Dharamvir Singh Ahlawat

Synthesis and Characterization of Sol–Gel Prepared Silver Nanoparticles

Silver nanoparticles (SNPs) have been successfully prepared using sol–gel method by annealing the sample at 550°C for 30 min. The SNPs were not confirmed by X-ray diffraction (XRD) analysis when the annealing temperature was considered at 450°C. They were also not confirmed without calcination of the sample. The physical mechanism of silver clusters formation in the densified silica matrix with respect to thermal treatment has been understood. The presence of silver metal in the silica matrix was confirmed by XRD analysis and TEM image of the samples. The average size of nanoparticles dispersed in silica matrix was determined as 10.2 nm by the XRD technique. The synthesized nanocomposites were also characterized by UV-Visible spectroscopy with a peak in the absorption spectra at around 375 nm. The distribution of particle size has been reported here in the range from 8 nm to 25 nm by TEM observations of the sample prepared at 550°C. The spherically smaller size (≈10 nm) SNPs have reported the surface plasmons resonance (SPR) peak less than or near to 400 nm due to blue-shifting and effect of local refractive index. Without annealing the silica samples the absorption spectra does not show any peak around 375 nm. The FTIR spectroscopy of the three types of samples prepared at different temperatures (room temperature, 450°C and 550°C) has also been reported. This spectra have provided the identification of different chemical groups in the prepared samples. It has been predicted that the size of SNPs by XRD, UV-Visible and TEM results have agreed well with each other. It may be concluded that formation of SNPs is a function of annealing temperature.

Effect of aligning pulse train on the orientation and alignment of a molecule in presence of orienting pulse

Field-free molecular alignment is studied theoretically in presence of orienting laser pulse and a delayed Infrared laser (IRL) pulse train. The pulse shapes taken are sine square (sin2) and square. The degree of alignment can be significantly enhanced by the combination of orienting pulse and IRL pulse train compared with only IRL pulse train. Special emphasis is laid on time delay between orienting and aligning pulse, the width and shape of the pulse train. By adjusting the time delay, width and intensity of coupling laser one can suppress a population of particular state while simultaneously enhancing the population of desired states.

A Critical Review on Mesoporous Photoanodes for Dye-Sensitized Solar Cells

Until breakthrough in 1991, commercialization of dye-sensitized solar cell (DSSC) has been a gradual process leading to a scarce production. A thorough study of dilemmas is needed to overcome the shortcomings of DSSC to make it stand against traditional silicon based solar cells. A DSSC is composed of important components including photoanode, dye, electrolyte and counter electrode. Among these photoanode is the focussed area of the presented article. The photoanode is a thin porous film of metal oxide semiconductor supported on to a transparent conducting oxide (TCO) glass. Extensive research in this field has revealed the photophysics of semiconducting electrodes like TiO2, ZnO and SnO2 etc. Selection of metal oxide for this purpose relies on crystallinity, particle size, and thickness of the film, surface area, dye affinity and porosity. These parameters related to the candidature of a particular metal oxide film as photoanode in DSSC have been discussed and optimized values have been quoted. The present study aims at emphasizing the history of DSSC as well as recent developments in electrodes, dyes and electrolytes in this specific area.

Effect of Material Parameters on the Optical Properties of Dye-Sensitized Solar Cell Photoanode

The presented theoretical analysis predicts the behaviour of optical properties of film with regards to materialistic parameters of the photoanode of dye-sensitized solar cell using the theory of dispersive transport. The porous nature of photoanode is considered for the simulation task. The variations in refractive index and absorption index of the semiconductor film with change in the values of thickness and porosity are studied by using finite element method. The theoretically demonstrates that refractive index increases with the increase in thickness and decreases with increase in porosity but absorption index shows a monotonic behaviour.