Eu3+ ions as a crystal-field probe for low-symmetry sites in doped phosphors - a case study: Eu3+ at triclinic sites in Li6RE(BO3)3 (RE = Y, Gd), YBO3 and ZnO and at trigonal sites in YAl3(BO3)4.

We present crystal-field (CF) calculations of energy levels (Ei) of Eu3+ ions doped in various hosts aimed at exploring the low-symmetry properties of CF parameters (CFPs) and reliability of CFP modelling with decreasing site symmetry. The hosts studied are: Li6Y(BO3)3, Li6Gd(BO3)3, YBO3, and ZnO with Eu3+ at triclinic sites; YAl3(BO3)4 with Eu3+ ions at trigonal D3 symmetry. Two independent CFP modelling approaches utilizing the hosts' structural data are employed: the exchange charge model (ECM) and the superposition model (SPM). We adopt the Eu3+ actual site symmetry and not the approximated one. The Ei values calculated using CFPs modelled by the ECM and SPM mutually agree with the observed ones. For triclinic symmetry, the ECM/CFPs and SPM/CFPs were numerically distinct, yet turned out to be physically equivalent yielding identical rotational invariants, Sk (k = 2, 4, 6) and Ei. For trigonal symmetry, both CFP sets agree numerically, thus Sk and Ei are identical. This disparity poses a dilemma, since the modified crystallographic axis system was used in both approaches. The standardization of the triclinic CFPs using the 3DD package was performed to solve this dilemma. It has enabled discussing standardization aspects in experimental and computed CFP sets and elucidating intricate low-symmetry aspects inherent in CFP sets. Understanding of low-symmetry aspects in CF studies may bring about a better interpretation of the spectroscopic and magnetic properties of rare-earth ion doped host crystals. Thus, our study could provide more deep insights into the importance of clear definitions of axis systems and adequate treatment of actual site symmetry in the modelling of CFPs for low-symmetry cases which is essential for technological applications and engineering of rare-earth activated phosphor materials.

Effects of distortions in ion-host systems on optical spectra, crystal-field and spin-Hamiltonian parameters of Cr3+ ions doped pyrochlores Y2Ti2O7 and Y2Sn2O7: exchange charge model and superposition model calculations.

Comparative modelling of the crystal-field parameters (CFPs), CF energy levels, and effective spin-Hamiltonian parameters (SHPs), i.e., the g-factors and zero-field splitting parameter (ZFSP), D, of the ground state 4A2g of the Cr3+ dopant ions in Y2Ti2O7 and Y2Sn2O7 is carried out. The CFPs are calculated using XRD structural data by employing two semi-empirical models: the exchange charge model (ECM) and superposition model (SPM). This two-fold approach ensures increased reliability of CFP modelling and thus of the final results. The modelled CFPs serve as the input to the crystal-field analysis/microscopic spin-Hamiltonian (CFA/MSH) program to predict CF energy levels and wave functions, and to extract SHPs. Since the site symmetry of Cr3+ ions in these crystals is trigonal D3d, a symmetry adapted axis system (SAAS) conforming to Watanabe convention is adopted for CFP modelling. The calculated CF energies and SHPs for Y2Ti2O7:Cr3+ are in good agreement with the experimental results. Variations of the Racah parameter B, as well as ECM and SPM parameters for Y2Sn2-xCrxO7 are correlated with the chromium concentration (x), which affects distortions of CrO6 structures. We find that the SHPs originate predominantly from the spin-orbit coupling, though contributions from spin-spin and spin-other-orbit couplings are also appreciable and thus important for analysis of lattice distortions and structural disorder. The uniqueness of the SAAS used for CFP modelling is also discussed. The present study enables exploring the influence of the radial and angular distortions of host clusters (Ti-O6/Sn-O6) introduced by Cr3+ ions on the structural and optical properties as well as the SHPs of Cr3+ ions doped in Y2Ti2O7 and Y2Sn2O7.

DFT computations combined with semiempirical modeling of variations with temperature of spectroscopic and magnetic properties of Gd3+-doped PbTiO3.

The rare-earth or 3d transition metal dopants in perovskites have potential to induce interesting features, thus opening opportunities for investigations and applications. Hence, understanding some features, i.e., defect structure, site of incorporation, valence state, and mechanism of charge compensation, in a wide range of temperature is crucial for their technological applications. A comprehensive understanding of the mechanism of structural changes in PbTiO3 doped with trivalent rare-earths is significant for their potential applications in photonics. To unravel the structural changes, we utilize the density functional theory (DFT) to optimize structural data, which then serve as input for the semiempirical superposition model (SPM) analysis of spectroscopic and magnetic properties of Gd3+-doped PbTiO3. We compute the formation energies of the doped compounds with and without O-vacancy to determine the stable composition. Analysis of the Bader electron charges computed using DFT plus quantum theory of atoms in molecules enables elucidating the effects of the Gd dopant and O-vacancy on the ionic and covalent bonds and, thereby, chemical stability of the compositions. To explain and corroborate the zero-field splitting parameters (ZFSPs) measured by EMR and the lattice parameter changes obtained from XRD, we employ SPM. The optimized structures obtained from ab initio computations for various structural models of Gd3+ doped PbTiO3 are utilized as input data for SPM calculations of ZFPs. This enables theoretical analysis of variations of ZFSPs from 5 to 780 K. The results were fine-tuned by matching with available experimental EMR data for Gd3+ probes in PbTiO3 nanoparticles. Modeling has been carried out considering several possible structural models and the role of an O-vacancy around Gd3+ centers. The results show that the two-fold modeling approach, combining DFT and SPM, provides a reliable description of experimental data. Comparative analysis indicates that the Ti-site is less favorable for being replaced by Gd3+ with/without O-vacancy. This analysis confirms the plausibility of the Pb2+ site for Gd3+ dopants and sheds light on the changes of crystal structure during the phase transitions occurring in PbTiO3 with decreasing temperature.

Understanding the effect of structural changes on slow magnetic relaxation in mononuclear octahedral copper(II) complexes.

Current advances in molecular magnetism are aimed at the construction of molecular nanomagnets and spin qubits for their utilization as high-density data storage materials and quantum computers. Mononuclear coordination compounds with low spin values of S = ½ are excellent candidates for this endeavour, but knowledge of their construction via rational design is limited. This particularly applies to the single copper(II) spin center, having been only recently demonstrated to exhibit slow relaxation of magnetisation in the appropriate octahedral environment. We have thus prepared a unique organic scaffold that would allow one to gain in-depth insight into how purposeful structural differences affect the slow magnetic relaxation in monometallic, transition metal complexes. As a proof-of-principle, we demonstrate how one can construct two, structurally very similar complexes with isolated Cu(II) ions in an octahedral ligand environment, the magnetic properties of which differ significantly. The differences in structural symmetry effects and in magnetic relaxation are corroborated with a series of experimental techniques and theoretical approaches, showing how symmetry distortions and crystal packing affect the relaxation behaviour in these isolated Cu(II) systems. Our unique organic platform can be efficiently utilized for the construction of various transition-metal ion systems in the future, effectively providing a model system for investigation of magnetic relaxation via targeted structural distortions.

Importance of the fourth-rank zero field splitting parameters for Fe2+ (S = 2) adatoms on the CuN/Cu(100) surface evidenced by their determination based on DFT and experimental data.

Due to their potential applications, single atoms on surfaces (adatoms) have been extensively studied using STM, IETS, INS, and EPR techniques or using DFT and ab initio methods. Especially interesting are Fe2+ (S = 2) adatoms on CuN/Cu(100) and Cu2N/Cu(100) surfaces due to their non-Kramers features described by the zero field splitting (ZFS) Hamiltonian. The 4th-rank ZFS parameters (ZFSPs), allowed for spin S = 2, are commonly disregarded. By extracting 4th-rank ZFSPs from DFT predicted spin energy levels for the Fe2+@CuN/Cu(100) system, we show that including only 2nd-rank ZFSPs yield incomplete description of magnetic and spectroscopic properties. The algebraic method developed by us is used to extract 2nd- and 4th-rank ZFSPs utilizing knowledge of energy levels without a magnetic field, which may be obtained experimentally or theoretically. Reasonable constraints on particular 4th-rank ZFSPs are considered based on comparison of data on ZFSPs and energies for Fe2+@CuN/Cu(100) and other Fe2+ (S = 2) systems. Influence on energies due to 2nd-rank ZFSPs alone versus that of both 2nd- and 4th-rank ZFSPs is analyzed. A series of simulations of ZFS energies for different ZFSP variants is carried out. The results prove the importance of 4th-rank ZFS parameters. Our method enables a more accurate description of 3d4 and 3d6 (S = 2) ions in various systems, including S = 2 adatoms.

The High-Resolution 4f-5d Absorption Spectrum of Divalent Dysprosium (Dy2+) in Strontium Chloride Host SrCl2: Fine Structure and Zero-Phonon Transitions Revealed.

The virtual lack of information on electronic spectra of divalent lanthanide elements (Ln2+) other than Sm2+, Eu2+, Tm2+, and Yb2+ has prompted us to set for synthesis and characterization of novel Ln2+ systems. First successful attempt concerned SrCl2/Nd2+ single crystals. Here, we report stabilization of divalent dysprosium in a chloride host. Importantly this has been accomplished with Dy ions introduced in a divalent state during synthesis, unlike by γ-irradiation of Dy3+ systems employed previously. This synthesis method yields good quality SrCl2/Dy2+ single crystals. The electronic absorption spectra of Dy2+ doped in SrCl2 have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000-45000 cm-1 is achieved. On the basis of theoretical calculations using semiempirical Hamiltonian model, assignment of bands and determination of the Hamiltonian parameters for Dy2+(4f95d1) configuration is carried out. The experimental and theoretical studies reveal fine structure and zero-phonon transitions and thus enable high-resolution assignment of spectral lines. It is shown that spin-forbidden transitions gain relatively high intensity due to significant admixing of low-spin character to nominally high-spin states.

Electron magnetic resonance data on high-spin Mn(III; S=2) ions in porphyrinic and salen complexes modeled by microscopic spin Hamiltonian approach.

The spin Hamiltonian (SH) parameters experimentally determined by EMR (EPR) may be corroborated or otherwise using various theoretical modeling approaches. To this end semiempirical modeling is carried out for high-spin (S=2) manganese (III) 3d4 ions in complex of tetraphenylporphyrinato manganese (III) chloride (MnTPPCl). This modeling utilizes the microscopic spin Hamiltonians (MSH) approach developed for the 3d4 and 3d6 ions with spin S=2 at orthorhombic and tetragonal symmetry sites in crystals, which exhibit an orbital singlet ground state. Calculations of the zero-field splitting (ZFS) parameters and the Zeeman electronic (Ze) factors (g||=gz, g⊥=gx=gy) are carried out for wide ranges of values of the microscopic parameters using the MSH/VBA package. This enables to examine the dependence of the theoretically determined ZFS parameters bkq (in the Stevens notation) and the Zeeman factors gi on the spin-orbit (λ), spin-spin (ρ) coupling constant, and the ligand-field energy levels (Δi) within the 5D multiplet. The results are presented in suitable tables and graphs. The values of λ, ρ, and Δi best describing Mn(III) ions in MnTPPCl are determined by matching the theoretical second-rank ZFSP b20(D) parameter and the experimental one. The fourth-rank ZFS parameters (b40, b44) and the ρ (spin-spin)-related contributions, which have been omitted in previous studies, are considered for the first time here and are found important. Semiempirical modeling results are compared with those obtained recently by the density functional theory (DFT) and/or ab initio methods.

Extension of High-Resolution Optical Absorption Spectroscopy to Divalent Neodymium: Absorption Spectra of Nd2+ Ions in a SrCl2 Host.

There is a lack of information on electronic spectra of divalent neodymium, and thus the synthesis and characterization of Nd2+ systems is now reported. Stabilization of neodymium is observed in a chloride host, which importantly has been accomplished with Nd ions introduced in a divalent state during synthesis, unlike by γ-irradiation of Nd3+ system employed previously. This method yields good-quality SrCl2 :Nd2+ single crystals. For the first time the electronic absorption spectra of Nd2+ doped in SrCl2 have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000-40 000 cm-1 (2000-250 nm) has been achieved and their tentative assignment proposed. This uniquely detailed Nd2+ absorption spectrum provides basis for fingerprinting method enabling identification of the presence of Nd2+ ions in future spectra as well as in existing but as-yet not fully resolved spectra.

EMR studies of the internal motion of Mn(4+) ions in the Sr overdoped (La(1-x)Sr(x))(Ga(1-y)Mn(y))O3 (x/y up to 8) supplemented by magnetic and optical spectroscopy measurements.

The effect of the Sr doping on electronic structure in single crystals of (La(1-x)Sr(x))(Ga(1-y)Mn(y))O3 solid solutions (LSGM) is investigated by means of electron magnetic resonance (EMR). The EMR results are supplemented by magnetic susceptibility and optical spectroscopy measurements. The compositions with small concentration of Mn doping (y<1%) and overdoped content of Sr (the ratio x(Sr)/y(Mn) up to 8) are used to maximally enhance the role of divalent doping. The experimental results provide evidence of the holes delocalization in the overdoped compound (x(Sr)/y(Mn)>1). This delocalization is accompanied by appearance of the new charge transfer transitions in the optical spectrum and dynamical valence change of manganese atoms. Additionally we observe the thermally activated narrowing of resonance EMR lines due to the internal motion, which is characterized by the energy barrier depending strongly on the ratio x(Sr)/y(Mn). The energy barrier is found to be associated with the charge carrier (hole) self-trapped energy. Fitting the EMR spectra in three orthogonal planes to an orthorhombic spin Hamiltonian enables extracting the zero-field splitting (ZFS) parameters and the Zeeman g-factors for Mn(4+) (S=3/2) ions in LSGM. The experimental ZFS parameters are modeled using superposition model analysis based on an orthorhombic symmetry approximation.

Software package SIMPRE--revisited.

This article elucidates the pitfalls identified in the software package SIMPRE recently developed by Baldoví et al. (J. Comput. Chem. 2013, 34, 1961) for modeling the spectroscopic and magnetic properties of single ion magnets as well as single-molecule magnets. Analysis of the methodology used therein reveals that the crystal field parameters (CFPs), expressed nominally in the Stevens formalism, exhibit features characteristic for the CFPs expressed in the Wybourne notation. The resemblance of the two types of CFPs introduces a serious confusion that may lead to wrong comparisons of the CFPs taken from various sources. To clarify this confusion, the properties of the CFPs Bkq ( Akq, Ckq) associated with the Stevens operators Okq(X = S, J, or L), which belong to the class of the tesseral-tensor operators, are contrasted with those of the CFPs Bkq associated with the Wybourne operators Cq(k), which belong to the class of the spherical-tensor operators. Importantly, the confused properties of Stevens and Wybourne operators may bear on reliability of SIMPRE calculations. To consider this question independent calculations are carried out using the complete approach and compared with those of the restricted approach utilized earlier. It appears that the numerical results of the package SIMPRE are formally acceptable, however, the meaning of the CFPs must be properly reformulated. Several other conceptual problems arising from misinterpretations of the crucial notions and the CFP notations identified therein are also discussed and clarified.

Comparative analysis of crystal-field parameters for rare-earth ions at monoclinic sites in AB(WO4)2 crystals: II. Pr3+ and Nd3+ ions in KRE(WO4)2 (RE = Y or Gd), Pr3+ ions in M+ Bi(XO4)2 (M+ = Li or Na and X = W or Mo), and Nd3+ ions in NaBi(WO4)2 and AgNd(WO4)2.

In part I, the crystal-field (CF) parameter (CFP) sets for important potential solid state laser systems Tm(3+), Ho(3+), and Er(3+) ions in KGd(WO4)2 and Tm(3+) ions in KLu(WO4)2 were thoroughly revisited using a general framework for the analysis of CF levels and CFP modeling. In this part the non-standard CFP sets for Pr(3+) and Nd(3+) ions in KR(WO4)2 (R = Y or Gd) and the standard CFP sets for Pr(3+) ions in M(+)Bi(XO4)2 (M(+) = Li or Na and X = W or Mo) and Nd(3+) ions in the related systems NaBi(WO4)2 and AgNd(WO4)2 are analyzed. Due to structural similarity of the hosts, the CFP values for a given trivalent rare-earth (RE(3+)) ion should be quite close in these systems. However, the fitted (and model) CFP sets appear disparate for the systems in question. The standardization criteria are utilized to ensure direct comparability of the apparently disparate CFP sets reported in the literature. The CFP sets standardized by us are compared with the originally standard CFP sets for Pr(3+) and Nd(3+) ions in related AB(XO4)2 systems. Following part I, we argue that meaningful analysis of the mixed CFP sets, i.e. standard and non-standard ones, must take into account the intrinsic features of CF Hamiltonians for orthorhombic and lower symmetry cases, which have not been fully recognized in the literature as yet. The model or fitted CFP sets that belong to disparate regions in the CFP space are intrinsically incompatible, i.e. such sets should not be directly compared. The correlated alternative CFP sets are calculated using monoclinic standardization transformations. The closeness of the standardized CFP sets is assessed in a quantitative way using the closeness factors and the norms ratios. Comparative analysis of the monoclinic CFP sets reported for the titled ion-host systems is carried out and several inconsistencies in the previous studies are clarified. The CFP sets determined by standardization are utilized as starting sets for applications of the multiple correlated fitting technique to independently obtain and additionally verify the fitted CFPs based on published energy levels data. Multiple correlated fittings offer an advantage over the single-fitting tactics by enabling an improved fine-tuning of the final fitted CFPs as well as their interpretation and comparability with the sets obtained by others. The present consistent methodology may enable better understanding of the intricate aspects inherent in the spectroscopic studies for other ion-host systems exhibiting orthorhombic, monoclinic, and triclinic site symmetry.

Determination of crystal-field energy levels and temperature dependence of magnetic susceptibility for Dy3+ in [Dy2Pd] heterometallic complex.

This study is the first in a series of experimental and theoretical investigations of the crystal-field (CF) energy levels obtained from optical electronic spectra for selected heterometallic 4f-3d compounds intensively studied for the development of novel single-molecule magnets (SMMs). An intriguing question is why the [{Dy(III)(hfac)3}2Cu(II)(dpk)2] (abbreviated as [Dy2Cu]; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, Hdpk = di-2-pyridyl ketoxime) has antiferromagnetic coupling, whereas [Gd2Cu] and heavy [Ln2Cu] systems usually show ferromagnetic coupling. As the first step to explain this peculiarity, the recently synthesized complex, [Dy2Pd], is investigated. This complex is isostructural with [Dy2Cu] yet contains the diamagnetic Pd ion instead of the magnetic Cu(II) ion. Experimental energy levels of Dy(3+) ions in the powder [Dy2Pd] sample were determined from the 4.2 K absorption spectra. CF analysis was performed yielding the fitted free ion and CF parameters. The number of freely varied parameters was restricted using the superposition model. The fittings yield very satisfactory agreement between the experimental and the calculated energy levels (rms = 12.0 cm(-1)). The energies and exact composition of the state vector for the ground multiplet (6)H(15/2) of Dy(3+) are determined. These results are used for the simulation of the temperature dependence of the magnetic susceptibility, which enables the theoretical interpretation of the experimentally measured magnetic susceptibility in the range 1.8-300 K for the [Dy2Pd] complex. This study provides background for the subsequent investigation of the magnetic exchange interactions in the pertinent heterometallic complexes.

Trends in orthorhombic crystal field parameters for trivalent rare-earth ions in high-Tc superconductors REBa2Cu3O7-δ - correct interpretation based on standardization.

Trends in orthorhombic crystal field parameters (CFPs) reported for RE(3+) ions in high-T(c) superconductors REBa(2)Cu(3)O(7-)(δ) are considered. The cases of trends based on the CFP sets belonging to different regions of CF parameter space are identified and clarified. The crucial feature of such correlated alternative CFP sets is their intrinsic incompatibility. This makes meaningless direct comparisons of such CFP sets and thus presentations of CFP trends involving a mixture of alternative CFP sets. The aim of this paper is to ascertain that correct interpretation of trends in orthorhombic CFPs must be based on standardization. Examples of graphs inappropriately representing trends in orthorhombic CFPs reported for REBa(2)Cu(3)O(7-)(δ) compounds are considered and the corrected graphs based on the standardized CFP sets are provided.

Comparative analysis of crystal-field parameters for rare-earth ions at monoclinic sites in AB(WO4)2 crystals: I. Tm3+ in KGd(WO4)2 and KLu(WO4)2, and Ho3+ and Er3+ ions in KGd(WO4)2.

The crystal-field (CF) parameters determined by various authors for rare-earth ions at monoclinic sites in AB(WO(4))(2) crystals are reanalyzed using a methodology incorporating several approaches, namely standardization, multiple-correlated fitting technique and closeness of CFP sets. In Part I recent spectroscopic data for Tm(3+) ions in KGd(WO(4))(2) (KGdW) and KLu(WO(4))(2) (KLuW), and Ho(3+) and Er(3+) ions in KGdW, which were interpreted using the free-ion (FI) and CF parameter (CFP) sets, are thoroughly revisited. Our reanalysis enables clarification of several doubtful aspects involved in the previous studies. The initial CFPs for fitting, calculated using the simple overlap model (SOM), differ markedly from the fitted CFPs for Tm(3+) ions in KGdW and KLuW. An inspection of the pertinent CFP sets reveals deeper intrinsic differences between the model and fitted CFPs. The model CFPs and the fitted CFPs for RE(3+) ions in both KGdW and KLuW crystals turn out to be non-standard. Importantly, the model and fitted CFP sets for Tm-KLuW belong to disparate regions of the CFP space and thus are intrinsically incompatible, i.e. such sets should not be directly compared. Thus the CFP sets reported in the literature require reconsideration in view of the intrinsic properties of monoclinic CF Hamiltonians previously not taken into account. Standardization of the originally non-standard CFP sets is carried out to ensure direct comparability of the CFP sets in question with other literature data. The correlated alternative CFP sets are calculated for each original set to facilitate future applications of the multiple correlated fitting technique, which enables improving overall reliability of the fitted CFPs. The closeness of the standardized CFP sets is assessed in a quantitative way. Our considerations indicate also the importance of proper definitions of the axis system used in the CFP model calculations and provide arguments for the nominal meaning of the axis systems assigned to the fitted CFPs. The consistent methodology proposed here may be considered as a general framework for analysis of CF levels and CFP modelling for rare-earth and transition-metal ions at monoclinic symmetry sites in crystals. CFP sets for other rare-earth ions in AB(WO(4))(2) crystals will be reanalyzed in Part II.

Clarification of terminological confusion concerning the crystal field quantities vs. the effective spin Hamiltonian and zero-field splitting quantities in the papers by Bayrakçeken et al. [Spectrochim. Acta Part A 66 (2007) 462 and 1291].

The physically distinct notions: crystal field (CF) [or equivalently ligand field (LF)] and effective spin Hamiltonian, which comprises zero-field splitting (ZFS) [or equivalently fine structure (FS)], are often confused each with other in literature. Confusion of the type X=Y consists in referral to the quantity Y by the name X of another well-defined quantity. Most prevailing is the CF=ZFS confusion, i.e. labeling the actual ZFS/FS quantities as purportedly the CF/LF ones. Unique cases of the inverse ZFS=CF confusion, identified in recent papers by Bayrakçeken et al. [Spectrochim. Acta A 66 (2007) 462 and 1291], is discussed here. To clarify this confusion, clear distinction between operators of various nature used in electron magnetic resonance (EMR), optical spectroscopy, and related studies is provided. Other deficiencies in the two papers in question, which overlap to a large extent, and misinterpretations therein are critically commented on.

Crystal-field energy level analysis for Nd(3+) ions at the low symmetry C(1) site in [Nd(hfa)(4)(H(2)O)](N(C(2)H(5))(4)) single crystals.

Optical absorption measurements of Nd(3+) ions in single crystals of [Nd(hfa)(4)(H(2)O)](N(C(2)H(5))(4)) (hfa = hexafluoroacetyloacetonate), denoted Nd(hfa) for short, have been carried out at 4.2 and 298 K. This compound crystallizes in the monoclinic system (space group P 2(1)/n). Each Nd ion is coordinated to eight oxygen atoms that originate from the hexafluoroacetylacetonate ligands and one oxygen atom from the water molecule. A total of 85 experimental crystal-field (CF) energy levels arising from the Nd(3+) (4f(3)) electronic configuration were identified in the optical spectra and assigned. A three-step CF analysis was carried out in terms of a parametric Hamiltonian for the actual C(1) symmetry at the Nd(3+) ion sites. In the first step, a total of 27 CF parameters (CFPs) in the Wybourne notation B(kq), admissible by group theory, were determined in a preliminary fitting constrained by the angular overlap model predictions. The resulting CFP set was reduced to 24 specific independent CFPs using appropriate standardization transformations. Optimizations of the second-rank CFPs and extended scanning of the parameter space were employed in the second step to improve reliability of the CFP sets, which is rather a difficult task in the case of no site symmetry. Finally, seven free-ion parameters and 24 CFPs were freely varied, yielding an rms deviation between the calculated energy levels and the 85 observed ones of 11.1 cm(-1). Our approach also allows prediction of the energy levels of Nd(3+) ions that are hidden in the spectral range overlapping with strong ligand absorption, which is essential for understanding the inter-ionic energy transfer. The orientation of the axis system associated with the fitted CF parameters w.r.t. the crystallographic axes is established. The procedure adopted in our calculations may be considered as a general framework for analysis of CF levels of lanthanide ions at low (triclinic) symmetry sites.