VUV excited luminescence of europium activated calcium borophosphate prepared in air

XAFS (EXAFS and XANES) at Eu-L-3 edge were used to determine the local structure and the valences of europium in CaBPO5:Eu prepared in air. The results of EXAFS showed that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu-O were 2.39 Angstrom in the host lattice. XANES at Eu-L-3 edge exhibited that Eu2+ and Eu3+ coexisted in the matrix. The luminescent spectrum of the material excited by VUV at 147 nm presented a similar spectrum with that excited by f-f transition of Eu2+ at 396 nm and f-d transition of Eu2+ at 312 nm. The broad emission band due to both 4f(6)5d - 4f(7) transition of EU2+ and f - f transition of Eu3+ could be observed in emission spectra, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V-Cn]" formed by aliovalent substitution between Ca2+ and Eu3+ ions. The UV excitation spectrum showed the typical f-f transition of Eu3+ and f-d transition of Eu2+. The bands with the maxima at about 113 and 158 nm in VUV excitation spectrum were assigned to originate from the absorption of the host lattice.

Preparation of borates doped with divalent rare earth ions (RE2+) in air and spectroscopy of divalent rare earth ions (RE2+ = Sm, Eu, Tm, Yb)

The spectroscopic feature of divalent Sm2+, Eu2+, Tm2+ and Yb2+ is discussed in this paper. Especially the spectroscopic properties of some berates containing tetrahedral BO4 group such as SrB4O7, SrB6O10 and BaB8O13 doped with these divalent ions are reported. When the divalent alkaline earth ion in these berates is replaced partially by the above trivalent rare earth ion, the charge carried in the produced defects can be used as reductant to reduce the doped rare earth ion into divalent state at high temperature even in air. Therefore, a convenient and safe method is provided to prepared phosphors doped with these divalent rare earths.

A comparative study on the electroluminescence properties of some terbium beta-diketonate complexes

By comparing the phosphorescence spectra of Gd(acac)(3) (acac=acetylacetone), Gd(TFacac)3 (TFacac=1,1,1-trifluoroacetylacetone), the effects of fluorine replacement of hydrogen on the triplet state energy of the ligands were revealed. Fluorine can lower the triplet state energy of Hacac and make it more suitable for energy transfer towards the D-5(4) state of terbium. Organic electroluminescent devices (OELDs) with the corresponding trivalent terbium complexes as emissive layers were fabricated. Triple-layer-type devices with a structure of glass substrate/ITO (indium tin oxide)/PVK [poly(N-vinylcarbazole)]/PVK : Tb complex: PBD [2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole]/PBD/Al exhibit bright green luminescence upon applying a dc voltage. The luminance of a device with Tb(TFacac)(3)phen (1,10-phenanthroline) and Tb( TFacac) 3 as emissive layer is higher than that of the corresponding devices with Tb(acac)(3)(phen) and Tb(acac)(3) as emissive layers. The EL device with Tb(TFacac)(3)(phen) as emitter exhibits characteristic emission of Tb3+ ions with a maximum luminance of 58 cd m(-2) at 25 V.

Luminescence of RE2+ (RE = Sm, Yb) in barium octoborate

The reduction process from trivalent to divalent state for Sm3+ and Yb3+ ions in barium berates (BaB8O13) prepared in air was observed. The luminescence properties of these divalent rare-earth ions were studied. Yb2+ shows an f-d broad emission band, due to the 4f(14) --> 4f(13)5d transition, while the Sm2+ ion shows an f --> f transition. From the spectra of Yb2+, and using the D-5(0) --> F-7(0) transition of Sm2+ as a structural probe, two crystallographic sites were found to be available for the cations in the host. Vibronic transitions of Sm2+ were observed at low temperature. BaB8O13 was found to be a good host for reducing the trivalent rare-earth ions to divalent state and to exhibit interesting spectroscopic properties,

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

Lanthanide ions for the hydrolysis of 5'-mononucleotides and 3'-mononucleotides

Cleavage of adenosine-5'-monophosphate (5'-AMP), guanosine-5'-monophosphate (5'-GMP), adenosine-3'-monophosphate (3'-AMP) and guanosine-3'-monophosphate (3'-GMP) by lanthanides was investigated by NMR and the method of measuring the liberated phosphates. Rapid cleavage of both 5'-mononucleotides and 3'-mononucleotides by Ce-III and Ce-IV under air at pH 9 and 37 degrees C was observed. Other lanthanides showed less efficiency for hydrolyzing 5'-mononucleotides but 3'-mononucleotides were catalyzed by a range of lanthanide ions. The mechanism for hydrolyzing 3'-mononucleotides by lanthanides was:investigated. The notable difference in reactivity between Ce-III and the other lanthanide ions under air was further studied showing that the cleavage is enhanced with increasing molar fraction of Ce-IV. The fast cleavage of mononucleotides by Ce-III under air at pH 9 is ascribed to the resultant Ce-IV in the reaction mixture. (C) 1997 Elsevier Science Ltd.

Studies on synergistic extraction of rare earths(III) with HBTMPTP and primary amine N1923

The synergistic extraction of rare earths(III) with binary systems containing HBTMPTP and primary amine N1923 from sulfuric acid medium was observed, The syner gistic extraction factor(R) decreased with increasing atomic number of lanthanides. Through the methods of slope analysis, constant mole and saturation titration, the synergistic extraction stoichiometry was obtained, The thermodynamic function was calculated, The IR spectra of the saturated synergistic extraction completely confirmed the mechanism.

Synthesis and crystal structure of [(C8H8)(3)(C6H5CH2C5H4)Nd2K(THF)3]

NdCl3 reacted with C6H5CH2C5H4Na in the ratio 1:1 at -78 degrees C giving [C6H5 CH2C5H4NdCl2 . nTHF], which then was reacted with C8H8K2/THF to yield the title complex [(C8H8)(3)(C6H5CH2C5H4)Nd2K(THF)(3)] (C6H5CH2C5H4 = benzylcyclopentadienyl). The crystal structure of the Nd complex was determined by X-ray diffraction and revealed that the benzyl group is coordinated to the potassium atom to form a new type of trinuclear complex [(eta(8)-C8H8)Nd(mu(2)-eta(8)-C8H8K(THF) (eta(3)-C6H5CH2-mu(2)-eta(5)-C5H4)Nd (THF)(2)(eta(8)-C8H8)]. Copyright (C) 1996 Elsevier Science Ltd.

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.

SYNTHESES AND CRYSTAL-STRUCTURES OF (C8H8)ND(C5H9C5H4)(THF)(2) AND [(C8H8)GD(C5H9C4H4(THF)][(C8H8)GD(C5H9C5H4(THF)(2)]

LnCl(3) (Ln = Nd, Gd) reacts with C5H9C5H4Na (or K2C8H8) in THF (C5H9C5H4 = cyclopentylcyclopentadienyl) in the ratio of 1:1 to give (C5H9C5H4)LnCl(2)(THF)(n) (or (C8H8)LnCl(2)(THF)(n)], which further reacts with K2C8H8 (or C5H9C5H4Na) in THF to form the title complexes. If Ln = Nd the complex (C8H8)Nd(C5H9C5H4)(THF)(2) (a) was obtained: when Ln = Gd the 1:1 complex [(C8H8)Gd(C5H9C5H4)(THF)][(C5H8)Gd(C5H9C5H4)(THF)(2)] (b) was obtained in crystalline form. The crystal structure analysis shows that in (C8H8)Ln(C5H9C5H4)(THF)(2) (Ln = Nd or Gd), the Cyclopentylcyclopentadienyl (eta(5)), cyclooctatetraenyl (eta(8)) and two oxygen atoms from THF are coordinated to Nd3+ (or Gd3+) with coordination number 10. The centroid of the cyclopentadienyl ring (Cp') in C5H9C5H4 group, cyclooctatetraenyl centroid (COT) and two oxygens (THF) form a twisted tetrahedron around Nd3+ (or Gd3+). In (C8H8)Gd(C5H9C5H4)(THF), the cyclopentyl-cyclopentadienyl (eta(5)), cyclooctatetraenyl (eta(8)) and one oxygen atom are coordinated to Gd3+ with the coordination number of 9 and Cp', COT and oxygen atom form a triangular plane around Gd3+, which is almost in the plane (dev. - 0.0144 Angstrom).