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[Display omitted] • Low symmetry aspects and effects in EMR comprehensively elucidated. • Key concepts underlying EMR and optical studies of 3d/4f ions categorized. • Key terms defined and their interrelationships concisely discussed. • Issues at interface between theory, computations and experiment considered. • Reference source for low symmetry aspects in EMR and optical spectroscopy. EMR and optical spectroscopy are important techniques enabling characterization of transition 3d/4f ions in coordination compounds, which often exhibit low symmetry sites. Low symmetry aspects are largely unexplored as yet due to lack of consistent methodology and guidelines, which has often led to their neglect or employing orthorhombic or higher symmetry approximations. To alleviate these problems, we provide comprehensive elucidation of low symmetry aspects in EMR, which are also relevant, to a great extent, for optical spectroscopy. Based on extensive survey of EMR-related monographs, reviews, selected papers and computer programs, definitions of the crucial notions underlying EMR studies of 3d/4f ions ions at low symmetry sites are systematized and their interrelationships clarified. Peculiar issues at the interface between theory, computations, and experiment, which affect proper interpretation of EMR data for low site symmetry systems, are discussed. Outline of the shortcomings, which may lead to employing deficient procedures in analysis of EMR data, is provided to help avoiding such deficiencies. To ensure comprehensive and up-to-date coverage, the survey of reviews and selected papers is supplemented by database of EMR studies of low site symmetry systems listing source references provided in Supplementary Materials. This review provides grounds for specialized reviews of low symmetry aspects occurring in: (i) studies of molecular nanomagnets containing transition ions, and (ii) density functional theory/ab initio modeling of zero-field splitting and crystal-field parameters. [ABSTRACT FROM AUTHOR]

Mn4+‐activated deep red‐emitting SrLaLiTeO6 phosphors are investigated for indoor plant growth LED applications for the first time. The phosphors crystallize in monoclinic (P21/n) symmetry is isostructural with SrLaLiTeO6 host. B‐site substitution of Mn4+ ions is confirmed from the redshift of high energy phonon modes in both Raman and IR spectra. The phosphor exhibited a far‐red emission centered at 696 nm corresponding to the 2Eg → 4A2g spin‐forbidden transition of the Mn4+ ions. Approximate crystal field parameters depict the weak influence of neighboring ligand fields on Mn4+ ions and the least covalence of Mn4+‐ligand bonding compared to other double perovskite phosphors. Moreover, the phosphors exhibit excellent thermal stability with an activation energy of 0.23 eV. Phosphor parameters including CCT, color purity, and quantum yield are evaluated and their values meet the requirements of a red‐emitting phosphor for LED applications. Furthermore, the PL emission spectrum of SrLaLiTeO6: Mn4+ matches with the absorption spectrum of plant phytochromes denoting the prospects of this phosphor for indoor plant growth LED applications. [ABSTRACT FROM AUTHOR]

The luminescence properties of Mn4+-doped β -Ga 2 O 3 are strongly affected by the surrounding crystal field within the [MnO 6 ] octahedral site, which is substitute for Ga Ⅱ site, as determined through the first-principles calculations. The crystal field strength parameters Dq, B, and C are computed, and the Tanabe-Sugano diagram is redrawn for C/B = 6.7. The temperature dependence of the optical spectra is thoroughly examined, revealing the thermal quenching mechanisms involving the thermal activation energy of 2E g and 4T 2g , which are 378 ± 26 cm−1 and 3527 ± 25 cm−1, respectively. In order to further investigate the temperature sensing characteristics, the absolute (S a) and relative (S r) sensitivities are obtained. At 303 K, the S r is determined to be 0.72 %K−1, while S a is estimated to be in the range of 10−2 (below 0.05 K-1) for the Mn4+ doped β -Ga 2 O 3 thermometers. The thermal resolution δT is demonstrated to be below 0.1 K, surpassing that of traditional Nd3+ and Er3+-doped thermometers. Moreover, a linear relationship between the energy separation ΔE of the thermally coupled 2E g -4T 2g energy levels and the crystal field strength Dq is observed in numerous materials. With this consideration, the nature of the thermometer, along with its S a and S r , can be roughly predicted and designed for various operational conditions. • The Mn4+ doped β -Ga 2 O 3 crystals was successfully grown via the optical floating zone method and their luminescence properties was first investigated in detail. • The temperature dependence of luminescence properties was further studied with the thermal quenching activation energy of 2E g and 4T 2g , respectively. • The temperature sensing properties of Mn4+ doped β -Ga 2 O 3 thermometers, whether the relative sensitivities (S r), the absolute sensitivities (S a) or the thermal resolution ΔT, is estimated to be surpassing that of traditional Nd3+ and Er3+-doped thermometers. • A linear relationship between the crystal field strength Dq and the energy separation of the thermally coupled energy levels 2E g -4T 2g was observed, which gives us a broaden idea to predict and design the nature of the thermometer for various conditions. [ABSTRACT FROM AUTHOR]

In this paper, the crystal field parameters (CFPs) have been calculated in the framework of the density functional theory using a novel theoretical approach proposed by Pavel Novák et al. and extracting the WANNIER functions from the Bloch eigenstates for the CeCl3 compound. Then, the calculated CFPs have been used in an effective atomic-like Hamiltonian, including the crystal field, 4f-4f correlation and spin-orbit coupling, and the splitted energy levels of Ce3+ ion by crystal field have been derived by diagonalization of the Hamiltonian. A hybridization parameter, , has been used to improve the results. The results are found to be in agreement with the experimental data

The cause of the split of 4A4E(4G) Mn2+ excited level measured on minerals spectra is discussed. It is our view that ∆E = |4E(4G) − 4A(4G)| should be considered an important spectroscopic parameter. Among the possible reasons for the energy levels splitting taken under consideration, such as the covalent bond theory, the geometric deformation of the coordination polyhedron and the lattice site’s symmetry, the first one was found to be inappropriate. Two studied willemite samples showed that the impurities occur in one of the two available lattice sites differently in both crystals. Moreover, it was revealed that the calculated crystal field Dq parameter can indicate which of the two non-equivalent lattice sites positions in the willemite crystal structure was occupied by Mn2+. The above conclusions were confirmed by X-ray structure measurements. Significant differences were also noted in the Raman spectra of these willemites.

Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxyapatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized Mn-HAp powders Ca9.995Mn0.005(PO4)6(OH)2. It is found that in the investigated species, the manganese is redistributed between both calcium sites with prevalence in Ca (I). Agreement between the calculated and experimental data proves that crystal field parameters in HAp can be calculated in the classical DFT model using the distributed electron density.

Graphical abstract Highlights • Crystal field parameters of neodymium in yttrium and scandium orthosilicate were determined. • Nd ions substitute Y ions in positions with seven nearest oxygen ions is established by ESEEM method. • The standardization procedure for crystal field parameters has been used. Abstract The ESEEM spectroscopy was used to determine positions of the 143 Nd3+ impurity ions in Y 2 SiO 5 single crystal. It is established that neodymium ions substitute yttrium ions in the Y2 positions with seven nearest oxygen ions. Crystal field parameters of 143 Nd3+ impurity centers in isotopically pure Y 2 28 SiO 5 and Sc 2 28 SiO 5 single crystals were determined using data of CW EPR spectroscopy and the known energy level schemes. [ABSTRACT FROM AUTHOR]

The effect of the spin probe VO2+ in 15BaO-15TeO2-10TiO2-(60-x) B2O3-xV2O5 (x = 0.2, 0.4, 0.6, 0.8 mol %) glasses has been studied by employing Electron Paramagnetic Resonance (EPR) and optical absorption spectroscopic techniques. The observed EPR spectra of VO2+ ions were attributed on the basis of well-known spin-Hamiltonian of C4V symmetry. The simulated EPR spectra for VO2+ ions in the present glass system were drawn using Easy spin software. Both the experimental and simulated spectra were found to be in good agreement with each other. The optical absorption spectra exhibited three d-d transition bands due to crystal and tetragonal fields of VO2+ ions. These bands were assigned to 2B2g→ 2Eg, 2B2g→ 2B1g and 2B2g→ 2A1g transitions. The crystal field parameters Dq, Ds and Dt values are calculated. From the EPR and optical data, the molecular bonding coefficients were evaluated. Employing the higher order perturbation formulae of the g factors for 3d1 ion under tetragonally compressed octahedral fields, theoretical studies were carried out. The spin-Hamiltonian parameters and obtained from both the experimental and theoretical methods were in good agreement with each other. [ABSTRACT FROM AUTHOR]

We report on photoluminescence (PL) measurements of InGaN:Yb 3+ nanorods (NRs) in combination with crystal field calculations. The observed near band edge (NBE) shift has been discussed in terms of its three possible factors: Indium content fluctuation, strain relaxation and quantum confinement. The transition lines between Stark energy levels of Yb 3+ ion were detected and analyzed. Ytterbium ions were described as having similar lattice locations in InGaN and GaN NRs after a comparison between their luminescent properties. Consequently, we established the experimental energy levels for Yb 3+ ion in InGaN NRs from the assignment of almost all the emission lines to Yb Ga substitutional site. The corresponding crystal field parameters were determined based on the observed Stark splitting of 4f manifolds. The In and Yb concentrations were calculated from the X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) reveal the single crystalline nature of the nanorods. [ABSTRACT FROM AUTHOR]

A high-quality Cr:CYA (Cr:CaYAlO 4) single crystal fiber was grown by μ-PD (Micro-Pulling-Down) method. The E//a and E//c polarized excitation spectra of Cr:CYA at room temperature was measured. The crystal field parameters were calculated and the energy level structure of Cr:CYA was analyzed. We also measured the polarization emission spectra and lifetimes at different temperatures and calculated the effective emission cross-section. Based on the above data and Boltzmann law, the thermal distribution between the excited energy levels 2E and 4A 2 at different temperatures was analyzed. The present work may be useful for guiding laser research on Cr:CYA and other Cr3+-doped laser crystals above room temperature. • Cr:CYA single crystal fiber was grown by μ-PD (Micro-Pulling-Down) method. • Excitation spectra and crystal field parameters of Cr:CYA crystals were investigated and analyzed. • The effective emission cross section of Cr:CYA at different temperatures was calculated. [ABSTRACT FROM AUTHOR]

Strontium aluminate (SrAl2O4) and the indium aluminate (SrIn2O4) spinels have been proven to be efficient host materials, which offer the possibility of generating broadband emission after doping with rare earth trivalent ions. The present work is devoted to the calculation of the crystal field parameters and the energy levels of the trivalent europium doped in SrAl2O4 and SrIn2O4 spinels, using the superposition model of the crystal field. Using the intrinsic parameters for Eu3+-O2− bonds, and the geometry structure of the each crystal, we modeled the CFPs and simulated the low-lying energy levels schemes. The obtained results are compared with the experimental data and discussed.

The electron paramagnetic resonance spectra (X-band, f ~ 9.42 GHz) of Yb3+ ions have been measured at temperature 15 K in YF3:Yb3+ single crystals. The principal values of the g-tensors, gb = g1 = 1.67, g2 = 2.42, g3 = 5.41, and directions n1 = [0, 1, 0], n2 = [±sin(54.8°), 0, cos(54.8°)], n3 = [∓sin(35.2°), 0, cos(35.2°)] of the corresponding principal axes for the Yb3+ ions which replace Y3+ ions at two magnetically nonequivalent sites with the local Cs symmetry in the orthorhombic crystal lattice have been obtained from analysis of the angular dependences of the spectra taken in the static magnetic fields lying in the crystallographic (bc) and (ac) planes. Experimental data are interpreted in the frameworks of the crystal field theory. Using the obtained set of crystal field parameters for Yb3+ ions in the YF3 host related to the crystallographic system of coordinates, we can reproduce satisfactorily the crystal field energies of Yb3+ ions determined earlier from optical measurements.

Stark structure of 3H6, 3H5, 3H4, 3F4, 3F3, 3F2 and 1G4 multiplets of impurity non-Kramers Tm3+ ions in the orthorhombic YF3 crystal has been determined from luminescence studies. High frequency electron paramagnetic resonance (EPR) spectra (~ 207 GHz) of Tm3+ ions have been measured at temperature 4.2 K in external magnetic field applied perpendicular to the b-axis of YF3:Tm3+ single crystal. The results of measurements are interpreted in the frameworks of the crystal field theory. The set of crystal field parameters related to the crystallographic system of coordinates of the YF3 lattice has been obtained and used to reproduce satisfactory the crystal field energies and the EPR spectra.

The Eu 2 O 3 -PbO-SiO 2 glassy system submitted to a long annealing time (100 ps) has been obtained by molecular dynamics calculations. The average of 87/86 sites of the Eu 3 + ion with six/seven nearest neighbours are used to discuss the number of lines and the local symmetry of the luminescent site through the crystal field parameters, using the simple overlap model in the frame of the method of equivalent nearest neighbours. The magnitude of the B q 2 (q = 0, 1, 2) and the non-negligible B 4 4 and B 4 6 ( B 3 4 , B 3 6 and B 6 6 ) lead to the indication of distorted C 4 h and C 3 i site symmetries of the six and seven nearest neighbours, respectively. We have then compared very satisfactorily our 7 F 1 sublevels calculations with those observed in the emission spectra of an Eu-borate glass annealed for 30 min and 17 h. This comparison is justified because the emission behaviour of europium ions in different glassy systems are honestly very similar. Further, the decrease observed in the 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 transition intensity ratio is a clear indication that the Eu 3 + ion are nucleating a crystalline phase. Such satisfactory comparisons indicate that we have obtained a transparent glass-ceramics. [ABSTRACT FROM AUTHOR]

The aim of this paper is to model the crystal field parameters and simulate the fine structure of optical energy levels scheme of Co 2+ :K(Mg,Zn)F 3 systems. The crystal field parameters were modeled in the frame of an Exchange Charge Model of the crystal field theory, taking into account the effects of the covalent bond formation between the Co 2+ and F − ions. The obtained parameters were used for simulating the fine structure of the system energy levels scheme, by diagonalization of the full Hamiltonian matrix, in the base of 100 wave functions of Co 2+ ion. For resolving some discrepancies, the electron–phonon interaction in 4 T 2g excited state is investigated in the frame of the Ham theory, with the Jahn–Teller stabilization energy calculation. The comparison of the calculated energy levels with experimental data gives a good agreement, which confirms the model and used method. [ABSTRACT FROM AUTHOR]

The experiment introduces the undergraduate students to the crystal field theory. The electronic spectra of the octahedral complexes of [Ni(L)n]2+ (L = H2O, dmso, NH3 and en) obtained in the experiment are used to calculate 10Dq and B parameters. The experiment shows how the parameters can be calculated and correlated with the nature of the ligands and the field intensities produced.

2-Mercaptobenzoxazole pentacyanoferrate(II/III) complexes, [FeII/III(CN)5(bzoxs)]3-/2- , were prepared in MeOH/H2O 75:25% solutions and characterized by spectroscopic UV-Vis, Mössbauer, electron paramagnetic resonance (epr) and electrochemical-cyclic voltammetry- techniques. UV-Vis and epr spectra along with the electrochemical behavior suggested the coordination of the multi-functional N,S,O- donor ligand, bzoxs, to iron(III) through the sulfur atom. The crystal field parameters, DqL and Dt, calculated for the iron(II) complex, in addition to the reversible redox process FeIII-bzoxs + e- -> FeII-bzoxs also pointed to coordination via the sulfur atom. The results were compared with the chemical properties of pentacyanoferrate complexes containing other monodentate N-, S- and O-donor ligands. Ab initio calculations revealed the composition of the frontier orbitals of bzoxs and are in agreement with the mode of coordination proposed from the experimental data.

In this paper we report the results of a detailed comparative crystal field analysis of the crystal field parameters and energy level schemes, for all three above mentioned materials. The crystal structure data was used to calculate the crystal field parameters in the framework of exchange charge model using the Symmetry Adapted Axis System centered at the impurity ion. A thorough consideration of the impurity center symmetry was performed and the calculated crystal field parameters were used to diagonalize the crystal field Hamiltonian for each system. Energy levels obtained in this way were compared with the corresponding experimental data to yield good agreement between the theoretical and experimental results. [ABSTRACT FROM AUTHOR]

A simple co-precipitation method has been used for the synthesis of Co 2+ and Ni 2+ -doped zinc borate nanopowders. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV/Vis absorption, Scanning electron microscope (SEM) with EDS and photoluminescence (PL) spectroscopies techniques has been employed for their characterization. Powder X-ray diffraction data reveals that the crystal structure belongs to monoclinic for both as-prepared samples. SEM images showed surface morphology of the prepared samples. Optical absorption spectra showed the characteristic bands of doped ions in octahedral site symmetry. From the optical absorption data crystal field and inter-electronic repulsion parameters are evaluated. The FT-IR spectra showed the characteristic vibrational bands related to ZnO, BO 3 and BO 4 molecules. Photoluminescence spectra exhibited the emission bands in ultraviolet and blue regions. [ABSTRACT FROM AUTHOR]

A new method to calculate the crystal field parameters (CFPs) is first applied to crystalline Nd2Fe14B as the representative of rare-earth iron boron permanent magnets. The CFPs are extracted from the one electron Hamiltonian expressed in the basis of Wannier functions. The low energy properties of 4 f orbitals and influence of hybridization with Fe(3 d) orbitals are investigated by solving the eigenvalue problems. Authors have found the fundamental property; the more the 4 f electron cloud is expanded to the a- b plane, the more the single-ion anisotropy along the c-axis increases. The magnetic anisotropy constant K1 increases as taking into account the hybridization with Fe(3 d) states. The results for CFPs are compared with previous theoretical and experimental studies. [ABSTRACT FROM AUTHOR]

Superposition model (SPM) analysis of the zero-field splitting parameters (ZFSPs), in short SPM/ZFSP, enables correlation of crystallographic, spectroscopic, and magnetic data for transition ions with an orbitally non-degenerate ground state in crystals. SPM analysis of ZFSPs requires knowledge of the model parameters, i.e. the intrinsic parameters – b ¯ k ( R 0 ) , power law exponents – t k , and the reference distance – R 0 . An extensive survey of literature has revealed that the model parameters for Ni 2+ ( S =1) ions are not available as yet. Hence, in this study we set for determination of the model parameters sets applicable for SPM/ZFSP analysis of Ni 2+ ions in the six-fold coordinated NiO 6 with axial symmetry. Our method utilizes the relationships between the intrinsic parameters b ¯ k ( R 0 ) and the experimental data for the uniaxial-stress parameters obtained for Ni 2+ ions in several crystals. The present results enable modeling of the ZFSP b 2 0 = D for Ni 2+ ( S =1) ions, which hitherto has been hindered by the lack of suitable model parameters sets. Applications of SPM/ZFSP analysis are carried out for Ni 2+ ions doped into α-Al 2 O 3 (corundum), α-LiIO 3 , and LiNbO 3 , as well as the series of fluosilicate crystals with general formula: ABF 6 ·6R 2 O (A=Zn, Mg, Co, Ni, Fe; B=Si, Ti, Sn, BF 4 ; R=H, D). These results will be utilized in studies of Ni 2+ -based systems suitable for pressure sensors in high-pressure electron magnetic resonance (EMR) measurements and spectroscopic properties of Ni 2+ ions in Haldane gap systems. [ABSTRACT FROM AUTHOR]

Cu(II) ion-doped NaCaAlPO4F3 phosphor has been synthesized using a solid state reaction method. The prepared sample is characterized by powder X-ray diffraction, scanning electron microscope, optical absorption, electron paramagnetic resonance photoluminescence and Fourier transform infrared spectroscopy techniques. The crystallite size evaluated from x-ray diffraction data is in nanometers. Scanning electron microscopy micrographs showed the presence of several irregular shaped particles. From optical absorption and electron paramagnetic resonance spectral data the doped Cu(II) ions are ascribed to distorted octahedral site symmetry. The synthesized phosphor exhibits emission bands in ultraviolet, blue and green regions under the excitation wavelength of 335 nm. The CIE chromaticity coordinates (x = 0.159, y = 0.204) also calculated for the prepared sample from the emission spectrum. The Fourier transform infrared spectroscopy spectrum revealed the characteristic vibrational bands of the prepared phosphor material. [ABSTRACT FROM AUTHOR]

The crystal field approach used by SIMPRE is analyzed, verifying the exactness of the results concerning energy levels and magnetic properties calculated by the package. To coincide with the prevailing conventions, we reformulate the presentation of the crystal field parameters, so that the results are now, also from a formal point of view, strictly correct. New calculations are presented to test the influence of neglecting the excited J states, a common but critical approximation employed by SIMPRE. For that, we examine the case of Er(trensal) complex (H3trensal = 2,2′,2″-tris(salicylideneimino)triethylamine) where the influence of this approximation is found to be minimal. A patched version of the code, SIMPRE 1.1, and an updated version of the user manual are now available. Finally, we comment on 'Software package SIMPRE - revisited,' which apparently revisits a software package without inspecting or using the code. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Highlights: [•] Various physical parameters are evaluated and non-linear behavior is observed. [•] Mixed alkali effect is observed in all physical and structural studies. [•] EPR and optical studies confirmed distorted octahedral site symmetry. [•] From optical absorption edges, optical band gap energies and Urbach energies are evaluated. [ABSTRACT FROM AUTHOR]

Abstract: Undoped and Fe(III) ions doped NaCaAlPO4F3 phosphor has been synthesized using solid state reaction method. The prepared phosphor material was characterized by powder X-ray diffraction (XRD), SEM with EDS, optical absorption, photoluminescence (PL), electron paramagnetic resonance (EPR) and FT-IR techniques. The average crystallite size was calculated from powder XRD data. SEM micrographs show the presence of several irregular shaped particles. Optical absorption spectrum exhibited the characteristic absorption bands of Fe(III) ions in distorted octahedral site symmetry. EPR spectrum exhibited two resonance signals at g=4.25 and g=2.00. PL spectrums of both undoped phosphor exhibits emission peaks at 407, 413 and 469nm and Fe(III) ions doped phosphor gave the emission peaks at 373 and 450nm under UV excitation. The Commission Internationale deI'Eclairage (CIE) chromaticity coordinates for undoped and Fe(III) ions doped NaCaAlPO4F3 phosphor material are calculated from the emission spectrum. Vibrational bands related to phosphate molecules, P–O–H and hydroxyl ions are observed in the FT-IR spectrum. [Copyright &y& Elsevier]

Analytical expressions are obtained for g-factors of the ground Kramers doublet of the impurity Ce3+ ions in LiYF4 crystal that rigorously take into account mixing of the 2F5/2 and 2F7/2 multiplets by crystal field. Dependence of g-factors on crystal field parameters is studied and possibilities of making conclusions about crystal filed parameters values on the basis of comparison with g-factors given in literature are considered.

Highlights: [•] Combined analysis based on crystal field theory and DFT independent methods have been used for (Na, Li)CrSi2O6 crystals. [•] Crystal field parameters modeling and energy levels scheme simulation of two Cr3+-bearing system have been made. [•] Structural and electronic properties of considered materials were predicted. [ABSTRACT FROM AUTHOR]

Highlights: [•] Spectroscopic properties of di-, tri- and tetravalent free 3d ions are analyzed. [•] Relations between the Racah parameters, spin–orbit constant and atomic number are found. [•] Variations of these parameters in several crystals are considered. [ABSTRACT FROM AUTHOR]

Abstract: Co2+ and Ni2+ ions doped β-BaB2O4 nanopowders have been prepared by co-precipitation method and their structural properties are studied by spectroscopic techniques. Powder XRD data reveals that the crystal structure belongs to monoclinic and the average crystallite size is calculated. Optical absorption spectra data reveal octahedral site symmetry for Co2+ and Ni2+ ions. Crystal field (Dq) and inter-electron repulsion (B and C) parameters are evaluated for Co2+ doped β-BaB2O4 nanopowders as Dq=960, B=900 and C=3850cm−1 and for Ni2+ doped β-BaB2O4 nanopowders, Dq=900, B=850 and C=3500cm−1. FT-IR spectra showed the characteristic vibrational bands related to BO3 and BO4 molecules. Photoluminescence spectra contain the emission bands in ultraviolet and blue regions. [Copyright &y& Elsevier]

Strontium aluminate (SrAl2O4) and the indium aluminate (SrIn2O4) spinels have been proven to be efficient host materials, which offer the possibility of generating broadband emission after doping with rare earth trivalent ions. The present work is devoted to the calculation of the crystal field parameters and the energy levels of the trivalent europium doped in SrAl2O4 and SrIn2O4 spinels, using the superposition model of the crystal field. Using the intrinsic parameters for Eu3+- O2- bonds, and the geometry structure of the each crystal, we modeled the CFPs and simulated the low-lying energy levels schemes. The obtained results are compared with the experimental data and discussed. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, we report on consistent crystal field calculations of the Cr3+ ions energy levels in KAl(MoO4)2 using actual D3d site symmetry of the Cr3+ position and employing the exchange charge model (ECM) of the crystal field. In addition to the energy level calculations, the Huang–Rhys factor S=5.7 and effective phonon energy ℏω=268cm–1 were evaluated in the single configurational coordinate model. Detailed treatment of the microscopic crystal field effects in the ECM framework allowed to obtain analytical dependence of the crystal field strength 10Dq on the Cr–O interionic distance and extracting from it the values of some parameters of the electron–vibrational interaction (EVI) in the KAl(MoO4)2:Cr3+ system. All obtained results are compared with experimental data and discussed; agreement between the calculated and experimental parameters is good. [Copyright &y& Elsevier]

Abstract: EPR and optical absorption studies on Fe3+ and Mn2+ doped strontium tetraborate (SrB4O7) glasses are carried out at room temperature. The EPR spectrum of the Fe3+ doped glass consists of signals with g-values 9.04, 4.22 and 2.04, whereas the EPR spectrum of Mn2+ doped glass exhibits a characteristic hyperfine sextet around g=2.0. The spectroscopic analyses of the obtained results confirmed distorted octahedral site symmetry for the Fe3+ and Mn2+ impurity ions. Crystal field and Racah parameters evaluated from optical absorption spectra are: Dq=790, B=700 and C=3000cm−1 for Fe3+doped glass and Dq=880, B=700 and C=2975cm−1 for Mn2+ doped glass. [Copyright &y& Elsevier]

Abstract: Absorption and fluorescence spectra observed between 450 and 750nm at 85K and room temperature (300K) are reported for Eu3+(4f6) in single-crystal Czochralski-grown garnet, Gd3Ga5O12 (GGG). The spectra represent transitions between the 2S+1L J multiplets of the 4f6 electronic configuration of Eu3+ split by the crystal field of the garnet. In absorption, Eu3+ transitions are observed from the ground state, 7F0, and the first excited multiplet, 7F1, to multiplet manifolds 5D0, 5D1, and 5D2. The Stark splitting of the 7F J multiplets (J=0–6) was determined by analyzing the fluorescence transitions from 5D0, 5D1, and 5D2 to 7F J . The Eu3+ ions replace Gd3+ ions in sites of D2 symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2J+1 non-degenerate Stark levels characterized by one of four possible irreducible representations (irreps) assigned by an algorithm based on the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels in D2 symmetry. The quasi-doublet in 5D1 was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between 5D1 and 7F1. A parameterized Hamiltonian defined to operate within the entire 4f6 electronic configuration of Eu3+ was used to model the experimental Stark levels and their irreps. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental Stark levels is 5.9cm−1. The choice of coordinate system, in which the nine are real and the crystal-field z-axis is parallel to the [001] crystal axis and perpendicular to the xy plane, is identical to the choice we used previously in analyzing the spectra of Er3+ and Ho3+ garnets. [Copyright &y& Elsevier]

Abstract: Potentialities of increasing the reliability of crystal field parameters (CFPs) obtained from an analysis of Stark splitting of J-states of spin–orbital multiplets 2S+1L J of the Ln3+ ions in cubic crystal field with rhombic distortions via a reduction of the region of their final fitting are examined. Suggested method of lowering the uncertainty of the CFP consists in determination of the relation of general cubic CFP of the fourth and sixth ranks (B 4 and B 6) by comparison of a fragment of the experimental Ln3+ spectrum with well known picture of dependences of Stark splitting of J-states on the relation mentioned. These dependences were calculated many years ago and published as a set of diagrams by K. Lea, M. Leask, W. Wolf, J. Phys. Chem. Solids, 23 (1962) 1381. Cubic parameters derived from the relation determined can be used for a narrowing of the fitting region for the rest of CFP. The method described is applied to the luminescence spectra of dimeric europium carboxylates with heterocyclic diimines. To justify application of this method to the spectra of Eu3+ ions in crystal field of cubic symmetry with rhombic distortions it was shown that the influence of the second rank components of the crystal field on the relative Stark splitting of J-states of europium ions is minimal for J =3, 4. In some cases, this peculiarity provides an approach of Stark splitting of the levels with J =4 in spectra of compounds with rhombic distortions of cubic crystal field to the image of the splitting at an effective field of cubic symmetry. It was demonstrated that for europium complexes under consideration the relation of the general CFP B 4/B 6 >119. Consequently, the CFPs of the sixth rank are very small and the region of fitting of the rest of CFP can be appreciably reduced. [Copyright &y& Elsevier]

The parameters of the crystal field acting on the Cr2+ ion in the triclinic site symmetry of monoclinic CrF2 crystal are modeled in the Exchange Charge Model (ECM) . With these parameters the Hamiltonian of the crystal has been diagonalized and the low-lying energy levels scheme is calculated. The comparison of calculated values of the energy level with experimental data demonstrates a satisfactory agreement. [ABSTRACT FROM AUTHOR]

Abstract: The environment of Eu3+ in zinc–thallium–tellurite glass of the molar composition 60TeO2–30TlO0.5–9.9ZnO–0.1Eu2O3 was investigated by laser-induced fluorescence line narrowing (FLN) techniques using Eu3+ as a local site probe. From the site selective luminescence spectra of Eu3+ at 7K, the energies of the Stark components of the 7 F 1 and 7 F 2 states were recorded and then the crystal field parameters B nm were calculated assuming a C 2v site symmetry. The ratios B 22/B 20 and B 44/B 40 for each excitation energy within 7 F 0–5 D 0 transition were obtained and compared with the values calculated for Eu3+ in other types of glasses. [ABSTRACT FROM AUTHOR]

Abstract: Low-temperature photoluminescent spectra of ZnGa2O4:Cr3+ nano-sized phosphors calcined at different temperatures were reported. The fine structure of the emission spectra has been designated to Cr3+ ions in different sites including ideal octahedral, Zn-interstitial, sites and Ga2O3 impurity. The vibronic sidebands for both Stokes’ and anti-Stokes’ sides are related to the host lattice vibrations, which were confirmed by IR and Raman spectra. Al3+ is substituted in Ga3+ sites to form (0≤y≤0.5). The blue shift and luminescent intensity variations of the charge transfer band and 3d–3d transitions in the spectra caused by Al substitution were related to larger band gap and stronger crystal field, respectively. The calculated crystal-field parameters indicated that Al incorporation enhanced the crystal field strength and induced more trigonal distortion due to different radii of Al3+ and Ga3+. [Copyright &y& Elsevier]

Abstract: This paper describes a computational study of extrinsic defect of Sr3Al2O6 induced by trivalent rare-earth dopants. Solution energies for a range of possible doping mechanisms are calculated, and predictions made of doping sites and charge-compensation schemes. It is shown that there are definite trends going along the rare-earth series. Atomistic modeling is used to calculate the symmetry and detailed geometry of the dopant ion-host lattice system, and this information is then used to calculate the crystal field parameters, which are an important indicator in assessing the optical behaviour of the system. The transition levels are then calculated for the Eu3+-substituted material, and comparisons with the experimental results were done. [ABSTRACT FROM AUTHOR]

Optical spectra of absorption and luminescence of LiNbO3:Yb3+ crystals are investigated experimentally and theoretically. Within the framework of the point charge approximation of crystal field, the Stark problem is solved: crystal field parameters and wave functions of Stark states are determined. Line strengths due to indirect electric-dipole and magnetic-dipole inter-Stark transitions are calculated and values of the Judd-Ofelt parameters are determined. Values of the branching ratios of luminescence. Einstein coefficients and, lifetime of the excited sublevel are calculated. A satisfactory agreement of calculated results with experimental data is obtained. [ABSTRACT FROM AUTHOR]

The results of the high-resolution absorption, selective excitation, time-resolved emission and emission kinetics of Eu3+ in GdCOB and EuCOB single crystals are presented. The Eu3+ spectra show at least three non-equivalent centers whose static spectral characteristics were used to assign structural models. The crystal field parameters were estimated for prevailing Eu3+ center in EuCOB. The inhomogeneous broadening and shifts of the 5D0→7F0 and 5D0→7F1 Eu3+ lines in GdCOB under selective excitation in main lines were explained by J mixing of 7F2 states into 7F1 and 7F0 by second order crystal field terms and connected to disordered structure in cationic spheres. [Copyright &y& Elsevier]

Novel complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and UO2(II) with a new Schiff base derived from 8-hydroxy-7-quinolinecarboxaldehyde and 2-aminoethanethiol (LH2) (system name: 2-(8-hydroxy-7-carboxalimino)ethanethiol.) have been prepared and characterized on the basis of analytical, thermal, magnetic moment, infrared, electronic, NMR and EPR spectral data. From the analytical, NMR and thermal data and stoichiometry of the complexes indicate that LH2 act as a dibasic tridentate ligand with ONS donors towards all the metal ions. The magnetic moment, electronic and EPR spectral data commensurate that the Mn(II), Fe(II), Ni(II) and UO2(II) complexes are dimeric with octahedral configuration while the Cu(II) and Zn(II) complexes are monomeric with square-planar and tetrahedral geometries, respectively. Various ligand field parameters Dq, B and β for complex 5 was calculated. The complexes 3+4 have lower symmetries and the amount of distortion in terms of DT/DQ applying NSH “Hamiltonian Theory” has been evaluated which indicate that the complexes are moderately distorted. [Copyright &y& Elsevier]

Optical absorption and EPR spectra of Co2+ and Ni2+ doped sodium phosphate glasses have been investigated. Crystal field parameters and g values are determined. For Co2+ doped glass Dq=890, B=700, C=4125 cm-1 and g values of 4.23 and 2.04 at 20 K, for Ni2+ doped glass Dq=890, B=770, C=3700 cm-1 and a g value of 2.28 at room temperature were found. Correlating the optical and electron paramagnetic resonance data suggests the bonding between transition metal ions and ligands as ionic in nature. [Copyright &y& Elsevier]

The cause of the split of 4A4E(4G) Mn2+ excited level measured on minerals spectra is discussed. It is our view that ∆E = |4E(4G) − 4A(4G)| should be considered an important spectroscopic parameter. Among the possible reasons for the energy levels splitting taken under consideration, such as the covalent bond theory, the geometric deformation of the coordination polyhedron and the lattice site's symmetry, the first one was found to be inappropriate. Two studied willemite samples showed that the impurities occur in one of the two available lattice sites differently in both crystals. Moreover, it was revealed that the calculated crystal field Dq parameter can indicate which of the two non-equivalent lattice sites positions in the willemite crystal structure was occupied by Mn2+. The above conclusions were confirmed by X-ray structure measurements. Significant differences were also noted in the Raman spectra of these willemites. [ABSTRACT FROM AUTHOR]