K.G. Gopchandran

Studies on surface plasmon resonance and photoluminescence of silver nanoparticles.

Silver nanoparticles of different sizes were prepared by citrate reduction and characterized by UV-vis absorbance spectra, TEM images and photoluminescence spectra. The morphology of the colloids obtained consists of a mixture of nanorods and spheres. The surface plasmon resonance (SPR) and photoemission properties of Ag nanoparticles are found to be sensitive to citrate concentration. A blue shift in SPR and an enhancement in photoluminescence intensity are observed with increase in citrate concentration. Effect of addition of KCl and variation of pH in photoluminescence was also studied.

Green synthesis of gold nanoparticles using Cinnamomum zeylanicum leaf broth.

Development of biologically inspired experimental processes for the synthesis of nanoparticles is an important branch of nanotechnology. The synthesis of gold nanoparticles using Cinnamomum zeylanicum leaf broth as the reducing agent is reported. The morphology of the particles formed consists of a mixture of gold nanoprisms and spheres with fcc (111) structure of gold. At lower concentrations of the extract, formation of prism shaped Au particles dominates, while at higher concentrations almost spherical particles alone are observed. Good crystallinity of the nanoparticles with fcc phase is evident from XRD patterns, clear lattice fringes in the high resolution TEM image and bright circular rings in the SAED pattern. Au nanoparticles grown are observed to be photoluminescent and the intensity of photoemission is found to increase with increase in leaf broth concentration. The ability to modulate the shape of nanoparticles as observed in this study for gold nanoparticles opens up the exciting possibility of developing further synthetic routes employing ecofriendly sources.

The preparation of transparent electrically conducting indium oxide films by reactive vacuum evaporation

Abstract Indium oxide thin films deposited by reactive thermal evaporation of indium in an oxygen atmosphere at different substrate temperatures and oxygen partial pressures are characterized by X-ray diffraction, scanning electron microscopy, optical transmission and electrical resistivity. Preparation conditions are optimized to obtain highly transparent and conducting ln 2 O 3 films.

Optical and electrical properties of zinc oxide films prepared by spray pyrolysis

Zinc oxide thin films were prepared on glass substrates from an aqueous solution of zinc acetate by spray pyrolysis. These films were characterized using X-ray diffraction, scanning electron microscopy and optical transmission. The films were highly transparent to the visible radiation and electrically conductive. Films deposited at optimum conditions exhibited a resistivity of 3·15×10−3 Ωm along with a transmittance of 98% at 550 nm.

Gold nanorods with finely tunable longitudinal surface plasmon resonance as SERS substrates

Advances in nanophotonics have shown the potential of colloidal metal nanoparticles with sharp tips, such as rods, to focalize plasmonic electromagnetic fields. We report on the synthesis of Au nanorods via a seed mediated approach and the influence of silver ions on the aspect ratio of the Au nanorods. The longitudinal surface plasmon resonance (LSPR) of the Au nanorods was successfully tuned with the concentration of silver ions. The surface enhanced Raman scattering (SERS) effect of 2-aminothiophenol (2-ATP) as a probe molecule on Au nanorods was systematically studied by varying the longitudinal surface plasmon resonance of the nanorods. The highest electromagnetic enhancement was observed when the longitudinal surface plasmon resonance of the Au nanorods overlapped with the laser excitation wavelength. The variation of the SERS enhancement factor with the longitudinal surface plasmon resonance and laser excitation lines is also discussed in detail.

Aqueous synthesis and characterization of CdS, CdS:Zn2+ and CdS: Cu2+ quantum dots

CdS quantum dots of different sizes approximately 3-5nm were prepared using aqueous solutions of CdSO(4) and Na(2)S(2)O(3) at 303K with thioglycerol as stabilizing agent and catalyst. The broad X-ray diffraction pattern and SAED pattern with bright circular spots and clear lattice fringes in the high-resolution TEM image indicate cubic phase of the nanocrystals. Band gap changes from the bulk value of 2.4 to 3.16eV in the nanoparticles indicating quantum size effect. The photoluminescence (PL) spectrum is blue-shifted to 528nm. The PL emission band is blue/red-shifted on doping with Zn(2+)/Cu(2+). In the case of Cu(2+), the PL intensity is found to be maximum at 10wt% doping and almost completely quenched at 15wt% doping. On doping with Zn(2+), the intensity and blue-shift of PL are found to be maximum at 2 and 6wt% doping, respectively.

Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots.

Nanoparticles of CdS were prepared at 303 K by aqueous precipitation method using CdSO4 and (NH4)2S in presence of the stabilizing agent thioglycerol. Adjustment of the thioglycerol (T) to ammonium sulphide (A) ratio (T:A) from 1:25 to 1:3.3 was done during synthesis and nanoparticles of different size were obtained. The prepared colloids were characterized by UV-vis and photoluminescence (PL) spectroscopic studies. Prominent first and second excitonic transitions are observed in the UV-vis spectrum of the colloid prepared with a T:A ratio of 1:3.3. Particle size analysis was done using XRD, high resolution TEM and dynamic light scattering and found to be approximately 3 nm. UV-vis and PL spectral features also agree with this particle size in colloid with T:A of 1:3.3. The band gap of CdS quantum dots has increased from the bulk value 2.4-2.9 eV. PL spectra show quantum size effect and the peak is shifted from 628 to 556 nm when the ratio of T:A was changed from 1:25 to 1:3.3. Doping of CdS with Zn2+ and Cu2+ is found to enhance the PL intensity. PL band shows blue-shift and red-shift on doping with Zn2+ and Cu2+, respectively. UV and PL spectral features of the CdS/Au hybrid nanoparticles obtained by a physical mixing of CdS and Au nanoclusters in various volume ratios is also discussed. Au red-shifts and rapidly quenches the PL of CdS. An additional low energy band approximately 650 nm is observed in the UV visible spectrum of the hybrid nanoparticles.

Surface enhanced Raman scattering, antibacterial and antifungal active triangular gold nanoparticles.

Shape controlled syntheses of gold nanoparticles have attracted a great deal of attention as their optical, electronic, magnetic and biological properties are strongly dependent on the size and shape of the particles. Here is a report on the surface enhanced Raman scattering (SERS) activity of Cinnamomum zeylanicum leaf broth reduced gold nanoparticles consisting of triangular and spherical like particles, using 2-aminothiophenol (2-ATP) and crystal violet (CV) as probe molecules. Nanoparticles prepared with a minimum leaf broth concentration, having a greater number of triangular like particles exhibit a SERS activity of the order of 10(7). The synthesized nanoparticles exhibit efficient antibacterial activity against the tested gram negative bacterium Escherichia coli and gram positive bacterium Staphylococcus aureus. Investigations on the antifungal activity of the synthesized nanoparticles against Aspergillus niger and Fusarium oxysporum positive is also discussed.

Organic mediated synthesis of highly luminescent Li+ ion compensated Gd2O3:Eu3+ nanophosphors and their Judd–Ofelt analysis

Highly luminescent red emitting Gd2O3:Eu3+, Li+ nanophosphor has been synthesized by the solvothermal combustion of the metal–citrate complex in diethylene glycol medium. The morphology and luminescence properties of these nanophosphors are found to be highly sensitive to the extent of lithium ion compensation. It is found that lithium ions promote grain growth and alter the morphology of the Gd2O3:Eu3+ nanophosphor from nearly spherical to cobblestone like. A significant enhancement in intensity of luminescence and quantum efficiency is observed in lithium compensated nanophosphors. The highest emission intensity is observed for the Gd1.75Eu0.1Li0.15O3 nanophosphor, about 1.83 times that of Gd1.9Eu0.1O3 and is attributed to the enhanced intra 4f–4f emission transitions arising from the modifications of the crystal field and distortion of the local symmetry around the europium ions. The luminescence decay profiles are found to be single exponential in nature and the lifetime measured was 1.36 ms for the Gd1.75Eu0.1Li0.15O3 nanophosphor. The chromaticity coordinates of these nanophosphors indicated high colour purity. Judd–Ofelt intensity parameters indicated that lithium compensation increases the polarization of the local environment and an increase of covalency and asymmetry around the europium ions.

SERS and Antibacterial Active Green Synthesized Gold Nanoparticles

Accurate control of size, composition, morphology, and stability, and the use of environmentally friendly procedures are highly desirable for the synthesis of nanoparticles. Here is a report on the use of Vitis californica leaf broth for the synthesis of gold nanoparticles. The morphology of the particles formed consists of a mixture of gold nanotriangles and spheres with fcc (111) structure. At lower concentrations of the extract, formation of triangular-shaped particles is found to dominate, while at higher concentrations, almost spherical particles alone are observed. The investigations made on the surface enhanced Raman scattering activity of these nanoparticles using 2-aminothiophenol and crystal violet as probe molecules are discussed in detail. The synthesized nanoparticles displayed efficient antibacterial activity against the tested gram-negative bacterium Escherichia coli and gram-positive bacterium Staphylococcus aureus.