Search

Molecular adsorption of hydrogen in lithium decorated smallest fullerene (C20Li2) has been carried out within the framework of density functional theory (DFT) at B3LYP/6311+G(d,p) level. Hydrogen molecules were added sequentially till maximum number of hydrogen molecules could be accommodate by the C20Li2. The kinetic stabilities of the hydrogenated clusters were confirmed through global reactivity descriptors and electronic band gaps. It was observed that the C20Li2 clusters could hold maximum up to eight hydrogen molecule with average adsorption energy in the range 0.11 - 0.06 eV/H2 resulting in gravimetric density of 5.98 wt% which was in accordance with the target set by US Department of Energy (US-DOE) for optimal hydrogen adsorption. The average adsorption energy value and the distance between Li atom and hydrogen molecules indicated the process to be physisorption type. Topological analysis using Bader's quantum theory of atoms in molecules (QTAIM) concluded that the interaction between H2 and Li atom to be closed shell type with ρ < 0.20 a.u with positive ∇2ρ corresponding to ionic or van der Walls bonds. [ABSTRACT FROM AUTHOR]

New bismuth tellurite boro-germanate glasses according to composition xBi2O3-(80-x)TeO2-10B2O3-10GeO2 where (x=40, 45, 50, 55, 60 and 65 mol%) have been prepared by melt quench technique at 1150 ◦C. The room temperature optical absorption spectra have been recorded. The indirect band gap energy Eg was determined and found to decrease with Bi2O3 content. The increase in Urbach energy with glass composition indicates the decrease in structural stability. The ionic and covalent bonding parameters were determined. The present glasses are found to be 99 % ionic in nature. The two-photon absorption coefficient was found to increase from 11.89 to 14 cm/GW. The non-linear optical properties such as non-linear refractive index, linear optical susceptibility and third order non-linear optical susceptibility were evaluated using optical data. The authors determined theoretically the optical band gap (Eg) and refractive index (n) of the present glasses using optical electronegativity data. The relationship between Eg and n followed the relation Eg n4 = 99. The present glasses were found suitable for drawing optical fibers. [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol (PVA)/Polyvinylpyrrolidone (PVP) (50/50) blends filled with various concentrations of Copper Oxide (CuO) nanofiller (0, 2 and 4 wt %) were prepared using solvent casting technique. The structural properties were carried out using XRD. The UV Visible studies reveal that the direct energy gap values declines with an increase in CuO nanofiller concentration in the blend. The surface morphology studies were carried out using atomic force microscope (AFM). The photoluminescence spectra measured at an excitation wavelength of 220 nm reveals that the intensity of the spectra increases with filler concentration.The mechanical properties measured using Universal testing machine (UTM) indicates enhancement in the properties upon addition of CuO nanofiller. These significant enhancements in the optical and mechanical properties of the blend upon addition of CuO nanofillers make it a potential material for device applications. [ABSTRACT FROM AUTHOR]

The present work reports structural and luminescence studies on Dy3+ doped borofluorophosphate (BFPDY) glasses prepared with the chemical composition of (40-x)B2O3 + 30P2O5 + 10ZnF + 10K2O + 10BaO + xDy2O3, where x = 0.1, 0.2, 0.5 and 1 mol% by melt quenching technique. The structural and optical properties of the prepared glasses were analysed by means of XRD, FTIR, UV-V is absorption spectroscopy and photoluminescence emission and excitation spectra. XRD results confirm the amorphous nature of glass and FTIR studies reveals the presence of various stretching and bending vibrations of different structural units within the sample. The optical absorption spectrum has been recorded at room temperature and different absorption transitions were obtained and it is found that the transition via 6H15/2→6P7/2 is more prominent. From the absorption spectrum, optical band gap energy, nephelauxetic ratio (β) and the bonding parameter (δ) were determined. Excitation spectrum was recorded in the region 300-500 nm by monitoring emission at 572 nm and characteristic excitation bands were observed. The band at 348 nm arising through the transition 6H15/2→6P7/2 shows maximum intensity. The photoluminescence spectra of the fitted glasses have been recorded at an excitation wavelength of 348 nm and the spectra contain two intense emission bands in the blue (483 nm) and yellow (572 nm) regions and a weak band in the red region (663 nm). Concentration dependent variations in emission intensities were analysed. It is observed from the emission spectra that the luminescence intensity increases with the increase in Dy3+ ion content up to 0.5 mol% beyond that it decreases due to luminescence quenching. The Y/B intensity ratio by varying the concentration of Dy2O3 is also studied. The emission intensity were characterized through Commission International d'Eclairage (CIE) 1931 chromaticity diagram to explore its suitability for white light emission applications. [ABSTRACT FROM AUTHOR]

Here we report numerical simulation results obtained by performing photonic band structure calculations for a 2D periodic array of dielectric cylinders, having square symmetry with a lattice constant of 600nm. We have performed electromagnetic calculations using finite element method by employing COMSOL Multiphysics software. The band structure of the infinite crystal is calculated using plane wave method using MIT Photonic Band gap Package software. The calculated reflectance spectra showed three photonic bands spanning over visible and Infra-red regions a for refractive index contrast of 2.98. In order to study the property of a resonator, a point defect is introduced by replacing the dielectric cylinder with an air-cylinder. A sharp dip within the band gap of the reflectance spectra is observed and is attributed to the localized mode associated with the defect. Q-factor associated with the localized mode is calculated. The effect of refractive index of the defect on the localized mode frequency have been investigated and results are reported here. [ABSTRACT FROM AUTHOR]

Herein we report a novel photocatalyst composite encompassing oxides of lanthanum and bismuth synthesized via a microwave assisted method. The characterization of the composite was carried out by fourier transform (FT-IR) spectroscopy, X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and tansmission electron microscopy (TEM). The low band gap incurred by the composite bolster efficient photocatalytic applications. The photocatalytic degradation studies were optimized with methylene blue (MB) and the composite with 47 weight percentage of lanthanum and bismuth showed effective degradation applications. It is anticipated that an efficient degradation of the basic dye MB within 120 minutes and a highly toxic insecticide acephate within 240 minutes. The total organic carbon (TOC) analysis shows the mineralization of about 81.32 % of MB after 120 minutes and about 65.21 % of acephate in 240 minutes solar irradiation. The prominent photocatalytic degradation property of the synthesized binary composite makes it a promising catalyst for future perspectives. [ABSTRACT FROM AUTHOR]

In this work, the impact of various concentrations of dopant ion on the structural and optical properties of manganese doped ZnS Quantum Dots (MnZnS QDs) in presence of a capping agent has been investigated. MnZnS QDs with various concentration of manganese were prepared by chemical precipitation method using thiourea as the capping agent. The prepared Quantum Dots were characterized by various techniques like X-ray diffraction spectroscopy (XRD), UV-vis. spectroscopy, FT-IR spectroscopy, Diffuse reflectance spectroscopy (DRS) and Fluorescence spectroscopy (PL). The results revealed that the size and optical properties of MnZnS QDs varied by dopant ion concentration. FT-IR and PL results confirmed the incorporation of manganese into ZnS crystal structure, and XRD results showed that MnZnS nanoparticles crystallized in a zinc blende structure.PL intensity of thiourea capped MnZnS QDs (TH- MnZnS QDs) were compared, and TH-MnZnS QD-3 (Mn- 1mmol) was found to have the highest PL intensity. The band gap values decrease with increase in concentration of dopant. [ABSTRACT FROM AUTHOR]