J. Drożdżyński

Analysis of absorption and luminescence spectra of U3+ doped Cs2NaYCl6 and Cs2LiYCl6 single crystals

Uranium(3+) doped single crystals of Cs2NaYCl6 and Cs2LiYCl6 with a 2.0% and 0.1% U3+ concentration have been obtained by the Bridgman-Stockbarger method. Luminescence spectra of the crystals were recorded at 160, 70, and 15 K. The emission bands observed in the visible and near infrared regions have been assigned to transitions from the lowest components of the 4I11/2, 4F3/2, and 4G7/2 multiplets to the crystal-field components of the 4I9/2 ground level. Absorption spectra were recorded from 4 000 to 25 000 cm−1 at 4.2 K. The zero phonon transitions were identified from an analysis of the vibronic side bands as well as in least-squares fits by applying a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions for an ion of the 5f3 configuration and Oh symmetry. Eight energy level parameters were varied simultaneously in the least-squares adjustments yielding a mean error of 57 and 61 cm−1 for U3+:Cs2LiYCl6 and U3+:Cs2NaYCl6, respectively. The analysis of the spectra enab...

SPECTROSCOPIC STUDIES AND CRYSTAL-FIELD ANALYSIS OF U3+ IONS IN RBY2CL7 SINGLE CRYSTALS

Single crystals of U3+ diluted into a matrix of RbY2Cl7 have been grown by the Bridgman–Stockbarger method. There are two different intrinsic U3+ sites in this crystalline host, each with an approximate C2v site symmetry. A third minor U3+ site was also found. Absorption, fluorescence, and excitation spectra of these crystals were obtained at 300 and 4.2 K. Transitions belonging to each U3+ site were distinguished by time-gated site-selective spectroscopy. The energy levels of the two intrinsic sites were assigned and fitted to a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions for a 5f3 ion at a C2v symmetry site. Quite different 4F9/2 fluorescence lifetimes were measured for the three sites, due to a multiphonon decay mechanism which is affected by differences in their respective crystal-field strengths. These results are analyzed quantitatively using the theory for the electron–phonon interaction.

Preparation and properties of hydrated uranium(III) complex chlorides. Part I. Uranium trichloride heptahydrate

Abstract The synthesis of uranium trichloride heptahydrate together with some of its structural, spectroscopic and magnetic properties is reported. The compound possesses the triclinic lattice of LaCl 3 ·7H 2 O (space group P 1 ). Controlled vacuum thermal dehydration of the substance enabled the preparation of the anhydrous trichloride in gram quantities. Magnetic susceptibilities of polycrystalline samples were measured by the Faraday method in the 6.5–295 K range. The uranium trichloride heptahydrate follows in this region the Curie-Weiss law with C = 1.0839 emu K mol −1 and θ = −32.7 K.

Spectrum analysis, correlation crystal-field effects and f-f transition intensities of U3+ in LaCl3

High resolution polarized absorption spectra of U3+:LaCl3 single crystals were recorded in the 4000–50 000 cm−1 range at 7 K. The experimental crystal-field energy levels of the U3+ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators. The performed analysis of the spectra enabled the determination of crystal-field parameters and reassignment of some of the observed 5f3→5f3 transitions. The effects of selected CCF operators on the splitting of some specific U3+ multiplets have been investigated. On the basis of the obtained electronic wave functions the electric-dipole intensity parameters of the total transition dipole strength were determined by fitting the calculated and experimental transition intensities. Among 67 transitions observed in the 4000–22 000 cm−1 range 56 were sufficiently well resolved for quantitative calculations.

Up-conversion in elpasolite crystals doped with U3+

Abstract Two elpasolite crystals Cs2NaYBr6 and Cs2NaYCl6, both doped with U3+ were investigated. The emission from the 4 G 7/2 , 4 F 3/2 , and 4 I 11/2 levels was found. Decay times of the visible emission were measured as a function of temperature. The strong influence of temperature on the decay times is discussed in terms of strong phonon coupling of the 5f3 and the 5f26d1 bands. Upon IR excitation a red emission, assigned to the 4 G 7/2 → 4 I 9/2 transition, was observed only in the bromide. The anti-Stokes emission is due to step by step absorption. The observed dependence of these phenomena on environment is discussed briefly.

CRYSTAL-FIELD ANALYSIS OF U3+ IONS IN K2LAX5 (X = CL, BR OR I) SINGLE CRYSTALS

Abstract An analysis of low temperature absorption spectra of U3+ ions doped in K2LaX5 (X=Cl, Br or I) single crystals is reported. The energy levels of the U3+ ion in the single crystals were assigned and fitted to a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions at the Cs symmetry site. An analysis of the nephelauxetic effect and crystal-field splittings in the series of compounds is also reported.

Synthesis, structural and spectroscopic properties of tetra(tetraethylammonium) heptaisothiocyanato uranate(III) and neodymate(III)

Abstract The synthesis and characterization of a new uranium(III) compound and its neodymium(III) analogue of the formulas [(C2H5)4N]4U(NCS)7 (I) and [(C2H5)4N]4Nd(NCS)7 (II) are reported. Both compounds are isomorphic and crystallize in the tetragonal system, space group I4/mmm with: a = 11.530 A , c = 45.555 A , Z = 4, V = 6056.1 A 3 (I) and a = 11.564(2) A , c = 45.801(9) A , Z = 4, V = 6125.0(9) A 3 (II) . The IR, Raman and electronic spectra of the compounds have been recorded in the 30–4000 cm−1 and 4000–30 000 cm−1 spectral ranges, respectively, and are further discussed. The assignments of the IR and Raman frequencies based on theoretical considerations are given.

Synthesis and characterization of potassium, rubidium and ammonium tetrachlorouranate(III) tetrahydrates

Abstract A new series of hydrated uranium(III) complex chlorides of the general formula M I UCl 4 · 4H 2 O (M I ≡ K,Rb or NH 4 ) were isolated and characterized. The compounds belong to the monoclinic crystal system. Unit cell parameters were determined from X-ray powder diffraction data. Non-static high vacuum thermal dehydrations enabled the anhydrous KUCl 4 and RbUCl 4 complexes to be obtained as well as UCl 4 . The magnetic susceptibilities of the hydrated chlorides were measured in the 6.5–300 K range. Plots of the inverse magnetic susceptibilities deviate from Curie-Weiss behaviour below 130 K. The IR and electronic spectra of the compounds in solid state were recorded in the 80–24000 cm −1 region and discussed.

Absorption spectra analysis of hydrated uranium(III) complex chlorides

Absorption spectra of powdered samples of hydrated uranium(III) complex chlorides of the formulas NH4UCl4 4H2O and CsUCl4 3H2O have been recorded at 4.2 K in the 4000‐26 000 cm ˇ1 range. The analysis of the spectra enabled the determination of crystal-field parameters and assignment of 83 and 77 crystal-field levels for the tetrahydrate and trihydrate, respectively. The energies of the levels were computed by applying a simplified angular overlap model as well as a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions. Ab initio calculations have enabled the application of a simplified parameterization and the determination of the starting values of the AOM parameters. The received results have proved that the AOM approach can quite well predict both the structure of the ground multiplet and the positions of the crystal-field levels in the 17 000‐25 000 cm ˇ1 range, usually obscured by strong f‐d bands. ” 2000 Elsevier Science B.V. All rights reserved.

Preparation and properties of hydrated uranium(III) complex chlorides. Part II. Uranium trichloride monomethylcyanide pentahydrate

Abstract The preparation and characterization of a new uranium(III) compound, UCl3·CH3CN·5H2O, is reported. The complex chloride belongs to the monoclinic system with a=1226.(2), b=1298.(3), c=662.(1) pm, γ=101.7(2)° and Z=4. Magnetic susceptibility measurements were carried out by the Faraday method in the 6.5–300 K range. An antiferromagnetic transition is observed at TN=12 K. In the 65–300 K region the compound exhibits Curie-Weiss paramagnetism with the paramagnetic constants C=1.430 emu K mol−1 and θ=−65.7 K. The electronic spectra of thin layers of the compound have been recorded in the 4000–24000 cm−1 region and discussed.