S.V. Godbole

Extraction of Am(III) using novel solvent systems containing a tripodal diglycolamide ligand in room temperature ionic liquids: a 'green' approach for radioactive waste processing

Extraction of Am3+ from acidic feed solutions was investigated using novel solvent systems containing a tripodal diglycolamide (T-DGA) in three room temperature ionic liquids (RTIL), viz. [C4mim][NTf2], [C6mim][NTf2] and [C8mim][NTf2]. Compared to the results obtained with N,N,N′,N′-tetra-n-octyl diglycolamide (TODGA), T-DGA gave significantly higher distribution coefficients in these RTILs. The DAm values decreased with increasing carbon chain length in the RTILs, which was related to the solubility of the RTIL in the aqueous phase. The distribution studies included the effect of equilibration time, aqueous phase acid concentration variation and T-DGA concentration variation. In general, significantly higher equilibration times were observed for the extraction systems, which was partly due to the viscous RTIL phase and partly due to the slow conformational changes of the T-DGA ligand during complexation. Apart from Am3+, extraction of Pu4+, UO22+, Eu3+, Sr2+ and Cs+ was also investigated, since they have significant implications in radioactive waste processing. Stripping studies indicated >99% stripping in three stages using 0.5 M EDTA or DTPA in 1 M guanidine carbonate. Slope analysis indicated the extraction of 1 : 1 complexed species of Am(III) with T-DGA. Time resolved laser fluorescence spectroscopy (TRLFS) studies showed a strong complexation with no inner-sphere water molecules in the Eu(III)–T-DGA complexes for [C4mim][NTf2] as the diluent. Radiolytic degradation studies of the solvent systems containing T-DGA in the three RTILs were also carried out and while the DAm values decreased marginally when the solvents were exposed to 500 kGy absorbed dose, a relatively sharp decrease (60%) was seen when the solvents were exposed further to 1000 kGy absorbed dose, suggesting the possibility of recycling. Extraction studies were also carried out at varying temperatures and the thermodynamic parameters were calculated.

On the unusual photoluminescence of Eu3+ in α-Zn2P2O7: a time resolved emission spectrometric and Judd–Ofelt study

Zn2P2O7:Eu3+ was synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM); Fourier transformed infrared spectroscopy (FTIR) and photoluminescence (PL) techniques. Based on the time resolved emission spectroscopic investigations (TRES), it was inferred that two different types of Eu3+ ions were present in the zinc pyrophosphate. The first type was a long lived species (∼τ = 1.77 ms) present at relatively few symmetric ‘5-coordinated Zn’ sites, while the second was a short lived species (∼τ = 620 μs) present at symmetric ‘6-coordinated Zn’ sites. This unusual behavior of the trivalent rare earth species could be explained with the help of Judd–Ofelt (J–O) calculations. From the calculations, the radiative (τR) and non radiative (τNR) life times were evaluated for both species. It was observed that the radiative life time of the Eu3+ species present in symmetric environment was higher than that of the species present in the asymmetric environment, which is consistent with the selection rules governing the transition. It was observed that the presence of a very strong non-radiative component at the symmetric site brings down the overall lifetime value. The J–O intensity parameters for all the Eu3+ species present in the pyrophosphate system were calculated adopting standard procedure. Ω4 > Ω2 was found that for short lived species; while for the long lived species, the reverse trend was observed further confirming the correlation between the asymmetry and bonding.

Color tunable YF3: Ce3+/Ln3+ (Ln3+: Eu3+, Tb3+, Dy3+, Sm3+) luminescent system: role of sensitizer and energy transfer study

Nano-fluorides with attractive optical properties have been proposed as potential phosphors for solid state lighting and bio-applications. In the present work, redispersible YF3: Ln3+ and YF3: Ce3+/Ln3+ nanocrystals were obtained by a simple one step ethylene glycol mediated soft chemical synthesis. Uniformly distributed nanoparticles with a leaf-like morphology and particle size of 10–15 nm were observed. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FT-IR), photoluminescence (PL) and decay studies were employed to characterize the samples. The highly intense emissions of various activators (Dy3+, Tb3+, Eu3+ and Sm3+) in the presence of Ce3+, their long lifetimes (∼ms) and significant reduction in the lifetime of Ce3+ proved an efficient energy transfer operating in the nanocrystals. The time resolved emission studies indicated towards the presence of two different sites for the activator ions. Under ultraviolet irradiation, the emission color of YF3: Ce3+/Ln3+ nanophosphors can be easily tuned by changing the Ln3+ ions. Bright blue (Dy3+), green (Tb3+), red (Eu3+) and purple (Sm3+) emissions were observed from corresponding YF3: Ce3+, Ln3+ nanocrystals under ultraviolet light.

Electronic spectra and co-operative optical transitions in CaWO4:Tb3+ single crystal

Abstract The absorption, fluorescence and excitation spectra of CaWO4:Tb3+ single crystal were studied at 300 and 77 K. The polarization studies on laser excited fluorescence spectra were also carried out at 77 K. These studies led to the complete identification of two fluorescing states viz. 5D4 and 5D3 and of all the 7F ground multiplets of Tb3+ ions. Co-operative electronic transitions were observed for the first time in the low dopant concentration crystal and inferred as due to multi-polar interactions.

Photoluminescence and thermoluminescence characteristics of KXSO4Cl : Eu (X = Zn or Mg) halosulfate phosphor

Polycrystalline KZnSO4Cl : Eu and KMgSO4Cl : Eu prepared by a wet chemical method have been studied for their thermoluminescence (TL) and photoluminescence (PL) characteristics. The PL emission spectra of the phosphor suggests the presence of Eu2+ and Eu3+ in the host compound occupying two different lattice sites. The TL glow curve of the KZnSO4Cl : Eu compounds has a simple structure with prominent peaks at 200 and 290 °C, while KMgSO4Cl : Eu peaks at 165 and 265 °C. The TL sensitivity of the phosphors is compared with CaSO4 : Dy and is found to be 3.4 and 2.4 times less in KZnSO4Cl : Eu and KMgSO4Cl : Eu phosphors, respectively.

Time resolved fluorescence spectroscopy of Eu(III) complexation with α-hydroxy isobutyric acid

Complexation of Eu(III) with alpha-hydroxy isobutyric acid (HIBA), a model compound of humic acid, has been studied by time resolved fluorescence spectroscopy. The ratio of fluorescence intensity of the two peaks at 616 and 592 nm (I(616/592)) was found to increase with increasing ligand to metal ratio. The I(616/592) data was used to deduce the stability constant of Eu-HIBA complexes of the type ML(i) (i=1-3). The formation of multiple ligand complexes was also corroborated by lifetime data which was found to increase with increasing [HIBA]/[Eu] ratio thus indicating replacement of coordinated water molecules by HIBA.

Spectroscopic investigation on europium complexation with humic acid and its model compounds.

Time resolved fluorescence spectroscopy (TRFS) of Eu(III) (an analogue of trivalent actinides) complexation with humic acid (HA) and its model compounds, namely phthalic acid (PA), mandelic acid (MA) and succinic acid (SA) has been carried out at varying concentration ratios of ligand to metal ion. The emission spectra were recorded in the range of 550-650nm by exciting at an appropriate wavelength. The intensity of the 616nm peak of Eu(III) was found to be sensitive to complexation. The ratio of the intensities of 616 and 592nm peaks was used to determine the stability constants of Eu-phthalate, Eu-mandelate and Eu-succinate complexes. In the case of model compounds, the life-time was found to increase with increasing ligand to metal ratio (L/M) indicating the decrease in quenching of the fluorescence by coordinated water molecules with increasing complexation. On the other hand in the case of HA, the life-time was found to be constant at least up to L/M of 5, indicating the formation of outer sphere complex. Beyond L/M=5 the life-time value was found to increase which can be attributed to the binding of the metal ion to the higher affinity sites in the HA macromolecule.

Complexation of trivalent lanthanides and actinides with several novel diglycolamide-functionalized calix[4]arenes: solvent extraction, luminescence and theoretical studies

Several diglycolamide-functionalized calix[4]arenes (DGA–Calix) were evaluated for actinide extraction from acidic feeds. The ligands with four diglycolamide (DGA) pendent arms are significantly more effective extractants than those with two DGA pendent arms. The ligands have a preference for the extraction of Eu3+, a representative trivalent lanthanide ion, as compared to Am3+, a commonly encountered trivalent actinide ion. The role of organic diluents on the metal ion extraction was investigated and the results were compared with the widely studied DGA-based extractant TODGA (N,N,N′,N′-tetra-n-octyl diglycolamide). Time resolved laser fluorescence spectroscopy (TRLFS) studies showed a strong complexation with no inner-sphere water molecules in the Eu(III)–DGA–Calix complexes and the complex formation constants (log β) were calculated. Ab initio density functional calculations were carried out to explain the higher stability of the Eu-complex of the DGA–Calix ligand with four pendent arms as compared to the one with two pendent arms.

Spectral interference study of uranium on other analytes by using CCD based ICP-AES

Due to the multi-electronic nature, uranium is having line rich emission spectra and is expected to interfere during the determination of analytes at the trace level in uranium matrix. Therefore, chemical separation of uranium followed by the determination of trace metallic impurities in the raffinate by ICP-AES is generally adopted procedure in nuclear industries. There is restriction on choosing alternate analytical lines of elements by photomultiplier tube based ICP-AES associated with the polychromator while monochromator needs significant time to scan different analytical lines of all the elements. Since charged coupled detector (CCD) consists of array of pixels, it is having more option in choosing alternative analytical lines of the analytes. Therefore, an attempt was made to study the spectral interference of uranium on different analytical lines of analytes viz. Al, Ga, In, Si, Li, Ti, Mg, Sr, K, Ce, Nd, Lu, Sc, V, Er, Y, Ba, Bi, Pb, W, La, Tl, Sn, Yb, Mo, Sb, Pr and Zr; and the correction factors were evaluated (where ever necessary) using CCD based ICP-AES technique. The sensitivity and the detection limits of the analytical channels of the elements in presence of uranium matrix were calculated. The present study also deals with the identification of suitable analytical lines of uranium and its detection limits.

UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors

Abstract Ultraviolet radiation induced changes in photoluminescence (PL) and thermally stimulated luminescence (TSL) of europium activated calcium sulphate (CaSO 4 :Eu 3+ , Eu 2+ ) and terbium doped calcium fluoride (CaF 2 :Tb 3+ ) phosphors have been studied. PL measurements suggest conversion of Eu 3+ to Eu 2+ on 254 nm irradiation corresponding to charge transfer band of Eu 3+ ions and reduction of Eu 2+ ions with 365 nm illumination representing a f–d transition of Eu 2+ ions. Similar studies carried out on CaF 2 :Tb 3+ phosphor, however, do not show any significant wavelength specific changes. The integrated TSL output appears to be rate-dependent for both phosphors. The wavelength dependent changes in TSL output observed for CaSO 4 :Eu phosphor have been correlated with those obtained in PL studies. The changes in TSL and PL characteristics of CaF 2 :Tb 3+ phosphor have been explained on the basis of stabilisation of traps based on matrix specific charge similarities.