Visible photoluminescence (PL) of porous silicon is found to be comple
tely quenched by the application of a cathodic polarization. Cathodica
lly biased lightly doped n-type porous layers in contact with an aqueo
us solution exhibit reversible, complete and energy-selective quenchin
g for a polarization variation of only about 500 mV. A spectral bluesh
ift along with a narrowing of the line width accompanies the observed
strong PL quenching. It results from a selective quenching starting by
the low luminescence energy and reaching progressively the high lumin
escence energy as the cathodic polarization is increased.