M. Karbowiak

Ag(I)/V(V) heterobimetallic frameworks generated from novel-type {Ag2(VO2F2)2(triazole)4} secondary building blocks: a new aspect in the design of SVOF hybrids.

A series of new silver(I)-containing MOFs [Ag(2)(tr(2)ad)(2)](ClO(4))(2) (1), [Ag(2)(VO(2)F(2))(2)(tr(2)ad)(2)]·H(2)O (2), [Ag(2)(VO(2)F(2))(2)(tr(2)eth)(2)(H(2)O)(2)] (3), and [Ag(2)(VO(2)F(2))(2)(tr(2)cy)(2)]·4H(2)O (4) supported by 4-substituted bifunctional 1,2,4-triazole ligands (tr(2)ad = 1,3-bis(1,2,4-triazol-4-yl)adamantane, tr(2)eth = 1,2-bis(1,2,4-triazol-4-yl)ethane, tr(2)cy = trans-1,4-bis(1,2,4-triazol-4-yl)cyclohexane) were hydrothermally synthesized and structurally characterized. In these complexes, the triazole heterocycle as an N(1),N(2)-bridge links either two adjacent Ag-Ag or Ag-V centers at short distances forming polynuclear clusters. The crystal structure of compound 1 is based on cationic {Ag(2)(tr)(4)}(2+) fragments connected in a 2D rhombohedral grid network with (4,4) topology. The neighboring layers are tightly packed into a 3D array by means of argentophilic interactions (Ag···Ag 3.28 Å). Bridging between different metal atoms through the triazole groups assists formation of heterobimetallic Ag(I)/V(V) secondary building blocks in a linear V-Ag-Ag-V sequence that is observed in complexes 2-4. These unprecedented tetranuclear {Ag(2)(VO(2)F(2))(2)(tr)(4)} units (the intermetal Ag-Ag and Ag-V distances are 4.24-4.36 and 3.74-3.81 Å, respectively), in which vanadium(V) oxofluoride units possess distorted trigonal bipyramidal environment {VO(2)F(2)N}¯, are incorporated into 1D ribbon (2) or 2D square nets (3, 4) using bitopic μ(4)-triazole ligands. The valence bond calculation for vanadium atoms shows +V oxidation state in the corresponding compounds. Thermal stability and photoluminescence properties were studied for all reported coordination polymers.

Site-selective emission spectra of Eu3+:Ca5(PO4)3F

Abstract The room temperature site-selective fluorescence and excitation spectra of Eu 3+ :FAP powder samples as well as the decay times of the observed emission lines associated with the 5 D 0 → 7 F 0,1,2 transitions have been measured. In sample I, prepared by the thermally stimulated diffusion of Eu 2 O 3 in the solid state, Eu 3+ reside only in the Ca(II) location which has C s symmetry. Experimental values for the Stark energy levels have been determined for three well-separated sites. Sites A and B exhibit very similar spectral features attributed to the presence of the charge-compensating O 2− ion in the F − position in the FAP lattice, whereas for Eu 3+ in site C the charge is most probably compensated by vacancies according to 3Ca 2+ →2Eu 3+ +Vacancy substitution. In sample II, prepared by precipitation of Eu 3+ (1%):FAP from solution, Eu 3+ substitute for calcium in the Ca(I) position exclusively and three sites with C 3 symmetry have been identified. Substitution of 3Ca 2+ /2Eu 3+ is the most probable charge-compensation mechanism. Heating of sample II stimulates the migration of Eu 3+ from the Ca(I) position to the low symmetry Ca(II) site.

Analysis of Eu3+ emission from different sites in Lu2O3

Abstract Lu 2 O 3 doped with Eu of varying concentrations was prepared using a convenient combustion technique. Emissions from two different crystallographic sites, C 2 and S 6 , were found and analyzed. Using various spectroscopic techniques, luminescence of Eu 3+ exclusively from site C 2 or site S 6 could be detected. Kinetics of both emissions was characterized and time constants of 1.5 and 4.3 ms were found, respectively. Energy transfer from Eu 3+ in site S 6 to Eu 3+ in site C 2 was proved to take place when the dopant content reaches about 1% or higher. For rising activator concentration the transfer becomes more efficient and for heavily doped samples the emission from S 6 site lasts in a vestige form only. The only emission transitions detected from Eu in centrosymmetric site S 6 were the 5 D 0 – 7 F 1 three-line band.

Analysis of absorption and luminescence spectra of U3+ doped Cs2NaYCl6 and Cs2LiYCl6 single crystals

Uranium(3+) doped single crystals of Cs2NaYCl6 and Cs2LiYCl6 with a 2.0% and 0.1% U3+ concentration have been obtained by the Bridgman-Stockbarger method. Luminescence spectra of the crystals were recorded at 160, 70, and 15 K. The emission bands observed in the visible and near infrared regions have been assigned to transitions from the lowest components of the 4I11/2, 4F3/2, and 4G7/2 multiplets to the crystal-field components of the 4I9/2 ground level. Absorption spectra were recorded from 4 000 to 25 000 cm−1 at 4.2 K. The zero phonon transitions were identified from an analysis of the vibronic side bands as well as in least-squares fits by applying a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions for an ion of the 5f3 configuration and Oh symmetry. Eight energy level parameters were varied simultaneously in the least-squares adjustments yielding a mean error of 57 and 61 cm−1 for U3+:Cs2LiYCl6 and U3+:Cs2NaYCl6, respectively. The analysis of the spectra enab...

SPECTROSCOPIC STUDIES AND CRYSTAL-FIELD ANALYSIS OF U3+ IONS IN RBY2CL7 SINGLE CRYSTALS

Single crystals of U3+ diluted into a matrix of RbY2Cl7 have been grown by the Bridgman–Stockbarger method. There are two different intrinsic U3+ sites in this crystalline host, each with an approximate C2v site symmetry. A third minor U3+ site was also found. Absorption, fluorescence, and excitation spectra of these crystals were obtained at 300 and 4.2 K. Transitions belonging to each U3+ site were distinguished by time-gated site-selective spectroscopy. The energy levels of the two intrinsic sites were assigned and fitted to a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions for a 5f3 ion at a C2v symmetry site. Quite different 4F9/2 fluorescence lifetimes were measured for the three sites, due to a multiphonon decay mechanism which is affected by differences in their respective crystal-field strengths. These results are analyzed quantitatively using the theory for the electron–phonon interaction.

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 compound were studied. The crystal field parameters were calculated using the Stark splitting of the Eu3+ electronic levels. The oscillator strengths were evaluated. Changes in the spectra and magnetic susceptibility of Eu(C5H11COO)3Phen 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 → 7F1 and 5D0 → 7F2 transitions was revealed. Several possible causes of this phenomenon, including resonant vibronic interactions and/or the possible effect of ion-pair interactions, are discussed.

Crystal-field analysis of Eu3+ in Lu2O3

Low temperature (7 K) absorption spectra of polycrystalline sintered ceramic Lu2O3:Eu3+ were recorded between 3950 and 50000 cm−1. There are two different intrinsic Eu3+ sites, C2 and S6 (C3i), in this host. A total of 105 crystal-field (CF) energy levels were assigned and fitted to a semiempirical Hamiltonian representing the combined free-ion (FI) and CF interactions for a 4f6 ion in the C2 symmetry site. 10 FI and 14 CF parameters were varied simultaneously in the least square adjustments yielding an rms deviation between the calculated and experimental levels of 15 cm−1. The CF strength parameter, S, obtained from calculated Bqk parameters is larger for Lu2O3 when compared to the Y2O3 host, which is in accordance with the smaller ionic radius of the Lu3+ ion. The CF splittings of the 7F 1 and 5D 1 levels were also determined experimentally for the Eu3+ ion in the centrosymmetric S6 site and the value of the second-rank B02 CF parameter was calculated.

4 f 6 → 4 f 5 5 d 1 absorption spectrum analysis of Sm 2 + : SrCl 2

The

The 5f2-->5f16d1 absorption spectrum of Cs2GeF6:U4+ crystals: A quantum chemical and experimental study.

4{f}^{6}\ensuremath{\rightarrow}4{f}^{5}5{d}^{1}

Spectrum analysis, correlation crystal-field effects and f-f transition intensities of U3+ in LaCl3

absorption spectrum of the