Broadly tunable deep blue laser based on a star-shaped oligofluorene truxene

We report amplified spontaneous emission (ASE) and optically pumped deep-blue-emitting distributed feedback (DFB) lasers based on a star-shaped oligofluorene truxene molecule. A low ASE threshold of 2.1 kW/cm² at 439 nm was achieved. The material exhibits a high net gain of 38 cm^?1 and also low optical loss coefficient of 3.5 cm^?1. Second-order DFB lasers show tuning of the emission wavelength from 422 to 473 nm, and a minimum threshold density of 515 W/cm². This is the broadest tuning range (51 nm) reported for organic deep-blue/blue lasing materials.     

Effects of thermal annealing on the photophysical properties of bisfluorene-cored dendrimer films

Annealing is widely used in the processing of organic semiconductors, and can modify their film morphology and photophysical properties. A study of the effect of annealing on films made from a blue emitting bisfluorene-cored dendrimer is reported. Annealing causes a 15 nm blue-shift in the photoluminescence (PL) spectrum and an 11 nm blue-shift in the amplified spontaneous emission (ASE) spectrum. It causes the PL efficiency to decrease only slightly from 0.92 to 0.83. The radiative decay rate of 1.3 × 10⁹ s^?1, the ASE threshold of 1.5 × 10¹⁸ cm^?3 and the singlet–singlet exciton annihilation rate of 5.5 × 10^?10 cm³ s^?1 are unaffected by annealing. The results indicate a scope for colour adjustment of dendrimer light-emitting diodes and lasers without affecting their efficiencies. Investigation by spectroscopic ellipsometry shows that on annealing, the films become anisotropic, with larger values of the refractive index and extinction coefficient observed for light polarised in the plane of the film than the corresponding out-of-plane values in the absorption region of the bisfluorene core. This anisotropy indicates a preferential in-plane orientation of bisfluorene cores upon annealing.     

Tensile stress and creep in thermally grown oxide

Structural components that operate at high temperatures (for example, turbine blades) rely on thermally grown oxide (TGO), commonly alumina, for corrosion protection. Strains that develop in TGOs during operation can reduce the protectiveness of the TGO. However, the occurrence of growth strains in TGOs, and mechanisms that cause them, are poorly understood. It is accepted that compressive strains can develop as oxygen and metal atoms meet to form new growth within constrained oxide. More controversial is the experimental finding that large tensile stresses, close to 1 GPa, develop during isothermal growth conditions in alumina TGO formed on a FeCrAlY alloy. Using a novel technique based on synchrotron radiation, we have confirmed these previous results, and show that the tensile strain develops as the early oxide, (Fe,Cr,Al)(2)O(3), converts to alpha-Al2O3 during the growth process. This allows us to model the strain behaviour by including creep and this diffusion-controlled phase change.     

Nondestructive optical determination of fiber organization in intact myocardial wall

Mapping the myocardial fiber organization is important for assessing the electrical and mechanical properties of normal and diseased hearts. Current methods to determine the fiber organization have several limitations: histological sectioning mechanically distorts the tissue and is labor-intensive, while diffusion tensor imaging has low spatial resolution and requires expensive MRI scanners. Here, we utilized optical clearing, a fluorescent dye, and confocal microscopy to create three-dimensional reconstructions of the myocardial fiber organization of guinea pig and mouse hearts. We have optimized the staining and clearing procedure to allow for the nondestructive imaging of whole hearts with a thickness up to 3.5 mm. Myocardial fibers could clearly be identified at all depths in all preparations. We determined the change of fiber orientation across strips of guinea pig left ventricular wall. Our study confirms the qualitative result that there is a steady counterclockwise fiber rotation across the ventricular wall. Quantitatively, we found a total fiber rotation of 105.7+/-14.9 degrees (mean+/-standard error of the mean); this value lies within the range reported by previous studies. These results show that optical clearing, in combination with a fluorescent dye and confocal microscopy, is a practical and accurate method for determining myocardial fiber organization.     

Conformations and Electronic Structure of Fullerene C24 and C26 Molecules

The quantum mechanical investigations of fullerene C₂₄, C₂₆, C₂₈ molecule conformers are performed in the framework of the point set group theory and semiempirical PM3 configuration interaction and the MNDO, AMI methods. The main criterion of stability of calculated fiillerene molecules we state the lowest total energy of various isomers and conformers that appears due to the Jahn-Teller distortion. The most stable occurs C₂₄ (D₆ symmetry) conformation with term¹A₁ and open shell C₂₆ (D_3h) conformation with term⁵A₁.     

Analysis of microstructure replication using vibratory assisted thermal imprint process

Microsystem Technologies - In this article, thermal imprint process for replication of high-quality microstructures on the surface of polymer is investigated. Vibrations has been previously...     

Exciton–Exciton Annihilation in Mixed‐Phase Polyfluorene Films

Singlet–singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of β‐phase chains using time‐resolved fluorescence. On a timescale of >15 ps after excitation, the results are fitted well by a time‐independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time‐dependent annihilation rate is observed during the first 15 ps in the glassy phase and in the β‐phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low‐energy sites. The annihilation rate in the mixed‐phase films increases with increasing fraction of β‐phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersedβ‐phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line‐dipole approximation for an exciton wavefunction extending over 2.5 nm. The results indicate that glassy andβ‐phase chromophores are intimately mixed rather than clustered or phase‐separated.     

Degradation of color photographic waste fix solution by anodic oxidation

By use of a capillary electrophoretic method for anion analysis the anodic oxidation of thiosulfate, present in color photo bleach‐fix solutions, was investigated. In a specially constructed electrolysis cell with a cation‐exchange membrane separating the electrode chambers and with a carbon flow‐through three‐dimensional anode the two‐stage anodic oxidation of S₂O₃^2? anions was realized. In the first stage, S₂O₃^2? anions were oxidized to a maximal degree to an intermediate compound – tetrathionate (S₄O₆^2?) – then S₄O₆^2? anions were oxidized to the sulfate (SO₄^2?), avoiding the decomposition of intermediate compounds and the formation of harmful sulfur compounds. © 2002 Society of Chemical Industry