-
[show abstract]
[hide abstract]
ABSTRACT: Detailed luminescence studies on Eu3+ doped SrSnO3 nano-rods having body centered tetragonal structure,
confirmed that up to 1.5 at% Eu3+ ions occupy Sr2+ site in the lattice and is having a less polarisable
environment. Experimentally obtained Judd–Ofelt parameters (X2 and X4 values) can be effectively used
to monitor the extent of incorporation of Eu3+ ions at Sr2+ site. Based on Rietveld refinement of diffraction
patterns and Sr K-edge EXAFS studies, it is inferred that average Sr–O and Sn–O bond lengths in SrO12 and
SnO6 polyhedra increase with incorporation of relatively smaller Eu3+ at Sr2+ site in SrSnO3 lattice.
Chemical Physics Letters 01/2013; 561-562:82. · 2.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The present study describes the structural and luminescent properties of SrSnO(3) nanorods containing Eu(3+) ions. Based on Rietveld refinement of XRD patterns corresponding to both undoped and europium doped SrSnO(3) nanorods, it is inferred that the average bond lengths of Sr-O1 linkages, which have a square planar geometry around Sr(2+) in the SrO(12) polyhedra present in SrSnO(3), remained unaffected with Eu(3+) incorporation into the lattice. However, the average bond lengths of shorter Sr-O2 linkages increase and longer Sr-O2 linkages decrease with Eu(3+) doping into the SrSnO(3) lattice. A lack of variation in the lattice parameters of SrSnO(3) with doped Eu(3+) ions is explained based on mutually compensating changes in the average bond lengths of the Sr-O2 linkages in the unit cell. Luminescence studies have confirmed that Eu(3+) ions occupy the centrosymmetric Sr(2+) site only up to 2 at%, beyond which Eu(3+) ions exist in a significantly distorted environment (grain boundaries). Beyond 3%, incorporation of Eu(3+) ions into the SrSnO(3) lattice leads to the formation of a Eu(2)Sn(2)O(7) phase. From the EPR studies it is confirmed that around 5% of the incorporated Eu(3+) ions get converted to Eu(2+) ions and they occupy Sr(2+) sites in the lattice.
Dalton Transactions 08/2012; 41(39):12023-30. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Thylakoids in Synechocystis 6803, though apparently uniform in appearance in ultrastructure, were found to consist of segments which were functionally dissimilar and had distinct proteomes. These thylakoid segments can be isolated from Synechocystis 6803 by successive ultracentrifugation of cell free extracts at 40,000×g (40 k segments), 90,000×g (90 k segments) and 150,000×g (150 k segments). Electron microscopy showed differences in their appearance. 40 k segments looked feathery and fluffy, whereas the 90 k and 150 k thylakoid membrane segments appeared tiny and less fluffy. The absorption spectra showed heterogeneous distribution of pigment-protein complexes in the three types of segments. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) showed unequal distributions in 40 k, 90 k and 150 k segments which were substantiated with low temperature fluorescence measurements. The ratio of PSII/PSI fluorescence emission at 77 K (λ(ex) = 435 nm) was highest in 150 k segments indicating higher PSII per unit PSI in these segments. The chlorophyll fluorescence lifetimes in the membranes, determined with a time-correlated single-photon counting technique, could be resolved in three components: τ(1) (=) <40 ps, τ(2) (=) 425-900 ps and τ(3) (=) 2.4-3.2 ns. The percentage contribution of the fastest component (τ(1)) decreased in the order 40 k > 90 k > 150 k segments whereas that of the other two components showed a reversed trend. These studies indicated differential distribution of pigment-protein complexes in the three membrane segments suggesting heterogeneity in the thylakoids of Synechocystis 6803.
Journal of Bioenergetics 05/2012; 44(4):399-409. · 2.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Layered structure of highly crystalline orthorhombic GaOOH nanorods undergo significant lattice distortions
leading to amorphisation even when very small amounts of Eu3+ ions (1 at.% or more) are present
during its synthesis. Local short range order around Ga3+ is unaffected by the structural collapse, even
though the lattice disorder increases with increase in Eu3+ content in the lattice, as confirmed from the
EXAFS studies. Incorporation of Eu3+ ions at the interlayer spacing of GaOOH lattice and its reaction with
structure stabilizing OH linkages in the lattice is responsible for the collapse of the structure leading to
amorphisation.
Chemical Physics Letters 01/2012; 528:21. · 2.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Boroaluminosilicate glass having a specific composition could be successfully used for the selective uptake of thorium from a mixture containing uranium by controlling the solution pH only. Single ion uptake studies showed that the uptake of uranium and thorium was maximum at pH of 4.5 and 7.5, respectively. But uptake studies using mixtures with uranium and thorium showed that irrespective of the pH, the uptake of thorium was higher than that of uranium.
Journal of hazardous materials 10/2011; 198:159-64. · 4.14 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Rare-earth-doped gadolinium fluoride nanocrystals were synthesized by a single step synthesis employing ethylene glycol as solvent. Based on X-ray diffraction studies, stabilization of hexagonal modification of GdF(3) has been inferred. The microscopic studies show formation of uniformly distributed nanocrystals (~15 nm). The nanoparticles are readily dispersible in water and show bright luminescence in colloidal solution. The luminescence properties have been investigated as a function of activator concentrations, and enhanced optical properties have been attributed to efficient energy transfer from the Gd(3+) to the activator RE(3+) ions, which has further been confirmed by steady-state and time-resolved optical studies. It has been demonstrated that on doping appropriate amount of activators in host GdF(3), a novel white-light-emitting phosphor is obtained with CIE co-ordinates and correlated color temperature (CCT) very close to broad daylight. This can have promising applications as phosphor for white-light ultraviolet-light-emitting diodes (UV-LEDs). Our experiments showed efficient labeling of human breast carcinoma cells (MCF-7) by Tb(3+)-doped GdF(3) nanoparticles. The fluorescence intensity was found to be dependent on the surface modifying/coating agent, and the results were validated using confocal microscopy in terms of localization of these functionalized nanoparticles.
Journal of Colloid and Interface Science 10/2011; 367(1):161-70. · 3.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A facile supramolecular approach to prepare surface functionalized silver nanoparticle conjugates has been established and their enhanced molecular recognition features have been explored to demonstrate the uptake and stimulus responsive release of a phototherapeutic porphyrin dye, the TMPyP.
Chemical Communications 08/2011; 47(32):9182-4. · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: GaPO4 nanoparticles having hexagonal structure with different amounts of Eu31 ions were prepared at 130°C based on precipitation method in glycerol medium. The interaction between GaPO4 nanoparticles and Eu3+ ions has been investigated using Eu3+ luminescence and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. Based on these studies, it is established that Eu3+ ions up to 2.5 at.% replace the protons of the hydroxyl groups attached on Ga3+ ions present on the surface of the nanoparticles and above 2.5 at.%, a separate EuPO4 phase is formed. The anisotropy parameters derived from the side band intensities of the 31P MAS NMR patterns from these samples confirmed the surface ion exchange at low Eu3+ concentration (2.5 at.%) and EuPO4 phase formation at high Eu3+ concentration (5 at.% and more). The increase in anisotropy at high Eu3+ contents has been attributed to the presence of paramagnetic EuPO4 phase.
Journal of the American Ceramic Society. 01/2011;
-
Acta Physica Polonica A. 01/2011; 119(2):95-98.
-
[show abstract]
[hide abstract]
ABSTRACT: A series of doped CeF(3): RE(3+) (RE(3+): Tb(3+), Eu(3+) and Dy(3+)) nanoparticles were synthesized, with the aim of obtaining a white light emitting composition, by a simple polyol route at 160°C and characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. Uniformly distributed and highly water-dispersible rectangular nanoparticles (length ~15-20 nm, breadth ~5-10 nm) were obtained. The steady state and time resolved luminescence studies confirmed efficient energy transfer from the host to activator ions. Lifetime studies revealed that optimum luminescence is observed for 2.5 mol% Dy(3+) and 7.5 mol% Tb(3+). The energy transfer efficiencies (Ce(3+) to activators) were found to be 89% for CeF(3): Tb(3+) (7.5 mol%) nanoparticles and 60% for CeF(3): Dy(3+) (2.5 mol%) nanoparticles. Different concentrations of Tb(3+), Eu(3+) and Dy(3+) were doped to achieve a white light emitting phosphor for UV-based LEDs (light emitting diodes). Finally CeF(3), triply doped with 2.0 mol%Tb(3+), 4.5 mol% Eu(3+) and 3.5 mol% Dy(3+), was found to have impressive chromaticity co-ordinates, close to broad day light. The colloidal solutions of doped CeF(3) nanoparticles emitted bright green (Tb(3+)), blue (Dy(3+)) and white (triply doped) luminescence upon host excitation. Composites of poly methyl methacrylate (PMMA) and poly vinyl alcohol (PVA) were made with CeF(3): 5.0 mol%Tb(3+), CeF(3): 5.0 mol% Dy(3+) and triply doped white light emitting composition. The CeF(3)/PMMA (PVA) nanocomposite films, so obtained, are highly transparent (in the visible spectral range) and exhibit strong photoluminescence upon UV excitation.
Journal of Colloid and Interface Science 10/2010; 353(2):445-53. · 3.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report morphological and ferromagnetic property control in ZnO nanorod structures by an optimum doping of Ni and Li. Nanostructures of Zn0.97-xNi0.03LixO (x = 0, 0.03, 0.05, 0.08, and 0.10) are prepared by a solvothermal method. High aspect ratio (5−15) ZnO nanorods transform to particles (with 1−3 aspect ratio) influenced by 3 at. % Ni substitution in ZnO (Zn0.97Ni0.03O). It is remarkable to note that the Zn0.97Ni0.03O particles completely retain the nanorod shape with significantly increased aspect ratio (15−30) when 3 at.% Li ions are codoped in Zn0.97Ni0.03O (Zn0.94Li0.03Ni0.03O). Li substitution also enhances ferromagnetism with largest magnetization (0.8 emu·g−1) observed for Zn0.94Li0.03Ni0.03O. For Li concentration >3 at.%, the aspect ratio as well as the magnetization decreased considerably. These experimental observations are explained by first-principles modeling. At low Li-on-Zn acceptor concentrations, the total magnetization is increased by lower Ni d-state populations, whereas at higher Li concentrations the population of ZnO host states decreases the ferromagnetism by induced magnetic moments on the oxygens. We discuss the significant implications of these results on the nanorods structures of room temperature ferromagnetic materials, which are expected to play pivotal role in developing spintronic devices.
09/2010;
-
Journal of Physical Chemistry C. 01/2010; 114(41):17428-17433.
-
Scripta Materialia. 01/2010; 62(9):662-665.
-
[show abstract]
[hide abstract]
ABSTRACT: Germanium tetra(tertiary butoxide), [Ge(OtBu)4], has been prepared by the reaction of GeCl4 with KOBut in benzene. It is a monomeric crystalline solid having a distorted etrahedral configuration, defined by the coordination of four OBut groups around germanium atom. The TG analysis showed that the compound is thermally stable and volatilizes at around 130 �C. Europium doped and un-doped germanium oxide nanoparticles
were prepared based on the urea hydrolysis of Ge(OtBu)4/Eu(OOCCH3)3 in ethylene glycol medium at 150 �C followed by heating the resulting product at 750 �C. The nanoparticles were characterized by XRD, TEM and PL measurements. The europium doped nanoparticles, which were nearly monodispersed
(�30 nm), showed luminescence and the Eu3+ ions were occupying the surface of the GeO2
nanoparticles.
Inorganica Chimica Acta 01/2010; 363:3680–3684. · 1.85 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 1D nanostructures of Zn1−xCoxO (x = 0, 0.03 and 0.05) and Co and Li codoped ZnO (Zn0.85Li0.10Co0.05O) were prepared by a soft chemical method. We report a very interesting observation of morphological control and transformation of ZnO nanorods to spherical particles induced by Co substitution. It is also remarkable to note that the morphology completely reverts back to rod shape by Li incorporation. In addition to this unusual observation, the Li incorporation enhances the room-temperature ferromagnetic (RTFM) properties. These experimental observations are well-supported by theory work as well. These results are significant, as the 1D RTFM will have implications in spintronic devices.
10/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: Barium borosilicate (BBS) and sodium borosilicate (SBS) glass samples, prepared by the conventional melt-quench method, were used for the uptake of Rhodamine 6G dye from aqueous solution. The experimental conditions were optimized to get maximum uptake and was found to be 0.4 mg of dye per gram of BBS glass sample. For the same network former to modifier ratio, barium borosilicate glasses are found to have improved extent of uptake for the dye molecules from aqueous solutions compared to sodium borosilicate glasses. Based on 29Si MAS NMR studies on these glasses, it is inferred that significantly higher number of non-bridging oxygen atoms present in barium borosilicate glasses compared to sodium borosilicate glasses is responsible for its improved uptake of Rhodamine 6G dye. 11B MAS NMR studies have confirmed the simultaneous existence of boron in BO3 and BO4 configurations in both barium borosilicate and sodium borosilicate glasses. The luminescence studies have established that the dye molecule is incorporated into the glass matrix through ion exchange mechanism by replacing the exchangeable ions like Na+/Ba2+ attached with the non-bridging oxygen atoms present in the glass.
Journal of hazardous materials 08/2009; 172(1):457-64. · 4.14 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Highly crystalline orthorhombic Sb2O3 nano-rods were prepared at room temperature by hydrolysis of SbCl3 in iso-propanol. Morphology induced changes in the photoluminescence properties of both the, as prepared as well as the annealed ones (at different temperatures) are presented. A distinct photoluminescence-
band observed over the region of 500–600 nm is arising due to the morphology of Sb2O3 nanorods. Changes in the Raman spectrum at �260 and 445 cm�1, corresponding to the Sb3+–O–Sb3+ stretching and bending modes, further confirm their shape selective nature. This study reveals significant effect of morphology on the structural and luminescent properties of Sb2O3.
Chemical Physics Letters. 01/2009; 474:180–184.
-
[show abstract]
[hide abstract]
ABSTRACT: Nanoparticles of GdVO <sub>4</sub> doped with Eu <sup>3+</sup> and core/shell of GdVO <sub>4</sub>: Eu <sup>3+</sup>/ GdVO <sub>4</sub> are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130 ° C . Unit cell volume increases when GdVO <sub>4</sub> is doped with Eu <sup>3+</sup> indicating the substitution of Gd <sup>3+</sup> lattice sites by Eu <sup>3+</sup> . From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu <sup>3+</sup> . Optimum luminescence intensity is found to be in 5–10 at . % Eu <sup>3+</sup> . Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu <sup>3+</sup> surroundings by bonding to GdVO <sub>4</sub> shell. The lifetime for <sup>5</sup>D<sub>0</sub> level increases with annealing and core/shell formation.
Journal of Applied Physics 12/2008; · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: ZnGa2O4 nanoparticles doped with lanthanide ions (Tb3+ and Eu3+) were prepared at a low temperature of 120 degrees C based on urea hydrolysis in ethylene glycol medium. X-ray diffraction studies have confirmed that strain associated with nanoparticles changes as Tb3+ gets incorporated in the ZnGa2O4 lattice. Based on steady state emission and excitation studies of ZnGa2O4:Tb nanoparticles, it has been inferred that ZnGa2O4 host is characterized by a broad emission around 427 nm and there exists energy transfer between the host and Tb3+ ions. Unlike this, for ZnGa2O4:Eu nanoparticles, very poor energy transfer between the host and Eu3+ ions is observed. These nanoparticles when coated with ligands like oleic acid results in their improved dispersion in organic solvents like chloroform and dichloromethane.
Journal of Nanoscience and Nanotechnology 12/2008; 8(11):5776-80. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: ZnGa2O4 nanoparticles doped with lanthanide ions (Tb3+ and Eu3+) were prepared at a low temperature of 120 °C based on urea hydrolysis in ethylene glycol medium. X-ray diffraction studies have confirmed that strain associated with nanoparticles changes as Tb3+ gets incorporated in the ZnGa2O4 lattice. Based on steady state emission and excitation studies of ZnGa2O4:Tb nanoparticles, it has been inferred that ZnGa2O4 host is characterized by a broad emission around 427 nm and there exists energy transfer between the host and Tb3+ ions. Unlike this, for ZnGa2O4:Eu nanoparticles, very poor energy transfer between the host and Eu3+ ions is observed. These nanoparticles when coated with ligands like oleic acid results in their improved dispersion in organic solvents like chloroform and dichloromethane.
Journal of Nanoscience and Nanotechnology 10/2008; 8(11):5776-5780. · 1.56 Impact Factor
