Zur Frage der Pb(Il)-Komplexe in den Alkalichloriden

The absorption of bivalent lead in solutions of alkali chlorides of different concentration was studied. The absorption bands that occur were ascribed to the complexes of lead with chlorine. The agreement between absorption bands in crystals doped with lead and in sufficiently concentrated solutions shows that lead in crystals of alkali chlorides forms an octahedral complex with six neighbouring atoms of chlorine.

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Die Verfasser sprechen Frau Z. Pecháková für ihre wirksame Hilfeleistung bei den Absorptionsmessungen ihren herzlichen Dank aus.     

Luminescence and lifetime characteristics of microphases in KCl:KI:Pb mixed crystals

Absorption and luminiscence measurements were performed on lead-doped KCl:KI mixed single crystals. Strong differences were found between as-grown and quenched samples. New bands were observed in the absorption spectra of unquenched samples in the spectral region between the limit positions of the A bands, corresponding to chloride or iodide lattices. The strong band at 449 nm dominates the luminescence of these samples at low temperatures. Its kinetics have a complicated form and the decay time is in the interval from ns to ms. Quenched samples have a well-known luminescence spectrum caused by octahedral lead impurity centres in KCl single crystals. The kinetics, however, also indicate mixed chlorine and iodine coordination of lead in the investigated crystals.     

The absorption and luminescence of (PbCl6)4− and (PbBr6)4− complexes

A comparison of the absorption and luminescence spectra of isolated octahedral complexes of lead with chlorine and bromine ligands in solutions, with the absorption and emission spectra of the crystals of alkaline chlorides and bromides activated by lead measured at various temperatures, and the eutecticum (Li, Na, K) Cl + PbCl₂ at 380 °C, showed that the absorption band A lies around the same wavelengths in all three cases. The same holds also for the fluorescence of crystals and cooled solutions. The above mentioned complexes can thus be regarded as luminescence centres.Presented in a shorter form on The Xth European Congress of Molecular Spectroscopy, Liège, 1969.     

Normal and wavelength-modulated absorption of thallium bromide solutions

New results on the absorption spectra of Tl ions in aqueous and alcoholic solutions of TlBr are reported and compared with spectra of Tl ions in single KBr crystals. We study the Tl absorption bands under different conditions and we show that the A-band can be attributed to Tl-Br complexes. The energy parameters of these complexes in alcoholic solutions are given.     

Optical absorption spectra of I3 - molecular ions in KI crystals and aqueous solutions

A semiempirical molecular orbital method including spin-orbit interaction is used to study optical absorption spectra of I₃ ^- molecular ions in (KI + I₂) aqueous solutions and in KI crystals coloured additively or electrolytically. The splitting of two strong absorption bands observed for these specimens is considered to be due to the spin-orbit interaction in the iodine atoms. The values of the spin-orbit coupling constants for I₃ ^- in aqueous solutions and coloured KI crystals are estimated to be 0·56 and about 0·47 eV, respectively. The oscillator strengths of the two strong bands for these specimens is also discussed.     

Morphology and optical spectra of metal iodate microcrystals in porous matrices

Microcrystals of iodates of mercury, lead, thallium, and bismuth were grown in pores of glass and polymer matrices from solutions or through sublimation in vacuum. Images of these microcrystals embedded in matrices were obtained with an electron microscope. Exciton absorption and luminescence spectra of the microcrystals revealed a strong difference in the temperature regions of stability of the various structural modfications between bulk crystals and microcrystals of some iodates. The absorption and luminescence spectra are broadened inhomogeneously because of considerable size dispersion of the microcrystals and exhibit quantum confinement effects. The exciton emission spectra show that exciton interaction in microcrystals becomes significant at very low optical pumping levels because of efficient excitation transfer from the matrix.     

Explanation of the temperature variation of Hall coefficient of doped bismuth

The Hall effect in single crystals of bismuth doped with tin and lead has been measured in the temperature range 80 to 300 K. An attempt has been made here to explain the observed variations of Hall coefficient with temperature by considering the relative variation of the free carrier concentrations with temperature in different bands in alloys of bismuth in addition to variation of other parameters. Calculations have been made to see the effect of the overlap on Hall coefficient for different values of band overlap. The experimental curves are in satisfactory agreement with the theoretical calculations.     

Thermal conductivity of bismuth tellurite

This paper reports on the results of investigations of the thermal conductivity along the three crystallographic directions in bismuth tellurite crystals. It is found that bismuth tellurite exhibits a low thermal conductivity inherent in glasses and disordered solid solutions. At temperatures below the Debye temperature, the thermal conductivity coefficients depend on the temperature as \(\sqrt T \), which is characteristic of disordered solid solutions. The temperature dependence of the thermal conductivity of bismuth tellurite is calculated in the framework of the Debye model.     

The optical properties of thallium,lead and bismuth in oxide glasses

Absorption, fluorescence, excitation and decay time measurements have been made on a range of glasses containing thallium, lead and bismuth. In calcium phosphate and sodium silicate glasses the bands in both absorption and emission have been assigned to the A band of the Seitz model. For the bismuth doped glasses the A band was always observed in absorption but the emission was very dependent upon glass composition. Configurational coordinate curves have been constructed for Tl⁺ and Pb² in a glass of composition CaO. P₂O₅. Coordinate diagrams are also used to explain the presence or absence of bismuth fluorescence in certain glass compositions. In some borate glasses containing bismuth a brown colouration was observed. This was probably due to particle separation. No A band emission was observed from bismuth in a calcium phosphate glass. Instead there was a faint red emission similar to the cathodoluminescent bands of crystalline calcium phosphates.     

Zur Frage der Pb(II)-Komplexe in den Alkalibromiden

Zusammenfassung Mittels der polarographischen Methode wurden die Bildungskonstanten der Bleibromokomplexe in Kaliumbromidlösungen berechnet, wobei als höchster der Komplex mit sechs Bromionen ermittelt wurde. Die gemessenen Absorptionsbanden von Blei in verschieden konzentrierten Kaliumbromidlösungen wurden den einzelnen Komplextypen zugeordnet.Auf Grund des Vergleiches des Absorptionsspektrums der mit Blei dotierten Alkali-bromidkristalle und der genügend konzentrierten analogen Lösungen ist man zur Ansicht gelangt, daß in Kristallen die die Gitterstelle des Alkaliions besetzenden zweiwertigen Bleiionen mit sechs benachbarten Bromionen als Liganden einen oktaedrischen Komplex bilden, analog wie dies bei Alkalichloridkristallen der Fall ist.

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On the problem of lead (II) complexes in alkaline bromides

The polarographic method was used to determine the stability constants of complexes of bivalent lead with bromide ions. The absorption bands of lead, measured in solutions of potassium bromide of varying concentration, were ascribed to these complexes. The agreement of the absorption bands of KBr crystals doped with lead and of analogical sufficiently concentrated solutions shows that in alkali bromide crystals lead is bound in the octahedral complex with six neighbouring bromine ions.

     

Radiative heat transfer in axisymmetric domains of complex shape with Fresnel boundaries

A detailed study of the peculiarities of the radiative heat transfer (RHT) in axisymmetric domains bounded with Fresnel surfaces is undertaken. The analytical (exact) solutions of the RHT problem in conical and cylindrical domains with refractive index more than unity were obtained for a variety of absorption coefficient and geometrical parameters of the domains. It is shown that due to Fresnel reflections the net radiative flux strongly varies over the base of cone and cylinder. The difference in RHT processes for the cases of constant reflectivity of the boundaries and that calculated by Fresnel formula is demonstrated. The influence of specular reflection at the crystal side surface on the shape of the solid/liquid interface in growing bismuth germanate crystals is shown.     

Electronic structure and optical properties of anatase doped with bismuth and carbon

The calculations of the electronic structure of pure anatase and the anatase doped with carbon and/or bismuth have been carried out using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the local spin density approximation with the inclusion of single-site Coulomb correlations (LSDA + U). The dielectric function, absorption coefficient, and refractive index have been calculated in the random phase approximation. It has been found that, upon doping, narrow bands of carbon and bismuth impurity states are formed in the band gap. The calculations of the optical absorption coefficient have demonstrated that the C,Bi-doping can lead to the absorption in the visible region and an enhancement of the absorption in the near-ultraviolet region. Therefore, the C,Bi-doping can increase the photocatalytic activity on the surface of doped anatase.     

A high-stability medium based on CaF<Subscript>2</Subscript>:Na crystals with colloidal color centers: I. Photothermochemical conversion of colloidal color centers in CaF<Subscript>2</Subscript>:Na crystals

Photothermochemical conversion of simple color centers (which include from one to four anionic vacancies) and highly aggregated ones in additively colored crystals of calcium fluoride doped by sodium is studied. The annealing of crystals with a low sodium content in a reducing atmosphere (additive coloration) leads to the predominant formation of simple color centers, which convert into highly aggregated centers under the joint action of heating and irradiation in absorption bands of simple centers. The irradiation of highly aggregated centers into their absorption bands and simultaneous heating causes these centers to convert into simple centers. The additive coloration of crystals with a relatively high sodium content leads to the predominant formation of highly aggregated centers. The heating of these crystals along with the irradiation in absorption bands of highly aggregated centers causes these centers to convert into simple centers. The formation of different color centers in the course of additive coloration of crystals with different impurity content and different results of photothermochemical conversion of centers in these crystals are connected with the dual action of impurities. Anion vacancies, which compensate the charge of the impurity alkali metal, facilitate the aggregation of color centers. At the same time, the alkali impurity stabilizes simple color centers.     

Spectral Properties of CuGaxIn1−xSe2 Solid Solutions

We have investigated the absorption spectra in the region of the fundamental absorption band edge and the photoluminescence spectra of single crystals of the ternary compounds CuInSe₂ and CuGaS₂, and of solid solutions based on them that were grown by the method of chemical transport reaction. The forbidden band width and the positions of the maxima of the radiation bands are determined. The concentration dependences of the indicated quantities are plotted and they are shown to be linear.     

The power and limits of the Judd—Ofelt theory: a case of Pr3+ and Tm3+ acetates and dipicolinates

Electronic absorption spectra of crystals and solutions of praseodymium and thulium acetates and dipicolinates are reported. The influence of spectral properties of both ligands on intensities of the f—f transitions in the crystals studied is discussed. In the near-IR region, overtone vibrations of ligands are strongly coupled with the f—f transitions, particularly with the hypersensitive ones. In the UV spectral range, absorption bands of the π → π?, n → π? and possible charge transfer of metal ? ligand transitions affect f—f transitions and should also be taken into account. The phenomenological Judd—Ofelt parameters evaluated for praseodymium complexes in solution and crystals are meaningless, because no set of intensities unbiased by ligand transitions and/or neighbouring f-d configurations is available. For Tm³⁺ compounds the Judd-Ofelt analysis has given quite good results, however no significant influence of the metal ion environment changes on the Ωλ parameters can be observed.     

Direct determination of the relaxation-time of electrons using Alfvén-waves

It is shown that the absorption coefficient of weakly-damped Alfvén-waves exhibits standing wave oscillations, amplitude of which grows exponentially in an increasing magnetic field. Measurements of the power absorption as a function of magnetic field are used to make a direct determination of the relaxation-time of the charge-carriers in single crystals of bismuth.     

A new approach to describing the statistical laws governing the formation of the contour of individual bands in the optical absorption spectra of liquid systems

A new approach to the problem of a quantitative study of the statistical laws governing the formation of the contour of individual bands in the optical absorption spectra of unordered molecular systems (liquids, solutions, liquid crystals, etc.) was developed. The approach is based on a joint consideration of two independent mechanisms of the inhomogeneous broadening of spectral bands; these mechanisms are related to fluctuations of the isotropic and anisotropic components of the total interaction potential of a molecule with the surrounding medium. A generalized expression for the total statistical contour was derived, which made it possible to describe quantitatively the Q-band contour in the vibrational-rotational IR absorption spectrum of a HCl solution in CCl₄ at room temperature.     

Ultrarot-Absorption und phononenfreie Übergänge in strahlungsverfärbtem LiF

Spectral positions, properties and behaviour of the lines and bands found in the infrared absorption of X-rayed LiF single crystals at 90°K are investigated. Thermal annealing and optical bleaching of the crystals give informations about the correlation of the lines and the bands. Both prove to be transitions in the same absorption centre. This agrees well with the fact that the lines are due to phonon-free transitions in colour centres, whilst the bands are broadened by multiphonon processes. For the thermal annealing process of the infrared absorption a characteristic temperature of 420°K and an activation energy of 0·44 eV for the recombination process can be calculated by analysing isochrone annealing curves. According to their similar behaviour the infrared bands are compared with theR-centre absorption.     

Fluorescence properties of Bi4Ge3O12(BGO) single crystals under laser excitation: Excited state dynamics and saturation effects

Laser-excited techniques were used to investigate the optical properties of bismuth germanate crystals. Absorption, reflectivity, excitation, emission, lifetime, time-resolved fluorescence, photoconductivity, thermally stimulated conductivity measurements were performed at various temperatures on single crystals of different origins.The absorption is shown to occur in bismuth and germanate centers while both intrinsic and perturbed Bi³⁺ ions together with impurities contribute to the total fluorescence.The emission mechanism at room temperature involves a thermally activated energy migration, and at low temperature localized emitting centers. Formation of deep holes in the wide emission band at room temperature reveals saturation effects on various luminescent centers, promoted by energy migration. Trapped exciton models are proposed to explain the excited state dynamics occurring at low and room temperature.     

On the colloidal absorption bands in rubidium chloride and rubidium bromide crystals coloured with sodium

Colloidal absorption bands in rubidium chloride and rubidium bromide crystals coloured with sodium have been investigated. After a certain heat treatment of the RbCl and RbBr crystals containing F-centers, colloidal bands were observed at 585 mμ for RbCl and at 600 mμ for RbBr. The measured positions of these bands were compared with those calculated by means of the theory ofDoyle. Measurements of the areas of the absorption curves were also carried out at different temperatures.