Parameter Dq Research Articles

EPR, optical and superposition model study of Mn2+ doped L+ glutamic acid

Electron paramagnetic resonance (EPR) study of Mn2+ doped L+ glutamic acid single crystal is done at room temperature. Four interstitial sites are observed and the spin Hamiltonian parameters are calculated with the help of large number of resonant lines for various angular positions of external magnetic field. The optical absorption study is also done at room temperature. The energy values for different orbital levels are calculated, and observed bands are assigned as transitions from 6A1g(s) ground state to various excited states. With the help of these assigned bands, Racah inter–electronic repulsion parameters B = 869 cm−1, C = 2080 cm−1 and cubic crystal field splitting parameter Dq = 730 cm−1 are calculated. Zero field splitting (ZFS) parameters D and E are calculated by the perturbation formulae and crystal field parameters obtained using superposition model. The calculated values of ZFS parameters are in good agreement with the experimental values obtained by EPR.

Temperature Evolution of the Intra-Ion Absorption Spectra of Cobalt in (NH2(CH3)2)2CoCl4 Crystals

On the basis of spectroscopic studies of (NH 2 (CH 3 ) 2 ) 2 CoCl 4 crystals the absorption bands corresponding to the internal electronic transitions in the Co 2+ ion were identified. The values of Dq and Racah crystal field parameters at room temperature were calculated. Patterns of changes in these parameters upon isomorphous cation and anion substitution were defined for the A 2 CoCl 4 family of crystals, where А = NH 2 (CH 3 ) 2 + , NH 2 (C 2 H 5 ) 2 + , N(CH 3 ) 4 + , N(C 2 H 5 ) 4 + . Evolution of the absorption spectra of (NH 2 (CH 3 ) 2 ) 2 CoCl 4 crystals in the region of their phase transitions at 238 and 263 K was investigated.

Vanadium States in Doped Bi12SiO20

We have investigated the absorption of the V doped Bi 12 SiO 20 in the spectral region 1.45-2 eV (11 696 – 16 129 cm -1 ). The observed absorption bands are due to the V 2+ , V 3+ and V 4+ ions in the same spectral region. These absorption bands do not contain information about the exact energy position of the vanadium levels. Therefore, we have calculated the second derivative of absorption. It is established that all vanadium ions are surrounded by distorted tetrahedral coordination in Bi 12 SiO 20 (BSO). The energy level structures of the vanadium ions in BSO are also presented. We have calculated the field parameters Dq and the Racah parameters B and C for V 2+ ion. We have determined the field parameters Dq, Ds and Dt for V 3+ ion. DOI: http://dx.doi.org/10.5755/j01.ms.21.2.6140

Theoretical studies on the spin Hamiltonian parameters and local environment of Mn2+ in ZnO nanocrystal and bulk

By employing the perturbation calculations, the spin Hamiltonian parameters (SHPs) and local structures are uniformly explored for Mn2+ in the ZnO nanocrystal and bulk. The EPR spectra are satisfactorily explained for both the systems, and the defect structure information is obtained, i.e., the substitutional impurity Mn2+ may undergo the axial displacements of 0.036 and 0.042Å away from the oxygen triangles along the C3 axis in the ZnO nanocrystal and bulk, respectively. The similar SHPs for Mn2+ in the nanocrystal and bulk can be illustrated as the approximately identical covalency (equal covalency factor N) as well as the smaller axial displacement, the stronger crystal–field (CF) interactions (larger cubic CF parameter Dq) and Mn2+ 3d–3s orbital admixture (larger core polarization constant κ) in the former.

Spectroscopic characterization of manganese-doped alkaline earth lead zinc phosphate glasses

Alkaline earth lead zinc phosphate glasses doped with Mn(II) are characterized by spectroscopic techniques like X-ray diffraction (XRD), UV–visible, differential scanning calorimetry (DSC), electron paramagnetic resonance (EPR), Fourier transform infrared (FTIR) and Raman. Optical absorption spectrum exhibits four bands which are characteristic of Mn(II) in distorted octahedral site symmetry. The crystal field parameter Dq and Racah interelectronic-repulsion parameters B and C have been evaluated. All investigated samples exhibit EPR signals which are characteristic to the Mn2+ ions. The shapes of spectra are also changed with varying alkaline earth ions content. FTIR spectra show specific vibrations of phosphate units. The characteristic Raman bands of these glasses due to stretching and bending vibrations were identified and analysed by varying alkaline earth content. The intensity and frequency variations for the characteristic phosphate group vibrations have been correlated with the changes of the structural units present in these glasses. Depolymerization of the phosphate chains in all the glasses is observed with replacement of alkaline earth content by spectroscopic studies. This leads to a strong decrease of the average chain length and a small decrease of the average P–O–P bridging angle with replacement of alkaline earth content.

EPR and Optical Absorption Study of Fe3+-Doped Mono Hydrated Dipotassium Stannic Chloride

Electron paramagnetic resonance (EPR) study of Fe3+ ion-doped dipotassium stannic chloride (K2SnCl4·H2O, DPSC) single crystal is performed at X band frequency and liquid nitrogen temperature. The Zeeman g-factor, axial zero-field splitting parameters and rhombic zero-field splitting parameters of Fe3+ ion in DPSC are determined with the help angular dependence of EPR spectra. Fe3+ ion enters the crystal lattice substitutionally replacing the K+ ion. The optical absorption spectra are recorded at room temperature in the wavelength range 195–1,100 nm. The transitions are assigned from the ground state \({}^{6}{\text{A}}_{{1{\text{g}}}} \left( {\text{S}} \right)\) to different excited states of Fe3+ ion. The observed band positions fitted by four parameters, Racah inter-electronic repulsion parameters (B and C), cubic splitting parameters (Dq) and Trees correction (α) yield: B = 831 cm−1, C = 2,198 cm−1, Dq = 820 cm−1, and α = 90 cm−1.

Structural relaxation around Cr3+ at the Na(Al1-x Cr x )P2O7 octahedral site: an XRPD and EAS study

Abstract The isovalent substitution of chromium for aluminium at octahedral site along the Na(Al1-x Cr x )P2O7 pyrophosphate solid solution has been investigated by means of the combined application of X-ray powder diffraction (XRPD) and electronic absorption spectroscopy (EAS). In agreement with the structural refinements, deconvolution of the optical spectra revealed a progressive decreasing of the crystal field strength parameter 10Dq moving toward the NaCrP2O7 end-member, meaning that the local chromium–oxygen bond distance increased along the join with the amount of chromium. The calculated structural relaxation coefficient around the substituent ion Cr3+ was ε=0.97 (i.e., very close to that predicted by the Hard Spheres model). A detailed comparison with compact crystal structures (i.e., perovskite, garnet, spinel, clinopyroxene, and corundum) as well as with other pyrophosphate compounds with II-NaMP2O7 structure-type (with M=Al, Cr, Fe, V, Ti, Mo and In) highlighted that compounds belonging to the Na(Al1-x Cr x )P2O7 solid solution – characterized by a network connectivity which is basically a framework topology – undergo a structural relaxation that is confined within the first shell (i.e., occurs at the octahedral site), while P2O7 dimers act as rigid units.

Tools for magnetostructural correlations for the 3d8(3A2 state) ions at orthorhombic sites: Comparative study with applications to Ni2+ ions in Y2BaNiO5 and Nd2BaNiO5

Abstract Three approaches are employed to study magnetostructural correlations for the 3d 8 ( 3 A 2 state) ions at orthorhombic sites in crystals: (i) the higher-order perturbation theory (PT) of the microscopic spin Hamiltonian (MSH) parameters, (ii) the crystal field (CF) analysis (CFA) within all 3d 8 states combined with the superposition model (SPM) calculations of CF parameters, and (iii) the second-order PT of MSH parameters. A comparative study is carried out to assess the merit of each modeling approach. These approaches enable predictions of the orthorhombic zero-field splitting parameters (ZFSPs) for the 3d 8 ions at orthorhombic sites. Hence, correlation of the magnetic and spectroscopic properties with the structural ones may be considered. The approach (i) and (iii) take into account only the spin–orbit coupling (SOC) and a limited set of low lying states. Analysis of the expressions used in the approach (i) reveals discrepancies concerning: the sign of the SOC parameter, the cubic crystal field parameter Dq , the energy levels sequence, and numerical errors, which diminish its reliability. The distinction between the first- and second-kind orthorhombic symmetry is also elucidated. The approaches (i)–(iii) are applied for Ni 2+ ( S =1) ions in the Haldane gap systems Y 2 BaNiO 5 and Nd 2 BaNiO 5 . The contributions to the ZFSPs due to the spin–spin and spin–other–orbit interactions considered using the approach (ii) are found nearly insignificant as compared with the dominant SOC ones. The results indicate that the approach (i)—corrected and (iii) may be employed only as an approximation. The approach (ii) together with the SPM/CFP modeling appear to be preferable and more reliable tools to study magnetostructural correlations and thus spectroscopic and magnetic properties of the 3d 8 ( 3 A 2 state) ions at orthorhombic sites in crystals.

Behavior of Ni2+ cations in aqueous and alcohol solutions of NiCl2 · 6H2O

We have investigated the optical properties of Ni2+ cations in aqueous and alcohol solutions of NiCl2 · 6H2O at room temperature. We measured the absorption spectra of these two types of solutions in the spectral region 395–795 nm. The Racah’s parameters and the exchange integrals of the aqueous complex [Ni(H2O)6]2+ have been calculated. The parameters Dq, Dt and Ds are also calculated on the basis of our experimental data. The parameters δσ and δπ, connected with the symmetry of the complex, are determined.

Visible absorption structure of chromium doped (80-x)Sb2O3-20K2O-xPbO glasses

Chromium doped glasses in the (80-x)Sb2O3-20K2O-xPbO:Cr system (x = 10–30 mol. %) have been investigated by absorption spectra in the 1–2,2 eV (8065–17 730 cm−1) spectral range. The synthesis of glasses has been carried out by using the melt-quenching method. The observed absorption band is due to the Cr-impurity in the visible spectral region. The absorption bands of glasses do not contain information about the exact energy position of the Cr levels. Therefore, we have calculated the second derivative of absorption curves. It is established that Cr3+ and Cr4+ ions are surrounded by distorted octahedral coordination in the investigated glasses. The energy level structure of the Cr3+ and Cr4+ ions in the samples are also presented. The crystal field parameter Dq and the Racah parameters B and C have been calculated.

Growth and characterization of nonlinear optical telluromolybdate CoTeMoO6 single crystals

Nonlinear optical (NLO) crystals CoTeMoO6 have been grown from high temperature solution by means of spontaneous crystallization. These crystals have been characterized by temperature-dependent X-ray diffraction, infrared and electron absorption methods. Moreover, polarized Raman spectra have been measured at room temperature. These studies showed that the Mo6+ and Te4+ ions are in asymmetric coordination environment, and CoTeMoO6 has the largest flexibility index among MTeMoO6 family of telluro-molybdates (M=Zn, Mg, Cd, Mn, Co), making this compound attractive NLO material. Raman and IR studies allowed assigning the observed modes to respective motions of atoms in the unit cell. They have also showed evidence for spin–phonon coupling at low temperatures and suggested that CoTeMoO6 is prospective material for solid-state Raman laser-frequency converters. Analysis of electron absorption data has shown that Co2+ ions are located in sites of weak crystal field with the crystal field parameters Dq and B equal to 548cm−1 and 882cm−1, respectively.

Studies on the spin Hamiltonian parameters for Mn2+ in the ZnS nanocrystals and bulks

The spin Hamiltonian parameters (zero-field splitting D, g factors and hyperfine structure constants) are theoretically studied for Mn2+ in the ZnS nanocrystals and bulks from the perturbation formulae of these quantities for trigonal and cubic tetrahedral 3d5 clusters, respectively. The trigonal Mn2+ centre in the ZnS nanocrystals is attributed to the impurity–ligand bond angle related to the C3 axis about 0.39° larger than that (≈109.47°) of an ideal tetrahedron. Almost the same g factors and hyperfine structure constants for the nanocrystals and bulks can be ascribed to similar crystal-field environments (i.e. comparable cubic field parameters Dq), nearly the same covalency (i.e. the equal covalency factors N) and the Mn2+ 3d–3s orbital admixture (i.e. the identical core polarisation constants κ) in both systems. The ligand orbital and spin–orbit coupling contributions are found to be important and should be included in the electron paramagnetic resonance analysis in view of significant covalency.

Room temperature synthesis and spectral characterizations of Fe3+-doped CdO powder

Fe3+ doped CdO powder was prepared at room temperature using a mild and simple solution method. X-ray diffraction (XRD) analysis showed that the prepared material has cubic structure. The average crystalline size evaluated using the Debye–Scherrer method is 24nm. Scanning electron microscope (SEM) images show the surface morphology of nano-crystalline CdO powder, and the Energy dispersive X-ray spectroscopy (EDX) spectrum indicates the presence of a transition metal ion. The optical absorption spectrum shows characteristic bands for Fe3+ with octahedral site symmetry. The crystal field parameter (Dq) and the Racah inter-electronic repulsion parameters (B and C) were evaluated. The electron paramagnetic resonance (EPR) spectrum shows a resonance signal at g=2.0128, which indicates Fe3+ ions in tetragonally-distorted octahedral site symmetry. This is also confirmed using the optical absorption spectrum. FT-IR shows the fundamental vibrations of the host lattice.

Corrigendum: Solvent-Dependent Cation Exchange in Metal-Organic Frameworks

The authors noticed errors in the y axis labels of Figures 4 and 5. The corrected versions are shown below. Co/Zn ratio plotted against ligand field parameter Dq. A best fit with R2 of 0.922 is depicted by the dashed line. Co/Zn ratio plotted against Snyder polarity indices. A best fit with R2 of 0.905 is depicted by the dashed line.

EPR and optical study of Mn2+ doped monohydrated dipotassium stannic chloride

Electron paramagnetic resonance (EPR) study at room temperature (RT) is used to investigate the property of Mn2+ doped monohydrated dipotassium stannic chloride (K2SnCl4⋅H2O) single crystal. EPR spectra show that there exist two substitutional sites, the spin Hamiltonian parameters for which are determined. The optical absorption study is also done at room temperature in the wavelength range 195–1100nm. The observed bands are assigned as transitions from 6A1g(S) ground state to various excited states. These bands are fitted with four parameters, namely Racah inter-electronic repulsion parameters B=792cm−1, C=2278cm−1; cubic crystal field splitting parameter Dq=700cm−1 and Trees correction α=76cm−1. The nature of metal–ligand bonding is discussed on the basis of EPR and optical data. Superposition model (SPM) is used to find out the crystal field (CF) parameters and the perturbation formulae are used to obtain zero-field splitting (ZFS) parameters. Theoretically calculated ZFS parameters match well with the experimental values obtained from EPR study.

Novel Garnet-structure Ca(2)GdZr(2)(AlO(4))3:Ce(3+) phosphor and its structural tuning of optical properties.

Aluminate garnet phosphors Ca2GdZr2(AlO4)3:Ce(3+) (CGZA:Ce(3+)) for solid-state white lighting sources are reported. The crystal structure and Mulliken bonding population of the CGZA:Ce(3+) have been analyzed. The larger 5d ((2)D) barycenter shift εc and smaller phenomenological parameter 10Dq of Ce(3+) in CGZA are related to the larger covalent character of Ce-O. The tuning spectral properties of the Ce(3+)-doped CGZA-based isostructural phosphors are presented. The splitting of cubic crystal field energy level (2)Eg in Ca2REZr2(AlO4)3:Ce(3+) (CREZA:Ce(3+)) (RE = Lu, Y, and Gd) increases as the radius of RE(3+) increases, and the splitting of (2)Eg may dominate the difference of spectroscopic red-shift D(A) in CREZA:Ce(3+). The splitting of the (2)Eg in CaGd2ZrSc(AlO4)3:Ce(3+) (CGZSA:Ce(3+)) phosphors increases seemly due to the decreasing of the covalent character of Ce-O. Thermal quenching properties of Ce(3+)-doped CGZA-based isostructural phosphors are also presented and analyzed. For CREZA:Ce(3+) phosphors, the increasing of the radius of RE(3+) results in an enhancement of thermal quenching. The quenching of CGZSA:Ce(3+) is obviously stronger mainly due to the smaller energy difference between the lowest 5d excited state and 4f ground state.

Enhancement of gastric cancer MKN28 cell line radiosensitivity induced by β-elemene

To study radiation-enhancing effects on human gastric cancer MKN28 cell line and underlying mechanisms of β-elemene. Inhibition of MKN28 cell proliferation at different concentrations of β-elemene was assessed using the methyl thiazolyl blue colorimetric method (MTT method), with calculation of IC50 value and choice of 20% of the IC50 as the experimental drug concentration. Irradiation group and β-elemene+irradiation group were established, and the cell survival fraction (SF) was calculated from flat panel colony forming analysis, and fitted by the 'multitarget click mathematical model'. Draw the survival curve and get the radiobiological parameters D0, Dq, SF2, N and SER. Flow cytometry (FCM) was used to detect changes in the cell cycle and cell apoptosis rates was detected by Annexin-V/PI assay. β-elemene exerted inhibitory effects on proliferation of gastric cancer MKN28 cells, with an IC50 of 45.6 mg/L and we chose 8 mg/L as the experimental concentration. The cell survival fraction of MKN28 cells with irradiation decreased significantly after treated with β-elemene; D0, Dq decreased, SER = 1.3. After combined treatment of β-elemene+irradiation, the results of FCM showed that cells could be arrested in the G2/M phase and the cell apoptosis increased significantly. β-elemene can enhance the radiosensitivity of gastric cancer MKN28 cell line. Mechanistically, β-elemene mainly influences the cell cycle distribution of MKN28 cells by inducing G2/M phase arrest, inhibits the repair of sublethal damage and induces cell apoptosis to enhance the killing effects of radioactive rays.

Polarized electronic absorption spectra of colourless chalcocyanite, CuSO4, with a survey on crystal fields in Cu2+ minerals

Polarized electronic absorption spectra of colourless chalcocyanite, CuSO4, have been measured using microscope-spectrometric techniques. The spectra are characterized by a structured and clearly polarized band system in the near-infrared spectral range with components centred at 11,720, 10,545, 9,100, and 7,320 cm−1, which have been assigned to crystal field d–d transitions of Cu2+ cations in pseudo-tetragonally elongated CuO6 polyhedra with point symmetry Ci (\(\bar{1}\)). The polarization behaviour is interpreted based on a D2(C2″) pseudo-symmetry. Crystal field calculations were performed for the actual triclinic point symmetry by applying the Superposition Model of crystal fields, as well as in terms of a ‘classic’ pseudo-tetragonal crystal field approach yielding the parameters Dq(eq) = 910, Dt = 395, and Ds = 1,336 cm−1, corresponding to a cubically averaged Dqcub = 679 cm−1. A comparative survey on crystal fields in Cu2+ minerals shows that the low overall crystal field strength in chalcocyanite, combined with a comparatively weak pseudo-tetragonal splitting of energy levels, is responsible for its unique colourless appearance among oxygen-based Cu2+ minerals. The weak crystal field in CuSO4 can be related to the lower position of the SO42− anion compared to, e.g. the H2O molecule in the spectrochemical series of ligands.

EPR and luminescence studies of Cr3+ doped MgSrAl10O17 phosphor synthesized by a low-temperature solution combustion route

MgSrAl10O17:Cr3+ powder phosphor has been synthesized by a solution combustion method at furnace temperature of 500°C in a short time (< 5min). The as-prepared phosphor was characterized by X-ray diffraction, Fourier transform infrared and scanning electron microscopic techniques. EPR spectrum of Cr3+ ions in MgSrAl10O17 phosphor suggested a variety of symmetries associated with Cr3+ ions. The optical studies show two broad and intense bands characteristic of Cr3+ ions in an octahedral symmetry. Upon 552nm excitation, an intense narrow red emission line centered at 690nm has been observed related to 2Eg→4A2g transition of Cr3+ ions. The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed.

Crystal fields of porphyrins and phthalocyanines from polarization-dependent 2p-to-3d multiplets

Polarization-dependent X-ray absorption spectroscopy is combined with density functional calculations and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal phthalocyanines and octaethylporphyrins (Mn, Fe, Co, Ni). The polarization dependence facilitates the assignment of the multiplets in terms of in-plane and out-of-plane orbitals and avoids ambiguities. Crystal field values from density functional calculations provide starting values close to the optimum fit of the data. The resulting systematics of the crystal field can be used for optimizing electron-hole separation in dye-sensitized solar cells.