We have studied the correlation between the visible photoluminescence (PL) efficiency and the nature and concentration of point defects by Raman spectroscopy, PL spectroscopy and electron paramagnetic resonance (EPR) spectroscopy in as-pre pared, highly porous (75%) Si films of various doping levels (p(+), p, p(-)). From the analysis of the Raman spectra we deduce that all three types of samples have significant (> 30%) amounts of crystallites with dimensions of less than 30 A required for the occurence of visible FL. However, the PL efficiency varies by up to three orders of magnitude between the p(+), p and p(-) layers. We have investigated whether the P-b centre, a non-radiative recombination centre, is responsible for this. The EPR measurements show that the P-b centre is indeed the dominant paramagnetic defect in all three types of samples. However, whereas the local P-b centre distribution is high (10(12)-10(13) cm(-2)), only a small fraction (similar to 10(-3)) of the total internal surface is oxidized in these freshly prepared samples. This demonstrates that the P-b centre concentration is not the limiting factor for the PL efficiency in as-prepared porous Si.