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.

Shape-Dependent Confinement in Ultrasmall Zero-, One-, and Two-Dimensional PbS Nanostructures

Abstract: Spatial dimensionality affects the degree of confinement when an electron-hole pair is squeezed from one or more dimensions approaching the bulk exciton Bohr radius (alpha(B)) limit. The etectron-hole interaction in zero-dimensional (0D) dots, one-dimensional (1D) rods/wires, and two-dimensional (2D) wells/sheets should be enhanced by the increase in confinement dimensions in the order 0D > 1D > 2D. We report the controlled synthesis of PbS nanomateriats with 0D, 1D, and 2D forms retaining at least one dimension in the strongly confined regime far below alpha(B) (similar to 10 nm for PbS) and provide evidence through varying the exciton-phonon coupling strength that the degree of confinement is systematically weakened by the loss of confinement dimension. Geometry variations show distinguishable far-field optical polarizations, which could find useful applications in polarization-sensitive devices.

Cryogenic magnetocaloric effect in zircon-type RVO4 (R = Gd, Ho, Er, and Yb)

Abstract: Low-temperature magnetic refrigeration has attracted the attention of the cryogenics research community in the areas of technology in space science and in the liquefaction of hydrogen or other fuel gases, although it has been less researched compared to room-temperature magnetic refrigeration. Here, we report that the RVO4 (R = Gd, Ho, Er, and Yb) series is promising for low-temperature cryogenic refrigeration. GdVO4 is the most promising material, exhibiting a maximum magnetocaloric effect (ΔSmaxM) of 41.1 J kg−1 K−1 at 3 K for a change in field (ΔH) of 50 kOe. The values of ΔSmaxM are also promising, with 7.94 J kg−1 K−1 at 15 K, 19.7 J kg−1 K−1 at 2 K, and 17.4 J kg−1 K−1 at 2 K with ΔH = 50 kOe for HoVO4, ErVO4, and YbVO4, respectively. The maximum value of adiabatic temperature change (ΔTmaxad) attributed to the large magnetocaloric effect is 18 K for GdVO4 with ΔH = 50 kOe. The results further indicate that demagnetization with 50 kOe field close to the liquid hydrogen temperature at 20.3 K leads to the remarkable decrease of temperature to 3.5 K. Satisfying its potential as a refrigerant material, the thermal hysteresis of magnetization is negligible, and the values of ΔSmaxM and ΔTmaxad are as high as 12.4 J kg−1 K−1 and 8.5 K for 20 kOe change in field, which can be achieved without a superconducting magnet.

α-Halo Ketone for Polyhedral Perovskite Nanocrystals: Evolutions, Shape Conversions, Ligand Chemistry, and Self-Assembly.

Abstract: Bright lead halide perovskite nanocrystals, which have been extensively studied in the past 5 years, are mostly confined to a six faceted hexahedron (cube/platelet) shape. With variations of ligand, precursor, reaction temperature, and surface modification, their brightness has been enhanced and phase became stable, but ultimate nanocrystals still retained the hexahedron cube or platelet shape in most of the hot injection reactions. In contrast, by exploration of α-halo ketone in amine as a halide precursor, different shaped nanocrystals without compromising the photoluminescence quantum yield (PLQY) are reported. Confining to orthorhombic CsPbBr3, the obtained nanocrystals are stabilized by 12 facets ({200}, {020}, {112}) and led to 12 faceted rhombic dodecahedrons. These facets are absolutely different from six ({110}, {002}) equivalent facets of widely reported orthorhombic cube shaped CsPbBr3 nanocrystals. These also retained the colloidal and phase stability, as well as showed near unity PLQY. With further annealing, these are transformed to 26 faceted rhombicuboctahedrons by dissolving all their vertices. Importantly, these 12 faceted nanocrystals showed wide area self-assembly in most of the reactions. It has also been concluded that primary ammonium ions led to six faceted nanocrystals, but tertiary ammonium ions obtained in this case stabilized different group of facets. While perovskite nanocrystals were broadly confined to only nanocubes, these new nanocrystals with intense emission would certainly provide a new avenue for continuing their further research.

Solvation Dynamics in Aqueous Polymer Solution and in Polymer−Surfactant Aggregate

Abstract: Solvation dynamics of 2,6-p-toluidinonaphthalene sulfonate (TNS) is studied using picosecond time-resolved emission spectroscopy in an aqueous solution of poly(vinylpyrrolidone) (PVP) and in a polymer−surfactant aggregate consisting of PVP and sodium dodecyl sulfate (SDS). On addition of PVP to an aqueous solution of TNS, the emission quantum yield (φf) of TNS increases about 210 times in 0.75 wt % aqueous solution of PVP. The solvation dynamics of TNS in 0.75 wt % aqueous solution of PVP is found to be biexponential with a major component (85%) of 60 ps and a slower one of 800 ps (15%). The retardation of the solvation dynamics in the dilute polymer solution compared to that in the bulk water is attributed to the restricted movement of water molecules in the vicinity of the polymer chains. The solvation dynamics of TNS in the PVP−SDS aggregate is described by two components, 300 ± 20 ps (55%) and 2500 ± 100 ps (45%). The slower solvation dynamics in PVP−SDS aggregate compared to PVP alone or SDS alone in...