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On Some Structural and Spectroscopic Aspects of Rare Earth Oxycompounds

100%

Hölsä J., Säilynoja E., Porcher P.

Acta Physica Polonica A

1996

vol. 90

issue 6

1193-1201

The aim of this account is to present the use and the advantages of different experimental and theoretical methods in the study of the structural and spectroscopic properties of rare earth (RE) oxyfluorides. The structural characterization was carried out with the X-ray and neutron powder diffraction techniques combined with the analysis of the acquired data with the Rietveld profile refinement method. The detailed spectroscopic studies were also used by employing the optical absorption and luminescence as well as inelastic neutron scattering data. Simple spectroscopic measurements gave, however, only qualitative description of the spectroscopic properties studied. More sophisticated and quantitative means was obtained by the application of the phenomenological crystal field theory to the spectroscopic data. On the other hand, the structural data was also used as initial input to electrostatic point charge calculation in order to extract the spectroscopic information. The structural and spectroscopic studies comprised the verification of the exact crystal and energy level structures and the characterization of the different interactions modifying the spectroscopic properties of the RE^{3+} ions. Finally, the results from the theoretical model were used to explain the evolution of the crystal field effect on the 4f^{N} energy level structure of the RE^{3+} ion in the RE oxyfluorides series.

Energy Level Scheme of Nd^{3+} Ion in Rare Earth Oxyhalides, REOX (X = F, Cl, and Br)

64%

Beaury L., Hölsä J., Korventausta J., Krupa J., Lamminmäki R., Porcher P., Rahiala H., Säilynoja E.

Acta Physica Polonica A

1996

vol. 90

issue 6

1203-1213

The energy level schemes of the neodymium oxyhalides (NdOX, X = F, Cl, and Br) were studied and simulated with a phenomenological model accounting simultaneously for both the free ion interactions and the crystal field effect. The former included the electrostatic and interconfigurational interactions as well as the spin-orbit coupling. The simulations were carried out by using the data from the optical absorption and luminescence as well as the inelastic neutron scattering measured at low temperatures between 2.5 and 77 K. The values of the Slater integral F^{2} describing the electrostatic interactions decrease while F^{4} and F^{6} increase as a function of the ionic radius of the halide anion. The strength of the spin-orbit coupling is quite the same in all three matrices. The crystal field effect - measured as the crystal field strength parameter S - is almost twice as strong in the hexagonal NdOF matrix (650 cm^{-1}) than in the tetragonal NdOCI or NdOBr (367 and 378 cm^{-1}, respectively). Similar evolution was obtained for the short-and mid-range crystal field strengths related to the spatial extension of the interaction.

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2 Acta Physica Polonica A

2 1996

2 Hölsä J.

2 Porcher P.

2 Säilynoja E.

1 Beaury L.

1 Korventausta J.

1 Krupa J.

1 Lamminmäki R.

1 Rahiala H.

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On Some Structural and Spectroscopic Aspects of Rare Earth Oxycompounds

Energy Level Scheme of Nd^{3+} Ion in Rare Earth Oxyhalides, REOX (X = F, Cl, and Br)