J. Legendziewicz

Optical properties of Eu(III) chelates trapped in silica gel glasses

Abstract Preparation and optical properties of silica gel glasses doped with Eu(III) chelates (the complexes of β-diketones) are described. In particular the emission and excitation spectra of the precursor salts and glasses are reported. The assignment of electronic levels was proposed and the intensity analysis of the f–f transitions was performed. The decay times of 5D0 levels of Eu(III) complexes in gels are analyzed and compared with those reported for precursor salts.

Spectroscopic and magnetic studies of mixed lanthanide complexes: LnL3α,α′Dipy in solution and in solid

Abstract New monomeric complexes LnL3bip(1/2bip) were synthesized (Ln=Eu3+, Tb3+); L-phosphoro-azo derivative of β-diketone: CCl3C(O)NP(O)(OCH3)2 and bip-α,α′dipyridyl and single crystals were grown. X-Ray diffraction studies were done. The complexes crystallize in the triclinic system, space group P 1 . Magnetic susceptibility and magnetization of the crystals were investigated. High resolution absorption, luminescence and excitation spectra were measured for crystals at 293, 77 and 4 K in order to characterize their physical properties. Radiative and nonradiative processes were analyzed. The role of the ligand singlet and triplet states in energy-transfer as well as the charge-transfer states in emission quenching were studied.

X-Ray analysis and excited state dynamics in a new class of lanthanide mixed chelates of the type LnPhβ3·Phen (Ln=Sm, Eu, Gd, Tb)

A new type of lanthanide complex with a derivative of β-diketone and phenanthroline, LnPhβ3·Phen [where Phβ = CCl3–C(O)–N–P(O)–(OCH3)2; Phen = 1,10-phenanthroline, Ln = Sm, Eu, Gd, Tb] was synthesised. The X-ray diffraction analysis of the Sm(III) complex shows that it is in the monoclinic system and P21/c space group. There are two different Sm3+ ions with insignificant differences between the Sm–O, –N distances (0.005 A) and a CN = 8. Absorption, emission and emission excitation spectra at 293, 77 and 4.2 K were used to characterise the title compounds in the solid state and in solution. The luminescence spectra at 77 K for the Eu analogue are complex and two components in the 5D0 → 7F0 transition show that Eu3+ ions reside in two symmetry sites. The spectroscopic results correspond well to the crystal structure of the SmPhβ3·Phen compound and confirm that the Sm3+, Eu3+ and Tb3+ monocrystals are isostructural. Efficient energy transfer sensitises the interion emission from 5D4 or 5D0 levels of Tb(III) and Eu(III) after ligand band excitation. Based on the splitting of the levels observed at 4.2 K in the single crystal spectra of Tb and Eu, as well as the absorption, phosphorescence and excitation spectra, energy level diagrams are proposed. The mechanism of energy transfer and excited state dynamics are discussed. Strong vibronic coupling was observed mainly in the 7F0 → 5D2 electronic transition. The IR spectra were used to analyse the vibronic components. Analysis of the emission spectra of a Eu3+-doped silica sol-gel sample was made and compared to those for the title monocrystals. The total spectral characteristics of the materials permits an evaluation of their potential applicability.

Application of luminescence and absorption spectroscopy and x-ray methods to studies of Ln+3 ions interaction with aminoacids

Abstract The Nd +3 , Ho +3 and Eu +3 compounds with glycine, alanine and glutamic acid were synthesized and obtained as monocrystals. Absorption spectra in the range 8000–35 500 cm −1 were measured along the crystallographic axes at room temperature on a Cary 14 spectrophotometer Luminescence spectra were recorded at the same temperature in the range 9000–16 600 cm −1 . Intensities of the ff transitions were analyzed on the basis of the Judd theory, taking the dependence of intensity on the crystallographic axis position into account. Considerable differences in hypersensitive transitions in crystals with alanine, glycine and glutamic acid, whose symmetry changed from triclinic to monoclinic, were explained in terms of differences in the MeO distances.

Ligand chirality effect on the structure and its spectroscopic consequences in [Ln2(Ala)4(H2O)8] (C104)6 crystals

Abstract Single crystals of [Ln 2 (Ala) 4 (H 2 O) 8 ](Cl0 4 ) 6 (where Ln = Eu, Nd and Ala = l -, dl -alanine) were grown from aqueous solutions and the neodymium complex has been studied by single-crystal X-ray diffraction. The space groups are triclinic P 1 and monoclinic C2/c for l - and dl -alanine, respectively, and Z = 1 and 4. The crystal structures consist of non-centrosymmetric and centrosymmetric dimer units in the complexes with l and dl ligand forms. In other words, in the latter two the lanthanide ions in the dimer are equivalent but in the former they are not. Thus the chirality of the ligand is responsible for the subtle differences in the structure. Each neodymium ion is coordinated by four carboxylate oxygens of the amino acids and four water molecules. The coordination polyhedra around the neodymium ions are distorted square antiprisms. Well-resolved absorption luminescence measurements down to 5 K are reported. The probabilities of electronic transitions were investigated. An attempt has been made to elucidate the dimer (centrosymmetric and noncentrosymmetric) structure reflection in the splitting pattern of the optical lines. The temperature effect on the spectra was studied and analysed in terms of the cooperative interaction of coupled ions. It is the first, to our knowledge, X-ray evidence of the ligand chirality effect on the dimer structure of lanthanide compounds.

The structure of ligands and effects of the europium luminescence excitation

Abstract Results of studies of the luminescence excitation spectra of europium compounds: β-diketonates, aromatic carboxylates, nitrates with sulfoxides are presented. The processes of transfer and degradation of the excitation energy are discussed. Alteration of the relative contribution of two inequivalent ligands to the luminescence excitation of europium β-diketonates with 1,10-phenanthroline derivatives upon modification of ligand radicals and variation of relative binding strength of ligands by metal ion was investigated. The participation of the ligand–metal charge transfer states both in degradation of the excitation energy and in enhancement of Eu3+ luminescence excitation was analyzed. Increase of intraligand charge transfer upon introduction of a ligands acceptor substituent such as nitro-group, decreasing the ligand–metal charge transfer, was demonstrated. Blocking effect of methylene or oxymethylene bridges on the energy transfer from ligand to Eu3+ ion was observed. This phenomenon witnesses about the electron exchange mechanism of the interaction between the disjuncted parts of the ligand.

Spectroscopy of nanometer-range media and mixed lanthanide Lnβ3L compounds: Their applications perspectives

Abstract To obtain cathode-ray pumped powder lasers for high resolution monochromatic displays, it is important to produce low density scattering media for optically pumped lasers with sufficiently low generation threshold and relatively small volume of the excited medium involved in generation of light. This study focuses on the physical properties and the methods of synthesis of nanosize systems incorporated in silica gel and glasses. Comparison of spectroscopic properties and types of species created in gels and silica glasses will be presented and discussed. On the other hand, basically similar compounds to those used as a precursor in creation of nanometer systems can be used in organic layered electroluminescent diodes (OLEDs). The important characteristics of these materials can be correlated with donor–acceptor properties of the substituents in the ligands. Moreover, these donor–acceptor properties are responsible for location of energy levels, efficiency of energy transfer, electron–phonon coupling and finally quantum yield of luminescence. Two types of lanthanide mixed β-diketonates will be characterized and their applicability based on spectroscopic data will be analyzed.

Spectroscopy and crystal structure of neodymium coordination compound with glycine: Nd2(Gly)6·(ClO4)6·9H2O

Abstract Neodymium complex compound with glycine: Nd2(Gly)6·(ClO46·9H2O was synthesized and obtained in the form of monocrystals. Absorption spectra recorded in the region of 8000–35 000 cm-1 were measured along the crystallographic axes. Intensities of the f-f transitions were analysed on the basis of the Judd theory. The X-ray crystal structure determination of the complex is reported. Crystals are triclinic, space group P I , with a = 11.554(4) A, b = 14.108(1) A, c = 15.660(3) A, α = 97.14(1)°, β = 102.82(2)°, γ = 105.28(1)°, V = 2355.25 A3 Z = 2, M.W. = 1495.4, Dc = 2.129)(3) g cm-3, Dm = 2.103(1) g cm-3. The structure was solved by Pattersons method and successive Fourier syntheses giving the locations of all nonhydrogen atoms. The final R factor was 0.062 and Rw = 0.073 for 12869 reflections with |Fo| > 5σ|(Fo)|. The asymmetric unit consists of a dimeric formula unit. The coordination polyhedron of Nd atoms comprises seven oxygen atoms from glycine and two from water molecules. The neodymium-glycine bonding mode is compared with that of the calcium-glycine complex.

Application of lanthanide (Eu, Nd) spectroscopy as a structural probe of diluted double phosphates

Abstract The present studies are focused on the application of europium(III) emission as a structural probe of diluted double phosphate and the determination of the number of metal sites, as well as their symmetries. The influence of the M(I) ions on the structure of phosphates is shown in the emission spectra at 77 K. The IR and Raman spectra were measured and used in the assignment of the vibronic components of electronic transitions. The electron–phonon coupling was analyzed in the emission and excitation spectra of europium double phosphate. Moreover, absorption spectra at 293 and 4 K as well as intensity analysis of Nd(III) f–f transition were used in the detection of structural modifications in both types of phosphates—rubidium (1) and sodium (2) salts. The energy level diagram was proposed and compared to the earlier reported data for different types of phosphates.

Structure, photophysics and magnetism of a europium mixed complex, Eu(HFAA)3bipy.H2O, in the solid state and solution

Abstract Lanthanide β-diketones were used recently in organic-layered electroluminescence diodes and can also find other optical applications. An important characteristic of these materials can be correlated with donor–acceptor properties of the substituents in ligands. Single crystals of C 35 H 21 EuF 18 N 4 O 7 were obtained. The X-ray diffraction analysis shows the triclinic system and space group P 1 . The europium ion is coordinated by six oxygen atoms of hexafluoroacetylacetone and two nitrogen atoms of the 2,2′-dipyridine molecule. The coordination number of Eu(III) is completed to nine by one water molecule. Besides, one non-coordinated 2,2′-dipyridine is located in the crystal lattice which is disordered over two positions. Absorption, emission and emission excitation spectra at 293, 77 and 4 K, as well as luminescence decay time measurements are used to characterize the title compound in the solid state and in solution. The emission properties are strongly dependent on the energy of the excitation beam and on temperature. Magnetic susceptibility measurements were carried out down to 1.7 K. Correlation of the spectra and magnetic properties with details of the structure of C 35 H 21 EuF 18 N 4 O 7 was studied. These results are compared with previously reported data for related systems.