The recombination of an electron-hole pair at a silicon dangling bond
located on the surface of a silicon crystallite is studied. We find th
at it is highly dependent on confinement. We show that the capture of
an electron or a hole by a neutral dangling bond is a nonradiative pro
cess in crystallites with bandgaps smaller than 2.2 eV. On the contrar
y, the capture by a charged dangling bond is radiative. Therefore the
presence of one dangling bond in a crystallite kills its luminescent p
roperties above 1.1 eV but can produce a luminescence below 1.1 eV. Th
e origin of the infrared luminescence of porous silicon is discussed i
n light of these results.