EPR and optical absorption studies on Cr3+ ions doped in KZnClSO4 x 3H2O single crystals

EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated.     

Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.     

EPR and optical absorption studies of Cr ions in d-gluconic acid monohydrate

EPR studies are carried out on Cr³⁺ ions doped in d-gluconic acid monohydrate (C₆H₁₂O₇·H₂O) single crystals at 77 K. From the observed EPR spectra, the spin Hamiltonian parameters g, |D| and |E| are measured to be 1.9919, 349 (×10⁻⁴) cm⁻¹ and 113 (×10⁻⁴) cm⁻¹, respectively. The optical absorption of the crystal is also studied at room temperature. From the observed band positions, the cubic crystal field splitting parameter Dq (2052 cm⁻¹) and the Racah interelectronic repulsion parameter B (653 cm⁻¹) are evaluated. From the correlation of EPR and optical data the nature of bonding of Cr³⁺ ion with its ligands is discussed.     

EPR, optical and infrared absorption studies of Mn2+ ions doped in zinc malate trihydrate single crystal

Electron paramagnetic resonance (EPR) studies have been carried out on Mn2+ ions doped in zinc malate trihydrate single crystals in the temperature range 123-413 K on X-band frequency. The EPR spectrum at room temperature exhibits a group of five fine structure transitions each splits into six hyperfine components. Angular variation studies reveal that Mn2+ ions enter the lattice substitutionally. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The variation of zero-field splitting parameter (D) with temperature is measured. From the optical absorption spectrum, the crystal field splitting parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The infrared spectrum exhibits bands characteristic of the carboxylic acid salts.     

A single crystal EPR study of VO ions doped in Cs2Co(SO4)2.6H2O Tutton salt

EPR spectra of VO²⁺ ions doped in single crystals of Cs₂Co(SO₄)₂.6H₂O single crystals have been studied at various temperatures (390–103 K) on X-band frequency. The detailed EPR analysis shows three vanadyl complexes with differing intensities. The g and A tensors are found to be axially symmetric. The intense vanadyl complexes in the lattice are found to occupy the Co²⁺ substitutional sites, whereas the weak vanadyl complex at the interstitial sites. The optical absorption spectrum at room temperature shows three absorption bands characteristic of VO²⁺ ions in tetragonal symmetry. By correlating the EPR and optical data, the molecular bonding coefficients and the Fermi contact interaction terms have been evaluated and discussed. The line broadening of VO²⁺ spectra on cooling the crystal is explained on the basis of spin-lattice relaxation narrowing. The spin-lattice relaxation time for the host Co²⁺ ions has been estimated at various temperatures.     

EPR, optical, infrared and Raman spectral studies of Actinolite mineral

Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been performed on a natural Actinolite mineral. The room temperature EPR spectrum reveals the presence of Mn(2+) and Fe(3+) ions giving rise to two resonance signals at g = 2.0 and 4.3, respectively. The resonance signal at g = 2.0 exhibits a six line hyperfine structure characteristic of Mn(2+) ions. EPR spectra have been studied at different temperatures from 123 to 433 K. The number of spins (N) participating in the resonance at g = 2.0 has been calculated at different temperatures. A linear relationship is observed between log N and 1/T in accordance with Boltzmann law and the activation energy was calculated. The paramagnetic susceptibility (chi) has been calculated at different temperatures and is found to be increasing with decreasing temperature as expected from Curie's law. From the graph of 1/chi versus T, the Curie constant and Curie temperature have been evaluated. The optical absorption spectrum exhibits bands characteristic of Fe(2+) and Fe(3+) ions. The crystal field parameter Dq and the Racah parameters B and C have been evaluated from the optical absorption spectrum. The infrared spectral studies reveal the formation of Fe(3+)--OH complexes due to the presence of higher amount of iron in this mineral. The Raman spectrum exhibits bands characteristic of Si--O--Si stretching and Mg?OH translation modes.     

Optical absorption and EPR spectroscopic studies of (30 − x)Li2O–xK2O–10CdO–59B2O3–1Fe2O3: An evidence for mixed alkali effect

Optical absorption and EPR spectroscopic studies were carried on (30 ? x)Li₂O–xK₂O–10CdO–59B₂O₃–1Fe₂O₃ (x = 0–30) glass system to understand the effect of progressive doping of Li⁺ ion with K⁺ ion. Optical absorption results show typical spectra of Fe³⁺ ions and the various optical parameters such as, optical band gap, Urbach energy, oxide ion polarizability, optical basicity and interaction parameter were evaluated from the experimental data. The observed optical band gap and Urbach energy values show large deviation from the linearity where as the other parameters show small deviation from the linearity with the progressive substitution of Li⁺ ions with K⁺ ions. The observed EPR spectra are representative of Fe³⁺ ion in octahedral and axial fields in the glass network. The number of paramagnetic centers and paramagnetic susceptibility values were evaluated at different resonance lines for all the specimens and these parameters show non-additive nature with the progressive substitution of Li⁺ ions with K⁺ ions in the glass network. This is first ever observation of mixed alkali effect (MAE) in EPR and optical parameters of mixed alkali borate glasses.     

Magnetic study of Cr ion in M2CrV3O11−x (MZn, Mg) compounds

Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements on the recently synthesized vanadates M₂CrV₃O_11−x (M=Zn, Mg) have been analyzed. Two absorption lines with g≈2.0 (type I) and g≈1.98 (type II) were recorded in the EPR spectra, which can be attributed to V⁴⁺ ions and Cr³⁺ ion clusters (pairs), respectively. The exchange constant J between Cr³⁺ ions has been calculated, using both EPR and magnetic susceptibility data. Fitting of the EPR and magnetic susceptibility data has been carried out. The sign of J is a negative one for all samples and indicates antiferromagnetic interactions. Some difference in the J constant value among samples has been obtained. Volumetric titration confirms distinctly the presence of vanadium V⁴⁺ ions in the investigated compounds.     

VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites.     

Structural investigations on sodium-lead borophosphate glasses doped with vanadyl ions

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium-lead borophosphate (Na(2)O-PbO-B(2)O(3)-P(2)O(5)) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO(2+) ions. The spin Hamiltonian parameters g and A are found to be independent of the V(2)O(5) content and temperature. The values of the spin Hamiltonian parameters indicate that the VO(2+) ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO(2+) ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V(3+) and V(4+) ions. The optical band gap energy (E(opt)) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E(opt) decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO(3), BO(4), PO(3), PO(4), and VO(5) structural units.     

Spectral studies on VO ions in potassium thiourea bromide single crystals using EPR and optical absorption spectroscopy

Electron paramagnetic resonance (EPR) studies have been carried out on VO²⁺ ions doped in single crystals of ferroelectric material, potassium thiourea bromide (PTB) at room temperature and in the temperature range 103–343 K on X-band MW frequency. An isotropic octet spectrum characteristic of VO²⁺ ion was obtained due to the fast re-orientation of the VO²⁺ in PTB lattice, which exhibits glassy nature at certain range around room temperature. The temperature dependant EPR spectra of VO²⁺ ions in this host lattice has been attributed to the occurrence of multiple phase transitions due to the combined environment effects of KBr and thiourea materials in the single crystal. From the optical absorption spectrum, the crystal field splitting parameter Dq, tetragonal parameters Ds and Dt have been evaluated and discussed.     

Investigation of some oxygen-containing chromium (III) complexes by epr and optical spectroscopy

EPR and electronic absorption spectra of chrome alum solutions in sulphuric and phosphoric acids have been studied. Broadening of the EPR lines and shifts in the positions of the electronic spectra absorption bands were observed at low acid concentrations. In concentrated acids the ⁴T_2g band splits into several well resolved components and the EPR spectra show two resolved areas of fine structure. Each structure may be described by a spinHamiltonian of the form

where D is the zero-field splitting parameter due to the action of the axial crystal fields. The changes in the spectra as the acid concentration is increased are explained by changes in the internal environment of the Cr^III complexes as a result of the substitution of H₂O by anions of the acid residue. The symmetry of the complexes predominating at particular acid concentrations and the parameters D, g and Dt have been determined from an analysis of the EPR and optical absorption spectra. The character of the bond of the Cr^III ion with the surrounding ligands has also been estimated.     

Environnement tetraedrique de l'ion Cu et structure fine du seuil d'absorption K dans quelques chromites: application à l'étude d'oxydes à valence mixte

Copper zinc and copper manganese spinel chromites are studied using neutron diffraction. Cr³⁺ ions in tetrahedral environments are observed in CuCr₂O₄ and Cu_0.25Zn_0.75Cr₂O₄. These results leads to a new interpretation of the optical spectra (drs). The measurement of X-ray absorption fine structure of copper in the near edge rayon (Xanes) have been obtained using the Lure synchrotron radiation sources (Orsay, France). The spectra of Cu²⁺ in the tetrahedral environment of a quadratic or cubic matrix are characterized by the splitting of the main peak in the range 18–23 eV above the 1s → 3d transition. The X-ray absorption spectroscopy reveals the two oxidation states of copper in mixed oxides such as CuCrMnO₄. The copper(I) 1s → 4s transition is observed as a shoulder located at 10 eV on the slope of the main peak. A finer structure appears in the derivative spectrum.     

Untersuchungen an oxidischen Katalysatoren. XXIII. Magnetische und Redoxeigenschaften von CrNaY-Zeolithen

Studies on Oxide Catalysts. XXIII. Magnetic and Redox Properties of Zeolites CrNaY After pretreatment in vacuo (110–460°C) and in air (45O°C) CrNaY zeolites with different exchange degrees are characterized by EPR and magnetic measurements. The chromium hyperfinc structure in the EPR spectra shows that stable octahedral [Cr(H₂0)]³⁺ complexes exist up to temperatures of 350–390°C. The decrease of EPR signal intensity with increasing temperature of vacuum pretreatment can be explained by migration of Cr³⁺ ions into the sodalite cage (S_I″, S_II″) and hexagonal prism (S_I), resp. The high values of μ_eff. correspond with the tetrahedra1 environment of Cr³⁺ ions. In the evacuated samples Cr²⁺ ions are present. The oxidizing pretreatment of samples with high Cr³⁺ exchange degrees leads to lattice break down. After pretreatment in air all CrNaY zeolites contain chromium with oxidation number +5 and +6.     

Characterization,EPR and photoluminescence studies of LiAl5O8:Cr phosphors

Red emitting Cr³⁺ doped LiAl₅O₈ powder phosphor was prepared by combustion route using corresponding metal nitrates and urea in a single step. The prepared powder was characterized by X-ray diffraction and surface area measurements were carried out by Brunauer–Emmet–Teller adsorption isotherms. The electron paramagnetic resonance spectrum in the low field regions is typical for isolated Cr³⁺ ions whereas the resonance signal in the high field region with g = 1.95 is due to exchange coupled Cr³⁺–Cr³⁺ pairs. The optical studies show two broad and intense bands characteristic of Cr³⁺ ions in distorted octahedral symmetry. The photoluminescence spectrum gives a narrow red emission at 710 nm corresponding to ²E_g → ⁴A_2g transition upon excitation of 562 nm. The crystal field parameter (Dq), Racah inter-electronic repulsion parameters (B and C) and nephelauxetic parameters have been evaluated and discussed.     

EPR and optical investigations of manganese ions in alkali lead tetraborate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Mn2+ ions in different alkali lead tetraborate glasses 90R2B4O7+9.25PbO+0.75MnSO4 (R=Li, Na and K) and 90Li2B4O7+(10-x)PbO+xMnSO4 (x=0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 mol%) have been studied. The EPR spectrum of all the glass samples exhibit three resonance signals at g=2.0, 3.3 and 4.3. The resonance signal at g=2.0 is attributed to the Mn2+ ions in an environment close to an octahedral symmetry. The resonance signals at g=3.3 and 4.3 have been attributed to the rhombic symmetry of the Mn2+ ions. The effect of temperature (123-433 K) and the composition dependence of EPR signals have been studied for Mn2+ ions in lithium lead tetraborate glasses. It is interesting to observe that the variation of paramagnetic susceptibility (chi) with temperature obeys Curie-Weiss law. From the slope of 1/chi versus T graph, the Curie constant (C) has been evaluated. The zero-field splitting (zfs) parameter D has been calculated for different alkali lead tetraborate glasses from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits three bands. An intense and broad band at lower energy side has been assigned to the spin-allowed (5Eg-->5T2g) transition of Mn3+ ions in an octahedral symmetry. The intense and sharp band and a broad band at higher energy side have been assigned to charge transfer bands. A red shift is observed with increase of alkali ion size. The optical band gap energy (Eopt) decreases, whereas the Urbach energies (DeltaE) increases with increase of Mn content. The theoretical values of optical basicity (Lambdath) of the glasses have also been evaluated.     

Interpretation of EPR and optical spectra of Ni(II) ions in crystalline lattices at ambient temperature

Many biologically important paramagnetic metal ions are characterized by electron paramagnetic resonance (EPR) spectroscopy to use as spin probes to investigate the structure and function of biomolecules. Though nickel(II) ions are an essential trace element and part of many biomolecules, the EPR properties are least understood. Herein, the EPR and optical absorption spectra measured at 300 K for Ni(II) ions diluted in two different diamagnetic hosts are investigated and reported. The EPR spectrum of a polycrystalline Ni/Mg(3-methylpyrazole)₆(ClO₄)₂ [Ni/MMPC] shows two transitions at X-band frequency (~9.5 GHz), suggesting the zero-field splitting parameter (D) is larger than the resonance field of the free electron (H_o). This incomplete and complex spectrum is successfully analyzed to obtain EPR parameters. The EPR spectrum of the polycrystalline Ni/Zn(pyrazole)₆(NO₃)₂ [Ni/ZPN] shows a triplet spectrum indicating D < H_o. A detailed analysis of single-crystal EPR data yielded the spin Hamiltonian parameters. The optical absorption spectra are deconvoluted to understand the symmetry of the coordination environment in the complex.     

Optical absorption,infrared, Raman,and EPR spectral studies on natural iowaite mineral

Natural iowaite, magnesium–ferric oxychloride mineral having light green color originating from Australia has been characterized by EPR, optical, IR, and Raman spectroscopy. The optical spectrum exhibits a number of electronic bands due to both Fe(III) and Mn(II) ions in iowaite. From EPR studies, the g values are calculated for Fe(III) and g and A values for Mn(II). EPR and optical absorption studies confirm that Fe(III) and Mn(II) are in distorted octahedral geometry. The bands that appear both in NIR and Raman spectra are due to the overtones and combinations of water and carbonate molecules. Thus EPR, optical, and Raman spectroscopy have proven most useful for the study of the chemistry of natural iowaite and chemical changes in the mineral.     

Fe(3+) ions in alkali lead tetraborate glasses--an electron paramagnetic resonance and optical study

Glass systems of composition 90R(2)B(4)O(7)+9PbO+1Fe(2)O(3) (R=Li, Na and K) and 90Li(2)B(4)O(7)+(10-x)PbO+xFe(2)O(3) (x=0.5, 1, 3, 4, 5, 7 and 9 mol %) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g approximately 6.0, 4.2 and 2.0. The resonances at g approximately 6.0 and 4.2 are attributed to Fe(3+) ions in rhombic and axial symmetry sites, respectively. The g approximately 2.0 resonance signal is due to two or more Fe(3+) ions coupled together with dipolar interaction. The EPR spectra of 1 mol % of Fe(2)O(3) doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g approximately 4.2 resonance signal decreases and the intensity of g approximately 2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g approximately 4.2 with increase in iron content for more than 4 mol % has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of Fe(3+) ion clusters in the glass samples. The paramagnetic susceptibility (chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/chi versus T graph. The optical absorption spectrum of Fe(3+) ions in lithium lead tetraborate glasses exhibits three bands characteristic of Fe(3+) ions in an octahedral symmetry. The crystal field parameter D(q) and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 cm(-1)) obtained in the present work suggests that the bonding is moderately covalent.     

E.p.r. and optical absorption of Mn2+ ions in ternary K2SO4 − Na2SO4-ZnSO4 glasses

Summary Electron paramagnetic resonance (e.p.r.) and optical absorption measurements were performed on K₂SO₄ ⁻ Na₂SO₄-ZnSO₄ glasses containing 1–10 mol % of MnSO₄·H₂O. The spectra of Mn²⁺-doped samples exhibit a sextet centred at g = 2.03. The e.p.r. signal clearly shows its dependence on the dopant ion concentration. The optical absorption spectrum at room temperature shows bands characteristic of Mn²⁺ ions in octahedral symmetry. The crystal field (Dq) and the Racah interelectronic repulsion (B and C) parameters have been evaluated. E.p.r. and optical absorption studies reveal that the Mn²⁺ ions go substitutionally to Zn ion sites and the site symmetry around the transition metal ion is octahedral.