Recently a quantum size effect was proposed to be responsible for the
blue shift of optical absorption edge and photoluminescence peak wavel
ength as well as for the porous silicon (PS) formation itself. In the
debate about the mechanism of light emission from PS a correlation bet
ween particle size and luminescence peak position would be a key test
of the confinement approach. In this letter X-ray diffraction results
of as-etched PS samples will be presented that indicate a decrease of
particle size and an increase of stress in conjunction with a blueshif
t of photoluminescence wavelength and absorption edge.