Particle wave

“Particle Wave” is comprised of six lenticular panels hung in an even, horizontal sequence. Each panel alternates between two solid colour fields as you move past it. There are six colours in total, with each colour represented twice in the spectrum. From left to right, the panels move through yellow, orange, magenta, violet, blue, green and back to yellow. The work’s title refers to the two competing theories of light, which can be understood as either paradoxical or complementary. Like these theories, the experience of viewing the work catches us in a double bind. While we can orient ourselves to see solid colour fields one by one, we are never able to fully capture them all at once. In fact, it is only through our continual movement, and the subsequent transitioning of visible colours that we register the complete spectrum. Through this viewing experience, “Particle Wave” actively engages with our peripheral vision and the transitory nature of perception. It plays with the fundamental pleasures of colour and vision, and the uneasy seduction of being unable to grasp multiple phenomena simultaneously.

The effect of temperature on the mechanism of photoluminescence from plasma-nucleated, nitrogenated carbon nanotips

Nitrogenated carbon nanotips (NCNTPs) have been synthesized using customized plasma-enhanced hot filament chemical vapor deposition. The morphological, structural, and photoluminescent properties of the NCNTPs are investigated using scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The photoluminescence measurements show that the NCNTPs predominantly emit a green band at room temperature while strong blue emission is generated at 77 K. It is shown that these very different emission behaviors are related to the change of the optical band-gap and the concentration of the paramagnetic defects of the carbon nanotips. The studies shed light on the controversies on the photoluminescence mechanisms of carbon-based amorphous films measured at different temperatures. The relevance of the results to the use of nitrogenated carbon nanotips in light-emitting optoelectronic devices is discussed.

1,3,6,8-Tetrasubstituted Pyrenes: Solution-Processable Materials for Application in Organic Electronics

(Equation Presented). A series of star-shaped organic semiconductors have been synthesized from 1,3,6,8-tetrabromopyrene. The materials are soluble in common organic solvents allowing for solution processing of devices such as light-emitting diodes (OLEDs). One of the materials, 1,3,6,8-tetrakis(4- butoxyphenyl)pyrene, has been used as the active emitting layer in simple solution-processed OLEDs with deep blue emission (CIE = 0.15, 0.18) and maximum efficiencies and brightness levels of 2.56 cd/A and >5000 cd/m2, respectively.

Two- and Three-Dimensional Open-Framework Uranium Arsenates: Synthesis, Structure, and Characterization

Hydrothermal reactions between uranium salts and arsenic pentoxide in the presence of two different amines yielded six new uranium arsenate phases exhibiting open-framework structures, ethylenediamine (en): [C2N2H9]-[(UO2)(ASO(4))] I; [C2N2H10][(UO2)F(HASO(4))]2 center dot 4H(2)O, II; [C2N2H9][U2F5(HASO(4))(2)], III; [C2N2H9][UF2(ASO(4))], IV; diethylenetriamine (DETA), [C4N3H16][U2F3(ASO(4))(2)(HAsO4)] V; and [C4N3H16][U2F6(AsO4)(HAsO4)], VI. The structures were determined using single crystal studies, which revealed two- (I, II, V) and three-dimensional (III, IV, VI) structures for the uranium arsenates. The uranium atom, in these compounds, exhibits considerable variations in the coordination (6 to 9) that appears to have some correlation with the synthetic conditions. The water molecules in [C2N2H10][(UO2)F(HAsO4)](2 center dot)4H(2)O, II, could be reversibly removed, and the dehydrated phase, [C2N2H10][(UO2)F(HAsO4)](2), IIa, was also characterized using single crystal studies. The observation of many mineralogical structures in the present compounds suggests that the hydrothermal method could successfully replicate the geothermal conditions. As part of this study, we have observed autunite, Ca[(UO2)(PO4)](2)(H2O)(11), metavauxite, [Fe(H2O)(6)][Al(OH)(H2O)(PO4)](2), finarite, PbCU(SO4)(OH)(2), and tancoite, LiNa2H[Al(PO4)(2)(OH)], structures. The repeated observation of the secondary building unit, SBU-4, in many of the uranium arsenate structures suggests that these are viable building units. Optical studies on the uranium arsenate compound, [C4N3H16][U2F6(AsO4)(HASO(4))), VI, containing uranium in the +4 oxidation state indicates a blue emission through an upconversion process. The compound also exhibits antiferromagnetic behavior.

Synthesis and properties of rare earth doped lamp phosphors

Red, blue and green emitting lamp phosphors such as EU(3+) doped Y2O3 (red phosphor), EU(2+) doped Ba0.64Al12O18.64, BaMgAl10O17 and BaMg2Al16O27 (blue phosphors) and Ce0.67Tb0.33MgAl11O19 and Eu2+, Mn2+ doped BaMgAl10O17 (green phosphors) have been prepared by the combustion of the corresponding metal nitrates (oxidizer) and oxalyl dihydrazide/urea/carbohydrazide (fuel) mixtures at 400 degrees-500 degrees C within 5 min. The formation of these phosphors has been confirmed by their characteristic powder X-ray diffraction patterns and fluorescence spectra. The phosphors showed characteristic emission bands at 611 nm (red emission), 430-450 nm (blue emission) and 515-540 nm (green emission). The fine-particle nature of the combustion derived phosphors has been investigated using powder density, particle size and BET surface area measurements.

Zn(II), Cd(II) and Hg(II) complexes with 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole: Syntheses, structures and luminescence

Five coordination compounds Zn(mbmpbi)(2)Cl-2 (1), Zn(mbmpbi)(2)Br-2 (2), Cd(mbmpbi)(2)Cl-2 (3), Hg(mbmpbi)(2)Cl-2 (4) and Hg(mbmpbi)(2)Br-2 (5) were synthesized by the reaction of 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole (mbmpbi) with the corresponding metal halides. The complexes have been characterized by elemental analysis, conductance measurements, FT-IR, H-1 NMR and photoluminescence spectral studies. The ligand mbmpbi exhibits the N-benzimidazole coordination. The structures of 3-5 have been determined by single crystal X-ray diffraction. These three complexes are isostructural, crystallizing in the monoclinic system. P2/n space group with a distorted tetrahedral geometry around the metal ion. Zn(II) and Cd(II) complexes show strong blue emission in solid state at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.

Investigations on structural and optical properties of co-doped (Ag, Co) ZnO nanoparticles

Undoped and co-doped (Ag, Co) ZnO powders were synthesized by chemical co-precipitation method without using any capping agent. The X-ray diffraction results indicate that the undoped and co-doped ZnO powders have pure hexagonal structure and are consisting of nanosized single-crystalline particles. The size of the nanoparticles increases with increasing Ag concentration from 1 to 5 mol% as compared to that of undoped ZnO. The presence of substitution dopants of Ag and Co in the ZnO host material was confirmed by the Energy dispersive analysis of X-rays (EDAX). Optical absorption measurements indicate blue shift and red-shift in the absorption band edge upon doping concentration of Ag and blue emission was observed by photoluminescence (PL) studies.

Synthesis, morphology, optical and photocatalytic performance of nanostructured beta-Ga2O3

Fine powders of beta-Ga2O3 nanostructures were prepared via low temperature reflux condensation method by varying the pH value without using any surfactant. The pH value of reaction mixture had great influence on the morphology of final products. High crystalline single phase beta-Ga2O3 nanostructures were obtained by thermal treatment at 900 degrees C which was confirmed by X-ray diffraction and Raman spectroscopy. The morphological analysis revealed rod like nanostructures at lower and higher pH values of 6 and 10, while spindle like structures were obtained at pH = 8. The phase purity and presence of vibrational bands were identified using Fourier transform infrared spectroscopy. The optical absorbance spectrum showed intense absorption features in the UV spectral region. A broad blue emission peak centered at 441 nm due to donor-acceptor gallium-oxygen vacancy pair recombination appeared. The photocatalytic activity toward Rhodamine B under visible light irradiation was higher for nanorods at pH 10.

Insights into the AIEE of 1,8-Naphthalimides (NPIs): Inverse Effects of Intermolecular Interactions in Solution and Aggregates

Systematic structural perturbation has been used to fine-tune and understand the luminescence properties of three new 1,8-naphthalimides (NPIs) in solution and aggregates. The NPIs show blue emission in the solution state and their fluorescence quantum yields are dependent upon their molecular rigidity. In concentrated solutions of the NPIs, intermolecular interactions were found to quench the fluorescence due to the formation of excimers. In contrast, upon aggregation (in THF/H2O mixtures), the NPIs show aggregation-induced emission enhancement (AIEE). The NPIs also show moderately high solid-state emission quantum yields (ca. 10-12.7 %). The AIEE behaviour of the NPIs depends on their molecular rigidity and the nature of their intermolecular interactions. The NPIs 1-3 show different extents of intermolecular (pi-pi and C-H center dot center dot center dot O) interactions in their solid-state crystal structures depending on their substituents. Detailed photophysical, computational and structural investigations suggest that an optimal balance of structural flexibility and intermolecular communication is necessary for achieving AIEE characteristics in these NPIs.

Tin-Incorporation Induced Changes in the Microstructural, Optical, and Electrical Behavior of Tungsten Oxide Nanocrystalline Thin Films Grown Via Spray Pyrolysis

Undoped and Sn-doped WO3 thin films were grown on cleaned glass substrates by chemical spray pyrolysis, using ammonium tungstate (NH4)(2)WO4 as the host precursor and tin chloride (SnCl4 center dot 5H(2)O) as the source of dopant. The XRD spectra confirm the monoclinic structure with a sharp narrow peak along (200) direction along with other peaks of low relative intensities for all the samples. On Sn doping, the films exhibit reduced crystallinity relative to the undoped film. The standard deviation for relative peak intensity with dopant concentration shows enhancement in heterogeneous nucleation growth. As evident from SEM images, on Sn doping, appearance of island-like structure (i.e., cluster of primary crystallites at few places) takes place. The transmittance has been found to decrease in all the Sn-doped films. The optical band gap has been calculated for both direct and indirect transitions. On Sn doping, the direct band gap shows a red shift and becomes 2.89 eV at 2 at.% doping. Two distinct peaks, one blue emission at 408 nm and other green emission at 533 nm, have been found in the PL spectra. Electrical conductivity has been found to increase with Sn doping.

Facile synthesis of PbWO4: Applications in photoluminescence and photocatalytic degradation of organic dyes under visible light

Stolzite polymorph of PbWO4 catalyst was prepared by the facile room temperature precipitation method. Structural parameters were refined by the Rietveld analysis using powder X-ray data. PbWO4 was crystallized in the scheelite-type tetragonal structure with space group I4(1)/a (No. 88). Field emission scanning electron microscopy revealed leaf like morphology. Photoluminescence spectra exhibit broad blue emission (425 nm) under the excitation of 356 nm. The photocatalytic degradation of Methylene blue, Rhodamine B and Methyl orange dyes were measured under visible illumination. The 100% dye degradation was observed for MB and RhB dyes within 60 and 105 min. The rate constant was found to be in the decreasing order of MB > RhB > MO which followed the 1st order kinetic mechanism. Therefore, PbWO4 can be a potential candidate for blue component in white LEDs and also acts as a catalyst for the treatment of toxic and non-biodegradable organic pollutants in water. (C) 2014 Elsevier B.V. All rights reserved.

Luminescence enhancement in monoclinic CaAl2O4:Eu2+, Cr3+ nanophosphor by fuel-blend combustion synthesis

Eu2+ ion doped into a suitable host results in an efficient luminophore with engineering relevance; however stabilizing this ion in a host is known to be a challenge. Here we report a novel approach for the synthesis of efficient CaAl2O4 phosphor containing Eu2+ luminophore and Cr3+ activator. CaAl2O4:Eu2+, Cr3+ is prepared by a solution combustion (SCS) method using (i) urea, (ii) oxalyl dihydrazide (ODH) and (iii) fuel-blend (in which overall fuel to oxidizer ratio (F/O) = 1). A Multi-channel thermocouple setup is used to measure the flame temperatures to study the nature of combustion of various fuel mixtures. The variation of adiabatic flame temperature is calculated theoretically for different urea/ODH mixture ratios according to thermodynamic concept and correlated with the observed flame temperatures. Blue emission of the CaAl2O4:Eu2+ phosphor is enhanced similar to 20 times using the fuel-blend approach. Using the observed reaction kinetics, and the known chemistry of smoldering type combustion, a mechanism is proposed for the observed stabilization of Eu2+ ion in the fuel-blend case. This also explains the observed improvement in blue light emission. We show that the right choice of the fuel ratio is essential for enhancing photoluminescence (PL) emission. The PL intensity is highest for ODH lean and urea rich combination (i.e. when the ratio of ODH:urea is 1:5); measured color purity is comparable to commercial blue phosphor, BAM:Eu2+. (C) 2015 Elsevier B.V. All rights reserved.

Eu3+-activated SrMoO4 phosphors for white LEDs applications: Synthesis and structural characterization

We report the synthesis of Eu3+-activated SrMoO4 phosphors by the facile nitrate-citrate gel combustion method. Powder XRD and Rietveld refinement data confirmed that these phosphors have a monophasic scheelite-type tetragonal structure with space group I4(1)/a (No. 88). FESEM micrographs indicate the agglomerated spherical particles. FTIR spectra showed four stretching and bending vibrational modes (2A(u) and 2E(u)). UV-Visible absorption spectroscopy illustrated that the optical band gap energy (E-g) values increase with increase in Eu3+ concentration. The host SrMoO4 phosphor exhibited an intense blue emission under UV excitation (368 nm). The Eu3+-activated SrMoO4 phosphors revealed characteristic luminescence due to Eu3+ ion corresponding to D-5(1) -> F-7(J) (J = 1,2) and D-5(0) -> F-7(J) (J = 1,2,3,4) transitions upon 465 nm excitation. The electric dipole transition located at 615 nm (D-5(0) -> F-7(2)) was stronger than the magnetic dipole transition located at 592 nm (D-5(0) -> F-7(1)). Intensity parameters (Omega(2), Omega(4)) and radiative properties such as transition probabilities (A(T)), radiative lifetime (tau(rad)) and branching ratio (beta) of Eu3+-activated SrMoO4 phosphors were calculated using the Judd-Ofelt theory. Based on the CIE chromaticity diagram, these phosphors can be promising materials for the development of blue and orange-red component in white LEDs. (C) 2015 Elsevier B.V. All rights reserved.

Structural, Optical, and Piezoelectric Response of Lead-Free Ba0.95Mg0.05Zr0.1Ti0.9O3 Nanocrystalline Powder

Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x = 0.025-0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x = 0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response aside from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 and 723 cm(-1) characteristic of tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm, respectively. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. A piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature.

Energy transfer and infrared-to-visible upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

We report on the energy transfer and frequency upconversion spectroscopic properties of Er3+-doped and Er3+/Yb3+-codoped TeO2-ZnO-Na2O-PbCl2 halide modified tellurite glasses upon excitation with 808 and 978 nm laser diode. Three intense emissions centered at around 529, 546 and 657 nm, alongwith a very weak blue emission at 4 10 nm have clearly been observed for the Er3+/Yb3+-codoped halide modified tellurite glasses upon excitation at 978 nm and the involved mechanisms are explained. The quadratic dependence of fluorescence on excitation laser power confirms the fact that the two-photon contribute to the infrared to green-red upconversion emissions. And the blue upconversion at 410 nm involved a sequential three-photon absorption process. (c) 2005 Elsevier Ltd. All rights reserved.