Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Catalysis & Excited state. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Amino acid based smart hydrogel: formation, characterization and fluorescence properties of silver nanoclusters within the hydrogel matrix

Abstract: N-Terminally Fmoc protected amino acid, Fmoc-Phe-OH (Fmoc-L-Phenylalanine-OH), forms an efficient, stable and transparent hydrogel with a minimum gelation concentration of 0.1% w/v. This hydrogel has been nicely utilized to prepare and stabilize fluorescent few-atom silver nanoclusters. Interestingly, in absence of any toxic reducing agents in a water medium, silver ions are complexed with the carboxylate group of the Fmoc-Phe-OH gelator, and they are reduced spontaneously in the presence of diffused sunlight at physiological pH (7.46) and room temperature to form silver nanoclusters. The three dimensional structure provided by the hydrogel helps to stabilize newly formed silver nanoclusters within the hydrogel matrix. These clusters have been examined using UV-Vis, photoluminescence spectroscopy, high resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRPD) and matrix-assisted laser-desorption ionization (MALDI) mass spectrometric analysis. MALDI mass spectrometric analysis shows the presence of just a few atoms within the silver cluster as Ag4. These silver nanoclusters exhibit interesting fluorescent properties including large Stokes shift (more than 110 nm), narrow emission band width (36 ± 1 nm) and a quantum yield of 3.76%. These silver nanoclusters are stable for up to 4 months of storage at 4 °C in the dark. The morphology of the hydrogel changes after the encapsulation of silver ions within the gel and this altered morphology is retained after the formation of silver nanoclusters within the gel. Interestingly, the rheological properties of the hydrogel alone are different from that of the silver nanocluster-containing hydrogel.

The Raychaudhuri equations: A brief review

Abstract: We present a brief review on the Raychaudhuri equations. Beginning with a summary of the essential features of the original article by Raychaudhuri and subsequent work of numerous authors, we move on to a discussion of the equations in the context of alternate non-Riemannian spacetimes as well as other theories of gravity, with a special mention on the equations in spacetimes with torsion (Einstein-Cartan-Sciama-Kibble theory). Finally, we give an overview of some recent applications of these equations in general relativity, quantum field theory, string theory and the theory of relativisitic membranes. We conclude with a summary and provide our own perspectives on directions of future research.

A new family of lead–bismuthate glass with a large transmitting window

Abstract: New glasses with high Li2O content have been obtained in the system Li2O–Bi2O3–PbO. The role of the different components in the glass formation has been explored from the density and thermal measurements. A wide transmitting window having sharp cut-off in both ultraviolet–visible (UV–VIS) and infrared (IR) regions for almost all compositions of these glasses has been observed, making them an appealing candidate for different spectral devices.

Shape selective growth of CdS one-dimensional nanostructures by a thermal evaporation process.

Abstract: CdS one-dimensional nanoforms such as nanowires, nanoribbons, networklike nanowires, pearl necklace type nanowires, helical-like nanowires, and nanowire arrays were formed on Si substrates by a simple thermal evaporation route. The shapes of the one-dimensional CdS nanoforms were controlled by varying the experimental parameters such as temperature and position of the substrates. Formation of the CdS one-dimensional nanoforms was initiated by the Au catalyzed vapor−liquid−solid technique, whereas the vapor−solid process played a crucial role in defining the shapes of the nanoforms. Different optical characterizations such as optical absorbance, photoluminescence, and Raman spectroscopy were adopted to explore the physical and structural quality of these CdS nanoforms.

Fabrication of ZnS nanoparticles and nanorods with cubic and hexagonal crystal structures: a simple solvothermal approach

Abstract: ZnS nanoparticles and nanorods with control over their crystal structure are fabricated through a solvothermal approach by changing the solvent used for the synthesis. The synthetic approach is suitable to fabricate ZnS nanoparticles with various sizes by varying the synthesis temperatures. Quantum confinement phenomena are studied by tailoring the particle sizes for both wurtzite and sphalerite polymorphs of ZnS. Photoluminescence studies reveal that the surface states greatly influence the emissions from the nanostructures. Wurtzite nanoparticles exhibit band-edge related UV emission owing to the effective surface passivation by the ethylene glycol molecules used as the solvent for the synthesis. On the other hand, the photoluminescence spectra of the cubic nanoparticles are mainly dominated by their surface states. Some of the nanorod samples exhibited Zn-vacancy related green emissions along with the surface defect related blue emission band. It is also demonstrated that ZnS nanostructures could be easily doped with useful impurities via this synthesis approach to tailor their luminescent properties.