Electronic Optical Transitions Research Articles

Electronic States and Optical Transitions in Solids

<i>Electronic States and Optical Transitions in Solids</i>

Theoretical calculations of the electronic structure and optical transitions of UF 6 and UF 5

The self-consistent-field Xα scattered wave (SCF Xα SW) approach to molecular orbital theory has been applied to the UF 6 molecule and to an assumed structure of UF 5 (in C 4v symmetry) to determine their electronic structures and optical transitions.

Optical properties of the(CuInSe2)1−x−(2ZnSe)xsystem

Optical electronic transitions were studied in the ${(\mathrm{CuIn}{\mathrm{Se}}_{2})}_{1\ensuremath{-}x}\ensuremath{-}{(2\mathrm{ZnSe})}_{x}$ system from 0.5 to 14 eV. The system crystallizes in the chalcopyrite structure for $x\ensuremath{\le}0.43$ and in the zinc-blende structure for $x\ensuremath{\ge}0.48$. The absorption edge was found to be direct for all the compositions and the energy gap varies with $x$ parabolically, without discontinuity at the structural transition. This dependence is associated with the substitutional disorder in the mixtures. Reflection measurements showed substantial differences between the compositions with the chalcopyrite structure and those with the zinc-blende structure. The additional peaks observed for the compounds with the chalcopyrite structure are ascribed to pseudodirect transitions which become allowed by zone folding. The optical constants in the visible and ultraviolet regions were determined from the reflection spectra by Kramers-Kronig analysis. The dependence of the absorption bands on composition and structure is discussed and possible assignments are suggested. The effective number of electrons per atom contributing, in the energy range studied, to optical transitions was calculated and was found to depend strongly on the amount of Cu $d$ electrons in the mixture as well as on the crystal structure.

Optical absorption and electronic transitions in MoO3 single crystals

Optical absorption and electronic transitions in MoO₃ single crystals

Group-theoretic analysis of the electron spectrum of semiconductors with a famatinite lattice

The topologlcal structure of the spectrum of famatinite charge carriers is investigated, the dispersion laws along the lines and planes and in the vicinity of the symmetry points of the Brillouin zone are formulated, and the zero slopes of the energy surfaces and selection rules for optical transitions of electrons are determined for semiconductors with a famatinite structure.

Complexes of trigonal symmetry involving hydride ions paired with trivalent rare earth ions in calcium fluoride

When hydrogen is diffused into calcium fluoride crystals which contain both rare earth (RE) and oxygen impurities, RE3+- H- complexes of trigonal symmetry, labelled T3, are formed. These centres have been detected by measurements of the infrared absorption from the localized vibrations of the paired H- (or D-) ions, and in the case of crystals containing Yb3+ ions these measurements have been correlated with EPR spectra and with optical electronic transitions. It is shown that the RE3+ and H- ions occupy nearest neighbour substitutional sites and that T3 is a simple modification of another trigonal centre, T1, which is sometimes present in crystals grown by the Czochralski technique. It is suggested that models proposed previously for T1 and for another centre of trigonal symmetry (T2) may be incorrect, and alternative proposals are put forward.

Electronic energy bands and optical transitions in tetragonal germanium dioxide

Electronic energy bands and optical transitions in tetragonal germanium dioxide

Electronic energy bands and optical transitions in tetragonal germanium dioxide

The electronic energy band structure of the tetragonal crystallographic modification of germanium dioxide (GeO 2) has been calculated by the APW method. Application of selection rules indicate only two allowed direct transitions at the center of the Brillouin zone which correlate with observed room temperature optical properties at the fundamental absorption edge in single crystals. The calculated band structure also predicts an indirect transition which, although not inconsistent with the optical data, cannot be completely verified without additional and more refined experimental work.

Temperature Dependence of the Width andgFactor of a Purely Electronic Optical Transition in MnF2

We report thermal broadening of the 18418-${\mathrm{cm}}^{\ensuremath{-}1}$ purely electronic transition in Mn${\mathrm{F}}_{3}$ split by an external magnetic field of 25 kOe. A differential broadening of the split line is observed, demonstrating the important role of Raman scattering of magnons as a mechanism for broadening this optical line at low temperatures. A temperature-dependent reduction of the effective $g$ factor is also observed. Calculations based on a simple model give satisfactory agreement with the observations.

Theory of optical properties of an excess electron in liquid helium

The excitation energies and cross sections for optical transitions of an excess electron in liquid 4He have been computed. The Raman cross section is found to be about 10 −29 cm 2, in disagreement with other estimates.

Optical spectra and electronic transitions in gallium phosphide crystals

Analysis of the long-wave edge of the self-absorption spectrum of gallium phosphide crystals not distorted by line structure at low temperatures enabled us to determine the characteristic parameters of indirect transitions. In GaP crystals of a different type the appearance of a discrete structure in the long-wave absorption edge is related to the localization of excitons near impurities of an unknown nature. This is confirmed by the appearance in these crystals of an intense green electroluminescence band at low temperatures.

Second-Order Optical Processes and Harmonic Fields in Solids

A consistent method has been developed to calculate induced electromagnetic fields and optical transitions of electrons in a solid, in response to an incident laser beam of (circular) frequency $\ensuremath{\omega}$. The analysis is based upon the independent-particle Schr\"odinger equation for electrons and Maxwell's equations for the electromagnetic fields. General expressions for linear and bilinear currents as well as second-order optical transition probabilities have been derived. It is shown that the second-order transition probability, which is proportional to the fourth power in the incident field, contains two different types of terms, describing double-photon transitions of the incident frequency $\ensuremath{\omega}$ and single-photon transitions of the harmonic frequency $2\ensuremath{\omega}$. An estimate has been made to show that in the case of centrosymmetric solids like metals, the relative contribution due to the single second-harmonic photon transition is of the order ${(\frac{{e}^{2}}{\ensuremath{\hbar}c})}^{2}\ensuremath{\ll}1$ in the optical region, compared with the double-fundamental-photon transition. However, in the case of solids lacking inversion symmetry, the contributions due to these two processes are estimated to be of the same order in magnitude.

Method of ``Magnetophotoselection'' of the Lowest Excited Triplet State of Aromatic Molecules

The unique intensity distribution as a function of the angles between the principal magnetic axes and the applied magnetic field of the Δm=±1 ESR transitions of a collection of randomly oriented photoexcited triplet-state molecules has been used as a magnetoselection device, to observe only the molecules whose principal magnetic axes are parallel to the magnetic field. The latter is possible because the shape of the derivative of the Δm=±1 ESR absorption curve gives special prominence to those resonant fields corresponding to transitions of molecules possessing a canonical orientation. Changes in the relative intensities of the derivative ESR lines of the magnetophotoselected collection of molecules were observed as a function of the angle between the external field and the polarization direction of the exciting monochromatic light. The results obtained for glasses of naphthalene-d8 and quinoxaline were analyzed in terms of the known ESR spectra and polarization of the electronic absorption bands; the conclusions agree very well with theoretical predictions. The known directions of polarization of the electronic absorption bands of phenanthrene-d10 were then used to assign the Δm=±1 ESR spectrum of phenanthrene-d10 in EPA glass at 77°K. The assignment is found to agree with the first-order spectrum calculated using the published D and E values determined from single crystal studies. A simple procedure based on the magnetoselection method, and making use of the symmetry properties of π,π* and n,π* states, is then outlined by which assignments can be made for randomly oriented aromatic hydrocarbon or N-heterocyclic molecules, of the Δm=±1 ESR lines corresponding to those molecules which have their molecular plane either perpendicular or parallel to the magnetic field. The polarization of the electronic transitions used to excite these molecules to their triplet states need not be predetermined. A discussion is given of the advantages of using the method of magnetophotoselection instead of the normal photoselection method (where optical luminescence is used for analysis) to such problems as the assignment of optical electronic transitions and the mutual orientation of donor and acceptor in triplet—triplet transfer processes.

Optical Spectra from Fast Ion Beams.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Spectra from Fast Ion Beams. Meinel, A. B. ; Bashkin, S. Abstract Bashkin and Meinel have explored the method proposed by Bashkin to use a van de Graaff accelerator as a source of optical electronic transitions in ionic species. The production of excited states is by stripping a fast beam of ions by means of a carbon foil of a few micrograms per square mm thickness. The foil strips the ion of additional electrons and produces, with a high probability, an ion with residual electronic excitation. Upon decay of these states an emission spectrum is produced. The spectrum, moreover, shows a decay of intensity with distance downstream from the foil that is in general different for each emission wavelength. This fact offers in principle a means for directly observing the lifetimes of excited electronic states in atoms and under certain conditions the measurement of absolute oscillator strengths. Our first experiments with C, N, and 0 species at energies of the order of 1 MeV yielded an emission spectrum that showed a remarkable similarity in the line intensities to the spectra of novae, encouraging us to feel that we have a new laboratory tool of considerable precision to investigate properties of spectra of importance in some types of astronomical objects. A van de Graaff accelerator has recently been added to the facilities of the Department of Physics in Tucson, where experimental studies are being continued. The assistance of the staff of the Naval Research Laboratory and the use of their 5 MV van de Graaff accelerator is acknowledged in this work. Publication: The Astronomical Journal Pub Date: October 1964 DOI: 10.1086/109496 Bibcode: 1964AJ.....69S.552M full text sources ADS |

The Assignment of Quantum Numbers for Electrons in Molecules. I

The Assignment of Quantum Numbers for Electrons in Molecules. I