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Research on the Optical and EPR Spectral Data and the Local Structure for the Tetragonal Nb^{4+} Center in Glasses

100%
Wu X.-X., Yu X.-P., Zheng W.-C.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1
72-75
EN
Two optical bands and four EPR (or spin-Hamiltonian) parameters (g factors g_{∥}, g_{⊥} and hyperfine structure constants A_{∥}, A_{⊥}) of the tetragonally-compressed Nb^{4+} octahedral center in glasses are calculated from two methods, the complete diagonalization (of energy matrix) method and the perturbation theory method. Both methods are founded on the two-spin-orbit-parameter model where both the contribution to the spectral data from the spin-orbit parameter of central d^{n} ion and that of ligand ion via covalence effect are considered. The calculated results from both the complete diagonalization (of energy matrix) method and perturbation theory method show reasonable agreement with the experimental values. The signs and possible misprint for the observed hyperfine structure constants A_{∥} and A_{⊥} are suggested, and the local structure of the tetragonal Nb^{4+} center in glasses due to the Jahn-Teller effect is gained from the calculations. The results are discussed.
2
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Efficient Two-Center Auger Mechanism of Electron Trapping by Fe^{3+} Ions in ZnSe:Fe,Cr

100%
Surma M., Godlewski M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
1017-1020
EN
A detailed analysis of decay kinetics of light induced electron spin resonance signals of Cr^{1+} and Fe^{3+} ions in ZnSe:Fe,Cr is given. We observe that the Cr^{1+} electron spin resonance signal decays once free electrons are thermally ionized from shallow donors of ZnSe. Such unusual behavior of the Cr^{1+} electron spin resonance signal is explained by efficient two-center Auger recombination: the Cr^{1+} center is ionized due to the Auger-type energy transfer from the electron being trapped by the Fe^{3+} ion. Such process is shown to be consistent with the temperature dependence of the decay times of electron spin resonance signals. Its quantum efficiency is estimated to be as large as 18% for Cr and Fe concentrations which were studied.
3
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Photo-ESR Studies of Ni doped ZnS and ZnSe

100%
Surma M., Zakrzewski A., Godlewski M., Surkova T.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
221-224
EN
The results of electron spin resonance experiments are presented for nickel doped ZnS and ZnSe. Energy level position of Ni^{1+} state in band gap of ZnS and ZnSe is determined. The nonradiative recombination processes of donor-acceptor pairs in Ni doped samples are discussed.
4
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Research on the Spin-Hamiltonian Parameters and Local Structure for the Tetragonal Mo^{5+} Centers in CaWO_{4} Crystal

100%
Mei Y., Zheng W., Wei C.
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vol. 126
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issue 6
1275-1279
EN
The spin-Hamiltonian parameters (g factors g_{∥}, g_{⊥} and hyperfine structure constants A_{∥}(A), A_{⊥}(A), A_{∥}(B) and A_{⊥}(B), A(A) and A(B) belonging to isotopes ^{95}Mo^{5+} and ^{97}Mo^{5+}) of Mo^{5+} ion at the tetragonally-compressed tetrahedral W^{6+} site in CaWO_4 crystal are calculated from the high-order perturbation formulae based on the two-mechanism model, where besides the contributions to spin-Hamiltonian parameters due to the crystal-field mechanism concerning the crystal-field excited states in the extensively-applied crystal-field theory, those due to charge-transfer mechanism concerning charge-transfer excited states (which are omitted in crystal-field theory) are included. The calculated results are in reasonable agreement with the experimental values. The calculations show that for the high-valence state d^{n} ions (e. g., Mo^{5+} considered) in crystals, the contributions due to charge-transfer mechanism should be taken into account in the studies of spin-Hamiltonian parameters. The local structure of Mo^{5+} center in CaWO_4 crystal due to the impurity-induced local lattice relaxation is estimated from the calculations. The results are discussed.
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