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Abstract: The effects of the intense high-frequency laser field on the optical absorption coefficients and the refractive index changes in a GaAs/GaAlAs parabolic quantum well under the applied electric field have been investigated theoretically. The electron energy levels and the envelope wave functions of the parabolic quantum well are calculated within the effective mass approximation. Analytical expressions for optical properties are obtained using the compact density-matrix approach. The numerical results show that the intense high-frequency laser field has a large effect on the optical characteristics of these structures. Also we can observe that the refractive index and absorption coefficient changes are very sensitive to the electric field in large dimension wells. Thus, this result gives a new degree of freedom in the optoelectronic device applications. [Copyright &y& Elsevier]

[Display omitted] • SnSrO 3 nanoparticles prepared by the sonochemical method and solid-state reactions. • Study of rare-earth doping effects on the structure and photoluminescent properties. • XRD results confirmed the orthorhombic phase of SrSnO 3. • Near-white light emission from Sm3+, Tb3+ co-doped SnSrO 3 perovskites. Sm3+, Tb3+ co-doped SrSnO 3 perovskites were successfully prepared by the sonochemical method and solid-state reactions. X-ray diffraction showed well-defined peak characteristics of the SrSnO 3 orthorhombic phase, while SEM analysis revealed the formation of rod-like structures composed of particles with a mean size of 100 nm. Under the excitation of 325 nm, the photoluminescence spectra exhibited a broad emission band (380–500 nm) related to intrinsic defects and peaks attributed to characteristic electronic transitions of Tb3+ (5D 4 →7F 6 , 489 nm, 5D 4 →7F 5 , 542 nm) and Sm3+ (4G 5/2 →6H 5/2 , 570 nm, 4G 5/2 →6H 7/2 , 605 nm) ions. Through co-doping with these rare earths, the emission from perovskite can be tuned. The obtained chromaticity coordinates are (0.33, 0.31) and (0.34, 0.32) for 4Sm2Tb and 4Sm4Tb perovskites, respectively. It indicates the promising application potential of Sm3+, Tb3+ co-doped SrSnO 3 as single-phase perovskite for UV excited white light-diodes. [ABSTRACT FROM AUTHOR]

In this work, the electronic structure and the inter-subband absorption coefficient (IAC) are theoretically studied for symmetric double n -type δ -doped GaAs quantum well considering the donor impurity atom effect. The electron states are determined by a diagonalization procedure, working within the effective mass and parabolic band approximations, and the effect of donor center is treated via the variational method. Meanwhile, linear and nonlinear contributions for the inter-subband absorption coefficient were evaluated from expressions usually derived within the perturbative solution of the Von Neumann equation for density matrix. We report the impurity binding energy by considering a donor atom located at the center of the system (at z i = 0). We found that the reported physical properties become more sensitive to the inter-well separation distance L w than to the δ -doping density, N 2 d. In the former case the total optical absorption coefficient undergoes an important red-shift as well as a significant decrease in its magnitude. When N 2 d values increase, the binding energy exhibits a contrary effect, and the total optical absorption coefficient exhibits an small blue-shift with no significant changes in its magnitude. The presence of the donor impurity atom in the system represents one factor that can modify the location of inter-subband absorption coefficient, by inducing a blue-shift of the optical response. The resonant peak energies are within the range of several terahertz, showing potential device applications within this range of the electromagnetic spectrum. • The absorption coefficient for symmetric double n -type δ-doped GaAs is reported. • The absorption coefficient is more sensitive to the inter-well distance. • The δ-doping density does not affect significatively the absorption coefficient. • Donor impurity atom induces a blue shift in the original system. • Absorption coefficients are in the THz region of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

• Conical shaped quantum dots under electric and magnetic field. • Electron-hole Coulomb correlation via perturbative and variational calculations. • Several orders of magnitude for the ground state exciton lifetime. • Evolution from quantum dot to quantum ring via electric field effects. • Oscilations of the ground state energy via magnetic field effects. Using the effective mass and parabolic band approximations, and the finite element method, we calculate the combined effects of axially applied electric and magnetic fields on the electronic properties of cone-shaped quantum dots. Once the one particle eigenvalue equations have been solved, both for electrons and holes, the available information on energies and wave functions is used as input in order to calculate the electron and hole positions along the axial axis, the overlap integral, the ground state exciton lifetime, and the exciton Coulomb interaction; all these properties are obtained as a function of the applied electric and magnetic fields. The main findings are: (i) the electric field separates the electrons and holes in opposite positions of the structure, giving rise to indirect excitons with a quite significant lifetime, (ii) the magnetic field is a useful tool to increase by several orders of magnitude the exciton lifetime, mainly when it is superimposed on the electric field effect, (iii) for spatially direct excitons, the magnetic field reinforces the Coulomb integral giving rise to a redshift of the photoluminescence energy transition, (iv) the magnetic field effects are much more visible on electrons than on the holes, and finally (v) the electric field allows to tune the evolution of the structure from a quantum dot to a quantum ring. Our results on the photoluminescence energy transition are in excellent agreement with previously reported experimental measurements [Phys. Status Solidi RRL 2018 (2018) 1800245 (4pp)..]. [ABSTRACT FROM AUTHOR]

The down-shifting and down-conversion emission properties of novel CdO–P 2 O 5 invert glasses activated with Pr3+ and Pr3+/Yb3+ were respectively studied. The down-shifting emission spectra of Pr 6 O 11 singly doped glasses upon 443 nm excitation (Pr3+: 3H 4 → 3P 2), displayed the feature Pr3+ transitions in the visible and near-infrared (NIR) regions, reaching the optimum intensity at 0.7 and 0.3 mol% of Pr 6 O 11 , respectively. The emission tonality can be adjusted from the reddish-orange to orange-pink region, depending on the Pr 6 O 11 content. Such fact coupled with the superposition of the blue light excitation might be attractive for white light-emitting diodes (W-LEDs) applications. The cross-relaxation processes involved between Pr3+-Pr3+ pairs seem to be mediated by an electric quadrupole-quadrupole interaction, as revealed by the Inokuti-Hirayama model. The emission spectra of the Pr 6 O 11 and Yb 2 O 3 doped glasses upon 443 nm excitation showed, in addition to the Pr3+ related transitions, a band at 977 nm associated with the Yb3+: 2F 5/2 → 2F 7/2 transition, which gradually grows at expenses of non-radiative energy transfer from Pr3+. This process might lead to a down-conversion (quantum cutting) emission with theoretical quantum efficiencies up to 144%. Analysis complemented by the Inokuti-Hirayama or Dexter model revealed that the non-radiative Pr3+ → Yb3+ energy transfer process arisen from Pr3+: 3P 0 and 1D 2 levels are most likely dominated by electric dipole-dipole and quadrupole-quadrupole interactions, respectively. The global emission properties suggest that the Pr3+ and Pr3+/Yb3+ activated CdO–P 2 O 5 invert glasses might be interesting for WLEDs and crystalline silicon (c-Si) solar cell applications. • CdO–P 2 O 5 invert glasses were synthetized with suitable transparency. • Pr3+ activated CdO–P 2 O 5 invert glasses exhibited tonalities from the orange to orange-pink region. • Theoretical quantum yield values up to 128% were estimated in the Pr3+ and Yb3+ activated CdO–P 2 O 5 glasses. [ABSTRACT FROM AUTHOR]

In this work, we have investigated theoretically the impact of intense laser, electric and magnetic fields on the linear and nonlinear optical properties of a quantum well heterostructure containing triple parabolic barriers (GaAs/AlGaAs). Within the framework of the effective-mass and parabolic band approximations, we have computed the confined lowest energy levels and their corresponding densities of probability, through the use of a finite difference technique to solve the corresponding differential equation. Besides, we evaluate the total optical absorption (TOACs) and relative refractive index change (RRICs) coefficients. The obtained findings show that an increase of the intensity of the intense laser field produces a blue shift at first and then a red shift of the TOACs and RRICs. A specific value of the laser field separating the two kinds of signal displacements is outlined. Contrarily to the intense laser field, an increment of the external static electric and magnetic fields induces only a blue shift in the variation of the TOACs and RRICs. In addition, we have discussed in detail the variation of diagonal and non-diagonal matrix elements which are responsible on the variation of the amplitudes of the TOACs and RRICs. We think that the obtained results can be useful in the design of new device's generation employed in optoelectronic domain. [ABSTRACT FROM AUTHOR]

The asymmetric potential profiles are of great interest from the nonlinear optical properties point of view for semiconductor devices. The reason for this statement is because the existing theories on nonlinear optical properties obviously depends on the dipole matrix element for the involved transitions and an complete characterization for asymmetric potential profiles enables to the semiconductor device designers to have possible ranges of implementation and because the dipole matrix elements strongly depends on the asymmetry of the potential profile. Once the potential profile is well defined, with the desired range on operation, the external factors play also an important role on the optical properties tuning. In particular, in this paper we reported the absorption coefficient and the relative refractive index changes for semi-infinite inverse Gaussian-like profile for an Al x Ga 1− x As/GaAs quantum well when is subjected to a z -directed electric field, to an in-plane x -directed magnetic field and finally to a non-resonant intense laser field effect, being the Al concentration the parameter that allows to shape the potential profile. In general, we conclude that the external factor are an efficient way to tune the optical properties that are in the range of the THz spectrum, at least for the intersubband transitions reported here. • The semi-infinite inverse Al x Ga 1− x As/GaAs Gaussian-like profile is investigated. • Electric and magnetic fields induce a blueshift for optical properties in this system. • The non-resonant intense laser field produces a redshift for optical properties. • Intra-band optical properties are in the THz region of the electromagnetic spectrum. • Optical properties could be tuned by combined effects of the studied external fields. [ABSTRACT FROM AUTHOR]

• The BPO with adsorbed gas could be employed as gas sensor. • The O2 induced the transition from semiconductor to conductor of the BPO. • The single oxygen vacancy turns out to be more favorable for adsorption. We report a first-principles study of the electronic and optical properties of BPO (Blue phosphorene oxide) and BPO-V (Blue phosphorene oxide with vacancy) with the adsorption of low molecular weight gases (CH 4 , CO 2 , CO, SO 2 , and O 2). Blue phosphorene oxide -with and without vacancies- shows different optoelectronic compared to blue phosphorene. The BPO has proven to be more energetically, and structurally stable than blue phosphorene under ambient conditions. Our calculations show that: Blue phosphorene oxide -with and without vacancies- exhibits different optoelectronic compared to blue phosphorene. Physical adsorption occurs for all gas molecules. Highest values of adsorption energy are found when the monolayers interact with O 2 and SO 2. This is associated with a modification of conducting nature, which is changed from semiconductor to conductor character, depending on the orientation of adsorbed molecules. By contrast, the coupling with CO and CO 2 molecules leads to the lowest values of the energy of adsorption. The observed features of the electronic properties and optical response of BPO + adsorbed-gas complexes allow to suggest that this phosphorene-based structures could be promising candidates for gas sensing applications. [ABSTRACT FROM AUTHOR]

This work introduces the recent so called Bravais–Moiré theory in the context of two dimensional photonic crystals. In particular, new periodic cells involving commensurable bilayer rotated square alignments of photonic crystals with different permittivity constants are considered. The corresponding band gaps are wider than those usually reported in literature for square lattice dielectric structures, and a practical comparison is carried out in the calculation in order to verify such assert. These photonic gaps can be adjusted by changing different lattice parameters, such as the commensurable angle, and the permittivities involved. • Design of Bravais–Moiré 2D lattices. • Photonic structure of Bravais–Moiré dielectric structures. • Enhancement of photonic band gaps compared to square lattice crystals. • Use of dielectric combinations with GaAs, InAs, and SiO 2. [ABSTRACT FROM AUTHOR]

• DFT-based first principles calculation. • Electronic structure and optical properties of CuGaSe2. • Effects of uniaxial and biaxial strain. • Variation of refractive index with strain. In this study, we have investigated the effect of bi-axial, ϵ ab , and uni-axial, ϵ c , strains on the optoelectronic properties of chalcopyrite semiconductor CuGaSe 2 through first-principles full potential linearized augmented plane wave method. These materials have recently attracted much interest within the materials science community. The results are obtained in the framework of Density Functional Theory (DFT), using the Generalized Gradient Approximation based on the minimization of total energy, together with the modified Becke-Johnson exchange-correlation potential, as implemented in the WIEN2k code. Our results show that unstrained CuGaSe 2 is a direct band gap semiconductor with a energy of 1.16 eV, thus improving the results of some previous DFT calculations, but still below the accepted experimental data. The incorporation of biaxial and uniaxial strain results in a monotonous decreasing behavior of the energy band gap when both ϵ ab and ϵ c change between -8% and +8%, with unstrained value being, approximately, at the middle of the variation range. It is also found that strain causes modifications in the index of refraction of the material, with modifications of its static value that rank above 10% over the entire range of deformations considered. [ABSTRACT FROM AUTHOR]

The Schrödinger equation in the effective mass approximation is commonly used to calculate the electronic states confined in low-dimensional semiconductor structures. Three-dimensional calculations are unavoidable in the general case of asymmetrical quantum structures and the solutions are not analytical, thus demanding resource-consuming numerical methods. In particular cases, the formalism may be simplified by several approaches: neglecting the gradient of the effective mass, approximating the confinement potentials by simple functions, and exploiting the symmetries in order to reduce the dimensionality of the equation. Particular approaches rarely lead to full analytical solutions, but often to more-convenient, semi-analytical or numerical calculations. We revisit the adiabatic approach for using the Schrödinger formalism in axisymmetric and asymmetrical quantum dots by discussing its reliability as compared with the direct finite element method. We discuss how the difference between the results obtained from the two methods depends on the shape and the symmetry of the quantum structures. We show that adiabatic approach and direct finite element calculation involve similar levels of complexity and computing resources for axisymmetric quantum dots, while providing larger relative differences for flatter structures. On the contrary, for asymmetrical quantum structures, the adiabatic approximation has clearly an advantage regarding the use of computing resources, yet maintaining a high degree of accuracy. • Quantum dots with various shapes are studied and compared. • The effective mass approximation and the finite element method are used. • The adiabatic approximation works better for stronger confinements. • The adiabatic approximation is faster than the direct calculation. • The errors are discussed and compared. [ABSTRACT FROM AUTHOR]

• First-principles calculations of electronic states of BP-QD with H2P are carryout. • The optical response through the imaginary part of dielectric function is obtaineds. • The rotations of H2P with respect to BP-QD do not change the binding energy. Electronic and optical properties of phosphorene quantum dots functionalized with an organic molecule, porphyrin, are investigated using density functional theory with two different van der Waals functionals. The electronic structure of this complex is obtained and with this information, the real and imaginary parts of the dielectric function are calculated, from which, the interband optical response can be determined. Depending on the size of the quantum dot and the relative orientation between the dot and the organic molecule, it is found that the porphyrin physisorption leads to important modifications of the energy spectrum of the functionalized blue phosphorene quantum dots. These changes reflect in the optical response of the complex which shows features that come from both the blue phosphorene structure and the organic molecule. It is also found that the rotations of the molecule with respect to the phosphorene quantum dot do not practically alter the value of the binding energy. [ABSTRACT FROM AUTHOR]