Raman spectroscopic, photoluminescence spectroscopic and electron paramagnetic resonance spectroscopic studies were made of the relationship between the visible photoluminescence efficiency and the type and concentration of point defects in 75% porous films which were variously doped (p+, p, p-). All 3 types of sample contained more than 30% of crystallites which were smaller than the 3nm which was required for the occurrence of visible photoluminescence. The photoluminescence efficiency varied by up to 3 orders of magnitude between p+, p and p-. The electron paramagnetic resonance results showed that the Pb center, a non-radiative recombination center, was the predominant paramagnetic defect in all 3 types of sample. Whereas the local Pb center distribution was high (1012 to 1013/cm2), only about 0.1% of the total internal surface was oxidized in freshly prepared samples. This demonstrated that the Pb center concentration was not the limiting factor which affected the photoluminescence efficiency in as-prepared porous material.

M.Schoisswohl, H.J.Von Bardeleben, V.Bratus, H.Munder: Thin Solid Films, 1995, 255[1-2], 163-6