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Visible Spectral Range (visible + spectral_range)

Distribution by Scientific Domains

Physics and Astronomy	40%
Chemistry	40%

Selected Abstracts

Tunable Guided-Mode Resonance Grating Filter

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
Adriana Szeghalmi
Abstract The optical characteristics of shallow 2D nanostructured polycarbonate samples are presented. Tunable guided-mode resonance filters are experimentally demonstrated for the visible spectral range when functional coatings are applied to 2D nanostructures by means of atomic layer deposition. The wavelength position of the reflection peaks can be easily tuned in a broad range (>150,nm) through rotation of the optical element around the axis normal to the substrate without changing the rest of the optical setup. Rigorous coupled wave approach simulation of model systems is performed to obtain insight into the complexity of the optical properties of these systems. The photonic nanostructures presented here are promising optics for application in ultra-compact, portable, miniaturized optical systems. [source]

Highly conductive and optically transparent GZO films grown under metal-rich conditions by plasma assisted MBE

PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3-4 2010
H. Y. Liu
Abstract We demonstrate a critical effect of a metal-to-oxygen ratio on the electrical, optical, and structural properties of ZnO films heavily doped with Ga (carrier concentration in the range of 1020,1021 cm,3) grown by plasma-assisted molecular beam epitaxy. The as-grown layers prepared under the metal-rich conditions exhibited resistivities below 3 × 10,4 , cm and an optical transparency exceeding 90% in the visible spectral range as well as a large blue shift of the transmission/absorption edge attributed to the Burstein,Moss shift of the Fermi level deep into the conduction band, indicating high donor concentration. In contrast, the films grown under the oxygen-rich conditions required thermal activation and showed inferior properties. Furthermore, electrical measurements point to the nonuniform depth distribution of free carriers. An oxygen-pressure-dependent surface disordering is suggested to be responsible for the drastic effect of the metal-to-oxygen ratio on the film properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Chemical bath deposition of CdSe and CdS nanocrystalline films: tailoring of morphology, optical properties and carrier dynamics

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2008

Abstract We review the results of our research towards tailoring morphology and optical properties of films consisting of closely-spaced nanocrystals of CdSe and CdS whose optical band-gap can be tuned to cover the whole visible spectral range. On basis of the obtained results, in particular of photoexcited carrier dynamics, we have proposed a microscopic model that describes well the optical properties of the films. We have also showed that the spin relaxation of electrons in these nanocrystalline films is different than that in mutually isolated nanocrystals of the same size. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Squaraines as Reporter Units: Insights into their Photophysics, Protonation, and Metal-Ion Coordination Behaviour

CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2008

Abstract The synthesis, photophysical properties, protonation, and metal-ion coordination features of a family of nine aniline-based symmetrical squaraine derivatives are reported. The squaraine scaffold displays very attractive photophysical properties for a signalling unit. These dyes show absorption and weakly Stokes-shifted, mirror-image-shaped emission bands in the visible spectral range and there are no hints of multiple emission bands. The mono-exponential fluorescence decay kinetics observed for all the derivatives indicate that only one excited state is involved in the emission. These data stress the interpretation that squaraines can be regarded as polymethine-type dyes. From a coordination chemistry point of view, the squaraines possess four potential binding sites; that is, two nitrogen atoms from the anilino groups and two oxygen atoms from the central C4O2 four-membered ring. These coordination sites are part of a cross-conjugated ,-system and coordination events with protons or certain metal ions affect the electronic properties of the delocalised ,-system dramatically, resulting in a rich modulation of the colour of the squaraines. The absorption band at around 640,nm is blue-shifted when coordination at the anilino nitrogen atoms occurs, whereas coordination to the C2O4 oxygen atoms results in the development of red-shifted bands. Addition of more than one equivalent of protons or metal cations could additionally entail mixed N,O - or N,N -coordinated complexes, manifested in the development of a broad band at 480,nm or complete bleaching in the visible range, respectively. Analysis of the spectrophotometric titration data with HYPERQUAD yielded the macroscopic and microscopic stability constants of the complexes. Theoretical modelling of the various protonated species by molecular mechanics methods and consideration of some of the title dyes within the framework of molecular chemosensing and molecular-scale "logic gates" complement this contribution. [source]

Photochemical Z,E Isomerization of a Hemithioindigo/Hemistilbene ,-Amino Acid

CHEMPHYSCHEM, Issue 11 2007
Thorben Cordes
Abstract The molecule HTI, which combines hemithioindigo and hemistilbene molecular parts, allows reversible switching between two isomeric states. Photochromic behaviour of the HTI molecule is observed by irradiation with UV/Vis light. The photochemical reaction, a Z/E isomerization around the central double bond connecting the two molecular parts, is investigated by transient absorption and emission spectroscopy. For a special HTI molecule, namely, an ,-amino acid, the Z,E isomerization process occurs on a timescale of 30 ps. In the course of the reaction fast processes on the 1,10 ps timescale are observed which point to motions of the molecule on the potential-energy surface of the excited state. The combination of transient absorption experiments in the visible spectral range with time-resolved fluorescence and infrared measurements reveal a photochemical pathway with three intermediate states. Together with a theoretical modelling procedure the experiments point to a sequential reaction scheme and give indications of the nature of the involved intermediates. [source]