Parameter Dq Research Articles

Zero-field splitting of tetrahedral Co2+in the trigonal crystal field

A new high-order perturbation formula for the zero-field splitting of the 4A2 ground state of d3,7 ions in a trigonal field is derived on the basis of the weak-field approximation. The formula obtained is shown to be a good approximation for the cases where the cubic field parameter Dq is less than the Racah electrostatic parameter B and is thus especially suitable for tetrahedral Co2+ complexes. By using it, the zero-field splitting of ZnO:Co2+ is calculated from a parametrised d orbit and the parameters are determined from the optical spectra. The result agrees well with the experimental finding.

Spin-orbit coupling effects in CdGa2Se4:Co2+ single crystals.

Single crystals of ${\mathrm{CdGa}}_{2}$${\mathrm{Se}}_{4}$:${\mathrm{Co}}^{2+}$ were grown by the chemical transport reaction method using iodine as a transporting medium. The optical absorption peaks observed at 4132, 4332, 5970, 6329, 12 903, and 13 793 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at 292 K can be explained in terms of the electronic transitions of ${\mathrm{Co}}^{2+}$ ion in ${S}_{4}$ symmetry. The crystal-field parameter Dq and the Racah parameter B were found to be 413 and 455 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. Also the absorption spectrum of ${\mathrm{CdGa}}_{2}$${\mathrm{Se}}_{4}$:${\mathrm{Co}}^{2+}$ single crystals obtained at 77 K in the 700--800-nm region was analyzed using ${S}_{4}$ symmetry along with spin-orbit coupling effects.

Synthesis and Biocidal Activity of Isothiocyanato-Chromium(III) Complexes of Some Newly Synthesized Heterocyclic Schiff Bases

Abstract Eight new bidentate Schiff bases were synthesized by reaction of 2-aminobenzothiazole or 2-amino-4-phenyl-5-phenylazothiazole with 2-hydroxy-1-naphthaldehyde or substituted (2-hydroxy-, 4-hydroxy-, 3-methoxy-4-hydroxy-) benzaldehyde. The reaction products of these Schiff bases with potassium hexathiocyanatochromium(III) were of the type: K[Cr(NCS)2(B1)2] and K[Cr(NCS)4(B2)], where HB1 [dbnd] N, O donor monobasic bidentate Schiff bases and B2 [dbnd] N, N donor bidentate Schiff bases. They were characterized on the basis of elemental analysis, molecular mass determination, conductance, magnetic measurements, infrared and UV-visible spectral studies. The complexes were of octahedral structure. Different ligand field parameters 10Dq, B, β35 and C.F.S.E. were calculated and discussed. The Schiff bases and the complexes were also screened for microbiological activity against the fungi Aspergillus niger, Alternaria alternata and bacterium Escherichia coli. The mixed ligand complexes were found more acti...

Spectroscopic properties of trivalent chromium in the fluoride garnet Na 3In 2Li 3F 12

The spectroscopic properties of the fluoride garnet Na 3In 2Li 3F 12:Cr 3+, relevant for tunable laser emission, are investigated. In view of the excitation spectrum, the 4 T 2 band can be assigned at 630 nm and the 4 T 1 band at 436 nm. The emission spectrum, corresponding to the 4 T 2- 4 A 2 transition, is centered at 770 nm at 300 K with a bandwidth of 130 nm. The Tanabe-Sugano parameter Dq B is 2.1. The 4 T 2 level lifetime is long even at 300 K (320 μsec). These properties favor the chromium-doped fluoride garnet as a promising material for a room-temperature, tunable, and Q-switchable laser.

Electronic transitions of nickel (II) ions in cadmium ammonium sulphate hexahydrate single crystals

The optical absorption spectra of Cd(NH 4) 2(SO 4) 2·6H 2O doped Ni 2+ at 300 and 80 K was recorded. The Dq, B and C parameters at 300 and 80 K are calculated and the transitions are assigned. The fine structure of Cd(NH 4) 2(SO 4) 2·6H 2O doped Ni 2+ are observed at 80 K from the well resolved double peaked red band. Finally, the matrices for the energy levels with spin orbit coupling are diagonalised and the experimental values were fitted with the theoretically calculated values. The oscillator strengths of the transitions were computed from the area under the curves. The best fit was obtained for the values of the crystal field parameters Dq = 892cm -1, B = 940cm -1, C = 3760cm -1 and λ = - 260cm -1 at 300 K and Dq = 922cm -1, B = 955cm -1, C=4202cm -1 and λ=-275cm -1 at 80K respectively.

Intra-manganese absorption and luminescence in Zn 1- xMn xSe semimagnetic semiconductor

Optical absorption and luminescence of Zn 1- x Mn x Se (0 < x < 0.53) is measured at T = 10, 77 and 300 K below fundamental absorption edge. Three absorption and one luminescence bands are observed and are attributed to the intra-ion transitions of Mn 2+ in 3 d 5 configuration. Crystal field parameter Dq and Racah parameters B and C are derived as well as stabilization energy.

Visible region absorption and excitation spectroscopy of K 2ReCl 6 and various ReCl 2−6 containing A 2MCl 6 host crystals

For pure K 2ReCl 6 and ReCl 2− 6 in K 2SnCl 6, K 2PtCl 6 and (NR 4) 2SnCl 6 (R = H, Et, Me, Pr) several new transitions located from 16000 to 20000 cm −1 were found using absorption and excitation spectroscopy which cannot be assigned to intraconfigurational transitions of ReCl 2− 6. These may be due to either impurity or site interaction effects or interconfigurational transitions. Everything possible has been done to rule out the former possibility and the host dependences are not consistent with site effects. If the latter source is correct, the appearance of these transitions indicates large deviations from the ligand field model in this sytem. In particular, exceptionally low values for the Dq parameter are required to fit the calculated ligand field energy levels to any interconfigurational assignment of the new transitions. This could be evidence of strong mixing of d-d and charge transfer states not represented in the ligand field model.

Electronic Absorption Spectrum of Vanadyl-Doped Lithium Rubidium Sulphate

The optical obsorption spectrum of LiRbSO4 single crystals doped with vanadyl ions is recorded both at laboratory and liquid nitrogen temperatures. The spectrum is characteristic of VO2+ in tetragonal (C4v) symmetry. From the analysis of the spectrum the values of the crystal field parameters (Dq, Ds, Dt) are evaluated. EPR spectrum of the polycrystalline sample also reveals the distorted octahedral site symmetry for the VO2+ ion. A correlation between EPR and optical absorption studies is drawn.

Solvent Effects on the Electronic Absorption Spectrum of CrC(NO3)36H2O

Abstract Non-specific solvent effects on the electronic absorption spectra of Cr(N03 36H20 in water, methanol, ethanol, t-butanol and in their binary mixtures were investigated. The spectra were carefully treated using a computer resolution technique. The high correlation between dielectric constant of solvents and the crystal field parameter Dq as well as between refractivity index and oscillator strength of the d-d bands were observed. A concept of a new spectrochemical series has been formulated.

ChemInform Abstract: Dependence of the Optical Spectrum of MnF6‐ on the Mn2+ ‐ F‐ Distance. ‐

AbstractFrom measurements of the crystal‐field transitions for RbCdF3:Mn2+ and KZnF3:Mn2+ by means of photoluminescence techniques and from data for RbMnF3 and KMnF3 the dependence of B, C, and 10 Dq parameters on the Mn" ‐ F ′ distance R (derived by EXAFS) for the MnFg" complex is derived.

Calculation of the spin-orbit-coupling parameter of deep impurities in semiconductors in the complete neglect of differential overlap approximation.

A complete neglect of differential overlap (CNDO) self-consistent-field calculation of the crystal-field-splitting parameter 10Dq is used to find the spin-orbit-coupling parameter and the orbital reduction factor. The general spin-orbit-coupling theory has been rewritten in terms of the CNDO approximation and applied to the systems ZnS:${\mathrm{Cu}}^{2+}$ and CdS:${\mathrm{Cu}}^{2+}$. The examination of 10Dq and the spin-orbit-coupling parameter \ensuremath{\zeta} in terms of the wave functions and some parameters involved shows that it is important to consider not only the effective charges but also the distribution of charge among the different atomic orbitals. The calculated spin-orbit-coupling parameters 600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ZnS:${\mathrm{Cu}}^{2+}$ and 620 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for CdS:${\mathrm{Cu}}^{2+}$ agree quite well with the experimental values of 600 and 565 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. The orbital reduction factors also agree with experiment. It must be emphasized, however, that our method does not include additional quenching of the spin-orbit-coupling parameter and the orbital reduction factor due to the Jahn-Teller effect. The method presented here can be used to find the quenching of various electronic properties due to covalency and is a uniform procedure for calculating the crystal-field and fine-structure parameters in the framework of the CNDO approximation.

Electronic absorption spectra of Mn 2+ ion in Cd(NH 4) 2(SO 4) 2 · 6H 2O and CdK 2(SO 4) 2 · 6H 2O single crystals

Electronic absorption spectra of Mn 2+ ion in Cd(NH 4) 2(SO 4) 2 · 6H 2O (CdASH) and CdK 2(SO 4) 2 · 6H 2O(CdKSH) crystals have been studied at room temperature (300 K) and low temperature (80 K) in the region 2500–6000 Å. The spectrum showed the characteristic features of Mn 2+ ion in octahedral crystalline fields. Band positions have been calculated theoretically by solving the energy matrices corresponding to octahedral symmetry and compared with the experimentally observed band positions. The crystal field parameter ( Dq), interelectronic repulsion parameters ( B and C) and the Trees correction (α) have been fixed and also the crystal field transitions are assigned for the best fit of experimental and calculated band positions. The evaluated parameters for the above two lattices are: CdASH:Mn 2+ Dq = 690 cm −1, B = 835 cm −1, C = 3011 cm −1, α = 76 cm −1. CdKSH:Mn 2+ Dq = 740 cm −1, B = 857 cm −1, C = 2977 cm −1, α = 76 cm −1.

Dependence of the optical spectrum of MnF4−6 on the Mn2+–F− distance

We have measured by means of photoluminescence the energy of crystal-field peaks for RbCdF3: Mn2+ and KZnF3: Mn2+ where the value of the Mn2+–F− distance, R, derived by EXAFS is R=2.13±0.01 Å and R=2.08±0.01 Å, respectively. From these data and those for RbMnF3 and KMnF3 we have studied the dependence on R of the B, C, and 10 Dq parameters for the MnF4−6 complex. This analysis reveals that within the experimental errors, B and C are constant in the range 2.07&amp;lt;R&amp;lt;2.14 Å, in agreement with recent self-consistent calculations for MnF4−6, which also predict that 10 Dq=KR−n, where K and n are constant. The present study confirms this dependence, n being 4.4 which is also in accord to the theoretical predictions. The best values of R derived from optical spectra are found to be R=2.141±0.004 Å (for RbCdF3: Mn2+) and R=2.075±0.004 Å (for KZnF3: Mn2+). The present analysis also points out that by measuring the changes induced on the optical spectrum of MnF4−6 in a given lattice we can detect changes in the Mn2+–F− distance down to 10−3 Å. In this way we have derived the difference, ΔR, between R at room temperature and at 77 K for KZnF3: Mn2+. The obtained value ΔR=(9±1)10−3 Å is in agreement with the one ΔR=(10±3.5)10−3 Å derived previously from the variations undergone by the isotropic superhyperfine constant As. Finally the present results are compared to those for some complexes of Eu2+, Co2+, Ni2+, and Cr3+.

Enhancement of Radiation Injury in Human Colon Tumor Cells by the Maturational Agent Sodium Butyrate (NaB)

Two subpopulations of human colon tumor cells (clones A and D) which differ in their intrinsic sensitivity to X irradiation were grown for several passages in tissue culture medium containing the differentiation-inducing agent sodium butyrate (NaB, 2 mM). Values of the single-hit, multitarget survival curve parameters for non-NaB-treated clone A cells were n = 17.1, D0(Gy) = 0.81, and DQ(Gy) = 2.31; corresponding parameters for NaB-treated cells were 1.04, 1.16, and 0.05. For non-NaB-treated clone D cells, the survival parameters were n = 4.27, D0 = 1.05, and DQ = 1.52; corresponding parameters for NaB-treated cells were 1.19, 1.15, and 0.20. The large reduction in the DQ parameters of both clone A and D cells after NaB treatment indicates that sodium butyrate-induced cell maturation is accompanied by increase in radiation cell kill, particularly in the low-dose region of the survival curve.

Gel growth and characterization of pure and vanadyl-doped strontium tartrate tetrahydrate single crystals

Pure and vanadyl-doped single crystals of SrC4H4O6·4H2O (SrTr·4H2O) were grown by controlled diffusion in silica gel. The crystals were characterized by EPR and electronic absorption techniques. The angular variation EPR spectra showed that the VO2+ ion has a fixed orientation in the lattice. Theg andA tensors and their direction cosines were evaluated from the EPR analysis. The above parameters for the observed sites were analysed assuming a spin Hamiltonian corresponding to a tetragonal symmetry. Electronic absorption studies carried out at 300 K as well as at 80 K showed three characteristic absorption bands at 12 500, 13 201 and 18 348 cm−1 which were assigned to crystal field (d-d) transitions and the site symmetry of the ion has been estimated to be tetragonal. To confirm the ascribed transitions, the band positions were calculated by solving the energy expressions corresponding to the tetragonal symmetry and compared with the observed band positions. The crystal field parameters (Dq) and tetragonal distortion parameters (Ds andDt) were obtained from the best fit of the observed and calculated band positions. The EPR and electronic spectral results showed that the VO2+ ion has occupied the interstitial site having C4V symmetry.

4f14to 4f135d optical transitions of divalent ytterbium in the potassium and sodium halides

The optical absorption spectra of Yb2+ in a range of potassium and sodium halide crystals are described and analysed. Attention is focused on the strongly allowed 4f14 to 4f135d transitions. Excellent general agreement is obtained between theory and experiment provided that a correction based on the nephelauxetic effect is included. Parallel linear dependencies for the potassium and sodium halides are established between a parameter Delta , representing the energy difference between the centre of energy of the excited 4f135d configuration and the 4f14 ground state, and the lattice parameter d. Similar dependencies are established between the crystal-field parameter Dq and d.

EPR and electronic absorption studies of the VO 2+ ion in 3CdSO 4·8H 2O single crystals

The EPR spectra of the VO 2+ ion in a 3CdSO 4·8H 2O lattice were studied at 300 K. In the lattice, the VO 2+ ion was found to enter a Cd 2+ substitution site with fixed orientations and showed high angular dependence EPR spectra. The principal g and A tensors and direction cosines were evaluated from the EPR analysis. The exact VO orientations were identified by comparing the direction cosines obtained from EPR and the calculated ones. The observed superhyperfine (shf) structure having an intensity ratio of 1:2:1 was analysed. The shf coupling was found to be highly angular dependent indicating that the transfer of the unpaired spin density from the vanadium metal orbital to the ligand orbital is different in all orientations. The above shf structure was attributed to the interaction of a single unpaired electron with a pair of equivalent protons through the oxygen ligands. Electronic absorption studies of the VO 2+ ion in 3CdSO 4·8H 2O crystals were carried out at 300 and 80 K. At both temperatures, the characteristic spectrum of the VO 2+ ion showed five absorption bands at 12 500, 13 245, 14 815, 18 348 and 31 056 cm −1. From the analysis of the spectrum, the first four bands were assigned to crystal field transitions and the last band at 31 056 cm −1 due to the charge transfer characteristic in nature. From the polarized absorption studies the most probable site symmetry of the ion was estimated. From the best fit of observed and calculated band positions, crystal field parameter ( Dq) and distortion parameters ( Ds and Dt) were evaluated.

Metal chelates of heterocyclic nitrogen-containing ketones. XIV. Metal ion, anion and substituent effects on the enolization of mono-keto compounds

A number of new complexes of iron(II), cobakt(II), nickel(II), copper(II) and palladium(II) containing 2-picolyl-p-nitrophenyl- or 2-picolyl-p-tolyl ketone, L and L′, respectively, and various anions (Cl −, Br −, NSC −, BF 4 − or ClO 4 −) have been synthesized and characterized by elemental analyses, magnetic susceptibility, ESR, IR and reflectance spectral measurements. The stereochemistry and the nature of the complexes are markedly dependent upon the molar of the reactants, the anions and the ligand substituents. In all complexes the ligands are cheated to the metal ion via the pryridine nitrogen and the carbonyl oxygen atoms, whereby in the case of [ML 2]X 2, M = iron(II) and [ML 3]X 2, M = cobalt(II) or nickel(II) and X = ClO 4 − or BF 4 −, the 2-picolyl-p-nitrophenyl ketone exists in its enol form which is only deprotonated in the presence of palladium(II). The ligand field parameters (Dq, B′, λ and β) are calculated and related to the electronic environment and the basicity of the ligands.

Jahn‐Teller Effect in EPR and Optical Absorption Spectra of Cu2+ in LiNbO3 Single Crystals

AbstractOptical and EPR spectra of LiNbO3 single crystal doped with copper ions are measured in the range of 200 to 6000 nm and in the X‐band, respectively. In the temperature range 60 to 200 K a transition is observed from the low‐temperature EPR spectra with Cs symmetry (g𝒵 = 2.403, gy = 2.121, gx = 2.095 and = 51°) to the high‐temperature spectrum with C3v symmetry (g′∥ = 2.22, g⟂ = 2.17 and 𝒵 ∥ C3) whose parameters are given by the average of the corresponding parameters of the low‐temperature spectra. EPR spectra of LiNbO3:Cu2+ are interpreted taking account of the static Jahn‐Teller effect in trigonal field and formation of non‐equivalent minima on the adiabatic potential surface. In case of the static Jahn‐Teller effect in trigonal field formulas for the g‐factors of d9 ions are derived theoretically. A new model of Cu2+ substitution in LiNbO3, i.e. formation of a Cu  VLi complex, is suggested. In optical spectra an absorption band at 5000 cm−1 is detected due to Jahn‐Teller splitting of the 2Etr ground state. The Jahn‐Teller stabilization energy EJT = 1250 cm−5 and crystal field parameters 10Dq = 8200 cm−1, ν = −1200 cm−1, and ν− = 600 cm−1 are determined.

Metal chelates of heterocyclic nitrogen containing ketones, XIII. Cobalt(II), nickel(II) and palladium(II) complexes of 2-picolyl- and 2-lutidyl-methyl ketones

The preparation and characterization of a series of new coordination compounds of cobalt(II), nickel(II) and palladium(II) containing 2-picolyl- or 2-lutidyl-methyl ketone (HPMK or HLMK) and various anions, Cl−, Br−, NO 3 − , NCS− or BF 4 − , are reported. Complexes of square planar, tetrahedral and octahedral stereochemistry as well as five-coordinate species were isolated. The reaction products were found to be dependent on the molar ratios, pH and the temperature at which the reaction takes place. Cobalt(II) thiocyanate was found to form a complex of the type [CoL3][Co(NCS)4] (L = HPMK or HLMK). Also complexes containing coordinated BF4 were isolated. The ligand field parameters (Dq, B′ and β) for the cobalt(II) and nickel(II) complexes were calculated using the averaged-ligand-field approximation. The influence of the substituents of theses parameters and on the stereochemistry are discussed.