Radiation-induced paramagnetic silver centers in LiNaSO4
TL;DR: The results of ESR investigations carried out on γ-irradiated Ag-doped lithium sodium sulphate (LiNaSO4) at LNT (77 K) are reported in this paper.
Abstract: The results of ESR investigations carried out on γ-irradiated Ag-doped lithium sodium sulphate (LiNaSO4) at LNT (77 K) are reported here Two different centres of Ag (Ag0, Ag2+) have been observed at 77 K In the case of Ag2+ the parameters are gxx=2071±0001, gyy=2102±0001, gzz=2402±0001, Axx=18±1 G, Ayy=20± 1 G,and Azz = 26 ± 1 G The ground-state wave function has been found to be consist primarily of dx2−y2 with a reasonable admixture of other orbitals The extent of delocalization of the electron in the Ag2+ has been estimated For Ag0 the parameters g and A are found to be isotropic
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TL;DR: In this article, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I-V characteristic, and a correlation is observed between the free hole carriers, the Ag 2+ centers, and the neutral acceptor bound excitons.
Abstract: ZnO:Ag films have been fabricated on a n-Si (1 1 1) substrate and then annealed in situ in an O 2 ambient, using Ag 2 O as a silver dopant by pulsed laser deposition. Hall measurements reveal that the films prepared at 400 and 450 °C show p-type behavior with a hole concentration of 6.3×10 16 –1.2×10 17 cm –3 and a mobility of 2.48–3.30 cm 2 /V s. By combining Hall measurements, electron paramagnetic resonance (EPR) signals, and photoluminescence (PL) spectra, a correlation is observed between the free hole carriers, the Ag 2+ centers, and the neutral acceptor bound excitons. Additionally, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I–V characteristic.
36 citations
TL;DR: In this article, the tetragonal distortion (characterized by Delta R=R(parallel to)-R(perpendicular to), where R(vertical bar) and R(perendicular to) represent the metal-ligand distances parallel with and perpendicular to the C(4) axis) of a guanidinium aluminium sulphate hexahydrate (GASH) crystal was studied by calculating its spin-Hamiltonian parameters.
Abstract: When Cu(2+) ion occupies the trigonal Al(3+) (II) site in guanidinium aluminium sulphate hexahydrate (GASH) (C(NH(2))(3)Al(SO(4))(2)center dot 6H(2)O) crystals, the trigonal Al(H(2)O)(6)(3+) octahedron in the host GASH crystal changes to the tetragonally-elongated Cu(H(2)O)(6)(2+) octahedron in the impurity center due to the Jahn-Teller effect. The tetragonal distortion (characterized by Delta R=R(parallel to)-R(perpendicular to), where R(vertical bar) and R(perpendicular to) represent the metal-ligand distances parallel with and perpendicular to the C(4) axis) of this Cu(H(2)O)(6)(2+) cluster is studied by calculating its spin-Hamiltonian parameters (g factors g(parallel to), g(perpendicular to) and hyperfine structure constants A(parallel to) and A(perpendicular to)) from two theoretical methods, the complete diagonalization (of energy matrix) method (CDM) and the perturbation theory method (PTM). Both methods are based on the cluster approach in which the admixture between the d orbitals of 3d(n) ion and the p orbitals of ligand ion is considered. The calculated results show that both methods can be used to calculate the spin-Hamiltonian parameters and to determine the structure of 3d(9) clusters in crystals. These results are discussed. (C) 2010 Elsevier BM. All rights reserved.
19 citations
TL;DR: In this paper, the spin-Hamiltonian parameters (g factors g//, g perpendicular to and hyperfine structure constants A//, A perpendicular to) of approximately-tetragonal Cr5+ centers in MVO3 (M = Li, Na, K, Rb) crystals are calculated from the complete high-order perturbation formulas for d1 ions in tetragonal symmetry with the ground state.
Abstract: The spin-Hamiltonian parameters (g factors g//, g perpendicular to and hyperfine structure constants A//, A perpendicular to) of the approximately-tetragonal Cr5+ centers in MVO3 (M = Li, Na, K, Rb) crystals are calculated from the complete high-order perturbation formulas for d1 ions in tetragonal symmetry with the ground state [image omitted]. These formulas are based on a two-mechanism model, in which not only the contribution to spin-Hamiltonian parameters from the crystal-field (CF) mechanism concerning CF excitations, but also that from the charge-transfer (CT) mechanism concerning CT excitations (which is neglected in the widely-used CF theory) are included. The calculated results are in reasonable agreement with the experimental values and the signs of hyperfine structure constants are suggested. The calculations show that for a high valence state dn ion (e.g. Cr5+) in crystals, the exact calculation of spin-Hamiltonian parameters should take the contributions due to both CF and CT mechanisms into account.
17 citations
TL;DR: In this paper, the spin-orbit parameters of the rhombic Cu2+ centers in the CuGaSe2 crystal were determined from the high-order perturbation formulae based on the cluster approach.
Abstract: The spin-Hamiltonian parameters (g factors gi and hyperfine structure constants Ai, where i = x, y, z) of the rhombic Cu2+ centres in the CuGaSe2 crystal are determined from the high-order perturbation formulae based on the cluster approach (sometimes also called two-spin-orbit parameter model). In the studies, some parameters in the analysis of g factors for the same centre within the tetragonal symmetry approximation in the previous paper are used, and the parameter due to the perturbation of rhombic crystal field caused by a charge compensator at, e.g., [110] direction are considered. As the result of a fitting process, the determined spin-Hamiltonian parameters are in reasonable agreement with the experimental values. The results are discussed.
15 citations
TL;DR: ESR studies indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) =2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical.
Abstract: The defect centres formed in the TL phosphor CaSO4:Dy,Ag are studied using the technique of Electron Spin Resonance. The Ag co-doped phosphor exhibits three glow peaks around 130, 220 and 375 degrees C in contrast with the two glow peaks observed in the CaSO4:Dy phosphor at 130 and 220 degrees C at a gamma ray dose of 1Gy. ESR studies show that the additional peak at 375 degrees C correlates with a Ag2+ centre formed due to gamma irradiation and observable only below -170 degrees C. The Ag2+ centre is characterised by an axial g-tensor with principal values g(parallel) = 2.38 and g(perpendicular) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) = 2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical. It is observed that there is more incorporation of Ag in the CaSO4:Dy system as compared with that in pure CaSO4 system.
13 citations
References
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TL;DR: In this paper, the atomic parameter ψ2(0) and the isotropic hyperfine interaction A for unit spin density in the corresponding s orbital are calculated for the most abundant nuclei of the elements from helium to bismuth from the Hermann-Skillman wavefunction.
808 citations
TL;DR: In this article, the EPR spectrum of copper doped in zinc fluoride has been analyzed and the observed g values led by a new method to a determination of the coefficients of the Kramer's doublet.
Abstract: With the aid of computer techniques, including a laboratory automation system, accurate computer simulation, and an accurate calculation method, the EPR spectrum of copper doped in zinc fluoride has been analyzed. The observed g values led by a new method to a determination of the coefficients of the Kramer's doublet. Copper hyperfine structure verified these values and fluorine transferred hyperfine structure gave a measure of covalency. The fractional orbital occupation showed predominantly σ bonding which is similar to other reported transition metal ions in ionic insulating crystals. Orbital reduction, though no doubt present, makes only an insignificant and undetectable contribution.
65 citations
TL;DR: In this article, a paramagnetic resonance was studied for Ag in the 4d 9 configuration substituting for alkali ions in alkali chlorides, and two spectra were observed corresponding to the low and high temperature modifications of the same spectrum under a "dynamical" Jahn-Teller distortion.
57 citations
53 citations
TL;DR: The dependence of the optical and spin-Hamiltonian parameters of NiF65- and NiF43- D4h units, with a b1g* (approximately x2-y2) unpaired electron, upon the equatorial (Req) and axial (Rax) Ni+-F- distances has been studied through multiple-scattering X alpha and self-consistent charge extended Huckel methods as discussed by the authors.
Abstract: The dependence of the optical and spin-Hamiltonian parameters of NiF65- and NiF43- D4h units, with a b1g* ( approximately x2-y2) unpaired electron, upon the equatorial (Req) and axial (Rax) Ni+-F- distances has been studied through multiple-scattering X alpha and self-consistent charge extended Huckel methods. Both methods lead to the following main conclusions: (i) A charge-transfer transition like eu( pi + sigma ,eq) to b1g*( approximately x2-y2) (termed Eu) is more sensitive than a crystal-field one like b2g* ( approximately xy) to b1g*( Delta 1) or eg* to b1g*( Delta 2) to variations in Req. The change experienced by Eu mainly reflects that of Vel(M)-Vel(L), where Vel(M) and Vel(L) are the electrostatic potentials experienced by an electron placed on metal and ligands, respectively, (ii) As regards the unpaired spin densities onto nLp and nLs ligand valence orbitals (termed fsigma and fs respectively), it is found that fsigma >>fs but fs is much more sensitive than fsigma to changes in Req. The microscopic origin of this relevant fact is explained in detail. (iii) The removal of axial ligands, keeping Req constant, induces a decrease of Eu as a result of the diminution of the electrostatic repulsion, Vel (M), and produces a slight increase of Delta 1 and a more important one of Delta 2. (iv) The dependence of g//-g0 and gperpendicular to -g0 on Req essentially reflects that of Delta 1-1 and Delta 2-1, respectively, because of the low covalency (fsigma approximately=2%).
35 citations