Luminescence and energy transfer between Ce3+ and Mn2+ in alkaline earth borates

The luminescence of Ce3+ and Ce3+, Mn2+ co-doped BaB8O13 and SrB4O7 prepared in air is studied. The results show that tetravalent cerium ion can he reduced to trivalent state in the hosts and gives rise to efficient luminescence. Energy transfer between Ce3+ and Mn2+ is possible. Mn2+ ions can be efficiently sensitized by Ce3+ and exhibit green and red emissions which implied that Mn2+ occupied the crystallographic sites of cations and boron sites of the anoins, respectively. The intensity ratio of red to Been emission in matrix increases with the increasing of manganese concentration.

Valence change and luminescence of divalent samarium in strontium berates

The valence change of samarium from trivalent to divalent state in strontium berates (SrB6O10) prepared in air was observed. The high resolution spectra of Sm2+ in matrix were studied between 10 K and 300 K. The results showed that three crystallographic sites for Sm2+ were available in the host. Energy transfer among these sites was possible. The vibronic transition of D-5(0) --> F-7(0) of Sm2+ was studied at room temperature and the Huang-Rhys factor S was calculated. Due to the thermal population, D-5(1) --> F-7(0) transition at room temperature was observed.

Luminescent properties of divalent samarium-doped strontium hexaborate

The valence change of samarium from trivalent to divalent in strontium hexaborate (SrB6O10) prepared in air is observed. The temperature dependence of the luminescence and vibronic transitions of Sm2+ are studied. The Sm2+ ions occupy three crystallographic sites. With increasing temperature, the D-5(0)-->F-7(0) transition line exhibits red shifts, and the half-width increases. At room temperature, due to the thermal population through the 4f(5)5d channel, the D-5(1)-->F-7(J) transitions are observed even though the vibrational energy is very close to the energy gap between the D-5(1) and D-5(0) levels in the host. A coupled phonon energy of about 108 cm(-1) is determined from the vibronic transitions of Sm2+ in the host.

Preliminary study on the charge transfer and bond ionicity of binary crystals

Charge transfer and bond ionicity of some monovalent, divalent, and trivalent binary crystals of A(N)B(8-N) type have been investigated using the self-consistent method. The method divides the binary crystal systems into two subsystems which contain only one kind of element each in physical space. The charge transfer values are obtained by adjusting the charge in a self-consistent way. Based on the obtained charge transfer values, an empirical formula for bond ionicity has been proposed. It has been shown that the present results for bond ionicity are in good agreement with the previous theoretical study delivered by Levine and Pauling. The results also indicate that a large magnitude of charge transfer (or less excess charge in the bonding region) gives rise to high bond ionicity (or low bond covalency); this agrees well with the viewpoint that the excess charge in the bonding region is the origin of the formation of bond covalency. (C) 1998 American Institute of Physics. [S0021-9606(98)00837-X].

Chemical bond properties of rare earth ions in crystals

By using the dielectric description theory of ionicity of solids, chemical bond properties of rare earth ions with various ligands are studied. Calculated results show that chemical bond properties of the same rare earth ion and the same ligand in different crystals depend on the crystal structures. In a series of compounds, chemical bond properties of crystals containing different rare earth ions are similar. The magnitude of covalency of chemical bonds of trivalent rare earth ions and various ligands has an order like F

FT-RAMAN SPECTROSCOPIC STUDIES ON THE INTERACTION OF METAL-IONS WITH SPHINGOMYELIN BILAYER

The interaction of trivalent lanthanide ions and divalent calcium ions with sphingomyelin bilayer has been studied by FT-Raman spectroscopy. The results showed that the bonding of metal ions to the phosphate group of sphingomyelin bilayer, either La3+ or Ca2+, did not change the conformation of the choline group, that is, O-C-C-N+ is still in its gauche conformation. The presence of metal ions changed the states of the interfacial region from liquid-like to amorphous state and even to crystalline. They increased the fluidity of acyl chains of sphingomyelin bilayer and made them packed disorderly.

THE EFFECTS OF LANTHANIDE IONS AND THEIR COMPLEXES ON THE PHASE-TRANSITION PROPERTY OF DIPALMITOYLPHOSPHATIDYLETHANOLAMINE LIPOSOMES

The effects of metal ions and lanthanide complexes on the gel-to-liquid crystal phase transition temperature T-m of dipalmitoylphosphatidylethanolamine liposomes have been studied by differential scanning calorimetry (DSC) method. The results show that the addition of metal ions to the dipalmitoylphosphatidylethanolamine (DPPE) liposomes dispersions increases the main phase transition temperature T-m in the order of monovalent< divalent< trivalent cations. The enhancement of T-m is not large as increasing the lanthanide ions concentration. The enhancement of Pr3+ is larger than that of La3+. Remarkable differences were observed between La-citrate and La-lactate complexes at different pH solutions. At pH 7.0, La-citrate complex has no effect on the T-m, La-lactate complex, however, increases the T-m value, and the increase is larger than that of free lanthanide ions at the same concentration. The decrease of pH of complexes solutions lowers the phase transition temperature. We have preliminarily discussed the mechanism of the enhancements of lanthanide ions and the synergism of lanthanide ion and lactate ligand follow the ion induced dehydration of lipid and the potential effects of ion-lipid interaction.

LANTHANIDE PERCHLORATE COMPLEXES OF 1,4-BIS(PHENYLSULFINYL)BUTANE

Seven trivalent lanthanide perchlorate complexes of the types [Ln(bphab)(4)ClO4] (ClO4)2 (where La = La(III), Pr(III), Nd(III) and Eu(III)) and [Ln(bphab)(3)ClO4] (ClO4)(2) (where Ln = Ho(III), Er(III) and Lu(III), and bphab = 1,4-bis(phenylsulfinyl)butane) have been synthesized by the reaction of bphsb with lanthanide(III) perchlorate in methanol-chloroform mixture. The complexes have been characterized by elemental analyses, molar conductance, electronic and infrared spectral techniques. Several bonding parameters have been calculated from the absorption spectra of the Pr(III), Nd(III), Ho(III) and Er(III) complexes. Infrared spectral data suggest that bphsb acts as bidentate ligand coordinating through the oxygen atoms of the S=O moieties.

ELECTROCHEMICAL STUDY OF ISOPOLY AND HETEROPOLY ANION TRANSFER ACROSS THE WATER NITROBENZENE INTERFACE .2. VANADIUM-CONTAINING HETEROPOLYTUNGSTATE ANIONS

The electrochemical transfer behaviour of vanadium-containing heteropolytungstate anions [PW12-xVxO40]((3+r)-) (x = 1-4) across the water \nitrobenzene interface has been investigated by cyclic voltammetry and chronopotentiometry with cyclic linear current scanning. The transfer of PW11V1O404-, HPW10V2O404-, H2PW10V2O403-, H3PW9V3O403- and H4PW8V4O(40)(3-) across the water \nitrobenzene interface can be observed within the potential window. The effects were observed of pH in the water phase on the transfer behaviour and the formation of vanadium-containing heteropolytungstate anions in solution. Heteropolytungstate anions become more stable due to their involving the vanadium atom. The degree of protonation and the dissociation constant of the trivalent vanadium-containing heteropolytungstate anion of protonation increase with increasing vanadium content. The transfer processes are diffusion-controlled The standard transfer potential, the standard Gibbs energy and the dissociation constant for vanadium-containing heteropolytungstate anions have been obtained and the transfer mechanisms are discussed.

EFFECT OF THE CONCENTRATION OF THE ER3+ ION ON THE SPECTRAL INTENSITY PARAMETERS OF ER-YAG CRYSTALS

The absorption spectra of Er:YAG (YAG, yttrium-aluminium-garnet) crystals containing different concentrations of the trivalent erbium ion were measured and the spectral intensity parameters were calculated from these experimental spectra using the Judd-Ofelt model. The results indicate that the phenomenological intensity parameters, OMEGA(lambda) (lambda = 2, 4 and 6), vary as a function of the concentration of the Er3+ ion in the Er:YAG crystal, but no variation in the fluorescence-branching ratios as a function of the concentration of the Er3+ ion is found. An empirical formula is proposed to describe the relationship between the spectral intensity parameters and the Er3+ ion concentration in the Er:YAG crystal. The spectral intensity parameters exhibit a maximum in Er:YAG crystals containing about 1-1.5 at.% Er3+ ion. The effect of the Er3+ ion concentration on the spectral intensity parameters may be attributed to the inhomogeneous lattice distortion in the cell of the Er:YAG crystal caused by the dopant erbium ions.

SYNTHESIS AND SPECTRAL CHARACTERISTICS OF DIVALENT SAMARIUM ACTIVATED BINARY FLUORIDES

A simple technique for preparation of powder binary fluorides activated with divalent samarium ions is described. The samarium impurity is introduced as samarium trifluoride SmF3 and hydrogen acts as the reducing agent to transform Sm3+ into Sm2+. Using this method, samarium has been stabilized in the divalent state in some fluorides: KMgF3, LiBaF3, BaBeF4, SrMgF4 and BaMgF4. Moreover, BaBeF4, SrMgF4 and BaMgF4 have never been activated with Sm2+ ions up to now. We also find that under the same synthetic conditions samarium can not be stabilized in the divalent state in some fluorides: KCaF3, CaBeF4 and CaMgF4, but the characteristic luminescence of trivalent samarium Sm3+ appears in these matrices. The emission and excitation spectra of samarium (Sm2+ and Sm3+) in these binary fluorides are presented and briefly discussed. The relationship between the oxidation state of samarium and the composition, the structure of matrices is also analyzed.

MAGNETIC-PROPERTIES OF LANTHANUM MANGANITE AND VALENCE EQUILIBRIA OF MANGANESE

The paramagnetic susceptibility of lanthanum manganite has been measured over a wide temperature range (100-1073 K). On the basis of the thermodynamic equilibria between the various manganese ions with different valence and spin states and the magnetic interactions between the various manganese ions, a semiempirical formula has been proposed to calculate the paramagnetic susceptibilities of lanthanum manganite at different temperatures. The results indicate that most of the discrepancies between the calculated and experimental reciprocal susceptibilities of lanthanum manganite are less than 10% and that the relative contents of the various manganese ions in lanthanum manganite vary with temperature. The relative content of the trivalent manganese ion with a high spin state is dominant over the whole temperature range, while be relative content of the tetravalent manganese ion with a high spin state decreases monotonously with increasing temperature. At 300 K the calculated relative content of the tetravalent manganese ion in lanthanum manganite is about 34%, which is in good agreement with the experimental result (30%). There are some divalent manganese ions present in lanthanum manganite from low temperature to high temperature. The ratio of the relative contents of the tetravalent and divalent manganese ions in the compound varies with temperature. Above 750 K the relative content of the tetravalent manganese ion is less than that of the divalent manganese ion. The variation in the electrical resistivity of lanthanum manganite with temperature has also been interpreted reasonably.

STUDIES OF SPINEL LICRXMN2-XO4 FOR SECONDARY LITHIUM BATTERY

X-ray and electrochemical studies of spinel-related manganese chromium oxides, LiCrxMn2-xO4 (0 less-than-or-equal-to x less-than-or-equal-to 1) were carried out in a lithium nonaqueous cell. X-ray diffraction spectra indicated that the substitution of manganese in LiMn2O4 by trivalent transition metals (Cr3+) cause the linear decrease of lattice parameter with the x in the LiCrMn2-xO4. Some discharge-capacity loss was obtained due to the lattice contraction of LiCrMn2-xO4, but it has a better rechargeability than LiMn2O4. Cyclic voltammetry and electrochemical impedance experiments have shown that the excellent rechargeability of LiCrxMn2-xO4 may be attributed to the good reversibility of the change in its crystal structure for the insertion and extraction of lithium ions.

MOSSBAUER-EFFECT STUDIES OF THE DIMER OF A BIMETALLIC EU-AL COMPLEX

Mossbauer spectra of the dimer of a bimetallic Eu-Al complex, [(CF3COO)3EuHAl(C2H5)2 . 2 THF]2 are measured at different temperatures (81 to 166 K) and some Mossbauer parameters, such as isomer shift, electric quadrupole splitting and asymmetric parameter, are derived from the experimental spectra. The Debye temperature of the compound determined by a Debye model is 128 K. The results indicate that europium in the organo-europium compound is trivalent and that a bridging hydrogen atom between two europium atoms exists in the dimer. The low Debye temperature implies that the weaker binding force between the europium atom and the lattice may be related to the structure and the chemical bonding in the organometallic compound of europium.

STUDIES ON THE ELECTRICAL AND MAGNETIC-PROPERTIES FOR LASR2-XCAXV3O9+/-Y

The electrical and magnetical properties of LaSr(2-x)Ca(x)V3O9 +/- y have been investigated. The compounds are antiferromagnetic. They show a metallic conduction other than semiconductivity. The trivalent and tetravalent vanadium ions coexist in the system. The magnetic susceptibility increases and the resistivity decreases at room temperature with the increase of x value. It is shown that the change of the valency state of vanadium obviously influences the electrical and magnetical properties of the system.