Wydział Chemii

Mirosław Karbowiak

Janusz Drożdżyński

2004

Journal of Physical Chemistry A

108

6397-6406

10.1021/jp038024q

Naukowa

Angielski

Artykuł

5f^N → 5f^N-16d¹ absorption spectra of U⁴⁺- and U³⁺-doped Cs₂NaYCl₆, Cs₂LiYCl₆, Cs₂NaYBr₆, CsCdBr₃, and Cs₃Lu₂Cl₉ single crystals were recorded at 4.2 K in the 14 000−50 000 cm^-1 spectral range. The 5f ² → 5f¹6d¹ absorption bands of U⁴⁺ ions were observed in the 30 000−37 000 cm^-1 energy range, and have been assigned as transitions from the ³H₄ ground multiplet of the 5f² configuration to crystal-field levels of the 5f¹6d(t_2g)¹ manifold. The energies of the lowest levels of the 5f¹6d(t_2g)¹ configuration have been for the first time determined for U⁴⁺ ions doped in a chloride or bromide host crystal. They are equal to 26 360 and 28 590 cm^-1 for U⁴⁺:CsCdBr₃ and U⁴⁺:Cs₂NaYBr₆ respectively and range from 30 360 to 31 010 cm^-1 for U⁴⁺ doped in the chloride hosts. Highly structured vibronic bands of 5f ³ → 5f²6d(t_2g)¹ absorption transitions of the U³⁺ ions appeared at an energy as low as 14 158 cm^-1, and have been assigned to transitions from the ⁴I_9/2 ground multiplet of the 5f³ configuration to crystal-field levels arising from the configurations 5f²(³H₄)6d(t_2g)¹(Γ_8g) (barycenter at ∼16 000 cm^-1) and 5f²(³H₄)6d(t_2g)¹(Γ_7g) (barycenter at ∼19 000 cm^-1). Besides, some low intensity bands observed at ∼18 600 and above 21 000 cm^-1 have been assigned as transitions to the 5f²(³F₂)6d(t_2g)¹(Γ_8g) and 5f²(³F₂)6d(t_2g)¹(Γ_7g) levels, respectively. Transitions to the 5f²6d(e_g)¹ levels of U³⁺ ions have been observed as broad and unstructured bands at wavenumbers higher than 38 000 cm^-1. The crystal field splitting (10Dq) of the 5f²6d¹ configuration for U³⁺ doped in Cs₂NaYCl₆ single crystals amounts to ∼23 000 cm^-1, and the separation between Γ_8g and Γ_7g components of the t_2g state, resulting from spin−orbit interaction for the 6d electron, can be evaluated as 3350 cm^-1. The splitting of the 5f²(^2S+1L_J)6d(γ)¹(Γ_ig) (γ = t_2g or e_g; i = 7 or 8) configurations, resulting from the coupling of the 5f² core electrons with the 6d electron is somewhat smaller and amounts to ∼3000 cm^-1. The main feature of the crystal level structure observed in the 5f³−5f²6d¹ absorption spectra of U³⁺ ions reflects the dominating influence of the crystal field splitting and spin−orbit coupling of the 6d electron.

Absorption spectroscopy, Crystal structure, Crystals, Energy, Ions

https://doi.org/10.1021/jp038024q

https://www.acs.org/content/acs/en.html