Sampat Raj Vadera

Bio: Sampat Raj Vadera is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topic(s): Photoluminescence & Nanocomposite. The author has an hindex of 26, co-authored 63 publication(s) receiving 2242 citation(s). Previous affiliations of Sampat Raj Vadera include Andhra University.

Microwave absorbing properties of a thermally reduced graphene oxide/nitrile butadiene rubber composite

Abstract: Reduced graphene oxide (RGO) with a layered and porous structure was synthesized by thermal exfoliation of graphite oxide. Synthesized RGO is very light weight and flaky. The formation of RGO was studied using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and scanning electron microscopy. Composites were prepared by dispersing 2%, 4% and 10% by weight of the synthesized RGO into nitrile butadiene rubber (NBR) matrix. Microwave absorption properties of RGO/NBR composites were investigated by measuring their complex permittivity and permeability by using waveguide method. Simulation studies show that 10 wt.% of graphene oxide in NBR matrix exhibits high values of reflection loss (>10 dB) over a wide frequency range 7.5–12 GHz and maximum loss is 57 dB at 9.6 GHz at a thickness of 3 mm.

Synthesis and photoluminescent properties of ZnS nanocrystals doped with copper and halogen

Abstract: A novel wet-chemical precipitation method is optimized for the synthesis of ZnS nanocrystals doped with Cu+ and halogen. The nanoparticles were stabilized by capping with polyvinyl pyrrolidone (PVP). XRD studies show the phase singularity of ZnS particles having zinc-blende (cubic) structure. TEM as well as XRD line broadening indicate that the average crystallite size of undoped samples is similar to2 nm. The effects of change in stoichiometry and doping with Cu+ and halogen on the photoluminescence properties of ZnS nanophosphors have been investigated. Sulfur vacancy (Vs) related emission with peak maximum at 434 nm has been dominant in undoped ZnS nanoparticles. Unlike in the case of microcrystalline ZnS phosphor, incorporation of halogens in nanoparticles did not result V-Zn related self-activated emission. However, emission characteristics of nanophosphors have been changed with Cu+ activation due to energy transfer from vacancy centers to dopant centers. The use of halogen as co-activator helps to increase the solubility of Cu+ ions in ZnS lattice and also enhances the donor-acceptor type emission efficiency. With increase in Cu+ doping, Cu-Blue centers (CuZn-Cui+), which were dominant at low Cu+ concentrations, has been transformed into Cu-Green (Cu-Zn(-)) centers and the later is found to be situated near the surface regions of nanoparticles. From these studies we have shown that, by controlling the defect chemistry and suitable doping, photoluminescence emission tunability over a wide wavelength range, i.e., from 434 to 514 nm, can be achieved in ZnS nanophosphors. (C) 2003 Elsevier B.V. All rights reserved.

Multicolor electroluminescent devices using doped ZnS nanocrystals

Abstract: Alternate-current electroluminescent (ac EL) devices based on doped ZnS nanocrystals emitting blue, green, and orange-red colors are reported. ZnS nanocrystals doped with Cu+ – Al3+ and Cu+ – Al3+ – Mn2+ combinations were synthesized by wet chemical method at room temperature. The ZnS:Cu+, Al3+ nanocrystals show blue (462 nm) and green (530 nm) EL emissions depending upon the presence and absence of sulphur vacancies, respectively. The orange EL emission (590 nm) is realized from ZnS:Cu+, Al3+, Mn2+ nanoparticles by way of nonradiative energy transfer from AlZn – CuZn pairs to MnZn. The EL devices show low turn-on voltage of ~10 V ac @100 Hz. The mechanism of ac EL in ZnS nanocrystals has been explained wherein the excitation is attributed to the electric-field-assisted injection of electron-hole pairs from the surface regions into the interiors and their subsequent recombination therein causes emission.

In situ synthesis of graphene oxide and its composites with iron oxide

Abstract: A single step method was developed for the preparation of graphene oxide/Fe2O3 composites by exfoliation of graphite oxide with an oxygen-rich ferric acetyl acetonate complex. The synthesized materials were characterized by Fourier transform infrared spectroscopy. X-ray diffraction, vibrating sample magnetometry, atomic force microscopy, and low temperature dc conductivity measurements. After exfoliation, the Fourier transform infrared studies reveal the decomposition of epoxy groups and the simultaneous formation of composites of iron oxide particles within the graphene oxide. Atomic force microscopy reveals the formation of an ~5 nm thick graphene oxide stack with layered morphology. The layered morphology of graphenc oxide degrades at higher concentrations of iron oxide. The vibrating sample magnetometer studies show ferromagnetic behavior of all composites in the range of 0.13-5.5 emu/g at room temperature. The conductivity of these composites is found to be governed by a quasi ID hopping mechanism.

Studies on conductivity and dielectric properties of polyaniline-zinc sulphide composites

Abstract: In the present paper, we report electrical conductivity and dielectric studies on the composites of conducting polyaniline (PANI) with crystalline semiconducting ZnS powder, wherein PANI has been taken as inclusion and ZnS crystallites as the host matrix. From the studies, it has been observed that the value of room temperature d.c. conductivity of the composites with volume fraction of PANI > 0.65 shows an unusual behaviour wherein, conductivity values of the composites exceed that of PANI itself with maximum value as high as 6 times that of PANI at the volume fraction of 0.85. A similar trend has also been observed for the real and imaginary parts of complex dielectric constant values of the composites. This unusual behaviour in the d.c. conductivity and dielectric properties has been attributed to the enhancement in the degree of crystallinity of PANI as a consequence of its interfacial interaction with ZnS matrix. The results of optical microscopy show coating of PANI all around the ZnS particles. The temperature dependent conductivity studies suggest the quasi one-dimensional VRH conduction in PANI as well as its composites with ZnS. FTIR and XRD studies have also been reported.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Abstract: Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Broadband and Tunable High‐Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam

Abstract: The broadband and tunable high-performance microwave absorption properties of an ultralight and highly compressible graphene foam (GF) are investigated. Simply via physical compression, the microwave absorption performance can be tuned. The qualified bandwidth coverage of 93.8% (60.5 GHz/64.5 GHz) is achieved for the GF under 90% compressive strain (1.0 mm thickness). This mainly because of the 3D conductive network.

ZnS nanostructures: From synthesis to applications

Abstract: Zinc sulfide (ZnS) is one of the first semiconductors discovered. It has traditionally shown remarkable versatility and promise for novel fundamental properties and diverse applications. The nanoscale morphologies of ZnS have been proven to be one of the richest among all inorganic semiconductors. In this article, we provide a comprehensive review of the state-of-the-art research activities related to ZnS nanostructures. We begin with a historical background of ZnS, description of its structure, chemical and electronic properties, and its unique advantages in specific potential applications. This is followed by in-detail discussions on the recent progress in the synthesis, analysis of novel properties and potential applications, with the focus on the critical experiments determining the electrical, chemical and physical parameters of the nanostructures, and the interplay between synthetic conditions and nanoscale morphologies. Finally, we highlight the recent achievements regarding the improvement of ZnS novel properties and finding prospective applications, such as field emitters, field effect transistors (FETs), p-type conductors, catalyzators, UV-light sensors, chemical sensors (including gas sensors), biosensors, and nanogenerators. Overall this review presents a systematic investigation of the ‘synthesis-property-application’ triangle for the diverse ZnS nanostructures.

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications.

Abstract: This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered Finally, some future trends and the prospects in these research areas are also discussed