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At least 163 records · Page 9

One pot synthesis of nanosized anion doped TiO{sub 2}: Effect of irradiation of sound waves on surface morphology and optical properties

Commercialization of AOP’s for remediation of pollutants from environmental matrix required the process to be operated by solar light. Semiconductor TiO{sub 2} has emerged as an effective and preferred photocatalyst in the field of environmental photocatalysis due to its; (i) biological and chemical inertness (ii) resistance to chemical and photo corrosion, (iii) can absorb natural UV light due to appropriate energetic separation between its valence and conduction band. However, unfortunately the optical band gap of TiO{sub 2} (3.0-3.23 eV) with absorption cut off ∼ 380 nm, enables it to harness only a small fraction (∼ 5%) of the entire solar spectrum. One of the current areas of research is modification of TiO{sub 2} photocatalyst. In present paper one pot greener synthesis from titanium isopropoxide and hydroxylamine hydrochloride has been used as titanium and nitrogen precursor under ultrasonic waves. The as synthesized TiO{sub 2} nanomaterials were dried at 100°C and further calcinated at different temperatures. The effect of reaction parameters such as ultrasonication time on the yield, surface morphology, spectroscopic data and optical properties was also investigated. The results confirm that the anatase phase is a main phase with a crystallite size of 35-77 nm and the calculated band gap of nanomaterials varies from 2.10-3.1 eV.

36 MATERIALS SCIENCE↗

Luminescent carbon quantum dots with high quantum yield as a single white converter for white light emitting diodes

Carbon quantum dots (CQDs) with high quantum yield (51.4%) were synthesized by a one-step hydrothermal method using thiosalicylic acid and ethylenediamine as precursor. The CQDs have the average diameter of 2.3 nm and possess excitation-independent emission wavelength in the range from 320 to 440 nm excitation. Under an ultraviolet (UV) excitation, the CQDs aqueous solutions emit bright blue fluorescence directly and exhibit broad emission with a high spectral component ratio of 67.4% (blue to red intensity to total intensity). We applied the CQDs as a single white-light converter for white light emitting diodes (WLEDs) using a UV-LED chip as the excitation light source. The resulted WLED shows superior performance with corresponding color temperature of 5227 K and the color coordinates of (0.34, 0.38) belonging to the white gamut.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Frequency-dependent photothermal measurement of transverse thermal diffusivity of organic semiconductors

We have used a photothermal technique, in which chopped light heats the front surface of a small (∼1 mm{sup 2}) sample and the chopping frequency dependence of thermal radiation from the back surface is measured with a liquid-nitrogen-cooled infrared detector. In our system, the sample is placed directly in front of the detector within its dewar. Because the detector is also sensitive to some of the incident light, which leaks around or through the sample, measurements are made for the detector signal that is in quadrature with the chopped light. Results are presented for layered crystals of semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pn) and for papers of cellulose nanofibrils coated with semiconducting poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (NFC-PEDOT). For NFC-PEDOT, we have found that the transverse diffusivity, smaller than the in-plane value, varies inversely with thickness, suggesting that texturing of the papers varies with thickness. For TIPS-pn, we have found that the interlayer diffusivity is an order of magnitude larger than the in-plane value, consistent with previous estimates, suggesting that low-frequency optical phonons, presumably associated with librations in the TIPS side groups, carry most of the heat.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Luminescent down shifting effect of Ce-doped yttrium aluminum garnet thin films on solar cells

Ce-doped yttrium aluminum garnet (YAG:Ce) thin films as luminescent down shifting (LDS) materials are introduced into the module of crystalline silicon solar cells. The films are deposited by RF magnetron sputtering on the lower surface of the quartz glass. They convert ultraviolet and blue light into yellow light. Experiments show that the introduction of YAG:Ce films improves the conversion efficiency from 18.45% of the cells to 19.27% of the module. The increasing efficiency is attributed to LDS effect of YAG:Ce films and the reduced reflection of short wavelength photons. Two intentionally selected samples with similar reflectivities are used to evaluate roughly the effect of LDS alone on the solar cells, which leads to a relative increase by 2.68% in the conversion efficiency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Optical devices combining an organic semiconductor crystal with a two-dimensional inorganic diffraction grating

We have fabricated optical devices using an organic semiconductor crystal as an emission layer in combination with a two-dimensional (2D) inorganic diffraction grating used as an optical cavity. We formed the inorganic diffraction grating by wet etching of aluminum-doped zinc oxide (AZO) under a 2D cyclic olefin copolymer (COC) diffraction grating used as a mask. The COC diffraction grating was fabricated by nanoimprint lithography. The AZO diffraction grating was composed of convex prominences arranged in a triangular lattice. The organic crystal placed on the AZO diffraction grating indicated narrowed peaks in its emission spectrum under ultraviolet light excitation. These are detected parallel to the crystal plane. The peaks were shifted by rotating the optical devices around the normal to the crystal plane, which reflected the rotational symmetries of the triangular lattice through 60°.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

A spatial light modulator that uses scattering in a cholesteric liquid crystal

When a cholesteric liquid crystal (helical pitch: 5 μm) was sandwiched between two glass plates with no alignment coating (gap: 20 μm), a random-domain texture appeared and a strong light scattering took place. This translucent texture turned to a transparent homeotropic phase when an electric voltage of 20 V was applied to the liquid crystal layer. This phase transition was used for constructing a spatial light modulator that needed no polarizers. Indium-tin-oxide electrodes (0.8 mm square) were arranged on a glass substrate to create a 20 × 20 pixel array (20 mm square). The liquid crystal was injected into a gap (20 μm thickness) between this substrate and another glass plate with a uniform electrode (ground). The transmittance of the pixels was originally below 10% and decreased to 0% by 7 V application because of increase in the scattering loss. As the voltage was raised, the transmittance increased gradually in the 7–17 V range and then rapidly in the 17–20 V range, attaining 40% at 27 V. Various transmittance distributions or gray-scale images were attainable by applying a suitable voltage (7–27 V) to each pixel. The transmission range of this spatial light modulator extended from ultraviolet (350 nm) to infrared wavelengths (>800 nm). Owing to this wide transmission range as well as capability of the polarizer-free operation, this spatial light modulator is useful to control a lamp spectrum in spectroscopic measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Synthesis and characterization of natural red dye from Caesalpinia sappan linn

The study reports the synthesis and characterization of natural red dye. The dyes were extracted from woods of Caesalpiniasappanlinn at varied temperatures of 70, 80, 90, and 100°C for three hours. The dry wood chips and water at a ratio of 6:1 were immersed in the reactor of 150 liters. The absorbance spectra of the natural red dyes were measured by ultra-violet-visible spectroscopy. Meanwhile, Fourier transform infrared spectroscopy was used to investigate the functional groups of the natural red dyes. In addition, the basic production cost was calculated and the fastness property towards cotton fabrics was investigated according to the Indonesia national standard of 105-C06:2010, 105-B01:2010, and 0288-2008. The results showed that the functional groups found the extracted red dyes indicated the complex bond of brazilein with peak absorbance at a wavelength of 538-540 nm. The extraction temperature also changed the functional group of brazilein. From the color, the absorbance peak, the functional groups, and the main production cost, the best parameter to synthesize the natural red dyes from Caesalpiniasappanlinn was at a temperature of 80°C for two hours. Moreover, the natural red dyes has the fastness to wash resistance, light resistance, and scrub resistance by 4-5, 4, and 3-4, respectively. However, further studies for synthesis the natural red dyes by using a continuous reactor are required to identify the naturally complex compounds in brazilein for improving the fastness properties and for reducing the cost.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Solution of reduced graphene oxide synthesized from coconut shells and its optical properties

Reduced graphene oxide (r-GO)powder has been prepared from coconut shells by carbonization process at 400°C for 3, 4 and 5 hours.Theresulted sample mass was reduced to be 60% relativelycompared to the starting material. The longer heating duration has also led to the rGO with reduced crystalinity according to the X-ray diffractometry data and TEM. The rGO solution was prepared by adding powders of 5, 10 and 15 grams into 50 ml destiled water and then centrifused at 6000 rpm for 30 minutes.The resulted solutions were seen to be varied form clear transparant, light and dark yellow to black. Measurement using particle size analyser shows that the individual rGO particles tends to be agglomerating each others to form bigger size clustering, manifested by the observed bigger size particles for the increasing amount of soluted rGO powders in water.The varying UV-visible spectra of these rGO solutions together with their optical bandgaps will also be discussed in this study.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Charge transport mechanism analysis of Al/CdS:Sr{sup 2+}/ITO device under dark and light

In this study, we have synthesized CdS:Sr{sup 2+} by hydrothermal technique. Material property has been studied by X-ray diffraction (XRD), Scanning electron microscope (SEM) and UV-vis absorption spectroscopy. XRD data revealed that there are mixed phases of CdS and SrS in the synthesized sample. The optical band gap of the material was estimated as 3.15 eV from UV-vis data. The synthesized material has been applied in metal-semiconductor device and transport properties have been analyzed by measuring current–voltage characteristics under dark and light conditions at room temperature. Variation in different device parameters like ideality factor, barrier height and series resistance of Al/CdS:Sr{sup 2+}/ITO device were analyzed by using Cheung’s function.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Synthesis and characterization of ferrite-semiconductor nano composite for photocatalytic degradation of aqueous nitrobenzene solution

Nanoparticles of semiconductor TiO{sub 2}, zinc ferrite (ZnFe{sub 2}O{sub 4}) and ZnFe{sub 2}O{sub 4}-TiO{sub 2} composite, were synthesized by auto combustion route. Subsequent characterization of synthesized photocatalysts was carried out by X-ray powder diffractometry, transmission electron microscopy, UV-Vis-Diffuse Reflectance Spectroscopy to study the structural and textural properties. The specific surface area, pore diameter and pore volume of synthesized materials were investigated by N{sub 2} adsorption analysis while the presence of TiO{sub 2} in the composite material was verified by infrared spectral analysis. The photocatalytic activity of synthesized photocatalysts was evaluated by degradation of nitrobenzene (NB) in aqueous medium under irradiation of ultraviolet light. The result revealed that 77, 73 and 70% of NB was degraded using TiO{sub 2}, ZnFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4}-TiO{sub 2} photocatalysts after 4h in the presence of UV irradiation. The composite photocatalyst was found easy to separate from the treated solution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Light-responsive polymer microcapsules as delivery systems for natural active agents

In this work we report the preparation and the release behavior of UV-responsive polymeric microcapsules containing essential oils as a core. The oil acted also as a monomer solvent during polymerization. Accordingly, the potentially toxic organic solvent traditionally used was replaced with a natural active substance, resulting in a more sustainable functional system. Polymer shell was based on a lightly cross-linked polyamide containing UV-sensitive azobenzene moieties in the main chain. The micro-sized capsules were obtained via interfacial polycondensation in o/w emulsion, and their mean size was measured via Dynamic Light Scattering. Shape and morphology were analyzed through Scanning Electron and Optical Microscopy. UV-responsive behavior was evaluated via spectrofluorimetry, by assessing the release kinetics of a fluorescent probe molecule upon UV light irradiation (λ{sub max}=360 nm). The irradiated samples showed an increase in fluorescence intensity, in accordance with the increase of the probe molecule concentration in the release medium. As for the un-irradiated sample, no changes could be detected demonstrating the effectiveness of the obtained releasing system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Synthesis of photochromic nanoparticles and determination of the mechanism of photochromism

Photochromic nanoparticles of zinc-silicon oxide were synthesized using plasma enhanced chemical vapor deposition. These particles turned black upon irradiating with ultraviolet light. We investigated this phenomenon using density functional theory calculations. Silicon inclusions create trap levels and oxygen defects that reduce the ionization potential of ZnO. This forms a quantum potential between ZnO and zinc-silicon oxide, and the excited electron is stable. Because oxygen defects also increase the bond overlap population between the zinc atoms in a ZnO crystal, they introduce further defects and help in the formation of quantum potentials. Growth of a perfect crystal of ZnO prevents the formation of oxygen defects, which is not desirable for photochromism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Latest experiences and future plans on NSLS-II insertion devices

National Synchrotron Light Source-II (NSLS-II) is the latest storage ring of 3 GeV energy at the Brookhaven National Laboratory (BNL). The horizontal emittance of the electron beam with the currently installed six damping wigglers is 0.9 nm.rad, which could be further reduced to 0.5 nm.rad with more insertion devices (IDs). With only one RF cavity the beam current is restricted to 200 mA. Five hundred mA operation is envisaged for next year with an addition of the second cavity. Six (plus two branches) beamlines have been commissioned in the initial phase of the project. In July 2015, three NIH funded beamlines called “Advanced Beamlines for Biological Investigations with X-rays” (ABBIX) will be added for operation. This paper describes the experiences of ID development, installation, and commissioning for the NSLS-II project as well as our future plans to improve the performance of the facility in terms of source development.

43 PARTICLE ACCELERATORS↗

Calibration of space instruments at the Metrology Light Source

PTB has more than 20 years of experience in the calibration of space-based instruments using synchrotron radiation to cover the UV, VUV and X-ray spectral range. New instrumentation at the electron storage ring Metrology Light Source (MLS) opens up extended calibration possibilities within this framework. In particular, the set-up of a large vacuum vessel that can accommodate entire space instruments opens up new prospects. Moreover, a new facility for the calibration of radiation transfer source standards with a considerably extended spectral range has been put into operation. Besides, characterization and calibration of single components like e.g. mirrors, filters, gratings, and detectors is continued.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Fluorescence-based remote irradiation sensor in liquid-filled hollow-core photonic crystal fiber

We report an irradiation sensor based on a fluorescent “flying particle” that is optically trapped and propelled inside the core of a water-filled hollow-core photonic crystal fiber. When the moving particle passes through an irradiated region, its emitted fluorescence is captured by guided modes of the fiber core and so can be monitored using a filtered photodiode placed at the fiber end. The particle speed and position can be precisely monitored using in-fiber Doppler velocimetry, allowing the irradiation profile to be measured to a spatial resolution of ∼10 μm. The spectral response can be readily adjusted by appropriate choice of particle material. Using dye-doped polystyrene particles, we demonstrate detection of green (532 nm) and ultraviolet (340 nm) light.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Observation of two regions of selective light reflection from a thin film of a cholesteric liquid crystal

Two regions of selective light reflection (in the short- and long- wavelength parts of the visible spectrum) from a thin film of a cholesteric liquid crystal (CLC), consisting of the mixture of two CLCs with opposite chirality and a nematic liquid crystal, are experimentally found for the first time. The spectral position of the reflection regions and the separation between them varies depending on the CLC composition and the temperature. The long-wavelength region of reflection corresponds to the region of Bragg reflection from the CLC helix, while the short-wavelength region is probably due to the defects in the structure of the CLC film. (letters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗