Production and characterization of refractive index gratings in high-birefringence fibre optics

In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar⁺ ion laser, whereas for rocking filters formation the visible Ar⁺ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented.     

Electrostatic potentials of molecules and prediction of the lewis acid-base properties of solvents,part I. General considerations

Summary Electrostatic potentials in the vicinity of isolated molecules of typical nonaqueous solvents were computed in the MNDO approximation. It was found that the calculated dipole moments are in good agreement with experimental values. However, it turned out that in many cases electrostatic interactions of ions with solvent molecules cannot be described in the frame of ion-dipole interactions. Thus, two computable parameters,UN andUP describing short-range electrostatic interactions of a solvent molecule with a cation or an anion of radiusR were proposed. The dependence ofUN andUP uponR is analyzed in the context of ion-solvent interactions.

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Elektrostatische Potentiale von Molekülen und Voraussage von Lewis-Säure-Base-Eigenschaften von Lösungsmitteln, 1. Mitt.: Allgemeine Grundlagen

Zusammenfassung Es wurden die elektrostatischen Potentiale in der Umgebung von isolierten Molekülen typischer nichtwäßriger Lösungsmittel in der MNDO-Näherung berechnet. Die berechneten Dipolmomente waren in guter Übereinstimmung mit den experimentellen Werten. Es wurde jedoch beobachtet, daß in vielen Fällen die elektrostatischen Wechselwirkungen von Ionen mit Lösungsmittelmolekülen nicht im Rahmen von Ionen-Dipol-Wechselwirkungen beschrieben werden können. Dafür wurden zwei berechenbare ParameterUN undUP zur Beschreibung von elektrostatischen Wechselwirkungen im Nahbereich eines Lösungsmittelmoleküls mit einem Kationen- oder AnionenradiusR vorgeschlagen. Die Abhängigkeit vonUN undUP vonR wurde im Zusammenhang von Ionen-Solvens-Wechselwirkungen untersucht.

     

Microsolvation of the [Ni(acac)(tmen)]+ complex

Microsolvation of the [Ni(acac)(tmen)]⁺ complex by a series of aliphatic n-alcohols (Solv) has been studied in ClCH₂CH₂Cl solutions by spectrophotometry. Based on the changes in the electronic spectrum of the afore-mentioned complex, observed under the influence of any alcohol, the equilibrium constants for the formation of the [Ni(acac)(tmen)Solv]⁺ and [Ni(acac)(tmen)Solv₂]⁺ species have been computed according to the algorithm presented in this work. It was found that, in all the systems studied, the stability of five-coordinated [Ni(acac)(tmen)Solv]⁺ is higher than that of octahedral [Ni(acac)(tmen)Solv₂]⁺. The resulting values are discussed in terms of the Lewis basicity of alcohols.     

Electrochemical studies of Tl(I) crown-ether complexes in nonaqueous media

Summary Complexation equilibria of the Tl(I) ion with 18-crown-6 and dibenzo-18-crown-6 were studied polarographically in 10 nonaqueous solvents. The stability of the complexes is strongly influenced by the nature of solvents and varies with their Lewis basicities. It has been found that the logK _s value (K _s is the stability constant of the complex) can be well described by empirical relation logK _s=a DN+b, whereDN stands for the Gutmann donor number anda andb mark the regression coefficient. Addition of the second explanatory parameter, the acceptor number, is not statistically significant. This result is in agreement with the predominant role of Tl(I) ion solvation.

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Elektrochemische Untersuchungen von Tl(I)-Kronenetherkomplexen in nichtwäßrigen Medien

Zusammenfassung Es wurden die Komplexierungsgleichgewichte des Tl(I)-Ions mit 18-Krone-6 und Dibenzo-18-krone-6 polarographisch in 10 nichtwäßrigen Lösungsmitteln untersucht. Die Stabilität der Komplexe wird sehr stark vom Solvens beeinflußt, wobei eine starke Abhängigkeit von der Lewis-Basizität beobachtet wird. Es wurde festgestellt, daß die logK _s-Werte (K _s ist die Komplexstabilitätskonstante) gut mit der empirischen Beziehung logK _s=a DN+b beschrieben werden können, wobeiDN die Gutmann'sche Donorzahl unda undb die Regressionskonstanten bedeuten. Hinzunahme der Akzeptorzahl als zweiten Parameter bleibt statistisch insignifikant. Dieses Ergebnis stimmt mit dem dominierenden Einfluß der Tl(I)-Ionensolvatation überein.

     

Pressure dependence of the Davydov splitting in tetracene single crystals

The reflection spectrum of the OO component of the first singlet transition of tetracene single crystal has been measured as a function of pressure in the range 1 atm–6.5 kbar. A discontinuous change in the Davydov splitting occurs near 3 kbar confirming the existence of a pressure-induced first order phase transition discovered recently by measurements of the magnetic field anisotropy in the single crystal tetracene fluorescence. The pressure-induced spectral red-shifts are larger in the low-pressure (LP) phase than those in the high-pressure (HP) crystal structure. The Davydov splitting of the OO band however increases with increasing pressure at a larger rate of 57 cm^?1/kbar for the HP phase as compared with 46 cm^?1/kbar for the LP phase.     

Magnetic field effects on recombination radiation in tetracene crystal

Recombination radiation in tetracene crystal is shown to be modified by the application of a magnetic field. Relative variations of radiation intensity with field and orientation can be explained in terms of molecular singlet fission and triplet exciton-charge carrier interaction.     

Polarographic study of Tl+, Li+, Na+, K+, and Cs+ complexes with monensin anion in dipolar aprotic solvents

Summary The stability constants,K _sof monensin complexes with Li⁺, Na⁺, K⁺ and Cs⁺ ions were studied by a competitive polarographic method using the Tl⁺/Tl(Hg) redox couple as a sensitive electrochemical probe. TheK _svalues are strongly influenced by the solvents (acetonitrile, propionitrile, acetone, N,N-dimethylformamide, N-methyl pyrolidinone, N,N-dimethylacetamide, dimethylsulfoxide, N,N-diethylformamide and N,N-diethylacetamide were used in experiments) and vary inversely with the Gutmann donicity scale. Molecular mechanics computations revealed the probable structures of the complexes.

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Polarographische Untersuchung von Tl⁺-, Li⁺-, Na⁺- und Cs⁺-Komplexen mit Monesin-Anion in dipolaren aprotischen Lösungsmitteln

Zusammenfassung Es wurden die StabilitätskonstantenK _svon Monesin-Komplexen mit Li⁺-, Ma⁺- und Cs⁺-Ionen mittels einer competitiven polarographischen Methode unter Verwendung der Tl⁺/Tl(Hg)-Redoxelektrode als sensitiver elektrochemischer Sonde bestimmt. DieK _s-Werte werden stark vom Lösungsmittel (Acetonitril, Propionitril, Aceton, N,N-Dimethylformamid, N-Methylpyrrolidinon, N,N-Dimethylacetamid, Dimethylsulfoxid, N,N-Diethylformamid und N,N-Diethylacetamid) beeinflußt, wobei sie invers zurGutmann schen Donizitätsskala variieren. Die wahrscheinliche Struktur der Komplexe wurde mittels molekularmechanischer Berechnungen ermittelt.

     

High-field recombination electroluminescence in vacuum-deposited anthracene and doped anthracene films

The electroluminescence (EL) study of anthracene and tetracene-doped anthracene films deposited by a vacuum evaporation onto a substrate at temperatureT ₀=–60 °C is reported. Such films show high resistence to electrical breakdown so that their EL behaviour at high electric fields up to above 10⁶ V/cm could be investigated. The high-field EL is interpreted in terms of electron-hole recombination mechanisms with creation of emitting singlet excitons; the electron and hole concentration being limited by injection at metal contacts and by field-independent carrier velocities. The theoretical expression for current density follows the experimental data for fields above 4×10⁵ V/cm at room temperature and the EL intensity is predicted to be a power function of the measured current. It is suggested that in pure anthracene layers the power is determined by the contact injection conditions, i.e. by barrier heights and the effective masses of holes and electrons. In the doped films a guest molecules-induced energy trap distribution leads to a decrease of the power as confirmed by the experimental plots of the host EL intensity versus current density.The work supported in part by the Polish Academy of Sciences under Program MR.I.9     

Electronic spectrum of dibiphenylene-ethene radical anion

The electronic absorption spectrum for the dibiphenylene-ethene radical anion ( ), generated electrochemically in dimethylsulfoxide solutions, is reported. Based on calculations by the LCAO-MO method in theHückel approximation and on the analysis of the band positions it is suggested that in the molecule two planar fluorenylidene fragments are twisted (60°) about the central C=C bond.

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Das Elektronenabsorptionsspektrum des Dibiphenylen-Radikalanions (Kurze Mitteilung)

Zusammenfassung Das Dibiphenylenethen-Radikalanion ( ) wurde elektrochemisch hergestellt und das Elektronenabsorptionsspektrum aufgenommen. Auf Grund von LCAO-MO Berechnungen in derHückel-Annäherung und der Analyse der Bandenlagen wird nahegelegt, daß im -Molekül zwei planare Fluorenyliden-Fragmente ca. 60° um die zentrale C=C-Bindung verdrillt angeordnet sind.