Cofluorescence of Eu in complexes of aromatic carboxylic acids

The fluorescence of Eu³⁺ in certain Eu³⁺–aromatic acid complexes were enhanced by over two orders of magnitude, by the addition of La³⁺; a process referred to as cofluorescence. Cofluorescence was observed only with certain aromatic acid ligands; trismesic acid, pyromellitic acid and mellitic acid; thereby clearly establishing a correlation between the structure of the ligand and the process of cofluorescence. While cofluorescence has been extensively studied using β-diketones as ligands, our studies demonstrate cofluorescence for the first time in ligands other than β-diketones. Furthermore, the mechanism of cofluorescence in the aromatic acid complexes studied by us appears to be different from that operating in the β-diketones. While intermolecular energy transfer is believed to occur in the β-diketones, formation of polynuclear complexes appears to be responsible for cofluorescence in the aromatic acid ligands.     

Fluorimetric estimation of DNA content using sensitized lanthanide fluorescence

Lanthanide fluorescence enhancement on complexation with calf thymus DNA was studied in aqueous solution. The DNA sensitized and enhanced fluorescence of terbium and europium by nearly two orders of magnitude. By applying this ligand sensitized lanthanide fluorescence enhancement, DNA could be estimated at 10 ppb level. Further, effect of addition of TOPO in Triton X-100 micellar medium to Tb-DNA complex in solution was also studied. On addition of TOPO, no synergistic terbium fluorescence enhancement was observed.     

Ferroelectric phase transition of Ba1− x Sr x Ti0.6Zr0.4O3 ceramics

Perovskite type Ba_{1? x} Sr _x Ti_0.6Zr_0.4O₃ (with x = 0.0, 0.1, 0.2, 0.4 and 0.5) ceramics have been synthesized through solid oxide reaction route. The room temperature XRD study suggests the compositions have single phase cubic symmetry. Microstructural studies have shown a step decrease in grain size. The dielectric study reveals that the materials are of relaxor type and undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in Sr contents in the studied composition range. The transition temperature decreases with increase in Sr contents due to the decrease in grain size.     

Ferroelectric studies for soft Gd-modified PZT ceramics

The polycrystalline samples of gadolinium-modified lead–zirconate–titanate (Pb_1?xGd_x (Zr_0.52Ti_0.48)_1?x/4O₃) (x?=?0, 0.07, 0.10 and 0.12) (PGZT x/52/48) ceramics near morphotropic-phase boundary were prepared using conventional solid-state reaction route. XRD patterns show the formation of single-phase compounds in rhombohedral crystal system. SEM textures of the samples reveal uniform grain distribution. Frequency and temperature dependence of dielectric constant of the materials indicates non-relaxor behavior and indication of the diffuse phase transition at higher values of Gd concentration. The temperature dependence of P–E loops confirms ferroelectricity in the materials. The piezoelectric studies of the samples show enhancement in piezoelectric coefficients on substitution of Gd at the Pb site.     

Dielectric properties of Ba3Sr2DyTi3V7O30 ceramics

A polycrystalline sample, Ba₃Sr₂DyTi₃V₇O₃₀, with tungsten bronze structure was prepared by a mixed-oxide method at high temperature (950°C). Preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound was studied by scanning electron microscopy. The dielectric anomaly at 321°C may be attributed to the ferro-paraelectric phase transitions. This was also confirmed from the appearance of a hysteresis loop. The nature of variation of the ac conductivity and value of activation energy at different temperature regions, suggest that the conduction process is of mixed-type (i.e., ionic-polaronic and space charge generated from the oxygen ion vacancies).     

A confocal laser scanning microscopic study on thermoresponsive binary microgel dispersions incorporated with CdTe quantum dots

Monodisperse poly(N-isopropylacrylamide) (PNIPAM) particles loaded with cadmium telluride (CdTe) quantum dots (QDs) of two different sizes (4.7 nm and 5.6 nm) were synthesized in aqueous medium by bonding the capping agent on the quantum dots to the amide groups of PNIPAM and incubating the samples at 45°C. A huge increase in the photoluminescence (PL) intensity (green and red regions) is observed for the PNIPAM-CdTe QDs composites compared to the parent CdTe QDs. We report here for the first time the imaging of binary dispersion of green and red luminescent PNIPAM-CdTe QDs composites using a fluorescence confocal laser scanning microscope. These composites have potential applications both in material science and biology.     

Layer-by-layer deposition of bimetallic nanoshells on functionalized polystyrene beads

Bimetallic nanoshells on functionalized polystyrene beads have been fabricated through a layer-by-layer deposition technique exploiting electrostatic interaction. The synthesis has been achieved through the immobilization and successive reduction of the corresponding precursor ions. It has been shown that the thickness of the shell can be controlled by a number of cyclic depositions of respective metals onto the surface of the polystyrene beads.     

Spectral radius of power graphs on certain finite groups

The power graph of a group $G$ is a graph with vertex set $G$ and two distinct vertices are adjacent if and only if one is an integral power of the other. In this paper we find both upper and lower bounds for the spectral radius of power graph of cyclic group $C_n$ and characterize the graphs for which these bounds are extremal. Further we compute spectra of power graphs of dihedral group $D_{2n}$ and dicyclic group $Q_{4n}$ partially and give bounds for the spectral radii of these graphs.