Ions In Corundum Research Articles

Absorption spectra, ligand field parameters and g factors of Cr3+ doped α-Al2O3 laser crystal: ab initio calculations

In this paper we present, in the unified frame, the results of the ab initio investigations of absorption spectra, ligand field parameters and g factors for three valence chromium doped α-Al2O3 crystal. Our calculations are based on a new methodology applied to a cluster [CrO6]9− embedded in an extended point charge field of host matrix ligands. After the differential functional theory optimization of the doped crystal, a vibrational theoretical spectroscopic study based on infrared spectroscopy has been employed in order to confirm the stability of the optimized doped crystal structure. The ab initio energy calculation of the electronic states and corresponding wave functions of Cr3+ are documented from the complete active space self-consistent field. The improved energy states from the N-electron valence second order perturbation theory, second order dynamic correlation dressed complete active space (DCD-CAS2), difference dedicate configuration interaction with three degrees of freedom (MRDDCI3) and spectroscopy-oriented configuration interactions, were analyzed. Based on the ab initio ligand field theory procedure we extracted ligand field parameters and spin–orbit coupling constant which were used to recalculate the energy levels of the studied system. In addition, g factors for the ground state 4A2 of Cr3+ ion in corundum are calculated taking into account the full configuration interaction. The results obtained are discussed and the comparisons with measured values from literature show a reasonable agreement, which justifies and recommend this new route of investigation.

Systematic analysis of the fine structure of energy levels and spin-Hamiltonian parameters of V3+ ion in corundum with dynamic Jahn-Teller effect

Systematic analysis of fine structure of the whole energy levels and spin-Hamiltonian parameters (zero-field splitting (ZFS) parameter D and g-factors g// and g⊥) for the ground state 3A2 (3T1) of V3+ ion in corundum are presented in detail with complete diagonalization method (CDM) of 45 × 45 energy matrix, in which the full configuration interactions are taken into account. The reduction of the splittings of excited electronic 3T2 (t2 ge) term with orbital triplet degenerate caused by spin-orbit (SO) and lower trigonal crystal field (CF) is studied by T2⊗e model dynamic Jahn-Teller theory, and Ham deduction factor, the Jahn-Teller energy EJT and Huang-Rhys factor S are estimated. The studies are performed within the strong-field scheme with molecular orbit (MO) approximation, in which the two SO coupling parameter model is used and the SO contributions from both the central 3d ion and ligands are taken in account. The calculated results are in good agreement with the experimental data, and the local structure of [VO6]9- cluster with C3 point group symmetry are determined quantitatively.

Theoretical studies of EPR parameters and defect structures for Ni2+ ions in corundum

In this paper, fourth-order perturbation formulae of zero-field splitting (ZFS) parameter D and g -factors g // , g ⊥ for ground state 3 A 2g of 3d 8 ions in the trigonal crystal field (CF) have been derived by perturbation theory method (PTM), and the complete energy matrices (45×45) including low symmetry ligand field ( C 3v ), Coulomb interactions and spin-orbital (SO) coupling interaction for 3d 8 ions have been constructed, in the strong-field scheme. In these formulae, both the contributions from the SO of the central 3d ion and the ligands taken into account by using the two SO coupling parameter model, and the contributions to the ZFS from all excited states are included. These PTM formulae and complete energy matrices are applied to investigate the EPR parameters D and g -factors for Ni 2+ ions in Al 2 O 3 crystals unifiedly, and the calculated results of PTM and complete diagonalization method (CDM) are not only close to each other but also in good agreement with the experimental data, and the local structure of [NiO 6 ] 10− cluster is determined quantitatively. Furthermore, the validities of the present formulae are tested further by the comparison of calculated results of the formula and these of CDM based on intermediate –CF scheme, and the comparison shows that the calculated results with these two different methods are in mutually good agreement with each other in all different trigonal crystal environments, which also suggest that these fourth-order perturbation formulae are suitable for explaining both D and g -factors for 3d 8 ions in trigonally distorted octahedral field.

Quantitative Measurement of Paramagnetic Fe3+ in Kaolinite

AbstractA method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

Theoretical study of the coordination of the Cr3+ ion in α-Al2O3

Abstract The local arrangement of a substitutional Cr3+ ion for an Al3+ ion in corundum is studied by means of first-principles pairwise simulations and quantum-mechanical ab initio Perturbed Ion calculations. Our investigation is organized in two steps. First, we determine the cohesive properties of the host lattice by calculating the set of four crystalline parameters that makes minimum the total energy of corundum. Secondly, we solve cluster models of increasing complexity centered at the Cr3+ site and embedded in the previously computed crystal potential. This is a consistent strategy that contributes to determine the local geometry of Cr3+ in α-Al2O3.

Coordination of Cr3+ Ion in α-Al2O3

The local arrangement of a substitutional Cr3+ ion for an Al3+ ion in corundum is studied by means of a Fluorescence XAFS method. The large single crystal is used and the removal method of the diffraction peak at various energy is described. The Cr3+ ion is coordinated in the nearly same structure as Cr2O3..

Luminescence of V4+ ions in corundum

Luminescence of V4+ ions in corundum

Local deformations in a corundum crystal submitted to a uniaxial stress

Low-temperature optical absorption on the zero-phonon lines and stress-induced linear dichroism on the broads bands for V3+, Cr3+ and Co3+ ions in corundum showed that the uniaxial stress induces a local deformation in the site of the doping ion different from the deformation for the whole crystal. Detailed examination of this local deformation is carried out and shows the importance of an odd deformation. Diagrams are proposed describing the local deformations epsilon xz* and epsilon xx* when stresses sigma xx and sigma xz respectively are applied.

Jahn-Teller effect in trigonal symmetry : 3dn ions in corundum

Jahn-Teller effect in trigonal symmetry : 3dn ions in corundum

Stress absorption spectra of V3+ in α‐Al2O3: Jahn‐Teller effect in the 3T2 state

AbstractStudy under stress of 3T2 state of the V3+ ion in corundum (α‐Al2O3) was performed at 77 K. Absorption spectra are made on 3A2(3T1)→3T2 zero‐phonon lines and on the 3A2(3T1) → → 1A1 sharp line. Under uniaxial stress, the degeneracy of vibronic levels is removed: curves show the shifts and splittings of 3A2 → 3T1 and 3A2 → 1A1 transitions as a function of the applied pressure. The strain interaction with 3T2 state only is deduced. The stress spectra cannot be quantitatively explained without taking into account a large S15* local elastic compliance. The local deformation around the V3+ ion is similar to this one around the Cr3+ or Co3+ ion. Studying the 3A2 → 3T2 band by the method of moments a coupling between the V3+ ion and a breathing mode A1 is found. Results of measurements cannot be interpreted by a Jahn‐Teller effect with only the pure tetragonal modes.

EPR and Spin–Lattice Relaxation of Mo3+ Ions in Corundum

AbstractThe EPR spectra of Mo3+ ions in corundum at v = 9.25 GHz and T = 77 °K were investigated. It is shown, that Mo3+ ions isomorphously replace Al3+ ions in the octahedral coordination. Due to the large zero‐field splitting, only the −1/2 ↔ +1/2 transition is observed. The zero‐field splitting constant 2D = (−49 ± 18) GHz, the spectroscopic splitting factor g⊥ = 1.968 ± 0.001, g ⊥ = 1.98 ± 0.01, and the hyperfine splitting constant A‖ = (119 ± 1) MHz, A⊥ = (121 ± 2) MHz are determined. It is shown that in the case of large zero‐field splitting 2D ≫ v the magnitude of 2D can be determined by measurements at a single frequency, using the value of geff at 35°2′ (cos2 θ = 2/3). The angular dependence of the hyperfine structure splitting due to the large zero‐field splitting is observed and good agreement with values calculated in first order of perturbation theory is obtained. The spin‐lattice relaxation times of Mo3+ ions in corundum are estimated from the magnitude of the broadening of the absorption curves with increasing temperature. In the temperature range of 77 to 500 °K the spin–lattice relaxation rate is τ1−1 ∼ T2.5.

The properties of (3d)4ions in corundum. I. APR spectra and their interpretation

Measurements have been made of the acoustic paramagnetic resonance spectra of both Cr2+ and Mn3+ in Al2O3 at frequencies between 8.4 and 9.5 GHz. Results have been obtained as the direction of the magnetic field H is verified in the ac plane, the bc plane and in a cone around the c axis. Two types of lines are in evidence: type 1 lines have an edge and type 2 lines a peak. The shapes are explained by assuming that random internal strains and electric fields of E type symmetry exist in the crystal. The variations of the positions of the peak or edge as H is varied are readily explained. This analysis shows that (3d)4 ions in Al2O3 are at a site which has predominantly trigonal symmetry and that the superimposed random tetragonal components are small.

The properties of (3d)4ions in corundum. II. Effects of electric fields on the APR spectra and lineshape analysis

For pt. I, see ibid., vol.5, 3397 (1972). The shape of APR lines from (3d)4 ions in Al2O3 has been investigated when the direction of the applied magnetic field and constant electric fields up to 70 kV cm-1 are varied. It is found that the spectrum is much more sensitive to an electric field applied along the a axis than the same field along the b axis. A detailed semiquantitative discussion of the intensities of the edges and peaks in the spectrum is given. From the results, information is obtained on the E type components of the random internal strains and electric field distributions experienced by the Cr2+ and Mn3+ ion impurities in Al2O3.

Ultrasonic Study of the Properties of the Ferrous and Ferric Ions in Corundum

Ferrous and ferric ions properties in corundum from observing acoustic paramagnetic resonance

Charge-Transfer Spectra of Transition-Metal Ions in Corundum

The ultraviolet absorption spectrum of corundum (${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$) containing dilute concentrations of the $3d$-series transition-metal ions ${\mathrm{Ti}}^{3+}$, ${\mathrm{V}}^{3+}$, ${\mathrm{Cr}}^{3+}$, ${\mathrm{Mn}}^{4+}$, ${\mathrm{Fe}}^{3+}$, and ${\mathrm{Ni}}^{3+}$ was measured at room temperature and at liquid-nitrogen temperature for photon energies in the range 3-9 eV. The most important features of the observed spectra are (a) the peak positions are characteristic of the particular impurity ion; (b) the peak positions and widths (\ensuremath{\sim}0.7 eV) are independent of temperature over the range studied; and (c) the integrated intensities are strong. The spectra are identified with the allowed transition whereby an electron is transferred from a nonbonding orbital, localized predominantly on the ${\mathrm{O}}^{=}$ ligands, to either the ${t}_{2g}({\ensuremath{\pi}}^{*})$ or ${e}_{g}({\ensuremath{\sigma}}^{*})$ antibonding orbital, localized predominantly on the metal ion. The position in energy of the first absorption peak for the various ions of the series relative to one another and to the position of the intrinsic absorption edge of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ is in good agreement with the charge-transfer model.

Jahn-Teller theory of Cr2+ in corundum

The dynamic Jahn-Teller effect is used in a theoretical study of the properties of the Cr2+ ion in corundum. The ion is produced in ruby crystals by X-irradiation. The trigonal distortion in the crystal is taken into account in setting up the Jahn-Teller interaction, in choosing zeroth-order orbital states for the ion and in the magnetic interactions. Using the cluster approximation, the effective Hamiltonian is thus derived. The effects of trigonal distortion are found to be small and thus the problem closely resembles that of Cr2+: MgO discussed previously in which there is a very strong orbit-lattice interaction. Theoretical values for the parameters needed to describe the low-lying energy levels of Cr2+: Al2O3 are deduced. They are in agreement with values calculated from preliminary acoustic resonance results when the applied magnetic field is along the trigonal axis. It is hoped that the theory given will serve as a satisfactory basis for the discussion of more detailed acoustic resonance results and measurements of the magneto-thermal resistance in irradiated rubies.

A wide range sub-millimetre radiospectrometer for studying absorption in solids at liquid helium temperature

A non-resonant radiospectrometer has been developed for studying the absorption spectra of solids at liquid helium temperatures in the range 0·5 to 2.5 mm, with a resolving power of 2 500. The absorption spectra can be studied both as a function of magnetic field and frequency. The measuring method is described and data are given on the resonance absorption of the V 3+ ion in corundum.

An Account of Configuration Interactions in Group‐Theoretical Classification of Electronic States in Crystals Composed of Complexes of Bound Impurity Ions

AbstractA group‐theoretical classification of the states of paramagnetic impurity ions is made taking into account charge transfer. The cases of an impurity ion in a spinel crystal and the first order pair of equivalent Cr3+ ions in corundum are studied as examples. A group‐theoretical classification of the states of complexes of N impurity ions (N = 2 to 4) is given. KMg(Co)F3 is discussed as an example.

Spin-Lattice Relaxation in theE¯(E2)State ofd3Ions in Corundum

Spin-Lattice Relaxation in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi>E</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover></mml:mrow></mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>E</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow><mml:mo>)</mml:mo></mml:math>State of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>d</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Ions in Corundum

Optical Spectra of Transition-Metal Ions in Corundum

The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point-charge model and p-d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational-electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal-field parameters have been calculated as convergent lattice sums. The observed trigonal-field parameter has the opposite sign from that calculated by the point-charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 Å displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.