Satendra Kumar

Fluorescence and co-fluorescence of Tb3+ and Eu3+ in acetonitrile using 2,6-pyridine dicarboxylic acid as ligand

Fluorescence from Tb(3+) and Eu(3+) complexed with 2,6-pyridine dicarboxylic acid (PDA) has been studied using acetonitrile (MeCN) as solvent. The enhancement in fluorescence intensity because of non-aqueous environment provided by the MeCN is less significant, where as fluorescence enhancement of more than two orders of magnitude has been observed with the addition of La(3+); a process known as co-fluorescence in MeCN. The present study demonstrates for the first time co-fluorescence of Tb(3+) and Eu(3+) with excitation through the absorption of PDA. Intermolecular energy transfer is believed to be responsible for co-fluorescence enhancement and it becomes possible as the quenching due to water at the secondary coordination spheres of Tb(3+) and Eu(3+) is reduced when MeCN is used as solvent.

Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: a new luminescent uranyl benzoate specie.

Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV-Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3](-) which is highly luminescent. In particular, three sharp bands at 431, 443, 461nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68μs which is much more compared to the lifetime of uncomplexed uranyl (20μs) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3](-) specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed.

Luminescence of uranyl ion complexed with 2,6-pyridine dicarboxylic acid as ligand in acetonitrile medium: observation of co-luminescence

Abstract Luminescence from UO22+ (uranyl ion) complexed with 2,6-pyridine dicarboxylic acid (PDA) has been studied using acetonitrile (MeCN) as solvent between pH 1.0 and 6.0. The enhancement in luminescence intensity because of sensitization by PDA in the non-aqueous environment provided by the MeCN is found to be one order better than in aqueous medium. The luminescence is further enhanced by about four times following the addition of Y3+; a process known as co-luminescence. This is the first study on co-luminescence of uranyl ion in its PDA complex. Lifetime studies indicate the presence of two species having different micro-environments. Formations of both intra and inter molecular complexes are believed to be responsible for enhancement due to co-luminescence.

Feasibility study for quantification of lanthanides in LiF–KCl salt by laser induced breakdown spectroscopy

Quantitative analysis of Pr, Nd, Ce, La and Sm were carried out simultaneously in LiF–KCl matrix using laser induced breakdown spectroscopic technique. Two non-interfering analytical emission lines have been identified for each lanthanide and using the internal standard method, the calibration curve is constructed from 0.3 to 5% for Pr, Nd, Ce and La and from 0.3 to 3% for Sm. Both the emission lines showed good regression coefficient (R2) ranging from 0.9953 to 0.9996. The analytical capability of this method is studied through the correlation uncertainty of measured values with its known value in synthetic samples containing all the lanthanides in equal amount (0.5, 1 and 2%). Low value of correlation uncertainty (less than 10%) confirms that LIBS has a great potential for quantitative analysis of lanthanides in LiF–KCl matrix.

Luminescent versus non-luminescent uranyl–picolinate complexes

Luminescence of uranyl ion (UO22+) complexed with picolinate (PA) has been studied in aqueous and acetonitrile medium. In aqueous medium, for UO22+ to PA ratio of up to 1:20, a 1:1 non-luminescent specie with stability constant of log β = 3.88 was formed. On the contrary, formed specie in acetonitrile medium was luminescent and the enhanced luminescence was due to sensitization by PA and reduction in non-radiative decay channels. UV–Vis absorption spectroscopy studies revealed that the luminescent specie was 1:2 type complex. Density functional theory and DLPNO-CCSD(T) methodologies were applied to arrive at the lowest-energy structures of the 1:1 and 1:2 uranyl–picolinate complexes.

Estimation of Eu3+ in bulk uranium by ligand sensitized fluorescence in dimethyl sulphoxide

Ligand sensitized fluorescence of europium ion using thenoyltrifluoroacetone (TTA) as a sensitizing ligand and dimethyl sulphoxide (DMSO) as a solvent is studied for the first time. TTA ligand enhances the fluorescence of Eu(3+) by a factor of 40000 in DMSO. Linearity is obtained for a concentration range of 0.076-7.6ng/mL of Eu(3+) with a detection limit of 7.6pg/mL. The quenching of Eu(3+)-TTA fluorescence by uranium matrix was studied in different solvents and found to be less in DMSO. Consequently, estimation of Eu(3+) in a large excess of uranium becomes a possibility without the need to separate uranium from the solution, which has been demonstrated in this paper. Satisfactory results are obtained when Eu(3+) is present at a concentration of 0.6μg/g in uranium.