Line broadening studies for U and U ions in RbY2Cl7 single crystals |
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Authors: | M Karbowiak |
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Institution: | Faculty of Chemistry, University of Wroc?aw, ul. F. Joliot-Curie 14, Wroc?aw 50-383, Poland |
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Abstract: | Temperature-dependent line broadening measurements of emission and excitation transitions for two intrinsic sites U(1) and U(2) of U3+ ions doped in a RbY2Cl7 single crystals as well as of U4+ ions have been performed. Values of the electron phonon (EP) coupling parameter were determined by a fit of experimentally observed line widths to an equation containing the temperature dependent broadening term due to the Raman two-phonon process. The parameters for U3+ ions in RbY2Cl7 are larger than those determined for this ion in LaCl3 host crystals. This is due to shorter M-Cl distances in RbY2Cl7 which leads to a stronger interaction of uranium with the chlorine ions and to an increase of covalency. The relatively large value determined for the multiplet of U3+ in RbY2Cl7 may result from the proximity of opposite parity 5f26d1 states. The parameters obtained for the U3+ ions are larger than those for U4+. The latter ones are affected by a stronger crystal-field (CF), however the position of the first 5f26d1 or 5f16d1 states, which for U3+ is observed at an energy of ∼15,000 cm−1 lower than for U4+, is the dominating one among the factors influencing the EP coupling strength. The EP coupling parameters for all investigated transitions of the U3+ ions are larger for U(2) than for U(1), which results mainly from the larger crystal field strength observed for the U(2) site. The differences in the EP coupling strength of the U3+ ions in the U(1) and U(2) sites are in accordance with decay times observed for emission for both sites from the multiplet. |
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Keywords: | U3+ doped RbY2Cl7 U4+ doped RbY2Cl7 Line broadening Line shifts Electron-phonon coupling |
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