Low Site Symmetry Research Articles

Synthesis, Lanthanide Coordination Chemistry, and Liquid–Liquid Extraction Performance of CMPO-Decorated Pyridine and Pyridine N-Oxide Platforms

Syntheses for a set of new ligands containing one or two carbamoylmethylphosphine oxide (CMPO) fragments appended to pyridine and pyridine N-oxide platforms are described. Molecular mechanics analyses for gas phase lanthanide-ligand interactions for the pyridine N-oxides indicate that the trifunctional NOPOCO molecules, 2-{[Ph2P(O)][C(O)NEt2]C(H)}C5H4NO (7) and 2-{[Ph2P(O)][C(O)NEt2]CHCH2}C5H4NO (8), and pentafunctional NOPOP'O'COC'O' molecules, 2,6-{[Ph2P(O)][C(O)NEt2]C(H)}2C5H3NO (9) and 2,6-{[Ph2P(O)][C(O)NEt2]CHCH2}2C5H3NO (10), should be able to adopt, with minimal strain, tridentate and pentadentate chelate structures, respectively. As a test of these predictions, selected lanthanide coordination chemistry of the N-oxide derivatives was explored. Crystal structure analyses reveal the formation of a tridentate NOPOCO chelate structure for a 1:1 Pr(III) complex containing 7 while 8 adopts a mixed bidentate/bridging monodentate POCO/NO binding mode with Pr(III). Tridentate and tetradentate chelate structures are obtained for several 1:1 complexes of 9 while a pentadentate chelate structure is observed with 10. Emission spectroscopy for one complex, [Eu(9)(NO3)3], in methanol, shows that the Eu(III) ion resides in a low-symmetry site. Lifetime measurements for methanol and deuterated methanol solutions indicate the presence of four methanol molecules in the inner coordination sphere of the metal ion, in addition to the ligand, with the nitrate anions most likely dissociated. The solvent extraction performance of 7-10 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions was analyzed and compared with the performance of 2,6-bis(di-n-octylphosphinoylmethyl)pyridine N-oxide (TONOPOP'O') and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO) measured under identical conditions.

Synthesis, Characterization and Luminescent Properties of La2Zr2O7:Eu3+ Nanorods

The Eu3+-doped La2Zr2O7phosphor with rod-like morphology was successfully synthesized by conventional solid state reaction and hydrothermal method. X-ray diffraction patterns, transmission electron microscopy, and photoluminescence spectra were employed to characterize its structure and morphology as well as luminescent properties. The results indicated that the red-emitting phosphor La2Zr2O7:Eu3+ had well crystallized and belonged to the cubic structure with space group of Fd3m. The as-obtained product mainly appeared as straight nanorods with an average diameter of 47 nm and length of 50–700 nm. The possible growth mechanism was also discussed. It was found that under blue excitation with a wavelength of 466 nm, the La2Zr2O7:Eu3+ phosphor exhibited a characteristic red emission at 616 nm that was attributed to the hypersensitive D50→7F2electric dipole transition of Eu3+ ions. Meanwhile, it was more interesting to note that the emission of D51→7FJ (J=0, 1, 2) transitions and the splitting patterns of 5D0→7FJ (J=1, 2, 4) transitions of Eu3+ ions can be observed in the luminescent spectra of La2Zr2O7:Eu3+. It was demonstrated that Eu3+ preferred to occupy a low symmetry site.

Site occupancy and magnetic properties of pyrochlore-structured AgOs2O6

AgOs2O6 prepared from ion-exchanged superconducting β-pyrochlore KOs2O6 has been shown to be non-superconducting. Synchrotron x-ray structure refinement suggests that AgOs2O6 has the Ag ion mostly occupying the low-symmetry 32e site in the space group of proper occupancy, which is different from the original major occupancy at the high-symmetry 8b site for KOs2O6, and similar to non-superconducting Na1.4Os2O6⋅H2O. Magnetic susceptibility measurements found no magnetic ordering down to ∼1.7 K. The trace amount of isolated spins suggests that the Ag could be neutral and lead to a pure Os6+ valence state of zero spin in the newly prepared AgOs2O6.

Optical properties and crystal structure of lanthanide(III) coordination compounds with 2-propenoic acid

Coordination compounds of a new type, Ln(C3H3O2)3·xH2O (where Ln=Nd3+, Dy3+; C3H3O2−=2-propenoic anion/acrylic anion, x=3 or 1.5 for Nd and Dy, respectively), were obtained in crystalline state and their structures were determined. Both crystals are composed of polymeric chains and in both crystals there are two symmetry-independent lanthanide ions, each with a different coordination sphere. The Nd crystal (I) is monoclinic, space group P21/c, and the Dy crystal (II) is triclinic, P1¯. The Ln3+ ions occupy low-symmetry sites in the dimeric structure of Ln(H2CCHCOO)3·xH2O. The spectroscopic investigations of the title monocrystals at room and low temperatures down to 4.2K were performed to explain the electrostatic nature of the Ln3+–ligand bond. Variations in the spectroscopic parameters and their correlations with the nature of the Ln3+–L bond are discussed. Analysis of the low-temperature spectra indicates the presence of ion-pair interactions. The influence of the –CC– double bond in the substituent of the carboxylate ions on the distribution of charge, polarity, strength, and character of the Ln–O(L) coordination bond is analysed. The number of electronic components observed in the absorption spectra measured at 4.2K is compatible with that expected for these systems. Spectroscopic measurements allowed us to compare the optical properties of Ln(H2CCHCOO)3·xH2O with lanthanide acetates and other carboxylates.

Synthesis, luminescence and NMR studies of lanthanide (III) complexes with hexafluoroacetylacetone and phenanthroline. Part II

The paper reports the syntheses, 1H NMR spectral and luminescence spectral studies of eight-coordinate Sm, Eu, Tb, Dy and Tm complexes of the type [Ln(hfaa)3(phen)] (hfaa=hexafluoropentanedione and phen=1,10-phenanthroline). These complexes have been synthesized in high yields by modifying a method reported in literature for synthesizing similar complexes. Large up field and downfield shifts were observed in their 1H NMR spectra. The lanthanide induced chemical shifts in these paramagnetic complexes are dipolar in nature. The H(2) and H(4) proton resonances of phen of the thulium complex have been shifted to highfields which is unusual. Inter- and intra-molecular chemical shift ratios are similar for Sm and Eu complexes as these are isostructural in solution. The quantum yields (Φ=46% for Eu, 32% for Tb, 2.7% for Sm and 2.1% for Dy) of the complexes indicate that energy transfer from ligands (hfaa and phen) to Ln(III) is efficient. The luminescence in the Dy(III) complex is the least intense due to poor intramolecular energy transfer match as compared to rest of the complexes. The lanthanide ions in these complexes have low symmetry sites.

Unincorporated iron pool is linked to oxidative stress and iron levels in Caenorhabditis elegans

Free radicals or reactive oxygen species (ROS) are relatively short-lived and are difficult to measure directly; so indirect methods have been explored for measuring these transient species. One technique that has been developed using Escherichia coli and Saccharomyces cerevisiae systems, relies on a connection between elevated superoxide levels and the build-up of a high-spin form of iron (Fe(III)) that is detectable by electron paramagnetic resonance (EPR) spectroscopy at g=4.3. This form of iron is referred to as "free" iron. EPR signals at g=4.3 are commonly encountered in biological samples owing to mononuclear high-spin (S=5/2) Fe(III) ions in sites of low symmetry. Unincorporated iron in this study refers to this high-spin Fe(III) that is captured by desferrioxamine which is detected by EPR at g value of 4.3. Previously, we published an adaptation of Fe(III) EPR methodology that was developed for Caenorhabditis elegans, a multi-cellular organism. In the current study, we have systematically characterized various factors that modulate this unincorporated iron pool. Our results demonstrate that the unincorporated iron as monitored by Fe(III) EPR at g=4.3 increased under conditions that were known to elevate steady-state ROS levels in vivo, including: paraquat treatment, hydrogen peroxide exposure, heat shock treatment, or exposure to higher growth temperature. Besides the exogenous inducers of oxidative stress, physiological aging, which is associated with elevated ROS and ROS-mediated macromolecular damage, also caused a build-up of this iron. In addition, increased iron availability increased the unincorporated iron pool as well as generalized oxidative stress. Overall, unincorporated iron increased under conditions of oxidative stress with no change in total iron levels. However, when total iron levels increased in vivo, an increase in both the pool of unincorporated iron and oxidative stress was observed suggesting that the status of the unincorporated iron pool is linked to oxidative stress and iron levels.

Synthesis and photoluminescent behavior of Eu3+-doped alkaline-earth tungstates

Eu3+-doped alkaline-earth tungstates MWO4 (M=Ca2+, Sr2+, Ba2+) were prepared by a polymeric precursor method based on the Pechini process. The polymeric precursors were calcined at 700°C for 2h in order to obtain well-crystallized powders and then characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and photoluminescence spectroscopy (PL). All prepared samples showed a pure crystalline phase with scheelite-type structure confirmed by XRD. It was noted that the charge-transfer band shifted from 260 to 283nm when calcium is replaced by strontium. However, this band was not observed for Eu3+-doped barium tungstate. Upon excitation at 260nm, the emission spectra are dominated by the red 5D0→7F2 transition at 618nm. By analyzing of the emission lines, it was inferred that Eu3+ ions occupy low symmetry sites in the host lattice. It was also found that Eu3+-doped SrWO4 displays better chromaticity coordinates and greater luminescence intensity than the other samples.

Energy levels and crystal field parameters for Nd 3+ ions in BaY 2F 8, LiKYF 5, and K 2YF 5 single crystals

The available experimental energy levels of Nd 3+ ions doped into single crystals of BaY 2F 8, LiKYF 5, and K 2YF 5, which exhibit low site symmetry, are reanalyzed. A combined approach based on the ascent/descent in symmetry (ADS) method, the superposition model (SPM) analysis, and the pseudosymmetry axes method (PAM) is utilized to extract the crystal field (CF) parameters, B kq , from experimental spectra. Corresponding sets of the free-ion parameters are also fitted. The crystallographic data are used to establish the axis systems most appropriate for approximation of the actual monoclinic C 2 site symmetry to higher orthorhombic D 2 and tetragonal D 4 symmetry used in CF calculations for BaY 2F 8. Similarly, for triclinic C 1 site symmetry in LiKYF 5 and K 2YF 5 approximation to monoclinic C 2 and orthorhombic D 2 symmetry for LiKYF 5, whereas the monoclinic C s symmetry for K 2YF 5, are considered. It is shown that the C 2v approximation used previously for K 2YF 5:Nd 3+ is not suitable. SPM enables to calculate for the unapproximated and idealized polyhedrons YF 8 in a given ion–host system of the combined coordination factors Sg k,q expressed in the modified crystallographic axis system CAS* and approximated symmetry adapted axis systems, respectively. The quantities Sg k,q serve as input for PAM calculations for independent determination of the axis system appropriate for higher symmetry approximations. The pseudosymmetry axes represent the axis system that reflects most closely the approximated higher symmetry of the nearest ligands in a paramagnetic complex embodied in the 4th-rank CF parameters. The combined ADS/SPM/PAM approach provides sets of starting CF parameters (CFPs) in well-defined axis systems. Multiple fittings starting from different points in the CF parameter space yield converging solutions, thus increasing the reliability of the final optimized solutions, which may be then considered as the global minima. The present CF analysis, unlike the previous ones, takes into account the low symmetry aspects inherent in the CF Hamiltonian and optical spectra. The improved and more reliable sets of CFPs are generated as well as modified assignments of the CF energy levels are proposed for BaY 2F 8:Nd 3+. The present considerations enable also clarification of some ambiguous points occurring in previous studies.

Lanthanide(III) complexes of N4O4 Schiff base macrocycle: Luminescence and formation of heterodinuclear d–f complexes

The new macrocyclic Schiff base lanthanide(III) complexes of the formula [Ln(H4L)Cl3]·nH2O (Ln=Pr(III), Nd(III), Sm(III), Gd(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)) have been synthesized in the template condensation of 1,3-diamino-2-hydroxypropane and 2,6-diformyl-4-methylphenol in the presence of the appropriate Ln(III) chlorides. The obtained compounds have been characterized in solution by NMR spectroscopy, and the 1H and 13C NMR spectra of [Pr(H4L)Cl3]·H2O, [Nd(H4L)Cl3]·H2O, [Sm(H4L)Cl3]·H2O and [Yb(H4L)Cl3]·4H2O complexes have been assigned on the basis of COSY, NOESY and HMQC techniques. The analysis of isotropic shifts of the paramagnetic Ln(III) derivatives indicate the unsymmetrical coordination of the lanthanide(III) ions within the macrocyclic ligand H4L. 1H NMR spectroscopy has also been used to follow transformation of the [Ln(H4L)]3+ complexes into heterodinuclear derivatives, [LnCo(H2L)]3+ and [LnCo(HL)]2+. Emission and excitation spectra as well as luminescence decay time measurements (at 293 and 77K) were used to characterize the photophysical properties of the mononuclear Eu(III), Gd(III) and Yb(III) [Ln(H4L)Cl3]·nH2O complexes in solid-state. Energy transfer from the ligand to the Yb(III) ions has been proved at both room temperature and 77K. The f–f luminescence of Nd(III) and Er(III) was not observed neither by the excitation through the ligand (1π–1π∗) nor the lanthanide ion absorption transitions both at 293 and 77K. In the case of Eu(III) complex the energy transfer only occurs at 77K, while at room temperature a thermally activated back energy transfer process from 5D0 Eu(III) excited state to the ligand triplet states has been proposed. The 4f–4f emission spectrum of Eu(III) in a low site symmetry with the dominating 5D0→7F4 transition has been demonstrated for the first time.

151Eu Mössbauer measurements of CuLa1 − x Eu x O2 with luminescent property

An increase of the asymmetric ratio of photoluminescence lines from CuLa1 − x Eu x O2 was observed under 100 K, suggesting a lower site symmetry for the Eu cation. Mossbauer spectra of CuLa0.8Eu0.2O2 measured at 77 K revealed that the valence of Eu is trivalent and that the crystal structure of CuLa1 − x Eu x O2 might contain a EuO6 octahedron with lower symmetry. The thermodynamic stability of the valence of Cu and Eu was calculated, showing agreement with Mossbauer spectra.

Lanthanide-DTPA grafted silica nanoparticles as bimodal-imaging contrast agents

The design and synthesis of a combined MRI-optical probe for bio-imaging are reported. The materials studied join the properties of lanthanide (Ln 3+) complexes and nanoparticles (NPs), offering an excellent solution for bimodal imaging. The hybrid SiO 2@APS/DTPA:Gd:Ln (Ln = Eu 3+ or Tb 3+) (APS: 3-aminopropyltriethoxysilane, DTPA: diethylenetriamine pentaacetic acid) system increases the payload of the active magnetic centre (Gd 3+) and introduces a Ln 3+ long-life excited state (Eu 3+: 0.35 ± 0.02 ms, Tb 3+: 1.87 ± 0.02 ms), with resistance to photobleaching and sharp emission bands. The Eu 3+ ions reside in a single low-symmetry site. Although the photoluminescence emission is not influenced by the simultaneous presence of Gd 3+ and Eu 3+, a moderate r 1 increase and a larger enhancement of r 2 are observed, particularly at high fields, due to susceptibility effects on r 2. The presence of Tb 3+ instead of Eu 3+ further raises r 1 but decreases r 2. These values are constant over a wide (5–13) pH range, indicating the paramagnetic NPs stability and absence of leaching. The uptake of NPs by living cells is fast and results in an intensity increase in the T 1-weighted MRI images. The optical properties of the NPs in cellular pellets are also studied, confirming their potential as bimodal imaging agents.

Copper (II) Complexes of Knoevenagel Condensate β-Diketimines as Models for Blue Copper and their Interaction with DNA

A series of copper(II) complexes with positive reduction potential have been synthesized by anin situfashion by the reaction of a Knoevenagel condensate, salicylidenebenzoylacetone (salbenz) with 4-X-anilines and copper(II) chloride. The electronic spectra of these complexes in acetonitrile show d–d bands around 540 nm with high molar extinction coefficient (ε~1600-1800 cm-1) due to lowering of symmetry around metal center, and MLCT band around 400 nm. The EPR spectral features with four g((lines having g((>2.0 >g⊥, and a broadening of g⊥component suggest a lowered site symmetry around Cu(II) monomer. The cyclic voltammetric studies of Cu(II) complexes in CH3CN shows a positive reduction potential (Epc = 492-451 mV) with moderately high peak to peak separation (∆Ep=126-163mV). All these results are comparable with the results of natural blue copper proteins even in the absence of S-coordination, and suggest that they can mimic the functional properties of blue copper proteins. These complexes on interaction with herring sperm DNA, the intense intraligand (IL) π-π*transition around 300 nm is found to be hypochromic with a slight red shift. The hypochromism and moderate binding constant are indicative of binding of the complexes with DNA with an affinity less than the classical intercalators, due to the possible substitution of the two chlorides with the DNA base pairs and relatively bulky structure of ligand molecule. Additional evidence of DNA-Cu(II) complex interaction was obtained by CD studies. The experimental results reveal that these complexes may serve as a model for blue copper proteins and as a tool for probing the structure of DNA.

Concentration influence on temperature-dependent luminescence properties of samarium substituted strontium tetraborate

The series of divalent samarium substituted strontium tetraborate (Sr 1− x Sm x B 4O 7) polycrystalline samples were prepared by the conventional solid-state reaction. The phase formation of the samples was investigated by X-ray powder diffraction measurements. The luminescence spectra and decay curves of the Sm 2+ ions were measured. Temperature dependent Sm 2+ luminescence properties were investigated. The f–d and 5D 1– 7F J transitions appeared at 350 K and increased with increase in the temperature while the intensity of 5D 0– 7F J transitions decreased. The emission spectra pointed out that Sm 2+ occupies of C 2v or lower symmetry site. The photoluminescence decay times of strontium tetraborate doped with different concentrations of Sm 2+ was investigated as a function of temperature in the range of 100–500 K. However, no obvious concentration quenching was observed.

Optical properties of LFZ grown β-Ga2O3:Eu3+ fibres

Due to their relevance for electronic and optoelectronic applications, transparent conductive oxides (TCO) have been extensively studied in the last decades. Among them, monoclinic β-Ga2O3 is well known by its large direct bandgap of ∼4.9eV being considered a deep UV TCO suitable for operation in short wavelength optoelectronic devices. The wide bandgap of β-Ga2O3 is also appropriate for the incorporation of several electronic energy levels such as those associated with the intra-4fn configuration of rare earth ions. Among these, Eu3+ ions (4f6) are widely used as a red emitting probes both in organic and inorganic compounds. In this work, undoped and Eu2O3 doped (0.1 and 3.0mol%) Ga2O3 crystalline fibres were grown by the laser floating zone approach. All fibres were found to stabilize in the monoclinic β-Ga2O3 structure while for the heavily doped fibres the X-ray diffraction patterns show, in addition a cubic europium gallium garnet phase, Eu3Ga5O12. The spectroscopic properties of the undoped and Eu doped fibres were analysed by Raman spectroscopy, low temperature photoluminescence (PL) and photoluminescence excitation (PLE). The Eu3+ luminescence is mainly originated in the garnet, from where different europium site locations can be inferred. The spectral analysis indicates that at least one of the centres corresponds to Eu3+ ions in dodecahedral site symmetry. For the lightly doped samples, the spectral shape and intensity ratio of the 5D0→7FJ transitions is totally different from those on Eu3Ga5O12, suggesting that the emitting ions are placed in low symmetry sites in the β-Ga2O3 host.

Crystal-field analysis for RE 3+ ions in laser materials: II. Absorption spectra and energy levels calculations for Nd 3+ ions doped into SrLaGa 3O 7 and BaLaGa 3O 7 crystals and Tm 3+ ions in SrGdGa 3O 7

Low temperature polarized absorption spectra are analyzed to achieve assignments of energy levels for Nd 3+ and Tm 3+ ions at monoclinic C s site symmetry in ABC 3O 7 crystals. Based on the concept of average optical center, the experimental energy levels for single crystals of SrLaGa 3O 7:Nd 3+ (SLG:Nd), BaLaGa 3O 7:Nd 3+ (BLG:Nd), and SrGdGa 3O 7:Tm 3+ (SGG:Tm) were analyzed in terms of the free-ion parameters and the crystal field (CF) ones, B kq . Assignments of the energy levels resolved in the spectra were done in stages applying the ascent/descent in symmetry method in CF analysis. The actual monoclinic C s site symmetry at the metal centers in ABC 3O 7 crystals and the approximated orthorhombic C 2v and tetragonal C 4v symmetry were considered. The starting values of B kq ’s for SLG:Nd and BLG:Nd crystals were obtained from superposition model (SPM) analysis. The final fitted crystal field parameters show high compatibility with the existing data for structurally similar ion-host systems. The obtained values of the intrinsic parameters provide basis for SPM analysis of CF parameters for rare earth ions in other similar systems, especially those exhibiting low-symmetry sites. The SPM parameters derived for SLG:Nd are used for simulation and assignment of the energy levels involved in the potential laser transitions at about 1800 nm due to Tm 3+ ions in SGG crystals. The evaluated emission cross-section is about two times lower than that obtained previously.

Synthesis and Sm 2+/Sm 3+ doping effects on photoluminescence properties of Sr 4Al 14O 25

Complete and partial samarium reduction was achieved under strong reducing atmosphere by solid-state and combustion synthesis of Sr 3.96Sm 0.04Al 14O 25. Dependence of different fluxing agents on the formation of various strontium aluminates was examined. The samples were investigated by X-ray powder diffraction, temperature dependent luminescence decay and photoluminescence measurements. Excitation with UV radiation resulted in sharp and well resolved emission lines of samarium ions. Distinct temperature behavior for Sm 2+ and Sm 3+ were detected in the range of 100–500 K. Estimated emission thermal quenching values ( TQ 1/2) for divalent samarium were approximately 270 K while for trivalent state around 660 K. Measured luminescence decay values of Sm 2+ are substantially lower than for Sm 3+,≈1.7 and ≈2.7 ms, respectively. The spectral feature of Sm 2+ emission spectrum indicates that dopant occupies low symmetry site in Sr 4Al 14O 25 compound.

Synthesis and optical properties of Eu-doped ZnO nanosheets by hydrothermal method

Eu-doped ZnO nanosheets with irregular porous microstructure were successfully prepared by a simple hydrothermal method. The microstructures, morphologies and optical properties of the as-prepared nanosheets were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and Raman spectroscopy. XRD and XPS results indicated that trivalent europium ions were successfully doped into the crystal lattice of ZnO matrix. Nanosheets with irregular porous can be seen from the TEM images. PL spectroscopy indicated that the peaks located at 580, 587 and 614 nm were attributed to the 4f–4f intrashell transitions of 5D 0→ 7F 0, 5D 0→ 7F 1 and 5D 0→ 7F 2 of Eu 3+ ions,respectively, and the intensity ratio of 5D 0→ 7F 2 to 5D 0→ 7F 1 indicated that Eu 3+ ions were incorporated into wurtzite ZnO host by substitution on the Zn sublattice and located at a low-symmetry site (C 3v) without inversion center.

Synthesis and Study of the Photophysical Properties of a New Eu3+ Complex with 3-Hydroxypicolinamide

This work reports on the synthesis and characterization of a new complex of Eu(3+) with the 3-hydroxypicolinamide ligand (Hhpa). Here we present an approach for obtaining bis[2-carbamoyl(κO)pyridin-3-olato(κO')] lanthanide complexes, which were characterized through elemental analysis, thermal analysis, infrared and photoluminescence spectroscopies (emission, excitation, luminescence lifetimes, quantum efficiencies, Judd-Ofelt parameters and quantum yields). Although hpa can act as a bidentate ligand in different conformations, the results attest for the occurrence of a unique coordination site of low symmetry for the Eu(3+) ions, in which two anionic hpa ligands coordinate the cations through an O/O chelating system. The phosphorescence of the synthesized gadolinium complex provides the energy of the triplet state, which is determined to be at 20,830 cm(-1) over the ground state. This makes the Hhpa ligand very adequate for sensitizing the Eu(3+) luminescence, which leads to a very efficient antenna effect and opens a wide range of applications for the complex in light emitting organic-inorganic devices.

Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite

aB stract Natural single-crystal specimens of the montebrasite/amblygonite series from Brazil, with general formula LiAlPO4(F,OH), were investigated by electron microprobe, Raman spectroscopy, X-ray diffraction, and infrared absorption. Since little is known about impurities and their local symmetries, electron paramagnetic resonance (EPR) was applied. Six different paramagnetic impurities and radiation defects were detected by EPR. Three of them, all substituting for Al 3+ ions, namely, iron (Fe 3+ ), vanadium (V 4+ ), and niobium (Nb 4+ ) impurities were characterized in this work. The Fe 3+ (3d 5 )-related EPR spectra and angular dependencies show occupation of low-symmetry sites that are revealed in the high asymmetry parameter of the electronic fine structure, E/D = 0.27. Vanadium and niobium impurities are identified through their typical strong hyperfine interactions. Both form interesting examples for which the properties of 3d 1 ion (V 4+ ) and 4d 1 ion (Nb 4+ ) in the same host matrix can be compared. It is shown that both ions form complex defects of type VO 2+ (vanadyl) and NbO 2+ (niobyl), showing superhyperfine interaction with two equivalent hydrogen ions and not to fluorine. The EPR rotation patterns are analyzed in detail for three mutually perpendicular crystal planes. Spin Hamiltonian parameters are calculated and discussed.

Influence of the Fluid-to-Film Transition on Photophysical Properties of MLCT Excited States in a Polymerizable Dimethacrylate Fluid

Photophysical properties of the salts [Ru(bpy)(3)](p-Tos)(2), [Ru(dmb)(3)](PF(6))(2), [Ru(vbpy)(3)](PF(6))(2), and [Ru(phen)(3)](p-Tos)(2) (bpy = 2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine, vbpy = 4-methyl-4'-vinyl-2,2'-bipyridine, phen = 1,10-phenanthroline, and p-Tos = p-toluene sulfonate) in fluid and film polyethylene glycol dimethacrylate containing nine ethylene glycol spacers (PEG-DMA550) are reported. MLCT absorption energies and bandshapes are similar in fluid and film PEG-DMA550 pointing to similar local dielectric environments, presumably dominated by the polar acrylate groups. Emission energies and excited-to-ground state 0-0 energy gaps (E(0)), determined by emission spectral fitting, are blue-shifted, and band-widths-at-half height (Δv(0,1/2)) decreased, due to an expected "rigid medium effect" in PEG-DMA550 film. The extent of loss of medium dipole reorientation in the rigid environment, and the increased emission energies in the film, resulted in enhanced emission quantum yields and excited state lifetimes in accordance with the energy gap law. The "rigid medium effect" in PEG-DMA550 is less pronounced than in films of poly(methyl methacrylate) (PMMA) pointing to a more fluid-like local environment presumably arising from the ethylene glycol linker spacers in PEG-DMA550. Comparison of the absorption, emission, emission spectral fitting, and emission lifetime results for [Ru(dmb)(3)](PF(6))(2) and [Ru(vbpy)(3)](PF(6))(2) shows that the vinyl groups of vbpy copolymerize with PEG-DMA550 covalently incorporating Ru(vbpy)(3)(2+) as a cross-linker into the polymer network. The most dramatic effect of the fluid-to-film transition is seen in the emission lifetime data for [Ru(phen)(3)](p-Tos)(2), with an increase of ~3 in the PEG-DMA550 film. Ru(phen)(3)(2+) cations appear to occupy a low symmetry site in the films probably close to the polar acrylate groups in a structurally confined environment.