Sol-gel optical nanocomposites: Design and applications

The history and method of producing gel-polymer composites is presented. Tailoring properties, such as density, refractive index, hardness, elastic modulus, compressive strength, abrasion resistance, and modulus of rupture is achieved through controlling the ratio of gel-derived silica to polymer phases. Several different applications of composite technology are presented. Solid-state lasing in dye-doped silica gel-PMMA composites has been recently achieved. The difficulties in generating stable photochromism in gels and gel-derived composites are discussed. Microlens arrays for data reading, employing large gel-polymer spheres, have been developed. In addition, a new flat-screen color display technology, based upon the periodic arrangement of dye-doped microsphere pixels, emitting blue, green and red light, is disclosed for the first time.     

Universal area product formulas for rotating and charged black holes in four and higher dimensions

We present explicit results for the product of all horizon areas for general rotating multicharge black holes, both in asymptotically flat and asymptotically anti-de Sitter spacetimes in four and higher dimensions. The expressions are universal, and depend only on the quantized charges, quantized angular momenta and the cosmological constant. If the latter is also quantized these universal results may provide a "looking glass" for probing the microscopics of general black holes.     

Temperature dependent structured absorption spectra of molecular chlorine

A dual wavelength range spectrometer system has been designed and constructed which can simultaneously perform single pass UV absorption spectroscopy and cavity enhanced absorption spectroscopy in the green region of the visible spectrum. Using the system the absorption spectrum of molecular chlorine has been measured, in the wavelength range 509-570 nm, using cavity enhanced absorption spectroscopy. Absolute absorption cross sections were obtained by simultaneous measurement of the UV spectrum to obtain the Cl(2) concentration. These are the first temperature dependent measurements of the Cl(2) absorption cross sections in this region which are vibronically resolved. Laboratory measurements were conducted at four temperatures (298, 273, 233, and 197 K). Spectral modelling of the Cl(2) B(3)Π(0(u)(+))-X(1)Σ(g)(+) electronic transition has been performed, the results of which are in good agreement with our measured spectra.     

A simple approach to T2 imaging in MRI

A simple method for obtaining images whose contrast depends only on T₂ is described and tested both on phantoms and in vivo. The method works reliably and effectively under clinically realistic operating conditions using standard imaging protocols. It can result in a substantial reduction in imaging times for T₂ weighted images.     

Deep Red Emitting Heteroleptic Ir(III) Complexes that Incorporate Unsymmetrical 4-quinoline Carboxylic Acid Derived Ligands

Six disubstituted ligands based upon 2-(2′-pyridinyl/pyrazinyl)quinoline-4-carboxylic acids have been synthesised, solvent-free, in one step from a range of commercially available isatin derivatives. These species behave as ancillary chelating ligands for Ir(III) complexes of the form [Ir(C^N)₂(N^N)]PF₆ (where C^N=cyclometalating ligand; N^N=2-(2′-pyridinyl/pyrazinyl)quinoline-4-carboxylic acids). An X-ray crystallographic study on one complex shows a distorted octahedral geometry wherein a cis-C,C and trans-N,N coordination mode is observed for the cyclometalating ligands. DFT calculations predicted that variations in N^N ligand from 2,2′-bipyridine to L^{1 – 6} should localise the LUMO on to the Lⁿ ligand and that the complexes are predicted to display MLCT/LLCT character. All complexes displayed luminescence in the deep red part of the visible region (674–679 nm) and emit from triplet states, but with little apparent tuning as a function of L^{1 – 6} . Further time-resolved transient absorption spectroscopy supports the participation of these triplet states to the excited state character.