On the photoluminescence of a-C:H films

a-C:H films deposited from methane and helium mixture in a capacitively coupled rf plasma were found to show photoluminescence (PL) with peak intensities at energies far above the Taue gap of these films. Apart from the PL the films were investigated with respect to their IR and UV/VIS absorption properties as well as their Raman spectra were examined. The ultraviolet (UV) and blue luminescence from hard a-C:H thin films are explained by incorporation of polycyclic hydrocarbons from gas-phase reactions in the methane helium plasma into the film.

Potential tuning of porous silicon luminescence

Electrochemical investigations were conducted of the effect of potential on the luminescence of porous silico (PS). The use of liquid contacts allows the potential to be controlled during studies of the photoluminescence (PL) and electroluminescence (EI). The PL and EL of PS samples prepared from n-type substrates is considered. To obtain luminescence from such PS it is necessary to generate holes in the valence band. This is achieved by either photoexcitation or an electrochemical process involving the reduction of persulfate. This paper describes the investigations of the effect of potential on the PL and EL of PS. A mechanism of 'potential tuning' based on electron occupancy and Auger quenching is then proposed.

Bimesogenic liquid crystals: New materials for high performance flexoelectric and blue phase displays

In this paper we will describe new bimesogenic nematic liquid crystals that have high flexoelectro-optic coefficients (e/K),of the order of 1.5 CN 1 m-1, high switching angles, up to 100° and fast response times, of the order of 100μs or less. We will describe devices constructed, using the ULH texture that may be switched to the optimum angle of 45° for a birefringence based device with the fields of 4Vμm-1 over a wide temperature range. Such devices use an "in plane" optical switching mode, have gray scale capability and a wide viewing angle. We will describe devices using the USH or Grandjean texture that have an optically isotropic "field off" black state, uses "in plane" switching E fields, to give an induced birefringence phase device, with switching times of the order of 20μs. We will briefly describe new highly reflective Blue Phase devices stable over a 50V temperature range in which an electric field is used to switch the reflection from red to green, for example. Full RGB reflections may be obtained with switching times of a few milliseconds. Finally we will briefly mention potential applications including high efficiency RGB liquid crystal laser sources. © 2006 SID.