Preliminary Evaluation of Local Structure and Speciation of

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A: Spectroscopy, Molecular Structure, and Quantum Chemistry

Preliminary Evaluation of Local Structure and Speciation of Lanthanoids in Aqueous Solution, Iron Hydroxide, Manganese Dioxide, and Calcite Using the L Edge X-Ray Absorption Near Edge Structure Spectra 3-

Atsuyuki Ohta, Kazuya Tanaka, and Hiroshi Tsuno J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b06168 • Publication Date (Web): 24 Sep 2018 Downloaded from http://pubs.acs.org on October 1, 2018

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The Journal of Physical Chemistry

Preliminary Evaluation of Local Structure and Speciation of Lanthanoids in Aqueous Solution, Iron Hydroxide, Manganese Dioxide, and Calcite using the L3-Edge X-Ray Absorption Near Edge Structure Spectra

Atsuyuki Ohta*†, Kazuya Tanaka‡, Hiroshi Tsuno§

†

Institute of Geoscience, Geological Survey of Japan, AIST, Tsukuba 305-8567, Japan

‡

Japan Atomic Energy Agency, Advanced Science Research Center, Tokai, Naka, Ibaraki 319-1195, Japan

§

College of Education, Yokohama National University, Kanagawa, 240-8501, Japan

This manuscript is the second version (14 September, 2018)

---------------------------------------------------------------------------------------------------------* Correspondence should be addressed to Atsuyuki Ohta (Tel. +81-29-861-3848, Fax. +81-29-861-3566, e-mail [email protected]).

1

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ABSTRACT: We elucidate the application of L3-edge X-ray absorption near edge structure (XANES) spectra to the local structural analysis of lanthanoids in aqueous solution, iron hydroxide, manganese dioxide, and calcium carbonate. The L3-edge XANES spectra of lanthanoid compounds showed sharp white lines. The full width at half maximum (FWHM) values of lanthanoid aqua ions exhibited a convex tetrad curve in the series variation across the lanthanoid series. The variation is attributable to 4f electron orbitals and can be explained by the refined spin-pairing energy theory. For each lanthanoid, the FWHM values of lanthanoid compounds roughly decreased with increasing local coordination numbers. However, they did not faithfully reflect the local coordination sphere of the lanthanoid complex having a high and distorted coordination sphere and were rather sensitive to their chemical forms. The relationship between the magnitude of the FWHM values was determined by the crystal field splitting or degeneracy of 5d orbitals. The systematic variation of FWHM can be explained by the ligand strength of the ligand molecules (-H2O0, -O−, -OH−, -CO32−, -Cl−, and -O2−) that cause the crystal field splitting. Therefore, the FWHM values of L3-edge XANES of lanthanoid compounds may be more useful in speciation analysis rather than structural analysis.

2


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1. INTRODUCTION X-ray absorption fine structure (XAFS) determination is a powerful tool for characterizing the local structures of poorly crystallized materials and trace elements in materials. XAFS is composed of the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). XANES spectroscopy is sensitive to chemical species and the valence state, whereas EXAFS spectroscopy is suitable for obtaining structural information. L3-edge XAFS spectra of lanthanoid (Ln) elements have been acquired to obtain information on the local coordination as such spectra are accessible even at low-to-middle-energy synchrotron facilities. Unfortunately, a narrow k-range is available to the L3- and L2-edge EXAFS spectra of lanthanoids for detailed structure analysis because of the proximity of L3-, L2-, and L1-edges, as reported by Glatzel et al. 1. K-edge EXAFS measurements would be one solution to this problem 2. However, the energy broadening from the short 1s core-hole lifetime strongly dampens the K-edge EXAFS oscillations at high k-range values 1. As a result, the data quality is poor for dilute samples 3-4. Concentrations of lanthanoids in natural materials are commonly low, ranging from several hundred mg kg−1 to several dozen µg kg−1. Therefore, L-edge EXAFS would be suitable to determine the local structures of lanthanoids in natural materials. However, it would be impractical because of L-edge EXAFS interference of lanthanoids in natural materials. Recently, D'Angelo et al. 5 successfully reproduced the experimental XANES spectra of hydrated lanthanoid ions in an aqueous solution using a full multiple-scattering algorithm, by providing the geometrical parameters of the first and second hydration sphere models as input. They demonstrated that the XANES spectra can be used for the structural analysis of lanthanoid complexes. However, their study involved spectral interpretation of lanthanoid compounds whose coordination structures are well known. It is difficult to apply their method to natural materials, whose coordination structures are unknown and complicated. However, Asakura's group reported that the intensity of the pre-edge peak of L1-edge XANES spectra 3



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and the full width at half maximum (FWHM) of the white line at the L3-edge XANES for lanthanoid compounds can also be used as an indicator of the distortion or coordination number of the local environment 6-8. In this study, we have examined the local coordination structures of lanthanoids and yttrium (Y) to elucidate their incorporation process in marine ores, minerals, and rocks, mainly using EXAFS spectra

9-13

. L3-edge EXAFS spectra of lanthanoid aqua ions and

lanthanoid-doped Fe hydroxide, Mn dioxide, and calcite, which are major rare earth element including lanthanoid and Y host minerals in marine environment were acquired in fluorescence mode. The ferromanganese nodule and crust were found to be composed of poorly crystalline Fe and Mn hydroxide/oxides and were highly enriched in Co, Ni, Cu, Pb, and rare earth elements 14. Therefore, Lα fluorescence of lanthanoids without interference of Kα and Kβ fluorescence of Mn, Fe, Co, and Ni may be measurable in the XANES region. By contrast, small amounts of Lanthanoids were found in calcite but did not interfere with the Kα and Kβ fluorescence of 3d transition metals. Our aim was to examine the relationships between the FWHM of L3-edge XANES for the mentioned synthetic compounds and their coordination structures to obtain local structural information of lanthanoids in natural materials.

2. MATERIAL AND METHOD 2.1. Sample Preparation and XAFS Measurement. XAFS spectra used in this study were taken from our previous studies at BL-12C in the Photon Factory at the Institute of Material Structure Science, High Energy Accelerator Research Organization (KEK-PF), Japan

9-13

. The KEK-PF storage ring was operated at 2.5

GeV with a 300–450 mA stored current. A Si(111) double-crystal monochromator produced a monochromatic X-ray beam with one crystal detuned to reduce harmonics. Ohta et al.

11

obtained the XAFS spectra of 1000 mg L−1 all lanthanoids and Y aqua ions in 1 mol L−1 4


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HNO3 solution. Ohta et al. 9-10 prepared Ln-doped FeOOH using La, Pr, Nd, Sm, Yb, Lu, and Y and Ln-doped δ-MnO2 using La, Pr, Nd, Er, Tm, Yb, Lu, and Y. Tsuno et al. 13 synthesized Yb-doped calcite, NaYb(CO3)2·nH2O, and Yb(OH)3·nH2O. Tanaka et al. 12 prepared Ho- and Y-doped calcites, and their aqueous ions, hydroxides, chlorites, and carbonates. Although Ce-, Nd-, Sm-, Tb-, Dy-, Er- and Lu-doped calcites were also prepared, their XAFS spectra have yet not been published. The L3-edge XAFS spectra of almost all samples were obtained in the fluorescence mode using a 19-element pure-Ge solid state detector, and those of HoCl3·6H2O, Ho2O3, and Ho2(CO3)3·nH2O were acquired in transmission mode.

2.2. XAFS Analysis. XANES analysis was conducted using REX2000 Version 2.3 (Rigaku Co.)

15

. The

pre-edge background was subtracted by extrapolating a linear polynomial fitted to the pre-edge absorbance in the range of 20–100 eV below E0 through the post-edge regions. The absorption edge (E0) value is the inflection point determined from the first derivative of each XAFS spectrum. After subtracting the background, absorbance was normalized by the mean absorption in the 150–300-eV region above E0. The normalized L3-edge XANES spectrum (µ(E)) was fitted using Lorentzian and arctangent functions according to the following equation in REX2000 software:

‫ܣ‬ ߁௪ ‫ܤ‬ ߤ ሺ‫ ܧ‬ሻ = ෍ ൬ ൰ ∙ ଶ + ൬ ൰ ∙ arctanሾ‫ ܧ‬− ‫ܧ‬௪ − ߜሿ ߨ ߁௪ + 4ሺ‫ ܧ‬− ‫ܧ‬௪ ሻଶ ߨ ௜

(1)

where Ew is the energy of the L3 excitation (2p3/2 → 5d); Γw means the full width at half maximum (FWHM) for the main transition; δ represents the phase shift; and A and B are constants. The deconvolution was conducted in the region ranging from 20 eV below E0 to 9– 5



10eV above it. The white lines of lanthanoid oxides and carbonates were wider than those observed for other samples; thus, their XANES spectra were fitted in the range of 20 eV below E0 to 15 eV above it. The L3-edge XANES spectra of Sm-doped calcite, Yb-doped calcite, La2O3, Ho2O3, Yb2O3, and HoCl3·6H2O were fitted using two or three Lorentzian functions and an arctangent function, as will be discussed later.

3. RESULTS Figures 1–4 show the deconvolution process of L3-edge XANES spectra for La, Sm, Ho, and Yb. The FWHM (Γw) values obtained using Eq 1 are summarized in Tables 1 and 2. The L3-edge XANES spectra of lanthanoid samples show sharp white lines. There seems to be not much significant difference among results obtained for Ln3+(aq), Ln-doped FeOOH, Ln-doped δ-MnO2, and Ln-doped calcite. However, the XANES spectra of lanthanoid oxide, chlorite, and carbonate show broadening and less intense white lines. As for Sm-doped and Yb-doped calcite, the L3-edge XANES spectra have distinct shoulder peaks below their white lines. The shoulder peaks are attributable to the L3 excitation (2p3/2 → 5d) of Sm2+ and Yb2+ 17-18

. Therefore, their XANES spectra were deconvoluted with two Lorentzian functions and

one arctangent function. The XAFS spectra of Ln-doped FeOOH, Ln-doped δ-MnO2, and some Ln3+(aq) samples were acquired 3–4 times

9-11

. The relative standard deviation of the FWHM of the L3-edge

XANES white line was estimated to be 0.1–4 % (mostly 1–2 %) (Table 1). This observation suggests that the FWHM could be determined with a high degree of precision. The FWHM value of lanthanoid complexes increased in the order Ln3+(aq) < Ln-doped FeOOH ≈ Ln-doped δ-MnO2 < Ln-doped calcite < Ln oxide (Tables 1 and 2). The FWHM values of Yb carbonate and hydroxide are lower than those of Yb-doped calcite and Yb oxide (Table 2). The FWHM value of Ho carbonate is similar to that of Ho-doped calcite, while that of Ho chloride is larger than that of Ho carbonate and smaller than that of Ho oxide (Table 2). 6


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Figure 5 shows the systematic variation of FWHM values of L3-edge XANES spectra across the lanthanoid series. For comparison, the natural widths (ΓN) of the lanthanoid L3 19

level

are also shown in Figure 5. FWHM values significantly differed for samples of each

lanthanoid element. The FWHM value of each lanthanoid compound increased with the atomic number. The variation of the FWHM values of Ln3+(aq) across the lanthanoid series shows a double-seated-like pattern, taking into account the increase from La to Eu, the decrease at Gd, the increase from Gd to Yb, and the decrease at Lu. The FWHM values of each lanthanoid complex increased gradually, but not smoothly with increase in the atomic number. The variation of FWHM values of Ln-doped calcite shows a zig-zag line. Lanthanoid oxide showed a larger increase with the atomic number than other samples.

4. DISCUSSION 4.1. Relationship of the White Line FWHM with Coordination Number. Figure 6 shows the relationships between FWHM and the coordination numbers of the first coordination sphere for La, Nd, Sm, Ho, Er, and Yb compounds. The coordination numbers of Ln3+(aq) and Ln-doped marine minerals have been determined using EXAFS spectra

9-12, 20

. Lanthanoid chloride for Dy, Er, Ho, Tm, Yb, and Lu was octahedrally

coordinated to six chloride atoms

21

. Ytterbium hydroxide belongs to the hexagonal system

and the Yb atom is coordinated to 9 oxygen atoms

22

. Lanthanoid oxide (Ln2O3) at room

temperature exhibited type A-Ln2O3 hexagonal for La–Nd and type C-Ln2O3 cubic for Pm– Lu

21

. The lanthanoid atom presented sevenfold coordination for type A-Ln2O3 and sixfold

coordination for type C-Ln2O3

. La was tenfold coordinated with oxygen atoms in

23

and Nd in NdOHCO3 and KNd(CO3)2 was ninefold coordinated with

24, 25

; Gd, Dy, Ho, and Yb in KM(CO3)2 (M = Gd, Dy, Ho, and Yb) were

La2(CO3)3·8H2O oxygen atoms

21

eightfold coordinated with the oxygen atoms belonging to carbonate ions 25. Based on these results, in this study, we suggest an eightfold-coordination sphere for commercially available 7



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Ho and Yb carbonates. The FWHM values of the L3-edge white line for La, Nd, Sm, Er, Ho, and Yb compounds roughly decreased with increasing coordination numbers (Figure 6). Asakura et al.

6, 7, 8

revealed that the pre-edge peaks of the L1-edge XANES spectra and the FWHM values of L3-edge XANES of lanthanoid compounds were roughly inversely correlated to the coordination number of the target metal and to a bond angle analysis parameter that parameterizes the degree of the distortion of the first coordination shell around the target metal. This is discussed in detail below. Our results are comparable to previous studies

6, 7, 8

(Figure 6). Antonio et al.

26

suggested that the 5d-orbital splitting due to the crystal-field effect

causes asymmetry of the XANES white line of Ln2O3 and Ln-glass having six-fold coordination and become inconspicuous for LnPO4 having eight-fold coordination. Lee et al. 27

reported that L3-edge XANES spectra of CeRu4P12 and PrRu4P12 can be deconvoluted with

two Lorentzian functions and an arctangent function. They also stated that double Lorentzian peaks correspond to excitation to the eg and t2g bands of 5d orbitals, which is split by the crystal field. Such 5d-orbital splitting would widen the FWHM of L3-edge XANES. Asakura et al.

8

conducted theoretical calculations for the Ho L1- and L3-edge XANES spectra of

virtual Ho3+(aq). They reported that the FWHM of L3-edge XANES spectra gradually increased from Ho(H2O)4, Ho(H2O)5, to Ho(H2O)6 because of 5d orbital splitting due to the crystal field effect. However, when the hydrated coordination becomes greater than 6, re-degeneracy of d orbitals resulted in narrowing of the width of L3-edge white line under the complete isotropic field. They concluded that the high coordination sphere and/or distorted coordination sphere of lanthanoid compounds lead to a similar potential field for the lanthanoid gas phase. In other words, the FWHM value indirectly indicates the disorder of the local configuration. This is the reason why FWHM values roughly decrease with increasing coordination numbers in Figure 6. 8


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However, the above explanation is not a rigorous rule for our samples. The La-, Pr-, and Nd-adsorbed δ-MnO2 show distorted structure tenfold-coordination spheres consisting of six short and four long Ln–O bonds, whereas La-, Pr-, Nd-, and Sm-doped FeOOH contained a mixture of eightfold- and ninefold-coordination spheres 9. Nevertheless, FWHM values of FeOOH and δ-MnO2 precipitates for La, Nd and Sm samples did not differ significantly (Figure 6). The Ln-doped FeOOH and δ-MnO2 and Ln3+(aq) species for Er, Tm, Yb, and Lu all consisted of eight-coordination spheres 10-11. The FWHM values of Ln-doped FeOOH and δ-MnO2 were similar but significantly larger than that of Ln3+(aq) (Figure 6). The coordination numbers of Nd- and Sm- and those of Tb-, Dy-, Ho-, and Yb-doped calcite were as small as 7 and 6, respectively

12, 18

. In contrast, commercially available Ho and Yb

carbonate compounds have eight-fold coordination. The FWHM value of Ho-doped calcite (CN = 6) was quite close to that of Ho carbonate (CN = 8), but their FWHM values were larger than that of Ho3+(aq) (CN = 8). In contrast, the FWHM value of Yb-doped calcite (CN = 6) was much larger than those of Yb carbonates (CN = 8). FWHM values of Yb carbonates were significantly larger than those of Yb3+(aq) and Yb-doped FeOOH and δ-MnO2 even though they commonly have eightfold coordination structures.

4.2. Relationship between the White Line FWHM and the Chemical Form and Coordination Geometry. The FWHM values did not faithfully reflect the local coordination sphere of lanthanoid complexes (Figure 6) as we discussed above. This would be partly because EXAFS analysis provides average values of structural parameters for Ln3+(aq) and Ln-doped poorly crystalline materials, as is not the case with crystalline materials. However, we assumed that the FWHM of lanthanoid compounds with larger coordination numbers or distorted coordination spheres changes systematically with ligand molecules. Hence, we regrouped lanthanoid compounds conveniently by ligand molecules: H2O0 for Ln3+(aq), -O− (including –OH0) for Ln-doped 9



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FeOOH and δ-MnO2, -CO32− for Ln-doped calcite, lanthanoid carbonate compounds, and synthetic lanthanoid carbonate precipitations; -Cl− for HoCl3·6H2O; -OH− for Yb(OH)3; -O2− for Ln2O3. Figure 7 shows that FWHM increased in the order -H2O0, -O−, -OH−, -CO32−, -Cl−, and -O2−. It can be concluded that the ligands increase the crystal field splitting of 5d orbital in this order, as is the case with the spectrochemical series proposed for the study of a cobalt complex 28. Although lanthanoid chloride is a more ionically bound complex, the FWHM value of HoCl3·6H2O is much larger than that of Ho3+(aq) and a little less than that of Ho2O3, as it is a more covalently bound compound (Figure 7). Because both HoCl3·6H2O and Ho2O3 show octahedral coordination (six-fold coordination sphere), 5d-orbital splitting by coordination geometry would strongly determine their FWHM values

8, 26-27

. Figure 8 shows that XANES

spectra of Ln2O3 (Ln = La, Ho, and Yb) and HoCl3·6H2O can be deconvoluted with two Lorentzian functions and an arctangent function. The obtained parameters are summarized in Table 3. The difference between the two peak energies (∆E) for La2O3, Ho2O3, Yb2O3, and HoCl3·6H2O were 2.1 eV, 3.0 eV, 3.1 eV, and 3.0 eV, respectively (Table 3), which are comparable to the magnitude of energy splits (3.2–3.4 eV) reported by Antonio et al.

26

and

Lee et al. 27. The difference in the FWHM values of Ho2O3 and HoCl3·6H2O can be explained by the difference in the two peak positions because of the ligand strength causing the crystal field splitting of O2− being larger than that of Cl−. Incidentally, the ∆E of La2O3 (2.1 eV) is smaller than those of Ho2O3 (3.0 eV) and Yb2O3 (3.1 eV). The ∆E of La2O3 would be narrowed by the re-degeneracy of 5d orbitals because the La atom in hexagonal A-type Ln2O3 is present not in six-fold coordination but in seven-fold coordination 21. FWHM values of Ln-doped calcite and lanthanoid carbonate were problematic to deal with. The FWHM value of Yb-doped calcite was not that much larger than those of Yb carbonate compounds but were a lot larger than those of the other Ln-doped calcite and Ln carbonate species. Tsuno et al.

13

reported that 15% of Yb in calcite exists as Yb2+, whose 10


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ionic radius suggests it is in six-fold coordination (1.02 Å) 29, similar to that of Ca2+ (1.00 Å). This suggests that Yb2+ substitutes at the calcium site of calcite with higher stability than Yb3+. By comparison, the FWHM value of Sm-doped calcite, in which divalent samarium ion exists, also seemed to be systematically larger than the value estimated from the FWHM values of Nd- and Tb-doped calcite. However, a significantly larger FWHM value was obtained for the main peak attributable to Yb3+. Furthermore, the ionic radius of Sm3+ ion with CN = 6 (0.958 Å) was closer to that of the Ca2+ ion than that of the Sm2+ ion with CN = 6 (1.15 Å) 29. Tsuno et al. 20 reported that Yb–O coordination in Yb-doped calcite is composed of four short Yb–O bonds (2.24 Å) and two long Yb–O bonds (2.77 Å) (the mean distance = 2.42 Å). The Yb-O distance is rather close to the Yb-O distance (2.42 Å) estimated from ionic radii of Yb2+ and O2−, which is much longer than the Yb-O distance (2.268 Å) estimated from the ionic radii of Yb3+ (CN=6: 0.868 Å) and O2− (1.40 Å) or those reported by Elzinga et al. 18. By contrast, the coordination number of Ca2+ in the crystal structure of calcite is 6 and the Ca–O distance is 2.36 Å. It is possible that the FWHM value for Ln-doped calcite becomes large when its Ln–O distance is close to the Ca–O distance in calcite. However, Tanaka et al. 12

determined the Ho–O distances in Ho-doped calcite and Ho carbonate to be 2.311 Å and

2.351 Å, respectively, using EXAFS spectra. The estimated interatomic distance of Ho carbonate was close to the Ca–O distance in calcite. However, the FWHM value of Ho carbonate was much smaller than that of Yb-doped calcite and closer to that of Ho-doped calcite (Figures 5 and 6). The white line of Yb-doped calcite can be fitted with two Lorentzian functions and an arctangent function (Figure 8). The ∆E of Yb-doped calcite was determined to be 3.0 eV, which is as large as that of Yb2O3 (3.1 eV) (Table 3). In contrast, the white lines of the other Ln-doped calcite and Ln carbonate samples could not be successfully fitted with two Lorentzian functions and an arctangent function. Accordingly, the large FWHM value of 11



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Yb-doped calcite can be explained by 5d-orbital splitting due to the crystal field effect, as is the case with Ln oxides and HoCl3·6H2O. We assume that the coordination sphere of lanthanoid atoms except for Yb in calcite may be distorted, which results in narrowing FWHM of the white lines for Ce, Nd, Sm, Tb, Dy, Ho, and Lu because of re-degeneracy of 5d orbitals 8. As a result, the FWHM values of Ln-doped calcite except for Yb-doped one were close to those of Ln carbonate materials having larger coordination spheres.

4.3. Series Variation of the White Line FWHM of lanthanoid L3-edge XANES Spectra. We have discussed the relationship between the FWHM values and the local structures or the chemical forms of lanthanoid complexes. Finally, we consider the zig-zag pattern appearing in the systematic variation of FWHM values of Ln3+(aq). It is known that the double-seated pattern is recognized in the series variations of the third ionization potential (4fq → 4fq−1)

30

and the f–d transition (e.g., 4fq+16s2 → 4fq5d16s2)

31-32

, which is shown in

Supporting Information (Figure S1a). These features are explained by a refined spin-pairing energy theory proposed by Jørgensen

33

. However, the L3 excitation (2p3/2 → 5d) does not

involve a change in the numbers of 4f electrons. Furthermore, the excitation of 2p → 4f was found to be quite weak at about 10 eV below E0 because it is a quadrupole transition 16. Kawabe 34 demonstrated that the energy level of the ground level electronic configuration of 4fq (E[4fq]) for the lanthanoid ion can be expressed using the refine spin-pairing energy theory of Jørgensen 33 as follows;

E[4fq] = −qW − (1/2)q(q−1)(E* − E0 + (9/13)E1) + (9/13)n(S)E1 + m(L)E3 + p(S, L, J)ζ4f,

(2)

where q is the number of 4f elections of Ln3+, W is the one-electron energy difference, and E* 12


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is a parameter to account for the stabilization of 4f electrons due to increase in the effective nuclear charge from one element to the next. E0, E1, and E3 denote Racah parameters for the inter-electron repulsion between 4f electrons 34. The parameters n(S), m(L), and p(S, L, J) are the constant coefficients given by the quantum numbers S, L, and J for the ground level electronic configurations, respectively

33

. The first and second terms in Eq 2 mean the

electron configuration average energy of 4f electrons. They can be approximated by a smooth polynomial curve of the number of 4f electron 34. The third, fourth, and fifth terms in Eq 2 provide the lowest energy electron configuration for the ground state according to Hund's rules. The series variations of n(S) and m(L) in the third and fourth terms across the lanthanoid series depict the octad and tetrad curves, respectively, which are shown in Supported Information (Figure S2). As a result, the series variation of E[4fq] do not change smoothly and has the tetrad curves obtained by the linear combination of n(S) and m(L) (Figure S2). Kawabe

34

interpreted that the tetrad effect appearing in the enthalpy changes of the

ligand-exchange reaction across the lanthanoid series is caused by the difference between the Racah parameters of the reactant and product. Such an energy difference does not involve a 4f-electron change. The convex tetrad curve is recognized in the ligand-exchange reaction enthalpy (∆Hr) between LnO1.5 (sesquioxides) and LnF3 (∆Hr = ∆Hf [LnF3] − ∆Hf [LnO1.5]), which is shown in Supporting Information (Figure S1b). The pattern is also similar to the series variation of FWHM values of Ln3+(aq). ∆Hr is composed of two kinds of energy differences: ∆Hr = ∆H0 + ∆E[4fq]. Here, ∆H0 is the enthalpy difference due to causes other than the 4f electronic configuration of Ln3+ and is expressed by the classical potential energy of equations with the masses, charges, and sizes of ions 34. Finally, the variation of ∆Hr across the lanthanoid series can be expressed as a function of q (4f electrons) as follows;

∆Hr(q) = ∆H0 −q∆W − (1/2)q(q−1)(∆E* − ∆E0 + (9/13)∆E1) 13



+ (9/13)n(S)∆E1 + m(L)∆E3 + p(S, L, J)∆ζ4f

Page 14 of 40

(3)

The first, second, and third terms in Eq 3 can be collectively approximated by a smooth polynomial curve; the sixth term is negligible in most cases because its contribution is much smaller

34

. Racah parameters (E0, E1, and E3) are systematically small for covalently bound

complex (e.g., Ln2O3) and large for ionically bound complex (e.g., LnCl3 and LnF3)

35-36

.

Consequently, a significant difference in the Racah parameters between LnF3 and LnO1.5 results in a tetrad curve depicted by the fourth and fifth terms in Eq 3 (Figure S2) in the ligand-exchange reaction enthalpy (∆Hr = ∆Hf [LnF3] − ∆Hf [LnO1.5]) across the lanthanoid series (Figure S1b). In the case of L3-edge XANES spectra, ∆E[4fq] is proportional to the energy difference between the final state (2p54fn5d1) and the initial state (2p64fn5d0). Therefore, it is expected that the systematic variation of E0 and the peak position of the white line across the lanthanoid series show a tetrad curve. However, they exhibit a smooth curve increasing with the atomic number because the monochromator at KEK-PF BL-12C was calibrated at each Ln-L3 absorption edge, which gradually increases with the atomic number, for every experimental run 11 (Figure 9). The ideal FWHM (Γ*) of L3-edge XANES is composed principally of the natural width (ΓN), the spectrometer slit (Γslit), and the resolution of the spectrometer (Γres): Γ* = {(ΓN)2 + (Γslit)2 + (Γres)2}1/2. The observed FWHM value for each lanthanoid compound increases with the atomic number (Figure 5). This is partly because the natural widths of L3 level increase with increase in the atomic number

19

(Figure 5). The systematic differences of observed

FWHM (Γobs) and ideal FWHM (Γ*) would be dominantly caused by the crystal field effect of 5d orbitals (∆cfs) as we discussed above: ∆cfs = {(Γobs)2 − (Γ*)2}1/2. The crystal field splitting energy (∆cfs) of d-orbitals is expressed by a simple equation using the electrostatic model

37

as ∆cfs = Q/[RLn–L]5, where Q is the constant and [RLn–L]5 is the fifth power of the 14


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lanthanoid –ligand distance. However, Dorenbos

38, 39

pointed out that the crystal field

splitting of 5d orbitals found in the 4f–5d transition energies for Ce3+ and Eu2+ empirically can be fitted by an asymptotic equation: it correlates to the square of the bond lengths corrected for the lattice relaxation. Thus, we assume that ∆cfs(q) expressing the increase in the FWHM value of L3-edge XANES across the lanthanoid series can also be approximately expressed as follows:

∆cfs(q) ≈ Q/[RLn–L]2

(4)

The reciprocal of the interatomic distance (RLn–L) of lanthanoid compounds is linked to the series variations of the hydration enthalpy (∆Hhyd(q)) and lattice energy (U(q)) of lanthanoid complexes as follows 34, 40;

−∆Hhyd(q) or U(q) ≈ A/RLn–L+B

(5)

Here, A and B are constants. Eqs 3, 4, and 5 indicate that the reciprocal of the interatomic distance (RLn–L) and ∆cfs(q) relate indirectly to the refine spin-pairing energy theory of Jørgensen 10, 11, 33. Finally, a difference (∆Γ) between observed FWHM (Γobs) of Ln3+(aq) and the natural width (ΓN) can be simply expressed as an approximate function of q (4f electrons) as follows;

∆Γ(q) ≈ ∆cfs = Q×{(∆Hr(q)−B)/A}2 = Q'×(a + bq + cq2 + dq3 + (9/13)n(S)∆E1 + m(L)∆E3)2

(6)

where a, b, c, and d are constants; and Q' means Q/A2 and is safely assumed to be a constant 15



for all lanthanoids. The cubic curve as a function of q is an approximate function of the first, second, and third terms in Eq 3, and constant B in Eq 4. Racah parameters (E1 and E3) are approximately expressed as a function of a constant depending on ligand molecules (C1 or C3) and the effective nuclear charge (Z*)

34

: ∆En = ∆Cn×Z* + Cn×∆Z* (n = 1 or 3). The

former (∆Cn×Z*) relates to the tetrad effect appearing in the ligand-exchange reaction, which is shown in Supporting Information (Figure S1b), because there is no change in the effective nuclear charge: ∆Z*=0. The latter (Cn×∆Z*) relates to a change in the Racah parameter in the one-electron excitation 2p3/2 → 5d because the constants C1 or C3 remain unchanged: ∆Cn = 0. The effective nuclear charge of 4f electrons (Z*) of the final state [2p54fn5d1] increases from that of the initial state [2p64fn5d0] during a core-hole lifetime. Finally, a convex tetrad curve expressed by the fifth and sixth terms and positive ∆E1 and ∆E3 parameters in Eq 6 would appear in the FWHM of L3-edge XANES spectra. Figure 10 shows a difference (∆Γ) between observed FWHM (Γobs) of Ln3+(aq) and the natural width (ΓN)

19

: ∆Γ = {(Γobs)2 − (ΓN)2}1/2. The datum of La is missing because Γobs is

smaller than ΓN for La. The ∆Γ values of Ce, Pr, and Nd are lower than those of Dy, Ho, Er, Tm, Yb, and Lu. In particular, the ∆Γ value of Gd is lower than those of Eu and Tb: a gadolinium break. Eq 6 could be successfully fitted to ∆Γ(q) of Ln3+(aq) (see cross symbols in Figure 10), and the parameters determined by the fitting are tabulated in Table 4. Incidentally, FWHM values (Γcal) calculated using the fitting result (Γfit) and ΓN (Γcal = {(Γfit)2 + (ΓN)2}1/2) can reproduce the systematic variation of observed FWHM values of Ln3+(aq) (see cross symbols in Figure 5). We assume that a similar tetrad curve should be recognized for the series variations of FWHM for all lanthanoid complexes. Therefore, the parameters of Eq 6, especially √Q’∆E1 and √Q’∆E3, provide the chemical-binding state information, i.e., the covalently or ionically binding property of each Ln complex.

5. CONCLUSION 16


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It has been observed that the FWHM value of a lanthanoid L3-edge XANES spectrum has a close relation with the local structure around the lanthanoid atom. Accordingly, we have examined the applicability of L3-edge XANES spectra of lanthanoids in the local structural analysis of marine minerals (Fe hydroxide, Mn dioxide, and calcite). Large FWHM values were obtained for lanthanoid oxides and chloride, which can be explained by the crystal field effect. Split 5d orbitals were induced by the octahedral geometry of the species (six-coordination sphere). In contrast, the FWHM values of lanthanoid complexes with larger coordination numbers (CN > 6) or with a distorted coordination sphere roughly decreased with increasing CN because of re-degeneracy of 5d orbitals. However, the systematic change in the FWHM value did not faithfully reflect the variation of the local coordination sphere of lanthanoid complexes. FWHM gradually increased in the order Ln3+(aq), Ln-doped FeOOH and δ-MnO2, Ln-doped calcite and lanthanoid carbonates, lanthanoid hydroxide and lanthanoid chloride, and lanthanoid oxide. These results indicate that the FWHM values of the L3-edge XANES of lanthanoid compounds are useful for speciation rather than structural analysis.

ASSOCIATED CONTENT Supporting Information Preparation of Ln-doped FeOOH, δ-MnO2, and calcite Figure S1: Series variations of the third ionization potential and the f–d transition Figure S2: Series variations of coefficients of n(S), m(L), and n(S)+ (3/10)m(L)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Phone +81-29-861-3848, ORCID 17



Atsuyuki Ohta: 0000-0002-0770-3273 Hiroshi Tsuno: 0000-0002-4844-5995 Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS The XAFS experiments were performed with the approval of the Photon Factory Program Advisory Committee (Proposal No. 2001G122, 2002G257, 2004G321, 2004G334, 2005G228, and 2006G336).

ABBREVIATIONS XAFS, X-ray absorption fine spectroscopy; EXAFS, extended X-ray absorption fine structure; XANES, X-ray absorption near edge structure; FWHM, full width at half maximum; Ln, lanthanoid; CN, coordination number

18


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(10) Ohta, A.; Kagi, H.; Nomura, M.; Tsuno, H.; Kawabe, I., Coordination Study of Rare Earth Elements on Fe Oxyhydroxide and Mn Dioxides: Part II. Correspondence of Structural Change to Irregular Variations of Partitioning Coefficients and Tetrad Effect Variations Appearing in Interatomic Distances. Amer. Mineral. 2009, 94, 476–486. (11) Ohta, A.; Kagi, H.; Tsuno, H.; Nomura, M.; Kawabe, I., Influence of Multi-Electron Excitation on EXAFS Spectroscopy of Trivalent Rare-Earth Ions and Elucidation of Change in Hydration Number through the Series. Amer. Mineral. 2008, 93, 1384–1392. (12) Tanaka, K.; Takahashi, Y.; Shimizu, H., Local Structure of Y and Ho in Calcite and Its Relevance to Y Fractionation from Ho in Partitioning between Calcite and Aqueous Solution. Chem. Geol. 2008, 248, 104–113. (13) Tsuno, H.; Kagi, H.; Takahashi, Y.; Akagi, T.; Nomura, M., Spontaneously Induced Reduction of Trivalent Ytterbium in Synthesized Crystal of Calcite. Chem. Lett. 2003, 32, 500–501. (14) Ohta, A.; Ishii, S.; Sakakibara, M.; Mizuno, A.; Kawabe, I., Systematic Correlation of the Ce Anomaly with the Co/(Ni+Cu) Ratio and Y Fractionation from Ho in Distinct Types of Pacific Deep-Sea Nodules. Geochem. J. 1999, 33, 399–417. (15) Taguchi, T.; Ozawa, T.; Yashiro, H., Rex2000: Yet Another XAFS Analysis Package. Physica Scripta 2005, T115, 205–206. (16) Röhler, J., X-Ray Absorption and Emission Spectra. In Handbook on the Physics and Chemistry of Eare Earths, Gschneidner, K. A. J.; Eyring, L.; Hüfner, S., Eds. Elsevier Science Publishers B.V.: 1987; Vol. 10, pp 453–545. (17) Tanaka, T.; Hanada, T.; Yoshida, S.; Baba, T.; Ono, Y., Valence Variation of Yb Encapsulated in the Supercage of Y-Type Zeolite. Jpn. J. Appl. Phys. 1993, 32 (Suppl. 32-2), 481–483. (18) Elzinga, E. J.; Reeder, R. J.; Withers, S. H.; Peale, R. E.; Mason, R. A.; Beck, K. M.; Hess, W. P., EXAFS Study of Rare-Earth Element Coordination in Calcite. Geochim. 20


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Cosmochim. Acta 2002, 66, 2875–2885. (19) Krause, M. O.; Oliver, J. H., Natural Widths of Atomic K and L Levels, Kα X-Ray Lines and Several KLL Auger Lines. J. Phys. Chem. Ref. Data 1979, 8, 329–338. (20) Tsuno, H.; Kagi, H.; Takahashi, Y.; Akagi, T.; Nomura, M., XAFS Study on the Trace Amounts of Ytterbium Ions Incorporated in Calcium Carbonate Crystal. Physica Scripta 2005, T115, 897–900. (21) Wyckoff, R. W. G., Crystal Structures. Vol. 2, Inorganic Compounds RXn RnMX2 RnMX3. 2nd ed. ed.; John Wiley & Sons Inc: 1964; Vol. 111, p 588p. (22) Milligan, W. O.; Mullica, D. F.; Grossie, D. A.; Lok, C. K. C., Crystal Structure of Yb(OH)3. J. Solid State Chem. 1983, 50, 129–132. (23) Shinn, D. B.; Eick, H. A., Crystal Structure of Lanthanum Carbonate Octahydrate. Inorg. Chem. 1968, 7, 1340–1345. (24) Christensen, A. N., Hydrothermalpreparation of Rare Earth Hydroxycarbonates. The Crystal Structure of Ndohco3. Acta Chem. Scand. 1973, 27, 2973–2982. (25) Kutlu, I.; Kalz, H. J.; Wartchow, R.; Ehrhardt, H.; Seidel, H.; Meyer, G., Potassium Lanthanoid Carbonates, KM(CO3)2 (M = Nd, Gd, Dy, Ho, Yb). Z. Anorg. Allg. Chem. 1997, 623, 1753–1758. (26) Antonio, M. R.; Soderholm, L.; Ellison, A. J. G., Local Environments of Erbium and Lutetium in Sodium Silicate Glasses. J. Alloy. Compd. 1997, 250, 536–540. (27) Lee, C. H.; Oyanagi, H.; Sekine, C.; Shirotani, I.; Ishii, M., XANES Study of Rare-Earth Valency in LRu4P12 (L = Ce and Pr). Phys. Rev. B 1999, 60, 13253–13256. (28) Tsuchida, R., Absorption Spectra of Co-Ordination Compounds. I. Bull. Chem. Soc. Jpn. 1938, 13, 388–400. (29) Jia, Y. Q., Crystal Radii and Effective Ionic Radii of the Rare Earth Ions. J. Solid State Chem. 1991, 95, 184–187. (30) Martin, W.; Hagan, L.; Reader, J.; Sugar, J., Ground Levels and Ionization Potentials for 21



Lanthanide and Actinide Atoms and Ions. J. Phys. Chem. Ref. Data 1974, 3, 771–780. (31) Nugent, L. J.; Vander Sluis, K. L., Theoretical Treatment of the Energy Differences between fqd1s2 and fq+1s2 Electron Configurations for Lanthanide and Actinide Atomic Vapors. J. Opt. Soc. Am. 1971, 61, 1112–1115. (32) Nugent, L. J.; Baybarz, R. D.; Burnett, J. L.; Ryan, J. L., Electron-Transfer and f–d Absorption Bands of Some Lanthanide and Actinide Complexes and the Standard (II–III) Oxidation Potential for Each Member of the Lanthanide and Actinide Series. J. Phys. Chem. 1973, 77, 1528–1539. (33) Jørgensen, C. K., Electron Transfer Spectra of Lanthanide Complexes. Mol. Phys. 1962, 5, 271–277. (34) Kawabe, I., Lanthanide Tetrad Effect in the Ln3+ Ionic-Radii and Refined Spin-Pairing Energy Theory. Geochem. J. 1992, 26, 309–335. (35) Caro, P.; Derouet, J.; Beaury, L.; Soulie, E., Interpretation of the Optical Absorption Spectrum and of the Paramagnetic Susceptibility of Neodymium a-Type Sesquioxide. J. Chem. Phys. 1979, 70, 2542–2549. (36) Caro, P.; Derouet, J.; Beaury, L.; de Sagey, G. T.; Chaminade, J. P.; Aride, J.; Pouchard, M., Interpretation of the Optical Absorption Spectrum and of the Paramagnetic Susceptibility of Neodymium Trifluoride. J. Chem. Phys. 1981, 74, 2698–2704. (37) Burns, R. G., Mineralogical Applications of Crystal Field Theory. Cambridge University Press: 1993; Vol. 5, p 575. (38) Dorenbos, P., A Review on How Lanthanide Impurity Levels Change with Chemistry and Structure of Inorganic Compounds. ECS J. Solid State Sci. Technol. 2013, 2, R3001– R3011. (39) Dorenbos, P., 5d-Level Energies of Ce3+ and the Crystalline Environment. III. Oxides Containing Ionic Complexes. Phys. Rev. B 2001, 64, 125117: 1–12. (40) Bratsch, S.; Silber, H. B., Lanthanide Thermodynamic Predictions. Polyhedron 1982, 1, 22


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219–223.

23



Table 1 FWHM values of Ln L3-edge XANES spectra of Ln3+(aq), Ln-doped FeOOH, and Ln-doped δ-MnO2 fitted using Eq 1. Samples 3+

Ln La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

n*

Γw (eV)

1s*

3 2 3 2 2 2 1 1 2 2 3 2 4 2

3.396 3.766 4.106 4.270 4.611 4.631 4.548 4.799 5.013 5.041 5.142 5.282 5.419 5.357

0.034

(aq)

0.089

0.019 0.066

Ln-doped FeOOH La 4 Pr 3 Nd 4 Sm 2 Yb 4 Lu 4

3.845 4.790 4.756 5.035 5.671 5.702

0.055 0.064 0.054 0.034 0.090 0.052

Ln-doped δ-MnO2 La 3 Pr 3 Nd 3 Er 4 Tm 3 Yb 3 Lu 3

4.041 4.731 4.894 5.495 5.653 5.724 5.700

0.071 0.196 0.044 0.063 0.004 0.018 0.081

*n and 1s denote the number of repeated measurements and the standard deviation of FWHM values, respectively.

24


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Table 2 FWHM values of Ln L3-edge XANES spectra of Ln-doped calcite and commercially available Ln compounds fitted using Eq 1. Samples

Γw (eV)

Ln-doped calcite Ce

4.772

Nd

5.069

Sm

5.672

Tb

5.391

Dy

5.926

Ho

5.703

Er

5.744

Yb

7.658

Lu

6.317

Ln oxide La2O3

4.719

Ho2O3

7.824

Yb2O3

8.060

Ln carbonate Ho2(CO3)3·nH2O

5.673

Yb2(CO3)3·nH2O

6.330

NaYb(CO3)2·nH2O

6.331

Ln chloride HoCl3·6H2O

7.319

Ln hydroxide Yb(OH)3·nH2O

6.294

25



Page 26 of 40

Table 3 Parameters of Ln L3-edge XANES spectra of Ln2O3 and Yb-doped calcite fitted using two or three Lorentzian functions and an arctangent function. Peak position Γ w (eV) (eV)

∆E* (eV)

Peak 1

5489.4

3.959

2.1

Peak 2

5491.5

3.957

Peak 1

8063.7

5.345

Peak 2

8066.6

5.808

Peak 1

8946.6

5.657

Peak 2

8949.7

5.844

La2O3

Ho2O3 3.0

Yb2O3 3.1

Yb-doped calcite Peak of Yb2+

8941.2

6.529

Peak 1

8948.3

6.087

Peak 2

8951.0

4.287

*∆E is the difference of peak positions of peak 1 and peak 2

26


2.7

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Table 4 Parameters determined by least square fitting of a difference (∆Γ) between observed FWHM (Γobs) of Ln3+(aq) and natural width (ΓN) using Eq 6. Parameter

Fitting value

Error

√Q’×a

8.9×10−4

1.0×10−4

√Q’×b

−3.25×10−2

0.29×10−2

√Q’×c

0.331

0.025

√Q’×d

0.908

0.033

√Q’×(9/13)∆E1

2.29×10−2

0.25×10−2

√Q’×∆E3

3.7×10−3

1.0×10−3

χ2 = 0.00192; R2 = 0.996* *χ2 and R2 indicate the chi-square value and the coefficient of determination for the fitting, respectively.

27



FIGURE CAPTIONS Figure 1. La and Nd L3-edge normalized XANES and the deconvoluted spectra of Ln3+(aq), Ln-doped FeOOH, Ln-doped δ-MnO2, La2O3, and Nd-doped calcite (Ln = La and Nd). The blue and green lines, and the green and red broken lines indicate the XANES spectra, Lorentzian function, arctangent one, and the fitting result, respectively. Figure 2. Sm L3-edge normalized XANES and the deconvoluted spectra of Sm3+(aq), Sm-doped FeOOH, and Sm-doped calcite. The blue and green lines, and the green and red broken lines are the same as those in Figure 1. The orange line indicates the Lorentzian function of Sm2+. Figure 3. Ho L3-edge normalized XANES and the deconvoluted spectra of Ho3+(aq), Ho-calcite, Ho2(CO3)3·nH2O, HoCl3·6H2O, and Ho2O3. The blue and green lines, and the green and red broken lines are the same as those in Figure 1. Figure 4. Yb L3-edge normalized XANES and the deconvoluted spectra of Yb3+(aq), Yb-doped FeOOH, Yb-doped δ-MnO2, Yb(OH)3·nH2O, Yb-doped calcite, Yb2(CO3)3·nH2O, NaYb(CO3)2·nH2O, and Yb2O3. The blue and green lines, and the green and red broken lines are the same as those in Figure 1. The orange line indicates the Lorentzian function of Yb2+. Figure 5. Systematic variation of FWHM of lanthanoid L3-edge XANES spectra and the natural width of the L3 level (plus symbol)

19

across the lanthanoid series. The

small bars indicate the standard deviations for repeated measurements, which are shown in Table 1. The cross symbol indicates the calculated FWHM values of Ln3+(aq) from the fitting result of ∆Γ using Eq 6 and the natural width. Figure 6. Dependence of FWHM of lanthanoid L3-edge XANES spectra on coordination number (CN) at the first coordination shell for La, Nd, Sm, Er, Ho, and Yb. Ln-FeOOH, Ln-δ-MnO2, and Ln-calcite indicates Ln-doped FeOOH, Ln-doped 28


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δ-MnO2, and Ln-doped calcite, respectively. Figure 7. Relationship between FWHM of lanthanoid L3-edge XANES spectra and the chemical forms. Figure 8. Deconvolution of the white line at the L3-edge XANES spectra of La2O3, Ho2O3, Yb2O3, HoCl3·6H2O, and Yb-doped calcite with two Lorentzian functions and an arctangent function. The blue, green, and orange lines and the green and red broken lines are the same as those in Figures 1 and 4. The brown line indicates the second Lorentzian function of Ln complexes. Figure 9. Variations of L3-edge absorption edge energies and peak positions of the white line of L3-edge XANES spectra of Ln3+(aq). Figure 10. Difference (∆Γ) between observed FWHM (Γobs) of Ln3+(aq) and natural width (ΓN) 19. The cross symbol indicates the fitting results of ∆Γ using Eq 6.

29



TOC Graphic

30


Page 30 of 40

Page 31 of 40

Normalized absorption

4.0

4.0 3.0 2.0

La3+(aq)

1.0

3.0 2.0 Nd3+(aq) 1.0 0.0

5.0

4.0 Normalized absorption

0.0

4.0 3.0 La-doped FeOOH

2.0 1.0

3.0 2.0

5.0


0.0

4.0 3.0 La-doped δ-MnO2

2.0 1.0

3.0 2.0

0.0

5.0

4.0

3.0 2.0

La2O3

1.0 0.0 5460

5480

5500 5520 Energy (eV)

5540

Nd-doped δ-MnO2

1.0

0.0

4.0

Nd-doped FeOOH

1.0

0.0





5.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.0 2.0

Nd-doped calcite

1.0 0.0 6180

6200 6220 Energy (eV)

6240

6260

Figure 1 (Ohta et al.)




4.0 3.0 2.0 Sm3+(aq) 1.0 0.0


4.0 3.0 2.0

Sm-doped FeOOH

1.0 0.0 4.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Sm3+

3.0 2.0 Sm2+

Sm-doped calcite

1.0 0.0 6690

6710

6730 6750 Energy (eV)

6770



Page 32 of 40

Page 33 of 40

3.0 2.0 Ho3+(aq) 1.0


4.0 3.0 2.0 HoCl3·nH2O 1.0

0.0

0.0

4.0

4.0

3.0 2.0

Ho-doped calcite

1.0 0.0




4.0

3.0 2.0 Ho2O3 1.0 0.0 6180


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6200

6240 6220 Energy (eV)

6260

3.0 2.0 Ho2(CO3)3·nH2O 1.0 0.0 6180

6200

6240 6220 Energy (eV)

6260




3.0 2.0

Yb3+(aq)

1.0


4.0 3.0

Yb2+

4.0

Yb-doped FeOOH

1.0


4.0

2.0

3.0 2.0 Yb2(CO3)3·nH2O 1.0 0.0

4.0

4.0

2.0

Yb-doped δ-MnO2

1.0


0.0

3.0

3.0 2.0 NaYb(CO3)2·nH2O 1.0

0.0

0.0

4.0

4.0

3.0 2.0 Yb(OH)3·nH2O 1.0 0.0

Yb-doped calcite

1.0 0.0

3.0

Yb3+

2.0

0.0





4.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 40

3.0 2.0 Yb2O3 1.0 0.0

8920

8940 8960 Energy (eV)

8980

8920

8940 8960 Energy (eV)

8980



Page 35 of 40

8.0

7.0

FWHM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6.0

5.0

4.0

3.0

Calculated values

La Ce Pr NdPmSmEuGdTb DyHo Er TmYb Lu Ln3+(aq) Ln-doped FeOOH Ln-doped δ-MnO2 Ln-doped calcite Ln carbonate Ho chloride Yb hydroxide Ln oxide Natural width of L3 level Figure 5 (Ohta et al.)



5.5

7.0

5.0

La

La2O3

La-FeOOH

3.5

La3+(aq)

FWHM

4.0

Er-δ-MnO2

5.0

Er3+(aq)

4.5

2.5

4.0 6

7

8

9

10 11

5

CN

6.0

Nd

5.5 Nd-calcite

5.0

Nd-δ-MnO2 Nd-FeOOH

4.5

Nd3+(aq)

4.0 3.5 3.0 5

6

7

8

9

6.0

Sm

Sm3+(aq)

3.5 6

7

8 9 CN

10 11

Ho2(CO3)3·nH2O Ho3+(aq)

6

7

8

9

10 11

CN

Yb

Yb2O3 Yb-calcite

7.0

NaYb(CO3)2·nH2O Yb2(CO3)3·nH2O Yb(OH)3·nH2O Yb-δ-MnO2 Yb-FeOOH Yb3+(aq)

5.0 5

Ho

Ho-calcite

6.0

4.0

10 11

HoCl3·6H2O

8.0 FWHM

Sm-FeOOH

8 9 CN

Ho2O3

5

5.5

4.5

7

9.0

Sm-calcite

5.0

6

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5

10 11

CN

6.5

Er-calcite

5.5

3.0

FWHM

FWHM

6.0 La-δ-MnO2

5

FWHM

Er

6.5

4.5

FWHM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 40

5

6

7

8 9 CN

10 11



Page 37 of 40

5.5

7.0 6.5

La

8.0 FWHM

5.5 5.0 4.5

-O2−

-Cl−

-OH−

-O2−

-H2O0

-O2−

-Cl−

-OH−

Sm

-O2−

6.0

9.0

-Cl−

6.5

-CO32−

-O−

-H2O0

3.0

-Cl−

3.5

-OH−

4.0

-OH−

4.5

Ho

-CO32−

FWHM

5.0

-CO32−

-H2O0

-O2−

Nd

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5

Yb

7.0 6.0

4.0 -O2−

-Cl−

-OH−

-CO32−

-O−

5.0 -H2O0

3.5

Ligand

-O−

5.5

-Cl−

4.0 -OH−

2.5 -CO32−

4.5 -O−

3.0

6.0

FWHM

5.0

-CO32−

3.5

5.5

-O−

4.0

-O−

FWHM

6.0

-H2O0

FWHM

4.5

Er

-H2O0

5.0

FWHM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ligand






5.0 4.0 3.0 2.0

La2O3

1.0 0.0 5460

5480

5500 5520 Energy (eV)

5540

2.0 HoCl3 1.0

6200

6240 6220 Energy (eV)

6260



3.0

0.0 6180

4.0 3.0 2.0 Ho2O3 1.0 0.0 6180

3.0

Yb3+

2.0

Yb-doped calcite

1.0

Yb2+

0.0 6200

6220 6240 Energy (eV)

6260

8920

8940 8960 Energy (eV)

8980


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 40

3.0 2.0 Yb2O3 1.0 0.0 8920

8940 8960 Energy (eV)

8980



Page 39 of 40

10000 L3-edge

9000 Energy (eV)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Peak position

8000 7000 6000 5000

LaCe PrNdPmSmEuGdTbDyHo Er TmYbLu




4.0 ΔΓ = {(Γobs)2 − (ΓN)2}1/2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 40

3.0 2.0 1.0 0.0

Ln3+(aq) Fitting result LaCePrNdPmSmEuGdTbDyHoErTmYbLu



Preliminary Evaluation of Local Structure and Speciation of

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