Photoluminescence spectra of large and small Si NPs before and after incorporation into aerogels. Photoluminescence spectra of free-standing PSi NPs of type LH (red dash-dot, second to top) and SO silicon nanospheres (blue dash-dot, third from top) and the silica aerogel without any particles (green dashed, bottom). The black, solid lines show PL spectra of aerogel-NP composites for a series of concentrations of LH particles increasing upwards (the initial concentrations in the gel preparation increase by factors of approximately 2 from 0.005 to 0.167 mg/ml). The arrow (bottom right) indicates the excitation energy of 3.81 eV (325 nm). All spectra are normalised to unit peak height. Top spectrum: un-normalised PL spectra of free-standing PSi NPs of type LH in vacuum (solid line) and in the presence of oxygen (dashed line); the arrow shows how the intensity drops on introduction of oxygen. No such change is observed for the same particles once incorporated in aerogel.
Amonkosolpan et al. Nanoscale Research Letters 2012 7:397 doi:10.1186/1556-276X-7-397