Ultraviolet and Long-lived Blue Luminescence of Oxidized Porous Silicon

Heavily oxidized porous silicon exhibits a strong blue light emission band including a long-lived phosphorescence component, particularly strong below 200 K, and which was modeled as the result of recombinations from triplet states to ground levels. Its origin is related to molecular species in the silicon/silicon oxide nanostructure. A new emission band, in the ultraviolet (UV) region, has been identified in this material. This UV band is associated to a very narrow absorption band, with a very small Stokes shift. The energy levels involved in its emission mechanism are correlated to those involved in the excitation of the blue emission. Moreover, the effect of exposure to water, pentane and ethanol on the luminescence was studied. The blue band was partially quenched, whereas the UV band was dramatically enhanced by exposure to ethanol. This phenomenon was attributed to a rise in the number of hydroxyl groups after ethanol exposure.