The optical properties of silicon and germanium nanowires grown within the pores of hexagonal mesoporous silica matrices have been characterised by ultraviolet absorption and photoluminescence (PL) spectroscopy. A clear blue-shift in the PL of the semiconductor composite materials was observed as the diameter of the nanowires decreased from 85 to 22 A ˚.Powder X-ray diffraction revealed that, as the diameter of the confined nanowires decreased, the strain on the crystallographic structure of the nanowires increased, due to escalating lattice expansion, resulting in a shift in the PL maximum to higher energies. The ability to manipulate the optical properties in templated semiconductor nanowires, through strain engineering, has important implications for the design of future optical devices.
We report single-pass optical gain measurement in poly͑styrene͒ waveguides doped with stilbenoid and phenylene vinylene derivative model compounds under picosecond excitation. Using a wavelength dependent model of amplified spontaneous emission, we produce optical gain spectra for these materials. Net optical gains of gϭ15-20 cm Ϫ1 are deduced. The spectra also exhibit features consistent with excited state absorption and fluorescence depletion via stimulated emission. A figure of merit describing the potential of a material for use as a laser medium is presented and comparisons with other recent publications are made. This comparison indicates that organic materials can compete with inorganic semiconductors for optically pumped applications.
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