Fluorescence of Porous Silicon Filled with Liquid Crystal 5CB

Abstract

In the present research, we consider nanoporous silicon filled with nematic liquid crystal (LC) n-pentyl-n' -cyanobiphenyl (5CB) as a specimen of hybrid systems with high quantum yield of fluorescence (FL). The steady-state and time-resolved FL spectra of this system excited by a nitrogen laser (λ = 337 nm) are measured. The maxima of the emission bands for porous silicon are obtained in the range 627–667 nm depending on the sample morphology. In case of porous silicon filled with 5CB, the short-wave bands of 5CB are detected along with the bands of porous silicon. The FL bands of 5CB and porous silicon were characterized by nanosecond and microsecond relaxation, respectively. It is revealed that the filling with 5CB enhances the luminescence of porous silicon by 2–3 times. Such an enhancement is due to the nonradiating energy transfer from 5CB to the porous matrix. A possible mechanism of this energy transfer is discussed.

Keywords:

• liquid crystal
• luminescence
• n-pentyl-n′-cyanobiphenyl
• porous silicon

Notes

This work was carried out in the frame of the project VC89 “The regularities of self-assembling of organic molecules and properties of nano-composite systems “metal-organic medium”, “semiconductor-organic medium”, “dielectric-organic medium” of the NAS of Ukraine.