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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
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1996
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vol. 90
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issue 6
1193-1201
EN
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.
2
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Vibration and Luminescence Spectroscopic Investigations of the Alkali Rare Earth Double Phosphates M_{3}(RE,Eu)(PO_{4})_{2} (M=K, Rb; RE=La, Gd)

100%
Kloss M., Schwarz L., Hölsä J.
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vol. 95
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issue 3
343-349
EN
The room temperature IR- and Raman spectra of the different M_{3}RE(PO_{4})_{2} (M = K, Rb; RE = La, Eu, Gd) double phosphates were analysed and used to interpret the vibronic side band structure in the photoluminescence spectra. The intraconfigurational 4f-4f electronic transitions in the photoluminescence spectra of the Eu^{3+} doped M_{3}RE(PO_{4})_{2} were analysed in detail. The crystal field fine structure of the ^{5}D_{0} → ^{7}F_{J} (J=0-4) transitions was analysed accounting for the information on the crystal structure. The effect of the temperature as well as the alkali host cation was evaluated. Finally, a preliminary crystal field energy level scheme for the ^{7}F_{J} (J=0-4) ground term was deduced from the analysis of the photo-luminescence as well as IR- and Raman spectra.
3
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Application of Bond Valence Model to Stability of RE Oxycompounds

88%
Hölsä J., Koski K., Lamminmäki R.-J., Rahiala H., Säilynoja E.
Acta Physica Polonica A
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1997
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vol. 91
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issue 3
563-568
EN
The bond valence model was used to study the stability of the non-stoichiometric LaO_{1-x}F_{1+2x} phases, the solid solubility in the (La_{1-x}Gd_{x}) OCl system and the phase transformation in the REOCl (RE^{3+}=La^{3+} -Nd^{3+}, Sm^{3+}-Gd^{3+}, Ho^{3+}, and Y^{3+}) series. The stability of the non-stoichiometric LaO_{1-x}F_{1+2x} (0 ≤ x ≤ 0.3) phase decreases with increasing excess fluoride. The global instability index values close to 0.2 indicate the instability of the non-stoichiometric phase. The relative stability of the (La_{1-x}Gd_{x})OCl (0 ≤ x ≤ 1.0) solid solutions achieved its minimum in the middle of the series. However, the X-ray powder diffraction results indicated complete solid solubility in the whole (La_{1-x}Gd_{x})OCl series and no phase separation was observed. The bond valence model was used to explain the structural transformation from the tetragonal oxychlorides, REOCl (RE = La-Er, and Y), to hexagonal beyond ErOCl. The calculated global instability index values did not show any clear trend across the REOCl series probably due to the inaccuracies and incoherencies in the original structural data.
4
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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
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1996
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vol. 90
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issue 6
1203-1213
EN
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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