Peaks In Optical Spectra Research Articles

Effect of electric field on optoelectronic properties of indiene monolayer for photoelectric nanodevices

In recent years, layered materials display interesting properties and the quest for new sorts of two-dimensional (2D) structures is a significance for future device manufacture. In this paper, we study electronic and optical properties of 2D indiene allotropes with planar and buckled structures. The optical properties calculations are based on density functional theory (DFT) simulations including in-plane and out-of-plane directions of light polarization. We indicate that the optical properties such as complex refractive index, absorption spectrum, electron energy loss function (EELS), reflectivity and optical conductivity spectra are strongly dependent on the direction of light’s polarization. High values and narrow peaks in optical spectra introduce indiene to the field of ultra-thin optical systems. The effect of external static electric field on electronic and optical properties of indiene is also observed and discussed. We show that the band gap in buckled indiene can be effectively changed by applying the external electric field. The discoveries here expand the group of 2D materials beyond graphene and transition metal dichalcogenides (TMDs) and give valuable data for future experimental realization of new mono-elemental materials with conceivable applications in optical devices.

Excitonic effects and optical spectra of graphene nanoflakes

By solving the Bethe-Salpeter equation within the Hartree-Fock formalism, we study the optical spectra, optical gap, quasi-particle gap, exciton binding energy, and wave function of a closed-shell graphene system. With the excitonic effects fully taken into account, we find that all peaks of optical spectrum are blueshifted to higher photon energy with either the enhancement of the long-range Coulomb interactions or the suppression of the short-range Coulomb interactions but are redshifted to lower photon energy due to the increased size and decreased confinement. Remarkably, the region of a much higher relative probability for an electron resides mainly around the geometrical center of the structure, whereas the hole strongly localizes in the peripheral region of the geometric center. Our results are found to agree well with both recent experimental and theoretical works.

A DFT Study of the Strain Effect on the Optical Properties of Linear and Dimerized Titanium Nanochains

Optical properties of both linear and dimerized nanochains of titanium at different atomic distances are calculated using the full potential linearized augmented plane wave plus local orbital method, and using the generalized gradient approximation. When Ti nanochains were compressed, the position of critical points such as static dielectric constants and the main peaks in optical spectra shifted with an increased or decreased energy comparative to that at equilibrium constants. Under tensile strain e1max(ω) decreases in linear and dimerized structures. The plasma frequency for both structures decreases as the bond length increases. Moreover, the peaks of the energy loss function move toward higher energies with increasing bond length for linear structure, while they do not change significantly for the dimerized structure. The absorption for both nanostructures decreases by increasing the bond lengths.

Pressure dependence of the optical properties of α, β and ω phases of titanium

In this study, the pressure dependence of the optical properties of hexagonal close-packed, body-centered cubic and hexagonal phases of titanium was investigated using density functional theory. When Ti phases were compressed, the position of critical points such as equilibrium constants, static dielectric constants and also the main peaks in optical spectra shifted with an increase or decrease in energy compared to that at zero pressure. The imaginary dielectric function of all the phases under normal pressure and hydrostatic pressure was calculated. Under hydrostatic pressure, the optical conductivity of α phase increased, and the main peaks moved toward higher energies. Moreover, our results showed that the optical properties of α and ω phases change more than those of β phase. It was also demonstrated that the intensity of peaks of the energy loss function increased from α to β and decreased from β to ω. The optical reflectivity and absorption coefficient increased under pressure effects.

Double quantum well in a semiconductor microcavity: Three-oscillator model and ultrafast radiative decay.

A complete study of excitons in double quantum wells embedded in a semiconductor microcavity is presented. In the strong coupling regime we predict the possibility of observing three peaks in optical spectra when the two quantum well excitons have different resonance energies, and discuss the best structure parameters for observing this phenomenon. In the weak coupling regime we show that a radiative lifetime as short as \ensuremath{\approxeq}100 fs can be obtained by taking advantage of the coherence between the wells in addition to the microcavity effect. This ultrashort radiative lifetime is shown to be observable even in the presence of disorder.

Relations among theories of excitation transfer. II. Influence of spectral features on exciton motion

The generalized-master-equation (GME) theory of excitation transfer is applied to the standard model of linearly interacting excitons and phonons, the spectral prescription for memory functions given by Kenkre and Knox is verified for the model, peculiarities of memory functions pertinent to isolated versus open systems are analyzed, and exciton transport relevant to representative memory functions is studied. Physical relations are established between the GME theory and the stochastic-Liouville-equation theories, thus completing the author's earlier formal study of these relations. The influence of spectral features on exciton motion is analyzed in detail and it is shown that the presence of zero-phonon peaks in optical spectra is an indication of long-time coherence in exciton motion. Criteria for the validity of theories in the context of a given real system are developed on the basis of the spectral analysis.