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Crystal Field Analysis of Cr^{3+} Energy Levels in LiGa_5O_8 Spinel

100%
Brik M., Avram N., Avram C.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
1055-1060
EN
Detailed and consistent crystal field analysis of the LiGa_5O_8:Cr^{3+} absorption spectrum is performed in the present paper by using the exchange charge model of crystal field. We calculate the crystal field parameters from the crystal structure date and diagonalize the crystal field Hamiltonian to obtain the energy level structure of Cr^{3+} ions in LiGa_5O_8. The obtained energy levels and estimated Racah parameters B and C were compared with the experimental spectroscopic data; good agreement was demonstrated.
2
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Comparative Study between Energy Levels of Cr^{3+} and Co^{2+} Ions Doped in MgF_{2} Crystal

100%
Nistora R., Andreici L., Avram N.
Acta Physica Polonica A
|
2009
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vol. 116
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issue 4
538-540
EN
The aim of this paper is to present a comparison of the energy level schemes of Cr^{3+} (3d^{3} electrons) and Co^{2+} (3d^{7} electrons), each of ions doped, separately, in MgF_{2} crystal. We report on the detailed and consistent crystal field analysis of Cr^{3+} spectra in MgF_{2} crystal and compare with results, previously obtained, for Co^{2+}, doped in same host matrix. The results are based on application of the exchange charge model of crystal field to the calculation of crystal field parameters and energy levels of both ions doped in MgF_{2}.The calculations have been performed on previously optimized geometry of MgF_{2} crystal. The obtained results are compared with experimental data and discussed.
3
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Calculation of Optical and Spin-Hamiltonian Parameters for Mn^{4+} Doped in LiGa_{5}O_{8}

100%
Ciresan M., Stanciu M., Avram N.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
547-549
EN
The aim of this paper is to investigate, from theoretical point of view, the optical spectra and EPR (g-factors) parameters for Mn^{4+}:LiGa_{5}O_{8}. The optical energy levels scheme has been obtained by the diagonalization of the Hamiltonian of the system, using all 50 wave functions of the LS terms of 3d^{3} electron configuration. The crystal field parameters have been obtained in the exchange charge model of crystal field, taking into account the structure of the host matrix and effects of the covalent bond formation between the Mn^{4+} with O^{2-}. The satisfactory agreement with experimental data is obtained.
4
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Crystal Field Analysis of Cr^{3+} Doped SrAl_{2}O_{4} Spinel

100%
Stanciu M., Ciresan M., Avram N.
Acta Physica Polonica A
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2009
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vol. 116
|
issue 4
544-546
EN
The present work is devoted to the crystal field analysis of trivalent chromium doped in SrAl_{2}O_{4} spinel in the frame of the exchange charge model of crystal field. Using the shell model and pair approximation, we optimize the geometric structure of the crystal. The approach enables the modeling of the crystal field parameters and thus calculates the energy level scheme of Cr^{3+} ions in spinel SrAl_{2}O_{4}. The obtained results are compared with experimental data and discussed.
5
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Angular Distortion around Cr^{3+} Ions Doped Diammonium Hexaaqua Magnesium Sulphate Single Crystal

100%
Ciresan M., Vaida M., Avram N.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
835-839
EN
The aim of the present study is to explain the local distortion around Cr^{3+} ions doped in the title crystal using the latest experimental data regarding optical and EPR spectra. We calculated g_ǁ, g_⊥, and D spin-Hamiltonian parameter as function of angle between the C_3 axis and metal-ligand chemical bond in local distorted octahedral cluster [CrO_6]^{9-} formed after doped crystal. The method is based on the single spin-orbit coupling parameter model, in the cluster approach using Macfarlane high order perturbation formulae. The results compared with experimental data give a reasonable agreement.
6
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Long-Range Correlation in Atomic Vibration οf Chicken Lysozyme Backbone

100%
Crăciun D., Isvoran A., Avram N.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
684-686
EN
Within this study we use methods such as spectral analysis that gives the spectral coefficient β, detrended fluctuations analysis that gives the scaling exponent α and the determination of Hurst exponent (H) to analyze the spatial series corresponding to the temperature factors of N, C-alpha, C and O atoms of 14 complexes of the chicken lysosyme. The mean values of the investigated parameters obtained for the 14 complexes are: β=1.779 ± 0.086, α=1.382 ± 0.009 and H=0.916. These values reveal long-range correlation in atomic vibrations corresponding to the chicken lysozyme backbone.
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