4f Configuration Research Articles

Optical properties of lutetium diphosphates powders doped by ytterbium

Sodium lutetium diphosphates doped with Yb3+ ions, NaLu1−xYbxP2O7 (x=0.5%, 2%, 5% and 10%), were synthesized by solid state reaction. These samples were characterized by X-ray diffraction, Raman and infrared spectroscopies. The obtained powders are formed by single monoclinic phase of condensed diphosphate NaLuP2O7 crystallized with P21/n space group. The evolution of crystal lattice parameters varied as a function of the ytterbium concentration in these host lattices. Near infrared (NIR) and UV–Visible spectroscopies of Yb3+ in NaLuP2O7 powders, at room temperature (RT), are carried out. In the IR range, a broad band relative to the Stark levels of the Yb 4f configuration. Four Stark levels of the ground 2F7/2 state are located on the emission spectra between 970nm and 1060nm. It was shown that spectroscopic properties of investigated samples depend on the concentration ratio of Yb3+ ions. The decay times of infrared Yb3+ (2F5/2 excited state) fluorescence were in the range of 2.78–2.91ms. The registered decay times of the emission at 1006nm, under excitation with length 925nm showed low sensibility to the Yb3+ concentration in NaLuP2O7. In the UV–Visible spectra, double band emission for the charge transfer band (CTB) luminescence of Yb3+ are observed under 266nm excitation.

CORE-HOLE EFFECT IN THE Ce L3 X-RAY ABSORPTION SPECTRA OF CeO2 AND CeFe2: NEW EXAMINATION BY USING RESONANT X-RAY EMISSION SPECTROSCOPY

We consider two different resonant X-ray emission spectra for Ce compounds: Ce 3d to 2p X-ray emission (denoted by 3d-RXES) and valence to 2p X-ray emission (v-RXES), both of which follow the Ce 2p to 5d resonant excitation. We propose that the comparison of the 3d- and v-RXES spectra is a new powerful method of directly detecting the core-hole effect in the final state of Ce L 3 X-ray absorption spectra (XAS). We applied this method to recent experimental RXES spectra for CeO 2 and CeFe 2, and showed unambiguously that the core-hole effect should be essential in the XAS of both materials. This result is confirmed by theoretical calculations, which reproduce well the experimental RXES and XAS spectra. We conclude that the ground state of CeO 2 is in the mixed state of 4f0 and [Formula: see text] configurations, where [Formula: see text] is a ligand hole, instead of a pure 4f0 configuration which was proposed recently by first-principles energy band calculations. Also, we conclude that the double peaks observed in L 3 XAS of CeFe 2 are caused by the 4f0 and 4f1 configurations, which are mixed in the ground state but separated in energy by the large core-hole potential in the final state of XAS.

Luminescence properties of red emitting phosphor NaSrBO3:Eu3+ prepared with novel combustion synthesis method

The red emitting phosphor NaSrBO3:Eu3+is synthesised by simple, time saving, economically modified method of solution combustion synthesis at comparatively lower temperature using urea as fuel. X-ray power diffraction (XRD) analysis confirmed the formation of the said phosphor. Photoluminescence measurements showed that the phosphor exhibited emission peak with good intensity at −614nm, corresponding to 5D0–7F2 (614nm) red emission andweak 5D0–7F1 (593nm) orange emission. The excitation spectra monitored at 614nm show broad band from 250 to 350nm ascribed to O–Eu charge-transfer (CTB) transition and the other peaks in the range of 350–410nm originated from f–f transitions of Eu3+ ions. The strongest band at 394nm can be assigned to 7F0–5L6 transition of Eu3+ ions due to the typical f–f transitions within Eu3+ of 4f6 configuration. The latter lies in near ultraviolet (350–410nm) emission of UV LED. For the excitation wavelength of 394nm the emission intensity increases initially with the increase of Eu3+ concentration and reaches to the maximum at x=0.09.The concentration quenching observed after that is mainly due to quadrupole–quadrupole interaction.The as synthesised phosphor NaSrBO3:Eu3+by this method shows CIE colour coordinates of (0.62,0.34) with good intensity.

Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis: Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced Uranyl–Rare Earth 5f1-4fn Complexes

The heterobimetallic complexes [{UO2Ln(py)2(L)}2], combining a singly reduced uranyl cation and a rare-earth trication in a binucleating polypyrrole Schiff-base macrocycle (Pacman) and bridged through a uranyl oxo-group, have been prepared for Ln = Sc, Y, Ce, Sm, Eu, Gd, Dy, Er, Yb, and Lu. These compounds are formed by the single-electron reduction of the Pacman uranyl complex [UO2(py)(H2L)] by the rare-earth complexes Ln(III)(A)3 (A = N(SiMe3)2, OC6H3Bu(t)2-2,6) via homolysis of a Ln-A bond. The complexes are dimeric through mutual uranyl exo-oxo coordination but can be cleaved to form the trimetallic, monouranyl "ate" complexes [(py)3LiOUO(μ-X)Ln(py)(L)] by the addition of lithium halides. X-ray crystallographic structural characterization of many examples reveals very similar features for monomeric and dimeric series, the dimers containing an asymmetric U2O2 diamond core with shorter uranyl U═O distances than in the monomeric complexes. The synthesis by Ln(III)-A homolysis allows [5f(1)-4f(n)]2 and Li[5f(1)-4f(n)] complexes with oxo-bridged metal cations to be made for all possible 4f(n) configurations. Variable-temperature SQUID magnetometry and IR, NIR, and EPR spectroscopies on the complexes are utilized to provide a basis for the better understanding of the electronic structure of f-block complexes and their f-electron exchange interactions. Furthermore, the structures, calculated by restricted-core or all-electron methods, are compared along with the proposed mechanism of formation of the complexes. A strong antiferromagnetic coupling between the metal centers, mediated by the oxo groups, exists in the U(V)Sm(III) monomer, whereas the dimeric U(V)Dy(III) complex was found to show magnetic bistability at 3 K, a property required for the development of single-molecule magnets.

The 1S0 emission from the minor site of Pr3+ in (Ba,La)F2:Pr

In this paper we present and discuss results of detailed spectroscopy studies of Pr3+ luminescence from the (Ba,La)F2:0.2 m%Pr crystals under UV and VUV synchrotron excitation. We have measured time resolved emissions from the minor site Pr3+ in (Ba,La)F2:Pr at 10 and 300 K. The spectra clearly show the 1S0 emission from the Pr3+ ions in some low symmetry Pr-sites (we designate them La-sites) previously identified in higher concentration (0.3 m%Pr and more) crystals. However most of emission from the Pr activated (Ba,La)F2 crystals originates in Pr3+ ions in other sites which produce an efficient d-f emission. As demonstrated by excitation spectra, the emission from some of these sites (denoted as Ba-sites) closely resembles the d-f emission from BaF2. The La-site, time resolved and long delay emission spectra are dominated by hypersensitive transitions from the 1S0 and 3P0 levels to lower energy levels of the 4f2 configurations. Only these transitions contribute to the photon cascade emission desired for some mercury free phosphor applications.

Synthesis and characterization of blue long‐lasting BaCa2Al8O15:Eu2+, Dy3+ phosphor

We have synthesized and characterized a new BaCa2Al8O15:Eu(2+),Dy(3+) phosphor prepared by the combustion method. X-ray diffraction, thermoluminescence, scanning electron microscope, time decay and optical spectral analysis photoluminescence excitation, emission spectra were used to characterize the phosphors. Broadband ultraviolet excited luminescence of the BaCa2Al8O15:Eu(2+),Dy(3+) was observed in the blue region (λ(max) = 435 nm) due to transitions from the 4f(6)5d(1) to the 4f(7) configuration of the Eu(2+) ion. Scanning electron microscopy has been used for exploring the morphological properties of the prepared phosphors. The BaCa2Al8O15:Eu(2+) phosphor has a blue afterglow when Dy(3+) ions were co-doped. The thermoluminescence spectra show that the Dy(3+) ion induces a proper trap in the phosphor with a depth of 0.67 eV and results in a long afterglow phosphorescence.

Antiferromagnetic ordering in an intermediate valence compound Ce9Ru4Ga5

We report on the low-temperature physical behavior in a novel compound Ce9Ru4Ga5 that crystallizes with its own type of crystal structure containing an anomalously short Ce–Ru distance. From the X-ray absorption spectroscopy data the compound was characterized as an intermediate valence system. Our bulk property (magnetic susceptibility, heat capacity and electrical resistivity) measurements revealed an antiferromagnetic ordering below TN=3.7K. The long-range magnetic order probably arises due to a fraction of Ce ions (nearly one third of cerium in the unit cell of Ce9Ru4Ga5), which possess nearly stable 4f1 configuration with the effective valence close to 3+.

Energy-Level Splitting of Cs2NaYCl6 Crystal Doped with Praeseodymium

The 91×91 complete energy matrix of 4f2 configuration ion praeseodymium in octahedral cubic crystal field has been constructed based upon the combination of Racah’s group-theoretical consideration with Slater’s wavefunctions. The energy levels of praseodymium (Pr3+) in hexachloride elpasolite crystals Cs2NaYCl6 have been calculated. The calculated results display a good agreement with the experimental values, which implies that the complete energy matrix method can be received as a recommendable tool to perform a theoretical analysis to the doped crystal.

Ligand field density functional theory calculation of the 4f2 → 4f15d1 transitions in the quantum cutter Cs2KYF6:Pr3+

Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4f(n)→ 4f(n-1)5d(1) transitions in rare earth compounds and apply it for the characterization of the 4f(2)→ 4f(1)5d(1) transitions in the quantum cutter Cs2KYF6:Pr(3+) with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of materials acting as phosphors in light-emitting diodes. The positions of the zero-phonon energy corresponding to the states of the electron configurations 4f(2) and 4f(1)5d(1) are calculated, where the praseodymium ion may occupy either the Cs(+)-, K(+)- or the Y(3+)-site, and are compared with available experimental data. The theoretical results show that the occupation of the three undistorted sites allows a quantum-cutting process. However size effects due to the difference between the ionic radii of Pr(3+) and K(+) as well as Cs(+) lead to the distortion of the K(+)- and the Cs(+)-site, which finally exclude these sites for quantum-cutting. A detailed discussion about the origin of this distortion is also described.

Theoretical Study of Energy-Level Splitting of Cs<sub>2</sub>NaPrCl<sub>6</sub> Crystal

The 91×91 complete energy matrix of 4f2 configuration ion Pr3+ in octahedral cubic crystal field has been constructed based upon the combination of Racah’s group-theoretical consideration with Slater’s wavefunctions. The energy levels of the neat hexachloride elpasolite crystals Cs2NaPrCl6 containing rare earth Pr3+ ion have been calculated. The results imply that the diagonalization to the complete energy matrix can be received as an effective method of performing a theoretical calculation to the rare earth compounds.

The dependence of 10 Dq crystal field parameter for Mn4+ (3d3 configuration) and the magnitude of 7F1 level splitting for Eu3+ (4f6 configuration) on pyrochlore compositions

The excitation spectra of the six-coordinated Mn4+ ion in the pyrochlores Ln2Sn2O7 (Ln=Lu3+, Y3+, and Gd3+) have been determined to examine the variation in the crystal field splitting parameter (10 Dq) on the Mn4+–O48f2- distance. The results obtained are entirely consistent with the expectation of the electrostatic point charge model since 10 Dq progressively increase with decreasing Mn4+–O48f2- distance. A comparative study pertaining to the behavior of the Eu3+ (4f6) and Mn4+ (3d3) ions in the pyrochlores, Ln2(Ti,Sn)2O7 (Ln=Lu3+, Y3+, and Gd3+) is presented. The results show that the crystal-field strength that are experienced by the Mn4+ and Eu3+ ions in the Ln2Sn2O7 (Ln=Lu3+, Y3+, and Gd3+) family of materials, are anti-correlated. Thus, for the Mn4+ ion with 3d3 configuration, the crystal-field strength increases with decreasing ionic radii of the Ln3+ cation, while for the Eu3+ ion with 4f6 configuration, an increase with increasing ionic radii of the Ln3+ cation is observed. However, when the Sn4+ ion of the Y2Sn2O7 lattice are replaced by the Ti4+ ion, the crystal-field strength is reduced to the extent that the exposed Mn4+ 3d3 electrons and the screened Eu3+4f6 electrons start to behave similarly. These results are explained by the variations in the covalent mixing between the ligand (O48f2-) and the activator (Mn4+ and Eu3+) cations, which is driven by the competition for the O48f2- electron density by the Ln3+, Sn4+, and Ti4+ ions of the Ln2(Ti,Sn)2O7 lattice.

Sm2+ fluorescence and absorption in cubic BaCl2: Strong thermal crossover of fluorescence between 4f6 and 4f55d1 configurations

The optical absorption and fluorescence spectra of polycrystalline cubic-phase barium chloride doped with divalent samarium is reported. X-ray diffraction shows that the cubic phase is stabilised at room temperature by the addition of 12.5% lanthanum trichloride; no evidence for the more common orthorhombic or hexagonal phases of barium chloride is found. Optical absorption measurements are in good agreement with a calculated spectrum for Sm2+ ions at a single site of cubic symmetry, even though the material must contain a substantial fraction of chlorine interstitials and lanthanum substitutional ions. The photoluminescence spectrum shows sharp red line emission from the 5D1 and 5D0 levels of the 4f6 configuration, again consistent with a single site of cubic symmetry, together with a broad emission, also in the red, which arises from the lowest levels of the 4f55d1 configuration. The relative strengths of these emissions are strongly temperature dependent; at room temperature the broad band from the lowest 4f55d1 levels peaking at 15,130cm−1 is dominant, while at low temperature (∼12K) sharp lines from the 5D0 level dominate. The most intense line corresponds to the 5D0→7F1 transition at 14,300cm−1, but the nominally forbidden 5D0→7F0 transition also has significant intensity. The marked temperature dependence of the intensity of the lines and bands is successfully modelled by rate equations and is explained on the basis of thermally activated crossovers between the 4f6 (5D0,1) levels and the lowest levels of the 4f55d1 configuration; it is necessary to include the three lowest levels of the 4f55d1 configuration sandwiched between the 5D0 and 5D1 levels.

Theoretical Investigation of Energy Levels Splitting of CsCdBr<sub>3</sub>:Pr<sup>3+</sup> Crystal

Based upon the single electron energy state information and the combination of Racah’s group-theoretical consideration with Slater’s wavefunctions, the 91×91 complete energy matrix of 4f2 configuration ion Pr3+ in C3v crystal field has been constructed. The calculated Stark energy levels of CsCdBr3:Pr3+ present a good agreement with the experimental values, which implies that the complete energy matrix method can be received as a recommendable tool to perform a theoretical analysis to the doped crystal. Besides, the influence of Pr3+ ions on the energy levels splitting of the host crystal CsCdBr3 has been compared with two doped trichlorides by Pr3+ ions, which indicates that the sixth order crystal field parameters play an indispensable role in splitting the energy levels.

Crystal-field splitting of Pr3+ ion multiplets in YPO4 with allowance for interconfigurational interaction

The crystal-field splitting of the Pr3+ ion multiplets is analyzed with regard to the influence of excited opposite-parity configurations 4f(N − 1)5d and a configuration with charge transfer. Such an approach makes it possible to (i) refine the characterization of the Stark structure of multiplets by 39% compared with the approximation of a weak configurational interaction and (ii) determine the covalence parameters and the parameters of an odd-symmetry crystal field from experimental data for the Stark structure. The covalence parameters thus determined coincide in order of magnitude with the respective parameters calculated for other ligands using microscopic models.

Automated compensation of misalignment in phase retrieval based on a spatial light modulator

In this paper, the issue of misalignment in phase retrieval by means of optical linear filtering is discussed. The filtering setup is based on a 4f configuration with a spatial light modulator (SLM) as an active element, located in the Fourier domain. From the analysis, crucial parameters for the alignment procedure of the setup's optical axes and the center of the SLM are identified. Furthermore, a method to automatically as well as electronically compensate such effects by modifying the phase pattern displayed on the SLM is introduced. Experimental results are presented that validate the compensation approach.

Crystal fields, disorder, and antiferromagnetic short-range order in Yb0.24Sn0.76Ru

We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence band photoemission and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a {\Gamma}7 doublet ground state and a {\Gamma}8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a {\Gamma}6 excited state resides at 32 meV; however, the {\Gamma}8/{\Gamma}6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch- Gr\"uneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K, there is a peak in specific heat that is too broad to represent a magnetic phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand, this peak also is too narrow to represent the Kondo effect in the {\Gamma}7 ground state doublet. On the basis of the field-dependence of the specific heat, we argue that antiferromagnetic shortrange order (possibly co-existing with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.

4f–5d Transitions of Tb3+ in Cs2NaYF6: The Effect of Distortion of the Excited-State Configuration

The low-temperature absorption and excitation spectra of interconfigurational 4f-5d transitions of Tb(3+) in a cubic fluoride host demonstrate the appearance of a first-order linear Jahn-Teller effect for the high-spin excited states of the excited electronic configuration 4f(7)5d involving 5d t(2g) orbitals. The τ(2g) mode is observed to be responsible for the splitting of the otherwise degenerate 5d t(2g) orbitals.

Fifty years of advances in solid-state laser materials

The year 2010 marks the 50th anniversary of the invention of the first laser device, ruby laser and it is therefore an appropriate time to look back at the developments in the laser field since its inception and to try to map out its milestones. In this presentation, consideration will be given only to the area of solid-state lasers mainly based on metal transition ions (3d configuration) and rare earth ions (4f configuration) used as oscillators or amplifiers.

Fast d–f emission in Ce3+, Pr3+ and Nd3+ activated RbCl

In the search for new scintillator materials, Ce3+ doped chlorides are a promising class of materials, combining a high efficiency and fast response time. Even shorter response times may be achieved by replacing Ce3+ by Pr3+ or Nd3+ as the lifetime of the d–f emission is substantially shorter for these ions. Here we report on the luminescence properties of Ce3+, Pr3+ and Nd3+ in RbCl and investigate the potential as a scintillator material. Under UV excitation Ce3+ shows d–f emission between 325 and 425nm. The emission originates from multiple (differently charge compensated) Ce3+ sites. The luminescence lifetime varies with wavelength and is ∼40ns for the longer wavelength emission. For RbCl:Pr3+ three d–f emission band are observed between 250 and 350nm which can be assigned to transitions from the lowest energy fd state to different 3HJ (J=4–6) states within the 4f2 configuration of Pr3+. The decay time is ∼17ns. For the Nd3+ activated sample a weak emission band around 220nm is observed only at 8K which may be due to d–f emission. The very short lifetime (4ns) is faster than the radiative lifetime, indicating that the d–f emission is quenched by relaxation to lower lying 4f3 states or by the process of photoionization. Under VUV excitation at wavelengths below 175nm (the bandgap of RbCl) the d–f emission is very weak for Ce3+, Pr3+ and Nd3+ doped RbCl and the emission spectra are dominated by defect related emission. This indicates that energy transfer from the host lattice to the fd states is inefficient which prevents application as a scintillator material.

Parameterizing intensity of [formula omitted] electric-dipole transitions in Pr3+ doped LiYF4

A parametrization method is reported to calculate the electric-dipole transition intensities within the 4f2 configuration in LiYF4:Pr3+ by considering the main perturbing component of 4f5d. On the basis of calculating the energy level of the 4f5d configuration, the main 4f5d components that can mix with the 4f2 transitional states are determined. We exhibit the calculated densities of the 4f5d states which can mix with the initial and the final states of 3P0 energy level in Pr3+ doped LiYF4. Whereafter a new set of phenomenological intensity parameters, Tkq, is put forward. In addition to the explicit static-coupling mechanism, the approach is extended by the non-explicit dynamic mechanism. Detailed description of the calculated method is brought out. The results of present fitting are compared with that obtained by the traditional parametrization scheme and obvious improvements are exhibited.