A 2D [FeII-bistetrazole] coordination polymer exhibiting spin-crossover properties

The reaction of 1,3-bis(tetrazol-1-yl)-2-propanol (btzpol) with Fe(BF4)2 · 6H2O in acetonitrile yields the remarkable 2D coordination polymer [FeII(btzpol)1.8(btzpol-OBF3)1.2](BF4)0.8 · (H2O)0.8(CH3CN) (1). This compound has been structurally characterized using an X-ray single-crystal synchrotron radiation source. The iron(II) centers are bridged by means of double btzpol bridges along the c direction, and by single btzpol bridges along the b direction. The reaction of part of the ligand with the counterion has forced the compound to crystallize in this extended two dimensional structure. The compound shows spin-transition properties, both induced by temperature and light, with T½ = 112 K and T(LIESST) = 46 K, respectively. The relaxation of the metastable high-spin state created by irradiation is exponential, following an Arrhenius type behavior at high temperature, and dominated by a temperature independent tunneling process at lower temperatures.

Recent advances in the heterogeneously catalysed aerobic selective oxidation of alcohols

The heterogeneously catalysed selective aerobic oxidation of alcohols is an important tool for the synthesis of valuable chemical intermediates and a hot topic within both academic and industrial arenas. In this mini-review, selected aspects of catalyst formulation, process operating conditions, and progress in identifying the active sites and surface reaction mechanisms notably through the application of synchrotron radiation, are highlighted. © 2010 Society of Chemical Industry.

The measurements of neutron and gamma dose rates in mixed radiation fields, using a liquid scintillation counter

Measurements of neutron and gamma dose rates in mixed radiation fields, and gamma dose rates from calibrated gamma sources, were performed using a liquid scintillation counter NE213 with a pulse shape discrimination technique based on the charge comparison method. A computer program was used to analyse the experimental data. The radiation field was obtained from a 241Am-9Be source. There was general agreement between measured and calculated neutron and gamma dose rates in the mixed radiation field, but some disagreement in the measurements of gamma dose rates for gamma sources, due to the dark current of the photomultiplier and the effect of the perturbation of the radiation field by the detector. An optical fibre bundle was used to couple an NE213 scintillator to a photomultiplier, in an attempt to minimise these effects. This produced an improvement in the results for gamma sources. However, the optically coupled detector system could not be used for neutron and gamma dose rate measurements in mixed radiation fields. The pulse shape discrimination system became ineffective as a consequence of the slower time response of the detector system.

Bessel beams from semiconductor light sources

We report on recent progress in the generation of non-diffracting (Bessel) beams from semiconductor light sources including both edge-emitting and surface-emitting semiconductor lasers as well as light-emitting diodes (LEDs). Bessel beams at the power level of Watts with central lobe diameters of a few to tens of micrometers were achieved from compact and highly efficient lasers. The practicality of reducing the central lobe size of the Bessel beam generated with high-power broad-stripe semiconductor lasers and LEDs to a level unachievable by means of traditional focusing has been demonstrated. We also discuss an approach to exceed the limit of power density for the focusing of radiation with high beam propagation parameter M2. Finally, we consider the potential of the semiconductor lasers for applications in optical trapping/tweezing and the perspectives to replace their gas and solid-state laser counterparts for a range of implementations in optical manipulation towards lab-on-chip configurations. © 2014 Elsevier Ltd.

Towards novel compact laser sources for non-invasive diagnostics and treatment

An important field of application of lasers is biomedical optics. Here, they offer great utility for diagnosis, therapy and surgery. For the development of novel methods of laser-based biomedical diagnostics careful study of light propagation in biological tissues is necessary to enhance our understanding of the optical measurements undertaken, increase research and development capacity and the diagnostic reliability of optical technologies. Ultimately, fulfilling these requirements will increase uptake in clinical applications of laser based diagnostics and therapeutics. To address these challenges informative biomarkers relevant to the biological and physiological function or disease state of the organism must be selected. These indicators are the results of the analysis of tissues and cells, such as blood. For non-invasive diagnostics peripheral blood, cells and tissue can potentially provide comprehensive information on the condition of the human organism. A detailed study of the light scattering and absorption characteristics can quickly detect physiological and morphological changes in the cells due to thermal, chemical, antibiotic treatments, etc [1-5]. The selection of a laser source to study the structure of biological particles also benefits from the fact that gross pathological changes are not induced and diagnostics make effective use of the monochromatic directional coherence properties of laser radiation.

Conical refraction with low-coherent light sources

We report on conical refraction (CR) experiments with low-coherent light sources such as light-emitting diodes (LEDs) that demonstrated different CR patterns. The change of a pinhole size from 25 to 100 μm reduced the spatial coherence of the LED radiation and resulted in the disappearance of the dark Poggendorf ring in the Lloyd's plane. This is attributed to the interference nature of the Lloyd's distribution and is found to be in excellent agreement with the paraxial dual-cone model of CR.