Optic

Photoacoustic spectroscopy was used to study nitrogen-doped titanium dioxide film. The energy positions of defect and impurity centre levels are reported. The energy levels were obtained using the excitation method and the mechanisms of the photoacoustic signal generation are discussed. The visible light absorption of the yellow film was explained considering electronic transitions between localized states within the band gap and the transitions from these states into the conduction band. Moreover, first principles calculations revealed that nitrogen doping and oxygen vacancies in titanium dioxide induce defect levels within the gap which account for the absorption in the visible light.

We present calculations of the band structure, density of states and the real and imaginary parts of the dielectric functions in intrinsic TlN and AlN, both for wurtzite and the zinc-blende polytypes. They are based on the local density approximation (LDA) within the density functional theory (DFT), employing the first-principles, full-potential linearized augmented plane wave (FPLAPW) method. We correct the band gap of the AlN by using a quasi-particle method proposed by Bechstedt and Del Sole. The calculated energy gaps, lattice constants and dielectric constants for AlN are in good agreement with available experimental values while for TlN there is no experimental investigation.

This paper presents an investigation on the use of tomography system using using optical and electrodynamic sensors. The system obtains data from both sensors which detect the flow in a process pipe. Information on the flow is processed in order to display the image reconstruction of a solid flow.

The electronic band-edges of lead chalcogenides PbY and tin chalcogenides SnY (where Y = S, Se, and Te) are investigated by the means of a full-potential linearized augmented plane wave (FPLAPW) method and the local density approximation (LDA). All six chalcogenide binaries have similar electronic structures and density-of-states, but there are differences in the symmetry of the band-edge states at and near the Brillouin zone L-point. These differences give the characteristic composition, pressure, and temperature dependences of the energy gap in Pb 1Àx Sn x Y alloys.

We present calculations of the band structure, density of states and the real and imaginary parts of the dielectric functions in intrinsic TlN and AlN, both for wurtzite and the zinc-blende polytypes. They are based on the local density approximation (LDA) within the density functional theory (DFT), employing the first-principles, full-potential linearized augmented plane wave (FPLAPW) method. We correct the band gap of the AlN by using a quasi-particle method proposed by Bechstedt and Del Sole. The calculated energy gaps, lattice constants and dielectric constants for AlN are in good agreement with available experimental values while for TlN there is no experimental investigation.

The optical properties in terms of dielectric function ϵ (ħω) = ϵ1(ħω) + iϵ2(ħω) of rocksalt Pb1–xSnx Te alloys (0 ≤ x ≤ 1) are investigated experimentally by spectroscopic ellipsometry and theoretically by first-principles electronic band structure calculation. We find a strong optical response in the 0.5–2.0 eV region arising from optical absorption around the LW-line of the Brillouin zone. The response peak of the imaginary part of the dielectric functions at E = 1.6–1.8 eV shifts towards lower energies for high Sn compositions as a consequence of narrower W-point band-gap Eg(W) for the Sn-rich alloys. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The nitride semiconductors such as AlN, GaN and InN have good thermal and chemical stabilities that are important in technological applications. These compounds are currently being studied because of their great potential for telecommunications electronics, light emitting diodes and lasers . They can be used for emission of light in green, blue and ultraviolet regions of the light spectrum that were not previously accessible with solid state light emitters .

The optical absorption and the dielectric functions of PbI2 and Sb x Bi 1-x I 3 have been investigated experimentally by means of absorption measurements and spectroscopic ellipsometry respectively, and theoretically by a full-potential linear muffin-tin-orbital method. These materials have been recognized as very promising detector materials with large technological applicabilities. The calculated band-gap energies, optical absorption and the dielectric functions were found to be in a very good agreement with the experimental results. The electron-energy-loss functions are also obtained for both experiment and theory for comparison. The band-gap energy as a function of temperature, for PbI 2 has also been measured by optical absorption. The temperature dependence has been fitted by a new relation, and a discussion of this fitting is given.