V. Zolin

Optical spectroscopy of the adducts of europium tris(dipivaloylmethanate) with derivatives of 1,10-phenanthroline

Abstract Spectroscopic investigations of the mutual influence of inequivalent ligands were undertaken using complex adducts of europium tris(dipyvaloylmethanate) with derivatives of 1,10-phenanthroline, Eu(DPM)3·Ph. The choice of a series of related Eu(DPM)3·Ph compounds provided the opportunity to study the dependence of the spectroscopic characteristics on the value of the effective charges at the atoms in the nearest surroundings of Eu3+ which, in turn, depends on steric factors and the donor–acceptor properties of the ligands. It was shown that steric factors are as significant as donor–acceptor properties of the ligands in the creation of the complexes. The changes in the strength and symmetry of the crystal field were evaluated from the Stark splittings of the Eu3+ transitions in luminescence spectra. Crystal field parameters were calculated. Two subgroups of compounds with similar spectra were distinguished. The relative efficiency of the excitation of Eu3+ luminescence through the ligand absorption bands and the relative luminance of the compounds were investigated. Changes of the ligand vibration frequencies and the strength of the electron–phonon interaction with various ligands were studied by IR and vibronic spectra.

Spectra and details of the structure of europium aliphatic carboxylates with 1,10-phenanthroline derivatives

Abstract Luminescence, excitation of luminescence, IR and Raman spectra of a variety of carboxylates Eu(RCOO) 3 .Phen (Phen–1,10-phenanthroline) consisting of acetate, propionate, lactate, capronate compounds, and Eu(CH 3 COO) 3 .Ph (Ph–six 1,10-phenanthroline derivatives) were examined. Crystal field parameters for model compounds were calculated. The crystal structure of the europium acetate Eu(CH 3 COO) 3 .Phen was solved by X-ray method. Dependence of the spectroscopic characteristics on variation of both types of ligands, indicating details of the structure of compounds, was examined. Reciprocal influence of inequivalent ligands in europium carboxylates was analysed. It was demonstrated that steric factors are as significant as the donor–acceptor properties of the ligands in creation of the structure of compounds under investigation.

Charge transfer bands in the luminescence excitation spectra of isomeric pyridinedicarboxylic salts of europium

Abstract The ligand–cation charge transfer band was observed in the region of 360–400 nm of the luminescence excitation spectrum of europium salt of 3,4-pyridinedicarboxylic acid but was absent in the spectra of europium 2,6- and 2,3-pyridinedicarboxylic salts. It was due to higher efficiency of the energy transfer through the charge transfer state conditioned by increased polarizability of the ligand of the former compound. Energy transfer through the excited ligand–lanthanide charge transfer state may explain the effect of the quenching of luminescence by the redox-sensitive lanthanide ions.

Vibronic spectra of europium compounds containing derivatives of 1,10-phenanthroline

Abstract Luminescence and excitation of luminescence vibronic spectra of europium β-diketonates, acetates and nitrates with 1,10-phenanthroline and its derivatives were studied. The influence of the donor–acceptor properties and of size of ligands on Stark splitting of electronic transitions and on intensity distribution in vibronic sidebands was investigated. An increase of acceptor properties of one ligand of the compound is equivalent to increase of the donor properties of the other ligand as far as their influence on Eu3+ spectra are concerned. Resonant vibronic effect was studied. Complex case of resonant vibronic interaction with participation of several vibrations of both ligands under conditions of simultaneously low and strong nonadiabaticity is presented.

Vibronic spectra and details of the structure of europium nitrates with derivatives of 1,10-phenanthroline

Abstract Luminescence and excitation of luminescence vibronic spectra as well as IR and Raman spectra of europium nitrates with 1,10-phenanthroline derivatives of formula Eu(NO 3 ) 3 .Ph 2 were studied. The effect of size of ligands and their effective charges on crystal structure and, as a consequence, on spectroscopic characteristics was investigated under conditions where one type of ligand (NO 3 − group) is sufficiently rigid. The second ligand, heterocyclic diimine, can change its size and donor-acceptor properties when the substituents are varied. Stark splittings and relative intensities of the Eu 3+ electronic transitions, the behaviour of vibration frequencies, and vibronic interaction were studied. It was demonstrated that nitrates under investigation have identical composition but form two different structural groups with small and bulky phenanthroline derivatives due to the influence of steric factor. All nitrate anions in the compounds are coordinated and the Eu-O (NO 3 − ) bonds are relatively strong. The values of the splitting of stretching vibrations of the NO 3 − -anions (▵= ν 4 − ν 1 ) and position of the band of ν (Eu–O) vibration show that the strongest Eu–O bonds are formed in Eu(NO 3 ) 3 .Nphen 2 , Eu(NO 3 ) 3 .Tmphen 2 and Eu(NO 3 ) 3 .Dphphen 2 due to high acceptor properties of nitro-phenanthroline and large size of tetramethyl- and diphenyl-phenanthroline molecules. Weak vibronic mixing of electronic and vibronic states was demonstrated in the region of 5 D 0 – 7 F 2 transition of Eu 3+ . The vibronic satellites of 5 D 0 – 7 F 0 -transition due to vibrations of the NO 3 − -group borrow about 1–2% of the intensity of the electric-dipole 5 D 0 – 7 F 2 transition yielding the increase of their relative intensity of 100 times in the Stokes sideband.

Optical spectroscopy and magnetic studies of dimeric europium capronate with 1,10-phenanthroline

Luminescence, excitation of luminescence and absorption spectra of europium capronate crystals as well as vibrational IR and Raman spectra at 4.2, 77 and 293 K were obtained. Magnetic susceptibility measurements were carried out down to 1.7 K. Correlations between the spectral and magnetic properties and details of the structure of the title n compound were studied. The crystal field parameters were calculated using the Stark splitting of the Eu3+ n electronic levels. The oscillator strengths were evaluated. Changes in the spectra and magnetic susceptibility of Eu(C5H11COO)3Phen n with increasing temperature from 4.2 to 293 K proves transformation of the crystal lattice. The subtle splitting of bands in the regions of the 5D0 n→ n7F1 and 5D0 n→ n7F2 transitions was revealed. Several possible causes of this phenomenon, including resonant n vibronic interactions and/or the possible effect of ion-pair interactions, are discussed.

Optical properties of Nd3+ in silica ceramics obtained by the sol–gel method

Abstract Heavily densified Nd 3+ doped silica ceramics were obtained by two different sol–gel based methods using distinct pH during gelation. The sample obtained at the higher pH showed more efficient emission. The morphology of the samples obtained was determined. It was found that Nd 3+ ions form nanosize as well amorphous aggregates. The optical properties of Nd 3+ doped silica ceramics were investigated.

Charge transfer bands in the Eu3+ luminescence excitation spectra of isomeric europium pyridine-dicarboxylates

A ligand-cation charge transfer band was observed in the region of 360–400 nm in the Eu3+ luminescence excitation spectrum of europium 3,4-pyridine-dicarboxylates, but was absent in the spectra of europium 2,6-and 2,3-pyridine-dicarboxylates. This band is due to noticeable energy transfer through a charge-transfer state formed owing to the high polarizability of the ligand in the former compound. Energy transfer through the excited ligand-lanthanide charge-transfer state can explain the well-known effect of luminescence quenching by redox-sensitive lanthanide ions.

Spectra and details of the structure of europium acetates with derivatives of 1,10-phenanthroline

Abstract Luminescence, excitation of luminescence, IR and Raman spectra of europium acetates with 1,10-phenanthroline derivatives (Ph), Eu(CH 3 COO) 3 .Ph, were studied. Crystal field parameters for model complexes were calculated. Some conclusions about details of the structure of the compounds were obtained. It was shown that both steric hindrances due to ligand–ligand crowding and donor–acceptor properties of the ligands are significant in creation of the structure. Maximum inequivalence of Eu–O bonds in compound containing 5-nitro-phenanthroline with electrophilic NO 2 -group was noted as well as in compounds with 3,4,7,8-tetramethyl- and 5-phenyl-phenanthroline having bulky substituents. There is the strongest polarisation of the carboxyl groups in these compounds. Nearly equalised Eu–O bonds were found in compound with 4,7-diphenyl-phenanthroline. Here a steric factor was minimised due to rotation of phenyl radicals in relation to the phenanthroline nucleus.

Influence of ligand architecture on the structure of coordination centre in dimeric europium carboxylates with 1,10-phenanthroline

Abstract Methods of optical spectroscopy and X-ray crystallography data were used to examine the effect of architecture of carboxylate anions on structure of the Eu3+ coordination centre in europium carboxylates with 1,10-phenanthroline Eu(RCOO)3·Phen. Luminescence spectra of europium acetate, nitropropionate, benzoate, naphthylcarboxylates, phenylacetates, phenoxyacetate, triphenylpropionate were investigated. A few of europium carboxylates with 2,2′-bipyridine Eu(RCOO)3·Bpy and europium salts Eu(RCOO)3·nH2O were also studied. Vibrational IR and Raman spectra of phenylacetate family were analyzed. The crystal structure of nitropropionate Eu(NO2C2H4COO)3·Phen was solved by X-ray diffraction method. The predominant influence of steric hindrances on Eu3+ coordination centre was observed at increase of the size of aromatic fragment of carboxylate anions. It was demonstrated, that introduction of the methylene bridges between the carboxylic group and aromatic rings of ligand weakens the effect of steric factor.