Photoluminescence (PL) spectra of porous silicon (PS) at 77-440 K have been studied. We report the observation of additional peaks on the PL band and pronounced fine structure at rather high temperature (77 K)We have found the transformation of the spectra when as-prepared green-emitting PS was subjected to drying in ambient air. The temperature quenching of the PL intensity revealed the same activation energy as the electroconductivity, similar to 0.3 eV, and is considered to be the ionization energy of the radiative centre. Optical absorption measurements reveal the Urbach-like behaviour of the fundamental absorption edge and the energy gap, the latter being similar to 2.4 eV.