Influence of preparation and storage conditions on photoluminescence of porous silicon powder with embedded Si nanocrystals

The time changes of photoluminescence (PL) characteristics of porous silicon (porSi) powder during storing in different ambients have been reported. A porous silicon material with embedded Si nanocrystals of size of few nanometers was prepared by an electrochemical method from 10 to 20 Omega cm p-type Si wafers, and both constant and pulse current anodization regimes were used. A powder with a submicron average particle size was obtained by simple mechanical lift-off of the porous layer followed by additional manual milling. The air, hexane, and water as storage media were used, and modification by a nonionic surfactant ( undecylenic acid) of the porSi surface was applied in the latter case. Dependence of PL characteristics on preparation and storage conditions was then studied. A remarkable blue shift of a position of PL maximum was observed in time for porSi powders in each storage media. In water suspension a many-fold build-up (10-30) of PL intensity in a time scale of few days was accompanied by an observed blue shift. Photoluminescence time behavior of porSi powders was described by a known mechanism of the change of porSi PL from free exciton emission of Si nanocrystals to luminescence of localized oxidized states on the Si nanocrystal surface.