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Effect of alkali charge compensator on luminescent properties in Eu3+ doped beta-dicalcium silicate
No full textRecent studies have shown that, Eu3+ doped silicates have gained lot of importance as an ideal red phosphor material in White Light Emitting Diode (WLED) application, due to Eu3+ electronic configuration. Studies have been carried out in the literature to observe the effect of charge compensation on photoluminescence properties of silicates. Alkali metals (Li+, Na+, K+, Cl-) and other halogens are used as charge compensators. The Li+ ion is known to be a good charge compensator because of its small size and such studies are well documented. Keeping this in view, we wanted to carry out such compensation using alkali metals but also curious to understand, the way a combination of alkali pair for such compensation process and the effect of charge compensator on the PL properties of this phosphor. We specifically chose the alkali pair, where charges are same but their size and mass ratio being vastly different. Europium doped calcium silicate (Ca2SiO4: Eu3+) has been prepared with charge compensators using alkali metals such as Li, Rb and Li-Rb. To start with, beta-dicalcium silicate (Ca2SiO4) has been prepared by solution combustion technique in the muffle furnace at a temperature of 500 degrees C. Diformyl hydrazine (DFH) was used as a fuel. In the second step, we synthesized Ca2SiO4 mixed with Eu3+ and their mixture with required alkali metals by solid state reaction followed by calcinations at 900 degrees C for 2 h. Subsequently obtained beta-Ca2SiO4: Eu3+ phosphor powders were characterized by powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), Fourier transform Infra Red (FTIR) spectroscopy. PXRD analysis confirmed the monoclinic phase with P2/m space group. However, SEM observation revealed agglomerated wafer and stony cluster morphology. The PL spectra of Ca2SiO4: Eu3+ was carried out with varying concentration of Eu3+. The samples with 5 mol% showed maximum PL intensity peak compared to other concentrations and spectra revealed PL at 588, 611, 620, 648, 685 and 701 nm. The same procedure was adapted for beta-Ca2SiO4: Eu3+, Li where Li act as a charge compensator. Surprisingly a new intense luminescent peak is observed at 574 nm and 588 nm, besides the intense red luminescent peak. The Hyper Sensitive Transition (HST) peaks around 612 nm and 621 nm have got their intensity pattern inverted indicating the effect of charge compensation on the Eu3+ environment which is a result of crystallographic effects and splitting of energy levels with changed transition probability
Electrochemical Aflatoxin B1 immunosensor based on the use of graphene quantum dots and gold nanoparticles
No full textElectrochemical immunosensor for aflatoxin B1 (AFB1) is described that uses a composite prepared from graphene quantum dots (GQDs) and gold nanoparticles (Au NPs). The GQD-AuNP conjugate was obtained by using 2-aminothiophenol (ATP) as a linker where the carboxy groups of GQD bind to the amino groups of crosslinker via conjugation of thiol binding to the AuNP. To evaluate the conjugation of the GQD-AuNP composite, Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) was applied. The composite was placed on an indium tin oxide (ITO) electrode and then modified with an antibody against AFB1. By using hexacyanoferrate as the electrochemical probe, the sensor works in the 0.1 to 3.0ngmL(-1) AFB1 concentration range, is highly specific, has good reproducibility and acceptable stability. The biosensor was applied to the analysis of (spiked) maize samples. Conceivably, the method can be utilized to sense other mycotoxins by using their respective antibodies
Magneto-dielectric and multiferroic properties in Bi0.95Yb0.05Fe0.95Co0.05O3
No full textBismuth ferrite (BFO) and (Yb, Co) co-doped BFO powder are successfully synthesized using the sol-gel method. The structural, electrical, magneto-dielectric and multiferroic properties of pure and co-doped BFO have been systematically investigated. The crystal structures of these samples are investigated using x-ray diffraction techniques, which confirmed the single-phase polycrystalline rhombohedral perovskite structure with the R3c space group. The co-substitution studies revealed that the electrical, ferromagnetic and ferroelectric properties of BFO were significantly enhanced compared to pure BFO samples
Melt spinning: A rapid and cost effective approach over ball milling for the production of nanostructured p-type Si80Ge20 with enhanced thermoelectric properties
No full textIn this work, we have adopted melt-spinning technique followed by spark plasma sintering (SPS) to synthesize a p-type nanostructured Si80Ge20 alloy. To illustrate the impact of the technique, the results are compared with that of prepared by ball milling and subsequent SPS. The room temperature XRD of the alloys prepared by both the techniques confirms that they crystallize with diamond-like cubic structure of space group Fd (3) over barm. The remarkably decreased thermal conductivity and increased Seebeck coefficient results in a higher ZT of melt spun sample (nearly similar to 46% higher at room temperature) as compared to the ball milled sample. The short preparation time of melt spun p-type Si80Ge20 alloy coupled with its enhanced thermoelectric performance indicate that this technique provides a novel strategy to improve the thermoelectric properties of SiGe alloys thus making this synthesis process of interest for commercial purposes
Novel anisotropic ordered polymeric materials based on metallopolymer precursors as dye sensitized solar cells
No full textDeveloping molecular self-assembly is an important step to generate ordered nanostructure materials. In this pursuit, a simple template-free method is reported to develop anisotropic nanostructures using metallopolymer precursors. The phenanthroline-based ruthenium complex monomer (PDAR) and its polymers [3-armed PPDAR (PPDAR-3) and 4-armed PPDAR (PPDAR-4)] were synthesized using ATRP method. These materials displayed higher glass transition temperatures (182 degrees C for PPDAR-4 and 176 degrees C for PPDAR-3) compared to the linear polymer, PPDAR (144 degrees C). The materials showed metal-to-ligand charge transfer (MLCT) absorption peak at 440 nm and armed polymers exhibited higher molar absorption coefficient (PPDAR-4: 7.6 x 10(5) M-1 cm(-1) and PPDAR-3: 6.58 x 10(5) M(-1)cm(-1)) compared to the linear polymer (4.6 x 10(5)M(-1)cm(-1)). The materials were self-assembled in the presence of non-polar solvents to form uniform nano-domain micelles. Thin films of these materials were formed and subjected to elevated annealing temperatures (180 degrees C) and were fully characterized by AFM, SEM, and XRD techniques to understand the mechanism of self-assembly. Furthermore, dye sensitized solar cell (DSSC) devices were fabricated using the materials as additional components of a liquid electrolyte (I-3(-)/I-)to explore the role of these architectures on open circuit voltage (V-OC) as well as cell power conversion efficiency (PCE). Overall, this study provides new insights in the area of metallopolymers
Anomalous nano-magnetic effects in non-collinear spinel chromite NiCr2O4
No full textWe present the results of a detailed investigation of magnetism in spinel chromite NiCr2O4 magnetic nanoparticles (MNPs). Compared to the bulk NiCr2O4, the finite crystallite size of about 10 nm lowers the Jahn-Teller distortion and greatly enhances the collinearity of the spin structure in MNPs with considerably reduced "frustration index" = vertical bar theta(CW)vertical bar/T-c. This leads to (longitudinal) ferrimagnetic ordering at much higher temperature, T-c approximate to 100 K and suppression of (transverse) antiferromagnetic ordering in MNPs (cf. T-c similar or equal to 65 K and T-s similar or equal to 30 K in the bulk); a transition to the cluster spin glass state occurs at T-g = 19.0 K. Moreover, the M-H hysteresis loops show anomalous "hour-glass" behavior at fields near H-c in the vicinity of T-g; this non-monotonous H-c (T) variation can not be accounted from the celebrated Stoner-Wohlfarth model. The present study interprets the anomalous H-c (T) behavior in the framework of magnetically interacting core-shell structure with large surface anisotropy, and points out the importance of surface effects in nanochromites compared to their counterpart ferrites
A Review of Diameter Measurement and a Proposal for the Improvement Thereof
No full textIn order to establish traceability of area of pressure measurement, piston-cylinder assemblies are characterized dimensionally. Piston, cylinder and master ring gauges demand diameter measurement uncertainty of about 30 nm. As focused efforts to achieve the requisite uncertainty, most of the trendy diameter measuring machines, used and available across the globe, are studied for their designs and performance. Conceptually, the uncompensated systematic error contributes significantly to the uncertainty of the measurements. In order to understand the magnitudes of the various errors, some of the key comparison reports are also studied. Based on the analysis of the review, laser-based displacement interferometer measurement systems are proposed. Theoretically, the proposed models reduce the Abbe's error
Binding of platinum derivative, oxaliplatin to deoxyribonucleic acid: structural insight into antitumor action
No full textPlatinum-derived chemodrugs constitute an active class in cancer therapeutics. Besides being potent against various solid tumors, oxaliplatin has been recognized as the first platinum compound to be approved for the treatment of colorectal cancer. Structurally, oxaliplatin consists of a platinum metal complexed to oxalate and diaminocyclohexane (DACH) and exert its anticancer action by inhibiting DNA replication and transcription. The present study highlights the binding properties of oxaliplatin with calf thymus DNA using spectroscopic methods to comprehend its binding mechanism at molecular level to overcome associated cellular resistance and side effects. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic outcomes confirm that oxaliplatin is a covalent binding agent and also provide sequence specificity in DNA molecule. Infrared spectral results further indicate that oxaliplatin alkylates purine nitrogenous bases majorly guanine residues (G) in the major groove via formation of either interstrand or intrastrand guanine-guanine d(GpG) and guanine-adenine d(GpA) (N7 position) crosslinks accompanied with a slight external binding to sugar-phosphate backbone. Again, circular dichroism (CD) spectroscopic results suggest subtle conformational changes in DNA molecule due to its complexation with oxaliplatin and duplex attains an intermediate conformational state, having characteristics of both B- and C-forms. Further, a moderate binding strength of 4.12 +/- 0.2 x 10(4) M-1 for the interaction has been estimated via ultraviolet-visible spectroscopy. The inferences obtained from these investigations are encouraging and can form the basis for further exploration in the field of rational drug development based on platinum compounds possessing preferential binding for nucleic acid with improved competence
Chemical Characterization of Fine Atmospheric Particles of Water-Soluble Ions and Carbonaceous Species in a Tropical Urban Atmosphere over the Eastern Indo-Gangetic Plain
Get PDFAmbient fine aerosols and their sources were evaluated in an eastern Indian megacity, Kolkata (KOL), from September 2010 to August 2011. A submicron aerosol sampler (SAS) with two stage stacked filter units (SFU) was devised for simultaneous but discrete collection of water-soluble inorganic ions (WSII) and carbonaceous aerosols (CA; elemental carbon (EC) and organic carbon (OC)). Characteristics of the WSII and CA were identified using ion chromatography and an OC-EC analyzer, respectively, adopting the Interagency Monitoring of PROtected Visual Environments (IMPROVE-A) protocol. The mean annual concentrations of the WSII showed a predominance of cations (anions), consisting of Ca2+, Mg2+, and Na+ (Cl-, NO3-, and SO42-), with secondary aerosols (NH4+, NO3-, and SO42-) and Ca2+ each constituting 25% and 30%, respectively, of the total WSII (T-WSII). The highest mean monthly concentration of SO42- and NO3- was observed during the winter month of February and the summer months of March and May, respectively. A pronounced peak in the monthly mean for the non-sea salt-K+ (nss-K+) concentration was noticed during October and April, implying the strong influence of biomass burning emissions during these months. Among the sea salt (SS), anthropogenic (AN), and dust (DT) sources of the T-WSII, a predominant contribution from DT in August and from AN in November, April, and May was inferred. The mean annual concentration of OC was three times higher than that of EC, with 43% of it being secondary OC. Whereas the major sources of OC were inferred to be paved dust, coal combustion, and biomass burning, those of EC were industrial and motor-vehicle non-exhaust emissions, coal combustion, and motor vehicle exhaust
Continuous Growth of Highly Reproducible Single-Layer Graphene Deposition on Cu Foil by Indigenously Developed LPCVD Setup
No full textContinuous growth of high-quality single-layer graphene (SLG) is highly desirable in several electronic and optoelectronic applications. To fulfill such requirements, we proposed a low-cost, highly reproducible high-quality SLG synthesized by indigenously developed low-pressure chemical vapor deposition (LPCVD) setup. The quality of SLG is examined by Raman spectroscopy, where we have probed the I-2D/I-G ratio for continuous 30 runs to assess the reproducibility and quality of single-layer using proposed indigenous LPCVD setup for device fabrication. The highest I-2D/I-G ratio of SLG (5.82) was found with full width at half maximum values of 2D peak and G peak of similar to 30.10 cm(-1) and similar to 20.86 cm(-1), respectively. Further, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy have been performed to study the quality of SLG. Thickness measurement of graphene with graphene grain size is calculated from atomic force microscopy studies, and the average grain size is found to be 1-3 mu m. Moreover, I-V characteristics have also been investigated by the two-probe method to ensure the quality of SLG. The lowest resistance of the SLG (similar to 387 Omega) was found at room temperature. Thus, this new indigenously developed low-cost setup provides a novel alternative method to produce highly reproducible metrology-grade continuous SLG on Cu substrate for next-generation quantum devices