on to the slit of a quartz spectrograph.

scholarly journals Pyropheophytin a Accompanies Pheophytin a in Darkened Light Grown Cells of Euglena1

1981 ◽  
Vol 36 (9-10) ◽  
pp. 827-833 ◽  
Author(s):  
Siegrid Schoch ◽  
Hugo Scheer ◽  
Jerome A. Schiff ◽  
Wolfhart Rüdiger ◽  
Harold W. Siegelman
Keyword(s):  
High Performance Liquid Chromatography ◽  
Absorption Spectrum ◽  
High Performance ◽  
Dilute Acid ◽  
Reverse Phase ◽  
Intact Cells ◽  
Pheophytin A ◽  
Long Wavelength ◽  
Dividing Cells ◽  
Ether Solution

Abstract Chromatography Light-grown non-dividing cells of Euglena gracilis Klebs var. bacillaris Cori form pheophytin a like pigments from chlorophyll a without loss of viability when they are allowed to incubate in darkness without shaking. This is accompanied by the loss of long-wavelength components in the red absorption band of intact cells. After extraction of these cells with acetone, transfer of the pigments to ether and treatment of the ether solution with dilute acid, two pigments can be separated by high performance liquid chromatography on reverse phase silica gel (RP-8) using methanol: water = 95:5 (v/v) as the eluting solvent: In addition to pheophytin a, the eluate contains an unknown pigment. With increasing times of incubation of the cells in darkness, the proportion of pheophytin a decreases and the proportion of the unknown increases suggesting, that the unknown is formed from pheophytin a. This pigment has been identified as pyropheophytin a. It has the same absorption spectrum as pyropheophytin a (prepared by pyridine pyrolysis of pheophytin a) and contains phytol as the longchain esterifying alcohol. On conversion to the methyl ester, the resulting methyl phorbide is identical with authentic pyromethylpheophorbide a by tic, hplc, absorption, absorption difference and mass spectros­ copy. This is the first report of pyropheophytin a or any pyrochlorophyll derivative from plants or oxygenic plant-like microorganisms where it may serve as an intermediate in chlorophyll degradation.

scholarly journals New Results in Optical Modelling of Quantum Well Solar Cells

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Silvian Fara ◽  
Paul Sterian ◽  
Laurentiu Fara ◽  
Mihai Iancu ◽  
Andreea Sterian
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Quantum Well ◽  
Absorption Coefficient ◽  
Quantum Efficiency ◽  
Quantum Confinement ◽  
Quantum Confinement Effect ◽  
Refraction Index ◽  
Absorption Process ◽  
Optical Modelling

This project brought further advancements to the quantum well solar cell concept proposed by Keith Barnham. In this paper, the optical modelling of MQW solar cells was analyzed and we focussed on the following topics: (i) simulation of the refraction index and the reflectance, (ii) simulation of the absorption coefficient, (iii) simulation of the quantum efficiency for the absorption process, (iv) discussion and modelling of the quantum confinement effect, and (v) evaluation of datasheet parameters of the MQW cell.

Comparison of photoconductivity and optical absorption spectra of trapped electrons in γ-irradiated 2,2,4-trimethylpentane/2,2-dimethylbutane/2-methyltetrahydrofuran mixture glasses at 77 K

1984 ◽  
Vol 62 (1) ◽  
pp. 64-68 ◽  
Author(s):  
Toyoaki Kimura ◽  
Kazunobu Hirao ◽  
Naoto Okabe ◽  
Kenji Fueki
Keyword(s):  
Absorption Spectrum ◽  
Optical Absorption ◽  
Absorption Spectra ◽  
Electron Mobility ◽  
Optical Absorption Spectrum ◽  
Lower Energy ◽  
Photon Absorption ◽  
Optical Absorption Spectra ◽  
Absorption Process ◽  
Trapped Electrons

Optical absorption and photoconductivity spectra of trapped electrons in -γ-irradiated 2,2,4-trimethylpentane (TMP)/2,2-dimethylbutane (DMB)/2-methyltetrahydrofuran (MTHF) mixture glasses at 77 K have been measured. It is found that the magnitude of the photocurrent increases with decreasing MTHF concentration, which is ascribed to the increase in electron mobility with decreasing MTHF concentration in TMP/DMB/MTHF systems. It is also found that the photoconductivity spectra shift to the lower energy side with decreasing MTHF concentration. Although the photoconductivity spectrum in the neat MTHF system is separated from the corresponding optical absorption spectrum, the spectrum becomes closer to the latter with decreasing MTHF concentration in TMP/DMB/MTHF systems. This result indicates that the extent of bound–free transitions increases relative to bound–bound transitions with decreasing MTHF concentration for the photon absorption process of trapped electrons in TMP/DMB/MTHF systems.

The A2Πi–X2Πi absorption spectrum of BrO

1981 ◽  
Vol 59 (12) ◽  
pp. 1908-1916 ◽  
Author(s):  
M. Barnett ◽  
E. A. Cohen ◽  
D. A. Ramsay
Keyword(s):  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Ground State ◽  
Flash Photolysis ◽  
Absorption Bands ◽  
Long Wavelength ◽  
Numbering Scheme ◽  
Ozonized Oxygen ◽  
Good Agreement

Absorption spectra of isotopically enriched 81Br16O and of normal BrO have been obtained by the flash photolysis of mixtures of bromine and ozonized oxygen. Rotational analyses are given for the 7–0, 12–0, 18–0, 19–0, 20–0, 21–0, 7–1, and 20–1 A2Π3/2–X2Π3/2 sub-bands of 81Br16O. The value for [Formula: see text] is found to be 722.1 ± 1.1 cm−1 in good agreement with the value calculated from microwave constants. Several additional bands have been found at the long wavelength end of the spectrum, necessitating a revision of the vibrational numbering scheme for both the emission and absorption bands. "Hot" bands up to ν″ = 6 have been observed in the absorption spectrum for the 2Π3/2 component of the ground state but no bands have yet been identified from the 2Π1/2 component.

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