Ligand Exchange and Nature of Luminescence Centers in the Crystals of Uranyl Nitrates and Perchlorates

We obtained complexes of uranyl nitrates and uranyl perchlorates with neutral ligands in crystalline and amorphous states and also with variable composition (as regards both water and the quantity of acid ligands entering into the first coordination sphere of UO₂ ²⁺). We studied their luminescence spectra at T = 77 K. Correlation between the frequencies of electronic and vibronic transitions and the donor numbers of neutral ligands has been established. The possible ways of replacing neutral ligands in the first coordination sphere of UO₂ ²⁺ have been analyzed as well as the composition and structure of the complex systems formed in this case.     

Electronic Spectra and the Mechanism of Complexing of Uranyl Nitrate in Water–Acetone Solutions

Based on the analysis of electronic absorption and luminescence spectra, the processes of complexing in an aqueous solution of uranyl nitrate hexahydrate (UO₂(NO₃)₂·6H₂O) on gradual addition of small amounts of acetone have been investigated. In a pure aqueous solution, uranyl exists as the UO₂·5H₂O complex. It is shown that addition of acetone to the solution leads to displacement of some water molecules from the first coordination sphere of uranyl and formation of uranyl nitrate dihydrate complexes, UO₂(NO₃)₂·2H₂O. It has been established that the stability of these complexes is determined by the decrease in both the water activity and the degree of hydration of uranyl and nitrate. This is the result of the local increase in the concentration of the molecules of acetone (due to its hydrophobicity) in those regions of the solution in which there are uranyl and nitrate ions. The experimental facts supporting the proposed mechanism are given.     

Raman spectroscopy of uranopilite of different origins—implications for molecular structure

Uranopilite, [(UO₂)₆(SO₄)O₂(OH)₆(H₂O)₆](H₂O)₈, the composition of which may vary, can be understood as a complex hydrated uranyl oxyhydroxy sulfate. The structure of uranopilite from different locations has been studied by Raman spectroscopy at 298 and 77 K. A single intense band at 1009 cm⁻¹ assigned to the ν₁ (SO₄)²⁻ symmetric stretching mode shifts to higher wavenumbers at 77 K. Three low‐intensity bands are observed at 1143, 1117 and 1097 cm⁻¹. These bands are attributed to the (SO₄)²⁻ ν₃ anti‐symmetric stretching modes. Multiple bands provide evidence that the symmetry of the sulfate anion in the uranopilite structure is lowered. Three bands are observed in the region 843 to 816 cm⁻¹ in both the 298 and 77 K spectra and are attributed to the ν₁ symmetric stretching modes of the (UO₂)²⁺ units. Multiple bands prove the symmetry reduction of the UO₂ ion. Multiple OH stretching modes prove a complex arrangement of OH groupings and hydrogen bonding in the crystal structure. A series of infrared bands not observed in the Raman spectra are found at 1559, 1540, 1526 and 1511 cm⁻¹ attributed to δ UOH bending modes. U‐O bond lengths in uranyl and O H/dotbondO bond lengths are calculated and compared with those from X‐ray single crystal structure analysis. The Raman spectra of uranopilites of different origins show subtle differences, proving that the spectra are origin‐ and sample‐dependent. Hydrogen‐bonding network and its arrangement in the crystal structure play an important role in the origin and stability of uranopilite. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl mineral pseudojohannite Cu6.5[(UO2)4O4(SO4)2]2(OH)5·25H2O

Raman spectra of pseudojohannite were studied and related to the structure of the mineral. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (SO₄)²⁻ units and of water molecules. The published formula of pseudojohannite is Cu_6.5(UO₂)₈[O₈](OH)₅[(SO₄)₄]·25H₂O. Raman bands at 805 and 810 cm⁻¹ are assigned to (UO₂)²⁺ stretching modes. The Raman bands at 1017 and 1100 cm⁻¹ are assigned to the (SO₄)²⁻ symmetric and antisymmetric stretching vibrations. The three Raman bands at 423, 465 and 496 cm⁻¹ are assigned to the (SO₄)²⁻ν₂ bending modes. The bands at 210 and 279 cm⁻¹ are assigned to the doubly degenerate ν₂ bending vibration of the (UO₂)²⁺ units. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Investigation of uranyl nitrate extraction from ketone solutions by dimethyl sulfoxide

Based on an analysis of low-temperature luminescence spectra (T=77 K) of UO₂(NO₃)₂·6H₂O solutions in acetone, the mechanisms of formation of a wide group of uranyl complexes in uranyl extraction from solutions by dimethyl sulfoxide are studied. It is shown that to increase the coefficient of uranyl distribution between the solution and solid phase (in the form of UO₂(NO₃)₂·2DMSO) it is necessary to add sulfoxide in small amounts, of about 0.35–0.5 mole per mole of uranyl. One-time introduction of DMSO in amounts of 1–3 mole per mole of uranyl leads to the formation of a number of uranyl complexes that are well soluble in acetone, and to a corresponding decrease in the distribution coefficient. The role of entropy and enthalpy in improvement of the stability of chelate complexes of uranyl nitrate is evaluated. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 358–362, May–Jene, 1997.     

Raman spectroscopic study of the uranyl selenite mineral marthozite Cu[(UO2)3(SeO3)2O2]·8H2O

The mineral marthozite, a uranyl selenite, has been characterised by Raman spectroscopy at 298 K. The bands at 812 and 797 cm⁻¹ were assigned to the symmetric stretching modes of the (UO₂)²⁺ and (SeO₃)²⁻ units, respectively. These values gave the calculated U O bond lengths in uranyl of 1.799 and/or 1.814 Å. Average U O bond length in uranyl is 1.795 Å, inferred from the X‐ray single crystal structure analysis of marthozite by Cooper and Hawthorne. The broad band at 869 cm⁻¹ was assigned to the ν₃ antisymmetric stretching mode of the (UO₂)²⁺ (calculated U O bond length 1.808 Å). The band at 739 cm⁻¹ was attributed to the ν₃ antisymmetric stretching vibration of the (SeO₃)²⁻ units. The ν₄ and the ν₂ vibrational modes of the (SeO₃)²⁻ units were observed at 424 and 473 cm⁻¹. Bands observed at 257, and 199 and 139 cm⁻¹ were assigned to OUO bending vibrations and lattice vibrations, respectively. O H···O hydrogen bond lengths were inferred using Libowiztky's empirical relation. The infrared spectrum of marthozite was studied for complementation. Copyright © 2008 John Wiley & Sons, Ltd.     

Photophysical studies of uranyl complexes 5. Luminescence spectrum of K4UO2(CO3)3

The photoluminescence of K₄UO₂(CO₃)₃ has been studied under conditions of high resolution at cryogenic temperatures. The origin corresponding to the pure electronic transition was located at 4774 Å (20945 cm^-1), and it was found that the totally symmetric uranyl stretching mode was coupled to this transition. A progression of four band systems thus resulted, and from an examination of the energies of corresponding peaks in each system, a value of 813 cm^-1 for the U-O stretching mode was determined. Two lattice modes (34 and 80 cm^-1) and two molecular vibrational modes (205 and 276 cm^-1) were also found to couple with the pure electronic transition, thus yielding approximately 15 major peaks in each band system. The 205 cm^-1 vibration corresponded to a CO^2-₃ vibration, while the 276 cm^-1 vibration was a UO²⁺₂ deformation. The low values obtained for the force constant and totally symmetric stretching frequency of the U-O bond suggested that in UO₂(CO)^4-₃, the uranium atom is bound in a complex species that may be considered as an intermediate between that of a uranyl (UO²⁺₂) and a uranate (UO^10-₈) ion.     

A Raman spectroscopic study of the uranyl carbonate rutherfordine

The molecular structure of the uranyl mineral rutherfordine has been investigated by the measurement of its Raman spectra at 298 and 77 K and complemented with infrared spectra. The infrared spectra of the (CO₃)²⁻ units in the anti‐symmetric stretching region show complexity with three sets of carbonate bands observed. This, combined with the observation of multiple bands in the (CO₃)²⁻ bending region in both Raman and IR spectra, suggests that both monodentate and bidentate (CO₃)²⁻ units are present in the structure in accordance with the X‐ray crystallographic studies. Complexity is also observed in the IR spectra of (UO₂)²⁺ anti‐symmetric stretching region and is attributed to non‐identical UO bonds. Both Raman and infrared spectra of the rutherfordine show the presence of both water and hydroxyl units in the structure, as evidenced by IR bands at 3562 and 3465 cm⁻¹ (OH) and 3343, 3185 and 2980 cm⁻¹ (H₂O). Raman spectra show the presence of four sharp bands at 3511, 3460, 3329 and 3151 cm⁻¹. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman and infrared spectroscopic study of the molybdate‐containing uranyl mineral calcurmolite

Raman and infrared spectra of calcurmolite were recorded and interpreted from the uranium and molybdenum polyhedra, water molecules and hydroxyls point of view. U O bond lengths in uranyl and Mo O bond lengths in MoO₆ octahedra were calculated and O H…O bond lengths were inferred from the spectra. The mineral calcurmolite is characterised by bands assigned to the vibrations of the UO₂ units. These units provide intense Raman bands at 930, 900 and 868 and 823 cm⁻¹. These bands are attributed to the anti‐symmetric and symmetric stretching modes of the UO₂ units, respectively. Raman bands at 794, 700, 644, 378 and 354 cm⁻¹ are attributed to vibrations of the MoO₄ units. The bands at 693 and 668 cm⁻¹ are assigned to the anti‐symmetric and symmetric A_g modes of the terminal MO₂ units. Similar bands are observed at 797 and 773 cm⁻¹ for koechlinite and 798 and 775 cm⁻¹ for lindgrenite. It is probable that some of the bands in the low wavenumber region are attributable to the bending modes of MO₂ units. Copyright © 2008 John Wiley & Sons, Ltd.     

Micro-Raman spectroscopy in polycrystalline CuInSe2 formation

The crystalline formation of CuInSe₂ thin films has been investigated using micro-Raman spectroscopy and AES composition analysis. It is confirmed that the Raman peaks are stongly dependent on the surface morphology and the Cu:In:Se ratio. In the films annealed at 315°C, crystalline grains larger than 2 m show Raman peaks at 174 cm^–1 and 258 cm^–1. The In content is very low and the Cu:Se ratio is about 1:1 in these grains. The low In concentration is thought to be due to the formation of In₂O₃ on the surface. On the other hand, random structures of 1–2 m grains found in films annealed at temperatures below 305°C show peaks at 174 cm^–1 and 186 cm^–1 instead of 258 cm^–1 and have a Cu:In:Se ratio of 1:1:3–4. Thus the 186 cm^–1 peak is thought to be related to a Cu, In-deficient phase when compared to stoichiometric CuInSe₂. The optimum annealing condition was found by analyzing the Raman spectra and composition of different crystalline CuInSe₂ grains. Films annealed under this condition exhibited a clear Raman peak at 174 cm^–1 and consisted of clusters of crystals less than 1 m in size.     

Raman spectroscopic study of the uranyl tellurite mineral moctezumite PbUO2(TeO3)2

The uranyl tellurite mineral moctezumite, Pb(UO₂)(TeO₃)₂, was studied by Raman spectroscopy and complemented with infrared spectroscopy. The presence of the stretching and bending vibrations of uranyl (UO₂)²⁺ and tellurite (TeO₃)²⁻ ions was inferred, and the observed bands were assigned to uranyl and tellurite units vibrations. U O bond lengths calculated from the spectra with two empirical relations are close to those inferred from the X‐ray single‐crystal structure of moctezumite. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Raman and infrared spectra of the uranyl mineral zellerite, Ca[(UO₂)(CO₃)₂(H₂O)₂]·3H₂O, were measured and tentatively interpreted. U O bond in uranyl and O H···O hydrogen bonds were calculated from the vibrational spectra. The presence of structurally nonequivalent water molecules in the crystal structure of zellerite was inferred. A proposed chemical formula of zellerite is supported. Raman bands at 3514, 3375 and 2945 cm⁻¹and broad infrared bands at 3513, 3396 and 3326 cm⁻¹ are related to the ν OH stretching vibrations of hydrogen‐bonded water molecules. Observed wavenumbers of these vibrations prove that in fact hydrogen bonds participate in the crystal structure of zellerite. The presence of two bands at 1618 and 1681 cm⁻¹ proves structurally distinct and nonequivalent water molecules in the crystal structure of zellerite. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectroscopic studies of uranyl-acetonitrate complex formation in solutions

In the present work uranyl-acetonitrile complex formation is studied on the basis of analysis of vibrational (IR absorption and Raman) spectra of UO₂(NO₃)₂·6H₂O and UO₂(ClO₄)₂·7H₂O. From the present results and coordination critera for nitrate groups and acetonitrile, it is concluded that in the UO₂ (NO₃)₂·6H₂O-acetonitrile system, acetonitrile molecules are in the second coordination sphere of the uranyl ion. In a benzene solution of uranylperchlorate with added acetonitrile, acetonitryl is substituted for a water molecule in the first coordination sphere of the uranyl ion. In the coordination the vibration frequency of C≡H of acetonitrile (2240 cm⁻¹) is shifted by 21 cm⁻¹ to the shortwave region. Possible reasons for the relatively small change in this frequency are discussed. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 179–183, March–April, 1997.     

Matrix reactions of alkaline earth metal atoms with ozone : Infrared spectra of the metal ozonide and metal oxide molecules

The 15°K deposition of alkaline earth metal atoms and ozone molecules at high dilution in argon yielded intense bands near 800 cm⁻¹ and in the region, 450–650 cm⁻¹. The bands near 800 cm⁻¹ showed the appropriate oxygen isotopic shifts for assignment to ν₃ of the ozonide ion; the use of scrambled isotopic ozones indicated that the metal cation is symmetrically bound to the ozonide anion which contains three oxygen atoms with two equivalent oxygens. For the case of Ca and Ba atoms and ozone, infrared absorptions appeared between 450–650 cm⁻¹ which showed appropriate oxygen isotopic shifts for vibrational assignment to several metal oxide species. In the calcium experiments, bands at 635.7 and 575.5 cm⁻¹ which showed diatomic oxygen-18 isotopic shifts were tentatively identified as (CaO)₂ species; a pair of bands at 593.0 and 592.2 cm⁻¹ were tentatively assigned to CaO₂. For the barium reactions, bands at 634.7, 571.3, and 460.0 showed appropriate oxygen-18 frequency shifts for assignment to BaO, BaO₂, and (BaO)₂, respectively. The BaO assignment was confirmed by the N₂O-nitrogen matrix reaction which yielded a nitrogen matrix counterpart for BaO at 612.4 cm⁻¹.     

Luminescent properties of erbium-activated glasses

The spectra, intensity, and duration of trivalent erbium luminescence in a large number of inorganic glasses of various compositions were investigated. The observed absorption and luminescence bands were attributed to transitions between certain^sL_j levels of the Er³⁺ ion. It is shown that in all cases the principal portion of the luminescence yield was associated with the⁴I_13/2 ⁴I_15/2 transition band with _max = 6500 cm^–1. The effects of glass composition, activator concentration, and temperature on the yield and duration of luminescence in the 6500 cm^–1 band were studied. An investigation of the effect of temperature on the structure of this band was used to construct a diagram of the crystalline splitting of the⁴I_13/2 and⁴I_15/2 levels in glass.     

Visible spectra and flourescence decay rates of a crystal and frozen solutions of uranyl nitrate

The absorption and fluorescence spectra of a UO₂(NO₃)₂.6H₂O single crystal at 77 K agree with those reported previously. Analysis of the absorption spectrum yielded four electronic levels at 20590, 20625, 21474 and 23240 cm^-1. The doublet at 20590 and 20625 cm^?1 converged to form a singlet when the crystal was dissolved in water. This doublet was then interpreted as the result of Davydov splitting. The fluorescence decay rate of the doublet was measured between 77 and 300 K and its small thermal dependence explained by a theoretical model. The fluorescence and excitation spectra of frozen uranyl nitrate solutions at 77 K were recorded, and found to depend on molarity. This dependence was explained by assuming that there were three uranyl-nitrate-water species. The existence of these species is consistent with other measurements.     

Raman scattering and photoluminescence in sodium uranyl acetate polycrystals

A technique of probe photoluminescence and Raman spectroscopy has been developed. This technique makes it possible to detect small (10^?6 to 10^?8 g) amounts of uranyl compounds at short exposure times (1?10 s). The photoluminescence spectra of Na[UO₂CH₃(COO)₃] polycrystals recorded upon excitation by short-wavelength radiation of LEDs and lasers are found to contain equidistant bands with a shift of 854 cm^?1, which corresponds to the frequency of totally symmetric uranyl vibration also manifesting itself in Raman spectra.     

A Raman spectroscopic study of the uranyl mineral rutherfordine—revisited

The molecular structure of the uranyl mineral rutherfordine has been investigated by the measurement of the near‐infrared (NIR) and Raman spectra and complemented with infrared spectra including their interpretation. The spectra of rutherfordine show the presence of both water and hydroxyl units in the structure as evidenced by IR bands at 3562 and 3465 cm⁻¹ (OH) and 3343, 3185 and 2980 cm⁻¹ (H₂O). Raman spectra show the presence of four sharp bands at 3511, 3460, 3329 and 3151 cm⁻¹. Corresponding molecular water bending vibrations were only observed in both Raman and infrared spectra of one of two studied rutherfordine samples. The second rutherfordine sample studied contained only hydroxyl ions in the equatorial uranyl plane and did not contain any molecular water. The infrared spectra of the (CO₃)²⁻ units in the antisymmetric stretching region show complexity with three sets of carbonate bands observed. This combined with the observation of multiple bands in the (CO₃)²⁻ bending region in both the Raman and IR spectra suggests that both monodentate and bidentate (CO₃)²⁻ units may be present in the structure. This cannot be exactly proved and inferred from the spectra; however, it is in accordance with the X‐ray crystallographic studies. Complexity is also observed in the IR spectra of (UO₂)²⁺ antisymmetric stretching region and is attributed to non‐identical UO bonds. U O bond lengths were calculated using wavenumbers of the ν₃ and ν₁ (UO₂)²⁺ and compared with data from X‐ray single crystal structure analysis of rutherfordine. Existence of solid solution having a general formula (UO₂)(CO₃)_1−x(OH)_2x.yH₂O (x, y ≥ 0) is supported in the crystal structure of rutherfordine samples studied. Copyright © 2009 John Wiley & Sons, Ltd.     

Laser-fluorescence diagnostics for condensation in laser-ablated copper plasmas

We are investigating the thermodynamic conditions under which condensation occurs in laser ablated copper plasma plumes. The plasma is created by XeCl excimer laser ablation (308 nm, 300 mJ/pulse) at power densities from 500–1000 MW/cm² into backing pressures of helium in the range 0–50 torr. We use laser-induced fluorescence (LIF) to probe velocity and relative density of both atomic copper and the copper dimer molecule, Cu₂, which is formed during condensation onset. At low pressure (10 mtorr), the atomic Cu velocity peaks at approximately 2×10⁶ cm/s. Copper dimer time-of-flight data suggest that condensation onset occurs after the Cu atoms have slowed very significantly. Excitation scans of the Cu₂A-X (0,0) and (1,1) bands yield a rotational and vibrational temperature in the neighborhood of 300 K for all conditions studied. Such low temperatures support the theory that Cu₂ is formed under thermally and translationally cold conditions. Direct laser beam absorption is used to determine the number density of atomic copper. Typical densities attained with 5 torr of helium backing gas are 6–8×10¹³ cm^–3. Rayleigh scattering from particulate is easily observable under conditions favorable to particulate production.     

Raman spectroscopic study of the uranyl titanate mineral euxenite (Y,Ca,U,Ce,Th) (Nb,Ta,Ti)2O6

Raman spectra of the uranyl titanate mineral euxenite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The observed bands are attributed to the Ti O and (UO₂)²⁺ stretching and bending vibrations, as well as lattice vibrations of rare‐earth ions. The Raman bands of euxenite are in harmony with those of the uranyl oxyhydroxides. The mineral euxenite is metamict as is evidenced by the intensity of the U O stretching and bending modes, which are of lower intensity than expected, and with bands that are significantly broader. Copyright © 2010 John Wiley & Sons, Ltd.