Chapter 46 Spectroscopic properties of triply ionized

Luminescence of undoped and Eu3+ activated zinc gallate phosphor: Synthesis, unusual intense 5D0 → 7F4 red emission

A series of Eu³⁺-doped ZnGa₂O₄ samples were synthesized via the urea-glycine combustion route. Powder X-ray diffraction (XRD) was used to investigate the crystallinity of the samples, energy dispersive spectroscopy (EDS) to explore the elemental composition, Fourier transform infrared (FTIR), to observe the vibrational modes of the samples, photoluminescence (PL) to determine the luminescence properties. The XRD data prove that the samples remain single cubic structure even at high concentrations of Eu³⁺, enabling the formation of a unique emission spectrum. The active ion concentration was varied to examine the influence of concentration on luminescent properties. This study revealed a ⁵D₀ →⁷F₄ transition located at 700 nm with unusual intensity that has not been documented in the literature, which suggests that the active ion concentration can influence the luminescent characteristics of the phosphors. The increasing Eu³⁺ content increases the number of Eu³⁺ ions in ZnGa₂O₄ host lattice, which enhances the luminescence efficiency of the phosphor. However, beyond a certain level of Eu³⁺content (i.e., 3 wt% Eu³⁺), the number of Eu³⁺ ions becomes excessive, resulting in a reduction in luminescence efficiency due to concentration quenching. The dipole dipole interaction is elucidated to play a prominent role in the mechanism of Eu³⁺ quenching in the ZnGa₂O₄. An assessment of color coordinates based on emission spectra reveals that the coordinates shift from blue to the white light region, and then to red as Eu³⁺ content increases. This suggests that there is a substantial relationship between the Eu³⁺ concentration and the measured color coordinates.

Luminescence Intensity Ratio Thermometry with Er3+: Performance Overview

The figures of merit of luminescence intensity ratio (LIR) thermometry for Er3+ in 40 different crystals and glasses have been calculated and compared. For calculations, the relevant data has been collected from the literature while the missing data were derived from available absorption and emission spectra. The calculated parameters include Judd–Ofelt parameters, refractive indexes, Slater integrals, spin–orbit coupling parameters, reduced matrix elements (RMEs), energy differences between emitting levels used for LIR, absolute, and relative sensitivities. We found a slight variation of RMEs between hosts because of variations in values of Slater integrals and spin–orbit coupling parameters, and we calculated their average values over 40 hosts. The calculations showed that crystals perform better than glasses in Er3+-based thermometry, and we identified hosts that have large values of both absolute and relative sensitivity.

End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N3O2] Ligand: Synthesis, Structure, and Magnetism

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N₃)C₂H₅OH]C₂H₅OH}_n where H₂DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N₃O₂] ligand and Ln = Dy (1), Y_0.930Dy_0.070 (2), Er (3), Y_0.923Er_0.077 (4), and Gd (5). X-ray diffraction analysis of 1-5 show that the central lanthanide atoms are eight-coordinated with the N₅O₃ donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N₃^- bridges connecting the metal centers into infinite chain. The [LnN₅O₃] coordination polyhedron can be regarded as a distorted dodecahedron (D_2d). AC magnetic measurements revealed that compounds 1-4 show field-induced single-molecule magnet behavior, with estimated energy barriers U_eff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln³⁺ ions mediated by the end-to-end azide bridging groups (J ≈ -0.015 cm^-1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln³⁺ ions.

Nephelauxetic effect and 〈r(k)〉₄f radial integrals of Tm³⁺ in crystals

Bonding and covalency parameters have been evaluated from the nephelauxetic ratios βk=Fk (crystal)/Fk (free ion), with k=2, 4, 6, for 24 halide and chalcogenide crystals containing Tm(3+) ions. The radial expectation values for 4f electrons 〈r(k)〉4f of Tm(3+) ion in certain complex oxides, fluorides, and a sulfide have been determined by means of experimental Slater parameter shifts ΔFk relative to the Fk values for the free ion Tm IV. The 〈r(k)〉1f values derived in the dielectric screening model have been compared with those computed by different types of 4f wave functions as well as with other estimates.

Radial integrals <r(k)>4f and nephelauxetic effect of Nd3+ in crystals

The radial expectation values <r(k)>4f,k=2, 4, 6, for oxygen- or halogen- coordinated Nd(3+) ions in 25 crystals have been obtained from experimental Slater parameter shifts ΔFk=Fk (free ion) - Fk (crystal) by means of the dielectric screening model. The <r(k)>4f values found by this new approach are compatible with those computed by relativistic 4f wave functions. The nephelauxetic ratios βk in respect to the free ion Nd IV have been also determined and related to covalency and bonding parameters.

Optical spectra and energy levels analysis of the 4f(N) ions doped into Ba2YCl7

Absorption emission and excitation spectra are measured and analyzed to achieve assignments of energy levels for 4f(N) ions in Ba(2)YCl(7):RE(3+) (RE = Pr, Nd, Tb, Dy, Ho, Er, and Tm) crystals. The experimental energy levels were analyzed in terms of the usual free-ion parameters and the crystal field (CF) ones, B(kq), in the Wybourne notation. The orthorhombic C(2v) symmetry is shown to be a good approximation of the actual triclinic C(1) site symmetry at the metal center. The starting values of the CF parameters B(kq) used for fittings for the studied crystals were obtained from superposition model analysis. A good agreement between the calculated and experimental energy levels was obtained with rms deviations in the range from 6.8 cm(-1) (for Ho(3+)) to 14.1 cm(-1) (for Pr(3+)). The fitted sets of B(kq) parameters are, in general, consistent across the 4f(N) series. This study has enabled determination and discussion of the trends in variation of the free-ion parameters and CF ones across the 4f(N) series. The CF parameter set and energy level structure obtained for Nd(3+) ion in Ba(2)YCl(7) crystal are consistent with those for Nd(3+) in structurally related RbY(2)Cl(7) crystal. This systematic analysis of CF parameters is one of only few such studies encompassing nearly whole series of RE(3+) ions.

Interpretation of multiple solutions and selection of the final crystal field parameter sets for orthorhombic and lower symmetry--case study: Er3+ ions at orthorhombic sites in ErNiAl4

Existence of multiple solutions for the crystal field (CF) parameter (CFP) sets obtainable from fitting or matching procedures for orthorhombic (as well as monoclinic and triclinic) site symmetry has recently been gaining wider recognition. However, the peculiarities encountered in interpretation of multiple solutions and subsequent selection of the final CFP sets appears not to be properly understood in many cases. In this paper pertinent explanations for the peculiarities in question are provided. As a case study, we carry out analysis of the CFP sets for Er(3+) ions at orthorhombic sites in ErNiAl(4) obtained using theoretical calculations as well as Mössbauer spectroscopy and inelastic neutron scattering data. It turns out that the original and revised CFP sets reported for Er(3+) in ErNiAl(4) require reconsideration in view of these explanations. Clarifications concerning the matching procedure used as well as interpretation of the CFP sets and the assigned axis systems are provided. It appears that the specific constraints involved in matching have generated some incorrect CFP solutions. The crux of the problem is in the intrinsic features of CFP sets for orthorhombic symmetry, which previously were not fully utilized. Consideration of these features enables proper interpretation of multiple solutions as well as discrimination between the physically valid alternative CFP sets, which must be internally correlated, and the additional incorrect solutions generated by inappropriate matching or fitting procedures. Five alternative and correlated CFP sets are calculated for each set obtained for Er(3+) in ErNiAl(4). These considerations provide guidance for reinterpretation of CFP sets reported in literature and may facilitate subsequent fittings. This would enable experimental identification of the alternative CFP sets.

Extraction of crystal-field parameters for lanthanide ions from quantum-chemical calculations

A simple method for constructing effective Hamiltonians for the 4f(N) and 4f(N - 1)5d energy levels of lanthanide ions in crystals from quantum-chemical calculations is presented. The method is demonstrated by deriving crystal-field and spin-orbit parameters for Ce(3 + ) ions doped in LiYF(4), Cs(2)NaYCl(6), CaF(2), KY(3)F(10) and YAG host crystals from quantum-chemical calculations based on the DV-Xα method. Good agreement between calculated and fitted values of the crystal-field parameters is obtained. The method can be used to calculate parameters even for low-symmetry sites where there are more parameters than energy levels.

A ligand-field analysis of the trensal (H(3)trensal = 2,2',2' '-tris(salicylideneimino)triethylamine) ligand. An application of the angular overlap model to lanthanides

The spectral and geometric trends of Ln(trensal) complexes (H(3)trensal = 2,2',2' '-tris(salicylideneimino)triethylamine) along the lanthanide series are analyzed. Low-temperature polarized absorption and luminescence spectra are reported for nine of the complexes with transitions suitable for analysis. Both the angular and radial geometry variations as a function of the lanthanide ion are quantified. The structural parameters are related to the trend in the ligand field found from an analysis of the f-f transitions. The ligand-field analysis is fitted globally across the whole series accounting for the contraction of the f orbitals as a function of atomic number. This study establishes the utility of describing the ligand field of f electrons within the one-electron operator approach of the angular overlap model.

Ligand-field analysis of an Er(III) complex with a heptadentate tripodal N4O3 ligand

Polarized absorption and emission spectra of trigonal single crystals of an Er(III) complex coordinated to a heptadentate tripodal ligand are reported at temperatures between 8 and 298 K. The assigned energy levels below the onset of ligand absorption (< 25 000 cm(-1)) are fitted to a parametrized electronic Hamiltonian. The C(3) site symmetry of the Er(III) ion requires eight parameters for a full description of the ligand field within a one-electron operator description. This compound shows unusually large splittings of the multiplets, and the fitted parameters imply that this heptadentate ligand imparts the largest ligand field reported for an Er(III) complex. The ligand field was also interpreted within the angular overlap model (AOM). We derive the AOM matrix to include both sigma and anisotropic pi bonding and show that a useful description of the C(3) ligand field can be made using only five parameters. The success of the AOM description is encouraging for applications on isomorphous complexes within the lanthanide series and in describing the ligand field of low-symmetry complexes with less parameters than in the usual spherical harmonic expansion.