High pressure studies of porous silicon reveal that a phase transition
occurs at approximately 170 kbar. The phase transition is detected by
an abrupt change in color of porous silicon from orange-yellow to bla
ck. Photoluminescence measurements show an initial blu shift of the lu
minescence peak. At approximately 25 kbar the blue shift ceases and a
reversal of shift is observed. The red shift continues up to approxima
tely 90 kbar at which point the luminescence is quenched. The shift re
versal is interpreted as a pressure-induced direct-indirect transition
in porous silicon. The results are best explained in the context of t
he quantum confinement model.