Electrostatic Model of Edge Luminescence of Heavily Doped Degenerate Semiconductors

We propose a model of the narrowing of a forbidden band due to doping of crystalline semiconductors with hydrogenlike impurities with allowance for the following factors: spatial fluctuations of an electrostatical potential, exchange interaction of majority charge carriers, screening of the minority charge carrier by a cloud of the majority ones, and also tunneling at the level of percolation. The dependence of the position of the edge luminescence band maximum on the concentration of impurities for the degrees of their compensation from a weak to an intermediate one has been calculated. The results agree with the experimental data for cryogenic temperatures in a wide range of change in the equilibrium concentration of electrons (holes).     

Preparation, Luminescence Properties, and Application of Scintillators Based on Lu3Al5O12:Ce Single‐Crystal Films

The possibility of obtaining scintillators with a high effective atomic number of the element Z _ef based on Lu₃Al₅O₁₂:Ce³⁺ singlecrystal films (SCF) on doping with La³⁺ and Sc³⁺ ions on Y₃Al₅O₁₂ substrates has been investigated. It is established that the SCF of (LuLaY)₃Al₅O₁₂:Ce³⁺ (Z _ef = 58.9 and = 6.67 g/cm²) does not rank below those of Y₃Al₅O₁₂:Ce³⁺ (Z _ef = 29 and = 4.52 g/cm²) in the conversion efficiency of radiation at the band with _max = 515 nm. This allows their use as screens of xray images with a space resolution of 0.75–1.00 m. It is suggested that in the SCF of Lu₃Al₅O₁₂ the isoelectronic impurities of lanthanum and scandium form radiative recombination centers of the type La_Lu, Sc_Lu, and ScAl as well as the centers Lu as a consequence of the effect of replacement of some Lu³⁺ ions by the La³⁺ ions to octanodes of the garnet lattice. The low efficiency of Ce³⁺ radiation in the SCF of (LuSc)₃(AlSc)₅O₁₂:Ce is explained by substantial losses due to excitation of the recombination luminescence in the UV region of the centers formed by the isoelectronic impurities of scandium and to the possible existence of the channel of energy excitation dissipation related to the transitions between extrema of the allowed energy bands and activator levels.     

Absorption Spectra of Pentamers of Tetrapyrrole Compounds in Aqueous Solutions

Pentamers of two types have been obtained in aqueous solutions containing mixtures of two tetrapyrrole compounds, in whose molecules there are positively or negatively charged peripheral groups. The pentamers of one type include one molecule of mesotetra(4Nmethylpyridyl) porphin (TMPP) and four molecules of the complex of mesomono(nsulfophenyl)etioporphyrin II with palladium (PdSPhEP), and the pentamers of the other type include one molecule of sulfonated phthalocyanine (PCS) and four molecules of TMPP. The absorption bands of the pentamers are broadened and shifted toward longer wavelengths in comparison with the bands obtained as a result of the addition of the spectra of the monomers. It seems that the changes in the absorption spectra are first of all due to the change in the interaction of the molecules of the pigments with the molecules of the surrounding in formation of associates and due to the influence of the resonance dipoledipole interaction between the molecules in the associates. The influence of the intermolecular photoinduced charge transfer is also possible (it is most probable for the associates with PCS). We have revealed an effective quenching of the fluorescence of PCS and TMPP solutions upon heteroassociation.     

Electron Energy Loss Spectra of the Organic Complexes of Europium

In the electron energy loss spectra (EELS) of the organic europium complexes Eu³⁺ (BTFA)₃TPPO and Eu³⁺(BrBTFA)₃TPPO in a gas phase obtained on excitation by monokinetic beams of electrons of different energies in the range 12–50 eV, we have identified the bands associated with the electron transitions S ₀–S ₁, S ₀–S ₂, and S ₀–S ₃. The connection of these transitions with the structural groups of the complexes is established. The addition of the bromine atom to the phenyl ring of diketonate leads to the rise in the relative intensity of the S ₀–S ₂ band. The singlettriplet transitions manifest themselves in the region 2.5–3.2 eV and contribute to the S ₀–S ₂ band of the electron energy loss spectra.     

Influence of Close‐Range Dipole‐Dipole Interactions on the Real Part of the Susceptibility of a Dense Resonance Medium

Based on a solution of the stationary modified Bloch equations, an investigation is made of the influence of the effect of internal optical bistability (IOB) on the behavior of the refractive index of a dense resonance medium as a function of the constant b of closerange dipoledipole interactions, frequency detuning, and the intensity of optical radiation. The conditions of existence of the IOB effect of the system dense resonance medium + optical radiation are found and the dynamics of the loop width of the hysteresis dependence of the population difference of the resonance levels of the medium on the characteristics of the system is traced. The domains of the parameters are determined in which the effects of selffocusing and selfdefocusing of the radiation propagating in a dense resonance medium can take place.     

Luminescence of Tm3+ Ions in Yttrium Oxide

The concentration and temperature dependences of the blue luminescence intensity of the Tm³⁺ ion in yttrium oxide under UV and IR excitation have been measured. We made a proposal that the main role in the formation of these dependences is played by the interionic cross relaxation of excited states of Tm³⁺; the presence of admixed secondary rareearth ions can strongly influence the shape of the temperature dependence of the antiStokes luminescence intensity, displacing the position of its maximum. It is shown that the quenching action of admixtures under Stokes and antiStokes excitation shows up differently because of the differences in the mechanisms of population of the luminescent level.     

Kinetics of the Decay of Prolonged Luminescence of Disordered Chrysene under the Conditions of Nonequilibrium Transfer of Energy

We present the results obtained in investigation of the decay of the prolonged luminescence of disordered chrysene in a microsecond range. At the temperature of liquid nitrogen, a highly nonexponential decay of both phosphorescence and annihilation of delayed fluorescence is observed. The observed character of decay is due to relaxation of the energy of electronic excitation in a system of energydisordered centers, when the value of kT is much smaller than the width of the excitedstate energy distribution. At the same time, in the system investigated there is a classical relationship between phosphorescence and delayed fluorescence, i.e., the rate coefficient for the reaction of triplettriplet annihilation is a constant.     

Specific Features of Light Scattering in [N(CH3)4]2CuCl4 Crystals with an Incommensurable Phase

We present the results of investigation of the optical birefringence and intensity of the main light beam that passed through an [N(CH₃)₄]₂CuCl₄ crystal under the conditions of viscous interaction of the incommensurable structure with defects. A nonmonotonic temperature dependence of the basic signal is revealed. The observed temperature dependence of the intensity (in the form of irregular steps) is related to different periods of the incommensurable structure. In transitions between adjacent metastable states the periodicity of the incommensurable structure changes. It is shown that in transition regions for the central beam one observes an anomalous decrease in the light intensity due to the appearance of a perturbation lattice with the wave vector q.     

Amplification Coefficient of the Anti‐Stokes Component of Raman Scattering

The theory of intracavity parametric interaction of the components of Raman scattering is developed in the prescribedintensity approximation, which takes into account the reverse reaction of the excited waves to the pumpingwave phase. It is shown that one can substantially improve the conversion efficiency or the amplification coefficient of the antiStokes component by selection of the intracavity geometry, the optimum phase relation between the interacting waves, the pumping level, and the phase mismatch.     

Equations for the Magnetization Modes in a System Having a Quadruple Nucleus with the Spin S = 1

Within the framework of the method of a density matrix, differential equations are obtained that describe the evolution of the modes of magnetization <Î₊>, <Î_{+ z} >, and <Î_{+ z} ²> for a spin system containing a nucleus with a 1/2 spin connected scalarly with the quadruple nucleus of the spin S = 1 in the presence of crosscorrelation between the dipole ISinteractions, anisotropy of the chemical shift of the I and S nuclei, and quadruple interaction of the S nucleus. The equations are used for analysis of the evolution of the intensities of each line in the triplet of the Raman spectrum of the 1/2 spin. Expressions for the times of crossrelaxation and the times of transverse relaxation of each of the lines of the triplet are obtained.     

Concentration Effects Manifesting Themselves in the Luminescence of Tm3+ Ions in an Oxychloride Matrix

We investigated the luminescence characteristics of Tm³⁺ ions depending on their concentration in an oxychloride matrix. We measured luminescence spectra, luminescence excitation spectra, concentration dependences of the intensity and kinetics of various luminescence bands of rareearth ions of the visible and IR ranges at different excitation wavelengths. We carried out calculations of the concentration dependences of the quantum yield of luminescence: total and individual spectral bands. The crossrelaxational nature of concentration effects in the luminescence of rareearth ions is discussed.     

Infrared Spectroscopic Study of N,N‐Dimethylthioformamide Complexes of the Hofmann Type

Four new Hofmanntype complexes, M(DMTF)₂Ni(CN)₄, (where DMTF is dimethylthioformamide, M=Mn, Cd, Co, or Ni) were synthesized and their structure was determined by an elemental analysis and infrared spectroscopy. The IR spectra of DMTF and its nickel tetracyanine complexes with Mn(II), Cd(II), Co(II), and Ni(II) have been investigated within the range 4000–400 cm^–1. The frequency shifts in the metal complexes agree with the assignment of the CS and CN frequencies. The complexes consist of infinite planar polymer layers of |MNi(CN)₄|. Ndimethylthioformamide is coordinated to this layer from above and below; it is a monodentate ligand and is Sbonded through the metal atom in these complexes.     

Updated Analysis of Gallium Chelate and Vanadium Chelate Solutions with 4‐(2‐Pyridylazo)Resorcinol and Xylenol Orange

The characteristic factors of the gallium and vanadium chelates with the ligands 4(2pyridylazo)resorcinol (PAR) and xylenol orange (XO) have been determined with the aid of the principle of correction, which makes it possible to eliminate the influence of the surplus ligand in the solution of its chelate with methane (which makes calculation easier) and thereby provides a more acceptable method in comparison with others. The real molar coefficients of extinction of the chelates Ga and V with PAR and XO have been determined and a detailed calculation of the stoichiometric ratios of chelates has been made. The results have shown that the chelates formed have the following structure: Ga(PAR), Ga(XO), V(PAR)₂, and V(XO).     

Electroluminescence and Spectral Properties of N9‐Isobutyl‐2‐Oxo‐3‐Phenyl‐3N‐Benzo[F]Chromene‐9‐Sulfonamide

Experimental data on the synthesis and spectral properties (UV, IRFourier, xray photoelectronic, and luminescence spectra) of the sulfonamide derivative of benzocoumarin in an isopropanol solution and in a film applied by thermal vacuum deposition (TVD film) are reported. The use of TVD films of the investigated substance as electroluminophors is shown to be promising.     

Application of the Method of Integral Equations to the Description of Brewster Reflection of Light From Discrete‐Structured Media

A theoretical explanation is given to the experiments on Brewster reflection of light from the surface of certain liquids on the basis of the nearfield effects in a transitional layer. The consideration was carried out within the framework of the concept of a discretecontinuous dielectric in which the fields of the dipoles of discretely distributed atoms inside the Lorentz sphere surrounding the observation point are taken into account.     

Specific Fluorescence Properties and Picosecond Transient Absorption of 8-Azasteroids

The specific fluorescence properties as well as picosecond transient absorption features have been studied for two 8-azasteroids. It is shown that at various excitation wavelengths the essentially different final excited electronic states are realized. Because of the multicenter character of 8-azasteroids the spectroscopic data obtained may be analyzed on a basis of the mesomeric tautomerism model taking into account the dynamic combination of cis- and trans-configurations. The dependence of fluorescence spectral characteristics on the solvent nature is a manifestation of intermolecular H-bond interactions.     

Calculation of Out‐of‐Plane Vibrations of a Porphin Molecule

Using the DFT/B3LYP method with the base set 631G^**, we carried out calculation of the frequencies of the normal vibrations of porphin and of its five isotopic types. Scaling of force constants for outofplane vibrations has been performed in independent natural coordinates. The symmetry coordinates are introduced and a force field for outof plane vibrations of a porphin molecule in independent coordinates of symmetry is obtained. A new correlation of the frequencies of vibrations in the type of the symmetry B _1u for the isotopic type of the d ₂ porphin molecule is suggested on the basis of discrete analysis of the distribution of a potential energy.     

Synthesis of peptidomimetics using a polymer-bound Boc-linker

Boc-resin-bound -hydroxy--amino-aldehydes are accessible starting from N-terminally bound amino acidesters by using Dondoni's C₁-homologationreaction sequence. The conversion of these synthons totwo different peptide mimetics – 2-hydroxy-1,3-ethyl-diamines and -hydroxy--amino-vinyl sulfones – hasbeen investigated. The successful transfer of thecomplex -amino acid homologation reactionsequence into solid-phase chemistry demonstrates thepotentials of the Boc-resin for synthesis of peptidomimetics.     

Microwave Photonic Signal Down‐Conversion Using a Novel Two‐Frequency Bragg Grating Based Brillouin Fiber Laser

A simple technique using a novel twofrequency Bragg grating based Brillouin fiber laser to downconvert high frequency microwave photonic signals is presented. The mechanism of the Brillouin fiber laser and the principle of this technique for microwave photonic signal downconversion are analyzed. The 12GHz microwave photonic signals are experimentally downconverted to 1.13GHz IF signal with the technique.     

Calculation of the Parameters of a One‐Coordinate Model of the VGaSAs and VGaSnGa Complexes in Gallium Arsenide

Experimental optical bands of the emitting complexes (a gallium vacancy with a donor at the nearest, from the vacancy, sublattice site) V_GaS_As and V_GaSn_Ga in GaAs are investigated in a wide temperature range. The parameters of a onecoordinate model of these centers are determined. A configurationcoordinate diagram of the V_GaS_As complex is constructed. Calculation of the field dependences of emission rates is carried out in terms of the parameters of the onecoordinate model of the V_GaS_As complex and the data obtained are compared with the results of experimental studies of the emission of electron holes from a deeplying center of the V_GaS_As complex.