Greater Blue Shift Research Articles

Synthesis and optical properties of PVC-CdS-based nanocomposites

Poly(vinyl chloride) (PVC)–cadmium sulfide (CdS) nanocomposite films were successfully synthesized by ex situ solution casting method. Scanning electron microscopy showed that CdS nanoparticles are well monodispersed in the PVC matrix. From the ultraviolet (UV) spectra of nanocomposites, the width of the forbidden band for polymer nanocomposites was determined by extrapolation method. UV-visible optical spectra revealed that the optical band of nanocomposites is increased with increasing concentration of CdS nanoparticles in the PVC matrix. It was found that the band gap is 3.8 eV for PVC-3% CdS nanocomposites, 2.7 eV for PVC-5% CdS, and 2.35 eV for PVC-10% CdS nanocomposites. Photoluminescence spectrum of PVC-CdS-based nanocomposites shows two luminescent peaks at the wavelengths of 436 nm and 472 nm at the luminescence spectrum which belongs to CdS nanoparticles. Photoluminescence study shows that PVC-CdS nanocomposites exhibit a great blue shift (approximately 100 nm) compared with bulk CdS nanoparticles.

Effects of Electrochemical Etching Time on the Performance of Porous Silicon Solar Cells on Crystalline n-Type (100) and (111)

Electrochemical etching was carried out to produce porous silicon based on crystalline silicon n-type (100) and (111) wafers. Etching times of 10, 20, and 30 min were applied. Porous silicon layer was used as anti-reflection coating on crystalline silicon solar cells. The optimal etching time is 20 min for preparing porous silicon layers based on crystalline silicon n-type (100) and (111) wafers. Nanopores with high porosity were produced on the porous silicon layer based on crystalline silicon n-type (100) and (111) wafers with average diameters of 5.7 and 5.8 nm, respectively. Average crystallite sizes for the porous silicon layer based on crystalline silicon n-type (100) and (111) wafers were 20.57 and 17.45 nm at 20 and 30 min, respectively, due to the increase in broadening of the full width at half maximum. Photoluminescence peaks for porous silicon layers based on crystalline silicon n-type (100) and (111) wafers increased with growing porosity and a great blue shift in luminescence. The minimum effective coefficient of reflection was obtained from porous silicon layers based on the crystalline silicon n-type (100) wafer compared with n-type (111) wafer and as-grown at different etching times. Porous silicon layers based on the crystalline silicon n-type (100) wafer at 20 min etching time exhibited excellent light trapping at wavelengths ranging from 400 to 1000 nm. Thus, fabricated crystalline silicon solar cells based on porous silicon (100) anti-reflection coating layers achieved the highest efficiency at 15.50% compared to porous silicon (111) anti-reflection coating layers. The efficiency is characterized applying I-V characterization system under 100 mW/cm2 illumination conditions.

Environment sensitive fluorescent analogue of biologically active oxazoles differentially recognizes human serum albumin and bovine serum albumin: Photophysical and molecular modeling studies

An environment sensitive fluorophore, 4-(5-(4-(dimethylamino)phenyl)oxazol-2-yl)benzoic acid (DMOBA), that closely mimics biologically active 2,5-disubstituited oxazoles has been designed to probe two homologous serum proteins, human serum albumin (HSA) and bovine serum albumin (BSA) by means of photophysical and molecular modeling studies. This fluorescent analogue exhibits solvent polarity sensitive fluorescence due to an intramolecular charge transfer in the excited state. In comparison to water, the steady state emission spectra of DMOBA in BSA is characterized by a greater blue shift (~10nm) and smaller Stokes' shift (~5980cm−1) in BSA than HSA (Stokes'shift~6600cm−1), indicating less polar and more hydrophobic environment of the dye in the former than the latter. The dye-protein binding interactions are remarkably stronger for BSA than HSA which is evident from higher value of the association constant for the DMOBA-BSA complex (Ka~5.2×106M−1) than the DMOBA-HSA complex (Ka~1.0×106M−1). Fӧrster resonance energy transfer studies revealed remarkably less efficient energy transfer (8%) between the donor tryptophans in BSA and the acceptor DMOBA dye than that (30%) between the single tryptophan moiety in HSA and the dye, which is consistent with a much larger distance between the donor (tryptophan)-acceptor (dye) pair in BSA (34.5Å) than HSA (25.4Å). Site specific competitive binding assays have confirmed on the location of the dye in Sudlow's site II of BSA and in Sudlow's site I of HSA, respectively. Molecular modeling studies have shown that the fluorescent analogue is tightly packed in the binding site of BSA due to strong steric complementarity, where, binding of DMOBA to BSA is primarily dictated by the van der Waals and hydrogen bonding interactions. In contrast, in HSA the steric complementarity is less significant and binding is primarily guided by polar interactions and van der Waals interactions appear to be less significant in the formation of the HSA-DMOBA complex. Electrostatic interactions contribute significantly in the binding of DMOBA to HSA (−2.09kcal/mol) compared to BSA (−0.47kcal/mol). Electrostatic surface potential calculation reveals that the DMOBA binding site within HSA is highly charged compared to BSA.

The family 6 carbohydrate-binding module (CtCBM6B) of Clostridium thermocellum alpha-L-arabinofuranosidase binds xylans and thermally stabilized by Ca2+ ions

The gene encoding CtCBM6B of Clostridium thermocellum α-L-arabinofuranosidase (Ct43Araf) was cloned in pET-21a(+) vector, over-expressed using Escherichia coli BL-21(DE3) cells and purified by immobilized metal-ion affinity chromatography (IMAC). The recombinant CtCBM6B showed a molecular size close to 15 kDa by SDS-PAGE analysis, which was close to the expected size of 14.74 kDa. The ligand-binding affinity of CtCBM6B was assessed against ligands for which the catalytic enzyme, Ct43Araf showed maximum activity. The affinity-gel electrophoresis of CtCBM6B with rye arabinoxylan showed lower equilibrium association constant (Ka, 4.0% C− 1), whereas, it exhibited higher affinity (Ka, 19.6% C− 1) with oat spelt xylan. The ligand-binding analysis of CtCBM6B by fluorescence spectroscopy also revealed similar results with low Ka (3.26% C− 1) with rye arabinoxylan and higher affinity for oat spelt xylan (Ka, 17.9% C− 1) which was corroborated by greater blue-shift in case of oat spelt xylan binding. The CtCBM6B binding with insoluble wheat arabinoxylan by adsorption isotherm analysis showed significant binding affinity as reflected by the equilibrium association constant (Ka), 9.4 × 103 M− 1. The qualitative analysis by SDS-PAGE also corroborated the CtCBM6B binding with insoluble wheat arabinoxylan. The protein-melting curve of CtCBM6B displayed the peak shift from 53°C to 59°C in the presence of Ca2+ ions indicating that Ca2+ ions impart thermal stability to the CtCBM6B structure.

Theoretical Study of Mixed Hydrogen and Dihydrogen Bond Interactions in BH4(NH3)n- Clusters

Ab initio calculations were used to analyze interactions of with 1–4 molecules of NH3 at the MP2/6‐311++G(d,p) and the B3LYP/6‐311++G(d,p) computational levels. In addition to H3B–H⋯H–NH2 dihydrogen bond, the H2N–H⋯NH3 hydrogen bonds were also predicted in clusters. Negative cooperativity in clusters constructed from mixed H3B–H⋯H–NH2 dihydrogen and H2N–H⋯NH3 hydrogen bonds are more remarkable. The negative cooperativity increases with size and number of hydrogen bonds in cluster. The B–H stretching frequencies show blue shifts with respect to cluster formation. Greater blue shift in stretching frequencies was predicted for B–H bonds which did not contribute to dihydrogen bonding with NH3 molecules. The structures were analyzed with the atoms in molecules (AIM) methodology.

Color-tunable Y2Si4N6C:Ce3+ Carbonitride Phosphors for Ultraviolet Light-Emitting Diodes

La3+/Ce3+-codoped carbonitride phosphors-Y2Si4N6C were synthesized via a carbothermal reduction nitridation route. For the Ce3+-doped Y2Si4N6C phosphors, the emission spectrum exhibited a broad band at around 538 nm due to the f–d transition of Ce3+ ions. When La3+ ions were incorporated into the host, the emitting colors of (Y, La)2Si4N6C: Ce3+ phosphors varied from a yellowish green to blue region. The great blue shift in emission bands was due to the variation in the crystal-field strength around the activators. In addition, (Y, La)2Si4N6C:Ce3+ phosphors exhibited high thermal stability, indicating the superior suitability in ultraviolet light-emitting diodes.

Great blue-shift of luminescence of ZnO nanoparticle array constructed from ZnO quantum dots

ZnO nanoparticle array has been fabricated on the Si substrate by a simple thermal chemical vapor transport and condensation without any metal catalysts. This ZnO nanoparticles array is constructed from ZnO quantum dots (QDs), and half-embedded in the amorphous silicon oxide layer on the surface of the Si substrate. The cathodoluminescence measurements showed that there is a pronounced blue-shift of luminescence comparable to those of the bulk counterpart, which is suggested to originate from ZnO QDs with small size where the quantum confinement effect can work well. The fabrication mechanism of the ZnO nanoparticle array constructed from ZnO QDs was proposed, in which the immiscible-like interaction between ZnO nuclei and Si surface play a key role in the ZnO QDs cluster formation. These investigations showed the fabricated nanostructure has potential applications in ultraviolet emitters.

Reflective behavior of strong absorption metallic photonic crystals

The growing interest in fabrication and investigation of metallic photonic crystals is determined by the potential for new properties and applications. In this work, reflective spectra of strong absorption metallic photonic crystals including metal/template composites and metalic inverse opals were systematically studied. Fe–Ni alloy were electrodeposited through self-assembly templates, and inverse opals were fabricated after removal of templates. For metal/template composites, enhanced stop gap is blue shifted due to strong absorption of metallic materials. An effective fraction of alloy is introduced for the first time to describe the alloy participating in the Bragg effect, which is mainly determined by metal. However, alloy inverse opals show greater blue shift of broaden gap to high frequency regions and metallic nature in low frequency regions due to the existence of windows. Scanning electronic micrographs results indicate that there is a critical thickness of wall materials where there are windows in inverse opals. It is proposed here that windows are formed due to the associated breaking of thin alloy walls with template.

Synthesis, Photophysics, and Electroluminescence of Copolyfluorenes Containing Jacketed and Silyl Units

New copolyfluorenes (PSiC8OF0∼PSiC8OF50) composed of 9,9-dioctylfluorene, jacketed units 2,5-bis[(5-octyloxy-phenyl)-1,3,4- oxadiazole]-1-(3,5-dibromophenyl)-benzene (35C8) and 2,5-bis(trimethylsilyl)benzene were synthesized by palladium-catalyzed Suzuki coupling reaction. They were characterized by GPC, 1H NMR, elemental analysis, DSC, TGA, absorption and emission spectroscopy, and cyclic voltammetry (CV). These copolymers were readily soluble in common organic solvents and exhibited high glass transition temperature (up to 173 °C). The copolymer films showed absorption peaks from 325 to 337 nm, and PL peaks from 402 to 408 nm with a great blue shift relative to polyfluorene (377 and 432 nm) originated from silyl and jacketed units. The transient PL spectra show a rapid rise in the lifetime, implying a sharp increase in molecular rigidity and an additional long decay time around 5∼6 ns, assigned to an “excimer-like” state, and its contribution increases with the increased jacketed fraction. The HOMO ener...

A strategy to incorporate monodispersed PbS nanoparticles into ordered mesoporous silica monolith

A new synthetic procedure has been developed for the preparation of ordered mesoporous silica monoliths doped with uniform PbS nanoparticles (NPs). Ordered mesoporous silica monoliths functionalized with thiol groups have been synthesized through co-condensation method in a lyotropic liquid crystalline system. Thiol groups on the interior wall facilitate the incorporation of Pb2+ cations and the formation of PbS NPs inside the ordered mesopores. Combined analysis results indicate that the PbS NPs with a uniform particle size of about 2.5 nm are mostly confined inside the ordered pores of hosts. A great blue shift in the absorbance spectrum has been observed, which shows an obvious quantum confinement effect.

Hydrothermal synthesis of novel sandwich-like structured ZnS/octylamine hybrid nanosheets

Novel sandwich-like structured zinc sulfide (ZnS)/octylamine (OA) hybrid nanosheets with exclusively sheet-like morphology were synthesized for the first time via a mild hydrothermal route using OA as structure-directing agent. The as-synthesized products were characterized by the X-ray diffraction, transmission electron microscopy, scan electron microscopy, energy dispersive analyses of X-rays, thermogravimetric analysis, and ultraviolet and visible absorption spectroscopy. The results showed that OA molecules were intercalated between wurtzite ZnS layers. As revealed from optical absorption measurements, the hybrid nanosheets exhibits strong quantum confinement effect with a great blue shift in the band gap.

Line shifts observed by BCS/Yohkoh

Using the observational data of Bragg crystal spectromater on Yohkoh for the period from October, 1991 to the end of 1995, we have made a statistical study for the flares which show to be in a single loop or a single loop dominated in the SXT images. It is found that although the blue asymmetry is very common during the impulsive phase, the number of events with great total blueshift is very small. It is also found that the blueshift for most flares appears at the early impulsive phase and is temporally correlated with the broadening of the line.

Spin orbital angular momentum coupling effects on the electronic structure of nanocrystalline semiconductor clusters

Abstract The effects of crystal structure and spin-orbital angular momentum coupling on spectroscopic transitions in CdS, CdSe, and CdTe semiconductor clusters are investigated using accurate pseudopotentials. These calculations reveal that spin-orbit coupling splits the exciton peak into A, B, and C transitions. The C transitions exhibit much greater blueshift with cluster size than the A and B transitions. Furthermore, the C transitions exhibit stronger quantum confinement effect in zinc-blende than in wurtzite clusters of the same size. The calculated transition energies are in good agreement with the experimental data and spin-orbit coupling is able to reveal many of the trends in the experimental spectral shifts.

Photophysics of atomic magnesium isolated in solid methane and perdeuteromethane. I. Optical absorption of an impurity species in a quantum solid

Optical absorption spectra recorded at 12 K for the 1 P–1 S transition of atomic magnesium isolated in solid methane and perdeuteromethane exhibit significant differences in their spectral positions and bandwidths. The greater blue shift in CD4 relative to CH4 was found to be unchanged upon sample annealing. Shifts in the spectral position of the resonance transition in the two solids are discussed in the context of mass related differences in the lattice parameters of these light solids which is a manifestation of their behavior as quantum solids. From the blue shift observed in CD4 , the isotope having the smaller cage size, it is proposed that repulsive forces dominate in the interaction of the atomic magnesium guest species with its host. The greater bandwidth of the absorption profile in CH4 , relative to CD4 is discussed in terms of a Jahn–Teller model where the effective frequency of the phonon modes coupling with the electronic transition of the optically active impurity are higher in the former solid.