Transitions In Optical Spectra Research Articles

Optical properties of stepped InxGa1−xAs/GaAs quantum wells

The presence of a ternary alloy as well material in InxGa1−xAs/GaAs(001) strained quantum wells introduces a disorder mechanism by which the optical selection rules for symmetric wells may be relaxed and forbidden transitions usually appear in optical spectra. Strain and alloy disorder are studied as a function of well thickness and indium concentration in noninteracting double quantum wells of InxGa1−xAs/GaAs(001). Optical spectra are compared with an accurate Wannier exciton model. The agreement between theory and experiments points out that the optical selection rule for symmetric wells is restored in “high quality” and rather thin quantum wells. Finally, the presence of forbidden transitions in optical spectra is used as a fingerprint of nonhomogeneous indium concentration in thick quantum wells. This property is promising in order to study indium composition for well thicknesses in the range of quasi-two-dimensional behavior of the Wannier exciton.

Interband optical transition spectra in GaAs quantum wires with rectangular cross sections

Interband optical transition spectra of rectangular GaAs quantum wires (QWR's) of various cross-sectional sizes are experimentally and theoretically studied. High-quality GaAs QWR's with lateral sizes below 20 nm are formed in AlAs trench structures with (110) vertical sidewalls by using metal-organic chemical vapor deposition. Polarization-dependent photoluminescence excitation (PLE) spectra in the QWR's clearly exhibit absorption peaks corresponding to optical transitions between quantized one-dimensional conduction and valence subbands. It is found that transition strengths and polarization anisotropies in the lowest- and higher-energy PLE peaks significantly vary, depending on the cross-sectional shape of the rectangular wires. The polarization-dependent interband transition matrix elements and the detailed absorption spectra are calculated by a multiband effective-mass theory considering heavy-hole and light-hole subband mixing. The theoretical results clarify the physical origin of observed PLE peaks and explain the strong dependence of interband transition properties on the cross-sectional ratio of QWR's.

Magneto-optics in a square-well quantum dot.

We calculate the optical transition coefficient of two electrons confined in a square-well quantum dot under a magnetic field. We determined that there are many different types of absorption, some induced when interacting electrons are under a magnetic field. As the magnetic field becomes strong, a spin-singlet--spin-triplet transition of the ground state occurs, resulting in a drastic change in optical transition spectra. In a strong magnetic field, an optical transition with double the cyclotron frequency is induced by electron-electron interaction and the confining potential. \textcopyright{} 1996 The American Physical Society.

FIR spectroscopy of the intra-Landau level excitations of strongly correlated quantum dots

By directly diagonalizing the many-body interacting Hamiltonian for two model confinement potentials, we calculate the dipole-allowed optical transition spectra for a few electrons confined in a small quantum dot subjected to a strong external magnetic field. We find substantial many-body corrections to the optical transition energies for quartic and flat-bottomed-parabolic confinement in contrast to the well-studied purely parabolic confinement, where optical transitions are known to be unaffected by interaction effects by virtue of the generalized Kohn's theorem.

A tight-binding study of energy levels of iron in SrTiO3

Using a tight-binding parametrisation of the band structure of SrTiO3 together with the Green function method, the authors calculate the energy levels of the Fe5+, Fe4+, Fe3+ and Fe2+ ions, with and without spin polarisation. The shape of the optical transition spectra is deduced and the results are compared with experimental results. A comparison is also given with a previous X alpha calculation.

ChemInform Abstract: OPTICAL AND ELECTRICAL PROPERTIES OF YTTRIA STABILIZED ZIRCONIA (YSZ) CRYSTALS

AbstractMit Hinweis auf vielfältige Anwendungen von YSZ (durch z.B. 9.5 mol‐% Y2O3 stabilisierte kubische Hochtemp.‐Phase von ZrO2) als "Diamant‐Ersatz" (hohe Werte für Brechungsindex, Dispersion, Härte),als hochfeuerfestes Material für Brennstoffzellen, für Laser, Linsen, IR‐ und O2‐Sensoren etc. wurden kommerzielle YSZ‐Einkristalle spektral (Transmission für 0.3‐5.0 um) und bez. Leitfähigkeit (25‐l0O0 °C) untersucht.