Photoluminescence excitation spectroscopy of porous silicon and siloxene

We investigate the optical excitation of visible room-temperature luminescence in electrochemically produced porous silicon and in siloxene obtained from the chemical reaction of calcium disilicide with hydrochloric acid. Luminescence and luminescence excitation spectra (2-5 eV) of different porous silicon and siloxene samples are compared. A characteristic feature of luminescence excitation in porous silicon is the appearance of an exponential tail in the low-energy region. As-prepared siloxene has a pronounced peak in the excitation spectrum at 2.5 eV which is attributed to excitons. A close agreement is found between the properties of porous silicon and annealed siloxene, both in photoluminescence and in luminescence excitation.