On the Effect of Increasing the Radiative-Transition Rate Near a Nanosize Point

A short review of theoretical and experimental studies concerning the photoexcited florescence and Raman scattering of light for a substance in a space containing small material bodies is presented. Calculations of the radiativetransition probability for atoms (molecules) in the vicinity of bodies with a size much smaller than the light wavelength are performed. The probabilities of the singlephoton and doublephoton transitions are shown to increase by factors of 9 and 81 in the vicinity of a nanosize sphere with dielectric constant ||\ 1. The probability of a radiative transition in the vicinity of the vertex of a conic needle bearing up against a plane (both with || 1) increases by factors of (/R _in)² and (/R _in)⁴ for singlephoton and doublephoton transitions, respectively (R _in is the curvature radius for the needle vertex). This theoretical result is suggested as an explanation of the effect of increasing the radiation process intensity in the experiments carried out in the studies cited below.     

Influence of Solvent Polarity and Viscosity on Nonradiative Processes in Oligothiophenes with Intramolecular Charge Transfer

By the methods of luminescence, picosecond spectroscopy, and quantumchemical calculations the mechanisms of electron excitation energy deactivation in some oligothiophenes with intramolecular charge transfer depending on the solvent polarity and viscosity have been investigated. While for 2Npiperidino5(2,2dicyanovinyl)thiophene (PDCVT) the main channel of nonradiative deactivation is the transition to a lower intermediate state with a twisted double bond controlled by the medium viscosity, in the case of (E){2[25piperidino2thienyl]6(trifluoridemethyl)4H4pyranylidene}propanedinitryl (PTFDN) fluorescence quenching is initiated by the solvent polarity. For two other oligothiophenes, 2Npiperidino5cyanothiophene (PCT) and 2Npiperidino5cyanoterthiophene (PCTT), differing in the length of the thiophene chain, we have revealed, along with the effective quenching of fluorescence in shortchain PCT (independent of the solvent polarity and viscosity), an increase in the radiation capacity in PCTT with increasing polarity of the solvent. The possible mechanisms of nonradiative deactivation in the investigated oligothiophenes are discussed.     

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.     

Manifestation of Extracoordination in the Resonance Raman Spectra of Water‐Soluble Cation Co‐Porphyrins

Resonance Raman spectra (RRS) of Co(II) and Co(III)5,10,15,20tetrakis(4Nmethylpyridinium)porphyrin ((Co^II(TmpyP4), and Co^III(TMPyP4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies ₂, ₄, ₈, and ₆ — the markers of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For Co^III(TmpyP4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for Co^II(TmpyP4). The spectral effects observed are related to different electron influence of the extraligands on the system of the porphyrin ring. In the case of Co(III)porphyrin, interaction of the d orbitals of the metal and the e _g ^*orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)complex. For Co^III(TmpyP4), a linear correlation between the oscillation frequencies ₂, ₄, ₈, and ₆ and the experimental Gutmann parameters characterizing the electronacceptor properties of solvents is found.     

A Hydrodynamic Model of the Interaction of Picosecond Laser Pulses with Condensed Targets

We consider a physical model of the interaction of highpower laser pulses with plasma created upon irradiation of condensed targets. The model is based on the equations of singlefluid, twotemperature hydrodynamics taking into account the ponderomotive force, and the Maxwell equations for laser radiation at oblique incidence in the cases of s and ppolarizations. The model takes into account the generation of fast electrons in the conditions of plasma resonance at the critical surface, and their transport with consideration for the friction force, caused by the ionization losses. Heating of ions in the plasma due to beats of the ponderomotive potential is considered. The results of numerical modeling of the interaction of a picosecond laser pulse, containing a prepulse, with a deuterium target at power densities of 10¹⁶–10¹⁷ W/cm² are presented. It is shown that the neutron yield of the DDreaction decreases with increase in prepulse energy, because the plasma created inhibits heating of the dense region of the target where a high rate of the reactions can be realized. It is also shown that the laser radiation losses caused by the stimulated scattering increase with increase in prepulse energy.     

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.     

Quantum‐Chemical Investigation of Hydrogen Bonds in Porphin

Using the DFT Becke–Lee–Yang–Parr exchangecorrelation threeparametric functional (B3LYP), we have calculated the geometry, the electron density distribution, and the vibration frequencies for pyrrole, porphin, and their 13 analogs with a regularly varying structure. It is shown that the determining role in the change in the frequencies of stretching and outofplane deformation vibrations of porphin compared to pyrrole is played by intramolecular hydrogen bonds at the porphyrin macroring center. We have separately considered and compared with the data for porphin complexes of pyrrole with different intermolecular hydrogen bonds: with an aromatic ring (NH··· cluster formed by the pyrrole selfaggregation in the liquid state) and an unshared electron pair (NH···OH₂ and NH···NC₄H₄ clusters). The degree of participation of the NH group in the hydrogen bonds increases in the series NH··· cluster, porphin, NH···OH₂ and NH···NC₄H₄ clusters.     

Anti‐Stokes Luminescence of Cadmium Telluride Nanocrystals

For the first time, the antiStokes luminescence in colloidal solutions of CdTe nanocrystals on excitation below the absorption edge has been discovered. The maximum spectral shift to the shortwave region relative to the excitation energy E _con ^max = 319 meV is obtained for meansized nanocrystals (2.5 nm). The conversion efficiency of the absorbed radiant energy is 1.3·10^–2%. The rise in the antiStokes photoluminescence intensity with increasing temperature and the linear dependence on the exciting radiation intensity have been established. It is shown that the effect observed cannot be caused by twophoton excitation or by Auger recombination. It is assumed that the basic mechanism of the luminescence observed is the radiative recombination through the energy levels of the states attributable to the disturbance of the crystal structure in the nanocrystals.     

Spectral‐Luminescence and Generation Properties of 1‐Aza‐2‐Methyl‐6‐Aminopyrene and of Its Protolytic Forms

Spectral manifestations of protolytic forms of 1aza2methyl6aminopyrene in ethanol and aqueous solutions are investigated. The ionization constants of the protolytic forms are determined. The generation properties and photostability of a neutral molecule and a cation in excitation by an excimer XeCl laser are studied.     

Spectral Complex for Controlling the Parameters of the Plasmachemical‐Reactor Working Medium

An automated spectral complex for controlling the parameters of the plasmachemicalreactor working medium by the emission and absorption spectra in the 200–1100 and 2000–5000nm ranges has been developed. To record radiation, a CCD array and a pyroelectric detector are used. Control of the spectral device functions, data recording, and the obtaining of results reflecting the workingmedium parameters and the concentration in it of components being measured are carried out by means of a personal computer. The complex makes it possible to study the temporal behavior of the workingmedium parameters being measured with a resolution of up to 10^–2 sec.     

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.     

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.     

Stability of an SHF Discharge Running in a Resonator‐Type Plasmatron on the Basis of a Waveguide‐Slit Applicator

Using the method of optical emission spectroscopy, the dynamics of the development and extinction of a pulsating SHF discharge, its time instability, and the ranges of stable pressurerelated operation of a resonatortype SHF plasmatron on the basis of an annular waveguideslit applicator were investigated. It is found that at the pressures of CF₄ and its mixtures with oxygen optimal for breakdown a virtually complete lack of reproducibility of the signals of the components of the emission spectrum (in particular, of the FI 703.7nm line) from pulse to pulse of the discharge has been established. A discharge in oxygen in the investigated range of pressures and powers is characterized by a good repetition of the form of the pulses of the emission spectrum line (considered in relation to the OI 844.6nm line).     

Photoluminescence Spectra of ZnS:Al Crystals Annealed in a Melt with Bismuth and Chlorine Ions

The results of the temperature investigations (77–520 K) of the photoluminescence (PhL) of lowohmage ZnS monocrystals annealed in bismuthbased melts are presented. It is shown that the ion composition of the annealing medium produces a determining effect on the formation of an impuritydefect composition of the radiative centers. The dominant contribution to the PhL radiation is attributed to the centers based on the vacancies of sulfur and zinc and aluminum and chlorine. In the nearsurface region and in the bulk of the crystal, the PhL spectra differ. The PhL spectra in the nearsurface region of the crystal are determined by the complex bismuth centers and correspond to the characteristic features of the intracenter transitions. We propose two possible models of radiative centers: (V_Zn ^/Bi_Zn )^times and DX centers. It has been found that the simultaneous action of the radiation from a pulsed nitrogen laser and the heating at a temperature from 410 to 518 K destroy the radiative bismuth centers and lead to the formation of precipitates Bi₂S₃ and BiS₂.     

Formation and Photoluminescence Properties of Porous Silicon Produced in Iodine‐Containing Electrolytes

Samples of porous silicon have been produced and investigated for the first time by the method of anodizing in a modified iodinecontaining electrolyte. It is shown that the addition of iodine to the electrolyte, all other things being constant, substantially influences the formation of porous silicon and leads to the occurrence of photoluminescence in poroussilicon layers on highly doped substrates of silicon of the n ⁺type. The morphology of the surface of the produced poroussilicon samples has been investigated and a marked decrease in the inhomogeneity scale as compared to the nonluminescent porous silicon produced without iodine under the same conditions has been detected. Investigation of the dependence of the spectral properties of photoluminescence on the density of the anodizing current has shown that with increase in the current density the maximum of the photoluminescence spectrum shifts to the shortwave region and the halfwidth of the photoluminescence spectrum decreases.     

Monochromatization of synchrotron radiation for nuclear resonant scattering experiments

An introduction to monochromatization of synchrotron radiation in the energy range of 5–30 keV is presented for applications involving nuclear resonant scattering. The relevant relationships of the dynamical theory of Xray diffraction are used to explain basic concepts of monochromatization. These relations are combined with raytracing techniques to design highenergyresolution monochromators. Transmissionoptimized and energyresolutionoptimized designs that achieve high energy resolutions (10⁶)< E/E < 10⁸) are discussed separately. Practical silicon monochromators of both types are presented for a variety of nuclear resonances in this energy range.     

Spectral‐Luminescence Characteristics of Polyphenyls and Polyacenes in the Gas Phase in Electron‐Beam Excitation

The spectra of electronenergy loss, excitation functions, and fluorescence spectra in excitation of the vapor of polyphenyls and polyacenes by electron beams of different energies are determined. The influence of successive complication of the molecules under study on these spectralluminescence characteristics is tracked. Unlike the optical absorption spectra, in the spectra of electronenergy loss of all the substances studied one observes a band which is related to the singlettriplet transition S ₀–T ₁. The transitions up to S ₀–S ₅ are recorded in excitation of the molecules by highenergy electrons, including the region of vacuum ultraviolet. From the functions of fluorescence excitation the authors have determined the excitation thresholds that correlate with the energies of the S ₁ levels, except for pyrene in which the S ₀–S ₁ transition is forbidden and does not show up not only in photon excitation but also in electronbeam excitation, although the intercombination forbiddenness in the latter case is removed and the S ₀–T ₁ band is observed.     

Radiative Losses of Plasma on Interaction of Ultrashort Laser Pulses with Matter

Radiative losses of plasma produced by ultrashort laser pulses near the surface of solid targets were studied by the methods of highresolution xray spectroscopy and using the numerical simulation of gasdynamics and radiation processes. The experiments were carried out at the NEODIM laser facility in the Central Research Institute for Machine Building. The flux density was as high as 10¹⁷ W/cm² when the radiation was focussed onto the surface of solid targets from Al and Cu. The timeintegrated discrete spectra of plasma of the multiply charged ions were recorded in the soft xray band from 0.8 to 3.0 keV. The experimental spectra were compared with the results of numerical calculations within the framework of the model, which considered both hydrodynamic and radiationcollisional processes. The association of the radiation dynamics of the individual groups of lines with the spatial and temporal dynamics of the laser torch was revealed. Such an association permits one to judge the nonstationary processes in the expanding plasma even by the spectra integrated over time. From comparison of the experimental results and model calculations, it follows that the line emission of a relatively narrow (in the charge number) group of ions constitutes the major portion of radiation losses.     

On the Influence of “Speckles” of Laser Radiation on Plasma Parameters when Irradiating Aluminum Foils by a Picosecond Pulse

The influence of the inhomogeneity of target heating on the plasma behavior when irradiating a target by a superhighpower short laser pulse (with intensity above 10¹⁶ W/cm² and duration of about 10^-12 s) was studied on the basis of twodimensional numerical calculations. In the presence of the specklelike structures in the laserradiation flux, the plasma parameters and, in particular, the temperature were shown to be essentially different from estimates based on the mean intensity within the focusing spot.     

Spectroscopic, Phototropic, and Lasing Properties of Cd1−x Mn x Te Single Crystals Doped With Chromium Ions

The spectroscopic properties of Cr²⁺ ions in Cr:Cd_1–x Mn _x Te (CMT) crystals are studied, and the possibility of using these impurity crystals as active media and saturable absorbers of solidstate lasers of medium IR range is demonstrated. The bands of absorption with a maximum at 1.9 m and of luminescence with a maximum at 2.6 m correspond to the transitions between the levels ⁵ T ₂ and ⁵ E of the tetracoordinated Cr²⁺ ions with more than 1·10^–18cm² cross sections. The pulsed and continuous lasing modes of a Cr:CMT laser are realized in the 2.6m region. The Cr:CMT crystals are characterized by effective saturation of impurity absorption. The cross sections of absorption from the ground and excited states of the Cr²⁺ ions at = 2.09 m are determined: _gsa = 1.1·10^–18 cm²; _esa/_gsa < 0.1. With the use of the Cr:CMT crystals as a passive gate the regime of Qswitching of the Cr,Tm,Ho:YAG laser emitting at = 2.09 m is obtained.