Enhancement of fluorescence of porous silicon upon saturation by liquid crystal |
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Authors: | Yu P Piryatinski L A Dolgov O V Yaroshchuk T A Gavrilko and S K Lazarouk |
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Institution: | (1) University of Rochester, Rochester, New York, USA |
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Abstract: | The fluorescence of samples of porous silicon of various morphologies that are filled with a liquid crystal (LC), n-pentyl-n′-cyanobiphenyl (5CB), is studied. The fluorescence spectra of the sample, along with the long-wavelength band of porous silicon
with a maximum in the range 627–667 nm, exhibit a short-wavelength band of 5CB with a maximum in the range 385–410 nm. The
radiative relaxation times of porous silicon and 5CB lie in the micro- and nanosecond ranges, respectively. It is found that
the filling of pores with 5CB enhances the fluorescence of porous silicon by two to three times. This enhancement is caused
by non-radiative energy transfer from 5CB to the porous matrix as a result of efficient interactions between LC molecules
and pore walls. Using IR spectroscopy, it is shown that the formation of hydrogen bonds between cyano groups of 5CB molecules
and silanol groups of pore surface is the predominant type of these interactions. A transfer mechanism is suggested according
to which excited associates of 5CB molecules transfer their energy via surface channels to excitons of porous silicon, enhancing
its fluorescence. |
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Keywords: | |
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