Spectroscopic probing of site symmetry in solids
TL;DR: In this paper, the site symmetry, coordination geometry and structural changes in rare-earth complexes of high and low symmetry are compared with X-ray data, and the use of electronic absorption spectra to explore the coordination geometry of a complexed rare earth ion is considered.
About: This article is published in Journal of Molecular Structure.The article was published on 1997-03-17. It has received 6 citations till now. The article focuses on the topics: Rule of mutual exclusion & Absorption spectroscopy.
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Journal Article•
TL;DR: In this article, the vibrational, electronic Raman and electronic spectra of the lanthanide elpasolite systems are presented and discussed, with particular reference to phase transitions.
Abstract: The Ln 3 + ion is situated at a site of octahedral symmetry in crystals of the lanthanide elpasolites, M 2 ALnX 6 . The syntheses and crystal structures of M 2 ALnX 6 are described, with particular reference to phase transitions. The centrosymmetric environment of Ln 3 + confers different spectral properties than are observed for most solid-state lanthanide ion systems, and the selection rules are deduced. The vibrational, electronic Raman and electronic spectra of the lanthanide elpasolite systems are presented and discussed. The electronic spectra are described in terms of the 4f N -4f N zero phonon line and the vibronic sideband structure and the success of intensity calculations is evaluated. The synergy of one- and two-photon studies is emphasized. The differences with the 4f N -4f N - 1 5d spectra of M 2 ALnX 6 are illustrated. The parametrization of the energy level data-sets is assessed and the success of recent refinements is analysed. Following a brief review of the theory of energy transfer in crystals, experimental studies of quenching, cross-relaxation, upconversion and photon avalanche in neat and doped elpasolite systems are reviewed. Physical mechanisms are given for spectral features and for energy transfer pathways.
55 citations
TL;DR: In this article, low-temperature electronic absorption and emission data are reported for Tm 3 + at the octahedral site in crystals of Cs 2 NaTmCl 6.
Abstract: Low-temperature electronic absorption and emission data are reported for Tm 3 + at the octahedral site in crystals of Cs 2 NaTmCl 6 . Thirty-seven crystal field levels (total degeneracy 88) of the f 1 2 configuration (totaldegeneracy 91) have been assigned, and in several cases the levels are split due to electron-phonon coupling interactions. The fitting of the energy levels, using the conventional f 1 2 analysis with 12 variable parameters, gives a mean deviation of 53.3 cm - 1 . This is reduced to 9.3 cm - 1 by including the 4f 1 2 np 6 /4f 1 3 np 5 configuration interaction, using 16 variable parameters. The results indicate a tendency for the early members in the series of Ln 3 + ions to interact with the p-electron, and the later members with the p-hole, configurations, following the redox properties of the ions. The interacting configuration is charge-transfer (n = 3) rather than metal ion (n = 5), and the mixing of ligand wave functions with those of the metal ion may be responsible for the unusually strong electron-phonon coupling identified for several electronic states of Tm 3 + in TmCl 6 3-.
28 citations
TL;DR: The results highlight the C(2)(v)() (k even) and C(1) (k odd) distortions from the ideal D(4)(d)() antiprismal structure, which slightly modify the 4f(2) energy level scheme, and largely determine the spectral intensities in Pr(H( 2)PO(2))(3), respectively.
Abstract: The lanthanide hypophosphite complexes Ln(H(2)PO(2))(3) (Ln = La, Pr, Nd) and Ln(H(2)PO(2))(3).H(2)O (Ln = La, Pr) crystallize in the space group Po (No. 2), Z = 2. The lattice constants for La(H(2)PO(2))(3) are a = 6.7912(6) A, b = 7.0801(8) A, c = 8.863(1) A, alpha = 82.64(1) degrees, beta = 74.43(1)( o), gamma = 71.91(1) degrees; for La(H(2)PO(2))(3).H(2)O, a = 7.2291(4) A, b = 7.983(1) A, c = 8.934(1) A, alpha =110.57(1) degrees, beta = 98.26(1) degrees, gamma = 104.35(1) degrees. In both structures hypophosphite ions bridge adjacent 8-coordinate lanthanide ions to give infinite chains. Infrared and Raman spectra (300-20 K) are shown to be consistent with the crystallographic data, with 52 of the 54 fundamental hypophosphite modes of vibration assigned. The electronic spectra of the anhydrous compounds consist mainly of bands due to pure electronic electric dipole transitions. Two-center vibronic transitions observed in the (3)H(4) --> (1)D(2) spectrum of Pr(H(2)PO(2))(3) are not well-simulated by a model with dipole-dipole interaction terms between the two centers. The energy level scheme of Pr(3+) in Pr(H(2)PO(2))(3) was fitted to a model Hamiltonian for a C(2)(v)() site symmetry Pr(3+) ion, including configuration interaction of 4f(2) with 4f6p. Theoretical crystal field parameters were in reasonable agreement with those derived from the energy level fitting. The results highlight the C(2)(v)() (k even) and C(1) (k odd) distortions from the ideal D(4)(d)() antiprismal structure, which slightly modify the 4f(2) energy level scheme, and largely determine the spectral intensities in Pr(H(2)PO(2))(3), respectively. The derived energy level scheme of Nd(H(2)PO(2))(3) is similar to that for 8-coordinated Nd(3+) in NdCl(3).6H(2)O.
25 citations
TL;DR: In this paper, the influence of site symmetry and electron phonon coupling in Cs2NaAlF6:Cr3+ is probed by correlation of optical and structural measurements based on neutron and x-ray analysis.
Abstract: The influence of site-symmetry and electron phonon coupling in Cs2NaAlF6:Cr3+ is probed by correlation of optical and structural measurements Based on neutron and x-ray analysis the structure is a distorted R3m¯, exhibiting a unique stacking interaction Selection rules have been used to assign the Raman-active zone-center vibrations Although local and bulk mode frequencies differ slightly, indicating that the guest Cr3+ ion does not significantly perturb the host structure, vibrational analysis indicates the Cr3+ ion is coupled to the first coordination sphere of the Al–F lattice
24 citations
TL;DR: In this paper, photo luminescence (PL) and extended X-ray absorption fine structure (EXAFS) measurements confirmed the single phase formation of uranium-doped alkaline-earth borophosphate samples.
Abstract: Alkaline-earth (calcium, strontium, and barium) borophosphates doped with uranium (U) are prepared through conventional solid-state reaction route. The form of stabilized uranium in these solid matrices was characterized and investigated using X-ray diffraction (XRD), photo luminescence (PL) and extended X-ray absorption fine structure (EXAFS). XRD measurements confirmed the single phase formation of uranium-doped alkaline-earth borophosphate samples. The PL characteristics of uranium in calcium and barium borophosphate are studied for the first time. Photoluminescence studies indicated presence of uranium as Uranyl in SrBPO5 and CaBPO5 matrices whereas in case of BaBPO5 the indication was for uranate species. The life time data corroborated the presence of a different uranium species in SrBPO5, CaBPO5, and BaBPO5. The site occupancy of uranium was further probed using EXAFS which confirmed that in case of BaBPO5, uranium enters the host as uranate whereas in case of SrBPO5 and CaBPO5, uranium enters as Uranyl.
7 citations
References
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Book•
01 Apr 1978
TL;DR: In this article, an extension of the donor-acceptor concept, characterized by the comparison between equilibrium structures in different molecular environments, is presented, in which changes in the positions of the nuclei are taken into account and the question of the nature of the molecular forces is no longer important.
Abstract: Recent developments in various areas of chemistry have been decisively influenced by the principles of structure and mechanism and by the ideas of coordination chemistry, in particular by the donor-acceptor approach, A unified view of almost all kinds of molecular forces is provided by quantum mechanics, and for practical purposes have been classified according to model assumptions, namely, dispersion, polarization, electrostatic, and short-range forces. The latter are divided into two- and three-center covalent chemical bonds, metallic bonds, and exchange-repulsion forces. This approach allows statements of principle and systematic analysis. However, quantitative predictions on concrete large systems are virtually impossible, and there are no general rules that account for structural and chemical changes due to intermolecular interactions. Chemists are therefore left with qualitative descriptions in which the changes in electron densities are considered. Such models as the MO theory or the resonance concept unrealistically assume that the nuclei remain in fixed positions. Further difficulties are encountered in the attempted description on the "nature" of the chemical bond, e.g., the forces involved. In order to avoid these difficulties an extension of the donor-acceptor concept, characterized by the comparison between equilibrium structures in different molecular environments, will be presented in this book. In this way, changes in the positions of the nuclei can be taken into account and the question of the nature of the molecular forces is no longer important.
1,640 citations
295 citations
TL;DR: In this article, the divalent and trivalent states of rare earth fluorides were reviewed under the following headings: introduction, nomenclature and definitions; the divalve state: A/sup +1/sub(w)Re/sup+2/sub (w)
203 citations