Sirshendu Ghosh

Enhanced Magnetic and Dielectric properties of Eu and Co co-doped BiFeO3 nanoparticles

Bi1−xEuxFe1−yCoyO3 (x = 0, 0.01; y = 0, 0.01) nanoparticles, having an average size of 13 nm, were prepared by a simple sol gel route. Strong electronegativity of Eu3+ and smaller oxidation-reduction potential of Co3+/Co2+ (0.55 eV) than Fe3+/Fe2+ (1.3 eV) increase the concentration of Fe3+ ions with doping. Distinct magnetic hysteresis and complete saturation of magnetisation indicate the presence of ferromagnetic phase. The successful co-doping of Eu and Co into BiFeO3 (BFO) lattice dramatically enhances the saturation magnetization (Ms) and coercivity (Hc) by about 20 times than that of pure BiFeO3. A large value of dielectric constant of about 650, low loss (<0.001), and small leakage current density (1.79 × 10−8 A/cm2) are observed for the co-doped sample.

Bright white light emitting Eu and Tb co-doped monodisperse In2O3 nanocrystals

Bright light emitting monodisperse In2−(x+y)EuxTbyO3 (x = 0.05, 0.1, 0.15, 0.2 and y = 0.05, 0.1, 0.15) nanocrystals were successfully synthesized by a versatile hot-injection colloidal route. The X-ray diffraction and X-ray photoelectron spectroscopy studies clearly showed that Eu and Tb were incorporated into the In2O3 lattice. Surface adsorbed NO3− and Cl− anions of Eu3+ and Tb3+ precursors assist the formation of flower like morphology through the oriented attachment process. Optical absorption spectra have been interpreted in terms of 4f → 5d (Eu, Tb) and 2p(O) → 5d (Eu, Tb) interband transitions. The observation of characteristic emission peaks related to Eu3+ and Tb3+ by indirect excitation suggests that In2O3 is an efficient sensitizer. Proper tuning of the compositions, 15% of Eu and 10% of Tb, gives the most intense white light and excellent chromaticity co-ordinates (0.35, 0.35). The shortening of lifetime with Eu and Tb doping improves the energy transfer from the host In2O3 to dopant Eu3+ and Tb3+ ions.

Synthetic studies towards complex diterpenoids—VI : New synthetic routes to tetracyclic bridged-bicyclo[3.2.1]octane intermediates by intramolecular alkylation reactions through α-diazomethyl ketones of hydroaromatic γ,δ-unsaturated acids

Abstract Two new synthetic routes to a number of tetracyclic intermediates, for the total synthesis of some diterpenoids incorporating the bicyclo[3.2.1]octane moiety, are described. The syntheses of the bicyclo[3,2,1]octane derivatives begin with preparation of the hydroaromatic γ,δ-unsaturated acids 6, 15 and 17, and proceed via the α-diazomethyl ketones to the corresponding pentacyclic ketones 20, 24 and 26 by an intramolecular carbenoid insertion reaction, followed by a regiospecific acid-catalysed cleavage of the aromatic conjugated cyclopropane bond to the respective unsaturated ketones 27, 29 and 30. The second route to these unsaturated ketones involves a single step boron trifluoride etherate catalysed intramolecular alkylation in the corresponding α-diazomethyl ketones. The tetracyclic ketones 31, 34 and 35 were obtained in quantitative yields by a regiostereospecific hydrogenolytic cleavage of the aromatic conjugated cyclopropane bond in the respective pentacyclic precursors with PdC in ethanol. Under the same conditions, reduction of the styrenoid bond in the ketones 29 and 30 proceeds stereospecifically leading to 34 and 35 respectively, whereas the unsaturated ketone 27 gave a mixture of epimeric ketones 31 and 32 in a ratio of 69:31.

Template free synthesis of SnO2 nanoflower arrays on Sn foil

The well aligned poppy-flower-like SnO2 nanoflower array on Sn-foil was successfully prepared by a simple solvothermal method without using any template or catalyst. The mixed solvent of aqueous sodium hydroxide and hydrazine hydrate plays a significant role for obtaining the crystalline pure SnO2 nanoflower array. Each petal of the nanoflower consists of the (110) plane of SnO2. The growth of the SnO2 nanoflowers has been described by the formation of layered Sn-hydrazine complexes. The surface defects and the oxygen vacancies of the SnO2 hierarchical nanoflowers are identified by Raman and electron paramagnetic resonance (EPR) spectroscopy and are analyzed in detail by steady state and time resolved photoluminescence spectra.

Bias dependent dielectric relaxation dynamics of electrically tuned large-scale aligned zinc oxide nanorods in nematic liquid crystal host

It was observed that mixed ZnO nanorods and twisted nematic liquid crystals (LCs) show highly ordered molecular system. The observed molecular relaxation arose due to a reorientation of long molecular axis of the order of 400 kHz for pure ZLI-1636, while such relaxation was shifted to a lower frequency for mixture. By using the proposed equations, f=fDB−α exp[−EV/(B−BC)] and σ=σDB−sα exp[−sEV/(B−BC)], the obtained equivalent activation energy was increased remarkably by the introduction of ZnO nanorods in pure LC. A strong long-range interaction is established in 0.01% ZnO nanorods mixed LC system.

Synthesis of a SO3H-bearing carbonaceous solid catalyst, PEG–SAC: application for the easy access to a diversified library of pyran derivatives

A SO3H-bearing carbonaceous solid catalyst (PEG–SAC) has been synthesized through sulfonation followed by a hydrothermal carbonization method from renewable resources like polyethylene glycol. The biodegradable catalyst was characterized by XRD, TEM, FT-IR and EDX. The surface area and pore diameter of the catalyst were determined from a nitrogen adsorption–desorption isotherm experiment. A highly convergent, efficient and practical PEG–SAC catalyzed heteroannulation protocol for the synthesis of a library of diversified pyran fused heterocyclic scaffolds has been demonstrated. This synthesis was established to follow the group-assistant-purification (GAP) chemistry process, which can avoid traditional chromatography. A recrystallization purification appeared to be a very good alternative to the traditional classical methods, demonstrating that a carbon-based catalyst is very effective in producing pyran fused heterocyclic molecules. The aqueous reaction medium, easy recovery of the catalyst and high yield of the products make the protocol attractive, sustainable and economic.

Shape Controlled Plasmonic Sn Doped CdO Colloidal Nanocrystals: A Synthetic Route to Maximize the Figure of Merit of Transparent Conducting Oxide.

The synthesis of different anisotropic shaped (eight different shapes) Sn4+ doped CdO (Sn:CdO) colloidal nanocrystals (NCs) by precise tuning of precursor reactivity and proper choice of capping agent is reported. In all these systems, formation of Sn:CdO quantum dots (QDs) of 2-3 nm is identified at very early stage of reaction. The colloidally stable QDs act as a continuous source for the formation of primary nanoparticles that can be transformed selectively into specific type of nanoparticle morphology. The specific facet stabilization of fcc (face centered cubic)CdO is predicted by particular choice of ligand. Fine tuning of plasmonic absorbance band can be achieved by variation of Sn4+ doping concentration. Different anisotropic Sn:CdO NCs exhibit interesting shape dependent plasmonic absorbance features in NIR region. High quality crack free uniform dense thin film has been deposited on glass substrate to make high quality transparent conducting oxide (TCO) coatings. figure of merit of TCO can be maximized as high as 0.523 Ω-1 with conductivity of 43 600 S cm-1 and visible transmittance of ≈85% which is much higher than commercially available tin doped indium oxide and other transparent electrodes.

Density functional calculations of hole induced long ranged ferromagnetic ordering in Mn doped Cd28Se28 nanocluster

We have investigated the possibility of long ranged ferromagnetic ordering in Mn doped Cd28Se28 nanocluster using density functional approach. Following the band repulsion theory we have explained that magnetic coupling between Mn atoms substituted in Cd sites is antiferromagnetic and short ranged. However, long ranged ferromagnetic coupling is possible via additional hole doping which leads to the spin splitting of the valence band. In this class of magnetic nanoclusters, additional hole doping induces spin polarization of host states at large distance. This property can lead to molecular magnets with tunable magnetic properties.

Fabrication of tungsten nanocrystals and silver–tungsten nanonets: a potent reductive catalyst

This communication reports the first synthesis of well-defined colloidal W nanocrystals, Ag–W heterostructures and their broad plasmon absorbance in the visible to near infrared region. Strong interparticle plasmonic interactions significantly improve the photocatalytic reduction performance of silver–tungsten heterostructures.

Efficient Charge Separation in Plasmonic ZnS@Sn:ZnO Nanoheterostructure: Nanoscale Kirkendall Effect and Enhanced Photophysical Properties

Tetravalent Sn doped ZnO nanocrystals show excellent plasmonic absorbance in the visible region. Plasmonic ZnS@Sn:ZnO core-shell heterostructures have been synthesized by the anion exchange process where the O2- is exchanged by S2- anion. An increase of sulfur concentration induces interior hollow structures arising from the different diffusion rates of O2- and S2- ions. Gradual transformation of wurtztie ZnO nanocrystals in the anion exchange process stabilizes the wurtzite crystalline phase of ZnS. Carrier concentration and various types of intrinsic defect states in both ZnO and ZnS result in ultraviolet, blue, and green emissions. The coexistence of exciton-plasmon coupling in the same nanoparticle and efficient electron-hole separation in type II heterostructure increases the photocatalytic activity and photo current gain.