151Eu Mössbauer study of luminescent Y2O3:Eu3 + core-shell nanoparticles

¹⁵¹Eu Mössbauer spectroscopy was applied to distinguish among different Eu microenvironments and phases in spherical Y₂O₃:Eu^3?+? and core-shell Y₂O₃@Eu^3?+? phosphor nanoparticles prepared by using homogeneous precipitation method. ¹⁵¹Eu isomer shift revealed that Eu atoms exist only in oxidation state Eu^3?+? in all spherical and core-shell phosphors. Significant differences have been found between the Mössbauer parameters (isomer shift, principal component of EFG and linewidth) characteristic of spherical Y₂O₃:Eu^3?+? and core-shell Y₂O₃@Eu^3?+? phosphor nanoparticles. The Mössbauer parameters of spherical Y₂O₃:Eu^3?+? were associated with Eu substituting Y in the Y₂O₃, while Mössbauer parameters of core-shell Y₂O₃@Eu^3?+? phosphor were attributed to Eu being in the Eu₂O₃ shell, proving the structural model and the successful preparation of these phosphors.     

Redox interactions between structurally different alkylresorcinols and iron(III) in aqueous media: frozen-solution 57Fe Mössbauer spectroscopic studies,redox kinetics and quantum chemical evaluation of the alkylresorcinol reactivities

Iron(III)-containing aqueous solutions of 5-methylresorcinol (5-MR), 5-n-propylresorcinol (5-n-PR) and 4-n-hexylresorcinol (4-n-HR) at pH ~ 3 were studied by means of ⁵⁷Fe transmission Mössbauer spectroscopy. Kinetic considerations were applied to the redox reactions. Density Functional Theory (DFT) calculations were performed for the alkylresorcinol (AR) molecules and their non-alkylated analogue (resorcinol). Mössbauer spectra consisted of quadrupole doublets assigned to high-spin Fe(III) and Fe(II) species. From changes in their relative spectral areas, a gradual reduction of Fe(III) by all the ARs studied was observed. However, significant differences were found for the reduction rates among the ARs. The following series of the reduction rates was established by means of Mössbauer spectroscopy: 4-n-HR ? 5-MR > 5-n-PR, supplemented by rate constants calculated using a kinetic model. DFT calculations resulted in the following series: 4-n-HR ? 5-n-PR > 5-MR ? resorcinol (the latter is not oxidised under the conditions applied). The reversed order of the experimentally observed 5-MR and 5-n-PR oxidation rates may be explained in terms of their different kinetic parameters related to their structure.     

General survey and microanalytical aspects of ion-selective electrodes

Summary A survey is presented of recent developments in the field of ion-selective electrodes. Special emphasis is placed on problems of electrode miniaturization and ISFET production. Different electrode types in present use are described and theories for the interpretation of electrode mechanisms are outlined. It is pointed out that the electrode potentials are due to the formation of a space charge. Different applications of ion-selective electrodes are dealt with and the problems connected with the determination of small concentrations are discussed. Attention is given to the selection of conditions under which a reliable measurement of extremely small amounts or extremely small concentrations can be ensured.     

Revisiting the construction of gap functions for variational inequalities and equilibrium problems via conjugate duality

Based on conjugate duality we construct several gap functions for general variational inequalities and equilibrium problems, in the formulation of which a so-called perturbation function is used. These functions are written with the help of the Fenchel-Moreau conjugate of the functions involved. In case we are working in the convex setting and a regularity condition is fulfilled, these functions become gap functions. The techniques used are the ones considered in [Altangerel L., Bo? R.I., Wanka G., On gap functions for equilibrium problems via Fenchel duality, Pac. J. Optim., 2006, 2(3), 667–678] and [Altangerel L., Bo? R.I., Wanka G., On the construction of gap functions for variational inequalities via conjugate duality, Asia-Pac. J. Oper. Res., 2007, 24(3), 353–371]. By particularizing the perturbation function we rediscover several gap functions from the literature. We also characterize the solutions of various variational inequalities and equilibrium problems by means of the properties of the convex subdifferential. In case no regularity condition is fulfilled, we deliver also necessary and sufficient sequential characterizations for these solutions. Several examples are illustrating the theoretical aspects.     

Mössbauer Study of Oxygenated Iron-Phthalocyanines,a Precursor of Magnetic Storage Material

⁵⁷Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study - and -polymorphs of iron phthalocyanines (FePc) to get information about their oxygenation in connection with controlled pyrolysis of flat layered phthalocyanines initiated by radicals at relatively low temperatures, to form acicular carbide particles encaged in carbon. Mössbauer spectroscopy and XRD revealed that the oxygenation of both - and -polymorphs of FePc was successfully achieved. New Mössbauer spectral components (doublets) appeared upon the oxygenation in both and FePc. This can be attributed to iron microenvironments containing oxygen between the layers of iron phthalocyanines.     

Comparative study of hydroxo-fluoro and hydroxo-sulphido mixed ligand complexes of aluminum(III) and gallium(III)

The mixed ligand complex formation had been studied in the aluminate-fluoride, gallate-fluoride, aluminate-sulphide and gallate-sulphide systems by spectrophotometric as well as potentiometric methods using glass and sulphide selective electrodes. The formation of the species Al(OH)₃F^? and Ga(OH)₂S^? has been demonstrated and the equilibrium constants have been determined. Similar interaction could not be detected in the aluminate-sulphide and gallate-fluoride systems.The differences in behaviour of the metal ions to the characteristically hard fluoride and soft sulphide ligands can be interpreted in that the Ga³⁺ ion may form complexes with charged soft ligands too, its behaviour then differing from that of the typically hard Al³⁺ ion.     

Mössbauer study of the effect of pH on the rate of redox interactions between iron(III) and 4-n-hexylresorcinol in aqueous media

Mössbauer spectroscopy is used for a comparative study of the rate of iron(III) reduction by 4-n-hexylresorcinol (4-n-HR, a chemical analog of microbial autoregulators excreted by cells into the environment that allow intercellular communication) in aqueous media in the pH range of 1.5–4.5 simulating acidic soil conditions. The concomitant process of 4-n-HR oxidation is monitored using UV spectrophotometry.