Ultrafast photoluminescence dynamics of blue-emitting silicon nanostructures

We report on ultrafast photoluminescence (PL) spectroscopy of blue and red-emitting silicon nanostructures. We prepared samples of porous Si with different dominating PL bands in time-integrated PL spectrum. These samples show also striking differences in ultrafast PL dynamics. For the red-emitting samples we observe rapid PL onset followed by a two-exponential decay, which is spectrally dependent. For the blue-emitting porous Si the PL builds up several picoseconds and decays mono-exponentially with spectrally independent PL rise and decay times.

Our results indicate that a dominant part of the blue and red emission comes from two distinct species with different energy states structures. This is furthermore supported by two-photon absorption induced PL mea-surements. The two-photon and one-photon absorption induced PL spectra, which are identical for the red-emitting samples, differ substantially for the blue-emitting ones. However, polarization properties of PL suggest that the blue PL band originates from several overlapping PL bands with sample-dependent importance. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)