The Influence of Hydrostatic Pressure on the Binding Energy of Hydrogenic Impurity State in a Wurtzite AlyGa1-yN/AlxGa1-xN Parabolic Quantum Well

The influence of hydrostatic pressure on the binding energy of hydrogenic impurity state in a wurtzite AlyGa1-yN/AlxGa1-xN parabolic quantum well and GaN/AlxGa1-xN square quantum well are studied using the variational method. The ground-state binding energies are presented as the functions of hydrostatic pressure, well width, composition and impurity center position. The anisotropic properties of the parameters in the system, and the changes (dependence) of electron effective mass, the dielectric constant, band gap with pressure and coordinate are considered in the numerical calculations. The results show that the hydrostatic pressure has obvious influence on the binding energy. The binding energy increase slowly with increasing the hydrostatic pressure p and the composition x, while the binding energy decrease significantly with increasing the well width and the position of impurity center. It is seen that the changing trends of the binding energy as a function of well width, pressure and the composition in the AlyGa1-yN/AlxGa1-xN parabolic quantum well are basically the same with that in the GaN/AlxGa1-xN square quantum well, but the changing trends of the binding energy as a function of impurity center position in the AlyGa1-yN/AlxGa1-xN parabolic quantum well are significantly greater than that in the GaN/AlxGa1-xN square quantum well.

The Effects of Doping on the Electronic Characteristics and Adsorption Behavior of Silicon Polyprismanes

Quantum–chemical calculations of the electronic characteristics of carbon and boron-doped silicon polyprismanes were carried out, and the atomic hydrogen adsorption on these structures was analyzed. It was established that silicon polyprismanes doped with boron and carbon retained their metallicity predicted earlier. It was shown that the doping of polyprismanes made them more thermodynamically stable. For the silicon prismanes doped with boron or carbon, hydrogen adsorption was found to be energetically favorable. In the case of boron-doped prismanes, adsorption on the boron impurity was much more advantageous than on the neighboring silicon nodes. For the carbon doping, the adsorption energy of polyprismane with a small diameter weakly depended on the position of the hydrogen atom near the impurity center. However, for the C-doped polyprismanes with a larger diameter, the hydrogen adsorption on the silicon atom belonging to the ring with impurity is more energetically favorable than the adsorption on the silicon atom from the adjacent ring.

Электронные состояния доноров V группы в германии: вариационный расчет с учетом короткодействующего потенциала

In the framework of the envelope function approximation, the wave functions of low-lying 1s(A1), 2s, 2p0, 2p±, 3p0 states of shallow donor centers P, As, Sb in germanium are calculated considering the short-range part of the impurity potential. The latter is constructed individually for each impurity, taking into account the spatial dispersion of the dielectric function and the difference between the ionic cores of germanium and the impurity center. The envelope function equation was solved using the Ritz variational method, and selected trial wave functions of the orbitally non-degenerate s-states are characterized by two spatial scales: the first one is of the order of the donor effective Bohr radius and corresponds to the long-range part of the potential, and the second one, which is an order of magnitude less, simulates the electron response to the short-range part of the donor potential. The electron density in the donor ground state is shifted to the nucleus due to the attractive “central cell” correction. The envelope functions of p-states, in turn, are constructed in such a way they are orthogonal to the ground state envelope functions for each impurity center, and, unlike previous works, are different for various donors.

Combined micro X-ray absorption and fluorescence spectroscopy to map phases of complex systems: the case of sphalerite

Combining micro-X-ray absorption spectroscopy (μXAS) and micro-X-ray fluorescence spectroscopy (μXRF) is a promising approach for the investigation of complex multi-phase systems. In this work, we have employed this approach to investigate natural sphalerite, the most common form of Zinc Sulfide. Spatially resolved elemental distribution maps of common 3d metal atoms (Zn, Cu, Ni, Co, and Fe) are superimposed with chemical speciation and structural parameter maps in order to understand the sphaleriteore-formation process and metamorphosis. Chemical speciation and structural parameters have been obtained by analyzing the μXAS spectra collected in several representative points of the sample, after μXRF mapping. In the present case, this X-ray based approach has permitted to determine the spatial distribution of the Zn species in sphalerite. The presence of two main zincite and smithsonite inclusions has been established, with the latter located close to copper impurity center. Since copper is known to remarkably reduce the corrosion resistance of zinc, resulting in the formation of carbonate as the corrosion product, this implies a possible role of Cu in the growth of the carbonate inclusions. The results obtained highlight the efficiency of this method in univocally identifying the spatial distribution of phases in complex systems, thanks to the simultaneous access to complementary information.

Статический и динамический вклады в расщепление основного состояния Eu-=SUP=-2+-=/SUP=- в SrMoO-=SUB=-4-=/SUB=-

The EPR spectrum of an Eu^2+ impurity center in a SrMoO_4 single crystal in the temperature range T = 1.8, 111–300 K has been studied, and the temperature changes in the spin Hamiltonian parameters describing the EPR spectrum of odd europium isotopes have been determined. It is shown that small temperature changes in the diagonal parameters of the spin Hamiltonian (for odd Eu^2+ isotopes) $$b_{2}^{0}$$ ( T ) = b _2( F ) + b _2( L ) and $$P_{2}^{0}$$ ( T ) = P _2( F ) + P _2( L ) are explained by the compensation of spin–phonon contributions b _2( F ) and P _2( F ) by the contributions of the lattice thermal expansion b _2( L ) and P _2( L ). The quantities b _2( L ) and P _2( L ) that are dependent on the static lattice parameters at a given temperature, are estimated in terms of the superposition Newman model. Then, the spin–phonon b _2( F ) and P _2( F ) contributions determined by the lattice ion vibrations are separated. An analysis shows that $$b_{2}^{0}$$ ( F ) and $$P_{2}^{0}$$ ( F ) > 0, b _2( L ) and P _2( L ) < 0, and the temperature behavior of the spin–phonon contribution is well described by G. Pfister’s model of local vibrations.

Спектроскопия и кинетика люминесценции ионов Pr-=SUP=-3+-=/SUP=- в K-=SUB=-3-=/SUB=-LuSi-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=- : Pr-=SUP=-3+-=/SUP=-

Abstract—The luminescent characteristics of K_3LuSi_2O_7:Pr^3+ (1%), which is a promising optical material for the use as a scintillator, have been studied using a set of techniques. The luminescence spectra of K_3LuSi_2O_7:Pr^3+ (1%) contain two bands in the UV-range with peaks at 284 and 330 nm, which correspond intraconfigurational 5 d → 4 f transitions in the Pr^3+ ions. The radiation in the visible and near IR range (480–850 nm) has been represented by the intraconfigurational 4 f → 4 f transitions. The kinetics of 5 d → 4 f -luminescence contains a build-up stage (τ_rise ∼ 7–12 ns), nonexponential decay stage (τ_1/2 ∼ 60 ns), and a slow component of the μs-range when excited by high-frequency (∼8 MHz) synchrotron radiation of the X-ray range. The fast component of the decay (τ = 54 ns) dominates in the decay kinetics of luminescence along with the build-up stage while the contribution of the μs decay component is less than 0.5% at the excitation by an pulse electron beam (5Hz). The excitation spectra of d – f - and f–f -photoluminescence in the ultraviolet and vacuum ultraviolet range that are measured using synchrotron radiation reveal features that are caused by both intracenter transitions and processes related to the energy transfer from the intrinsic electronic excitations to the impurity center.