Selective formation of visible light emitting porous silicon on focused ion beam implanted patterns on n-type Si(100) can be achieved by electrochemically polarizing the material, anodic to a distinct pore formation potential of the implanted surface but cathodic to the pore formation potential of the unimplanted surface. Within a broad range of electrochemical conditions and implant doses selectivity of the pore growth process can be maintained. However, significant photoluminescence (PL) is only obtained if the pr,rous structures are of a sponge-like morphology with an apparent feature size in the range of 100 nm. Within such structures, Raman spectroscopy indicates the presence of nanocrystallites with a size of similar to 5 nm. Both electrochemical conditions and implantation parameters strongly influence the morphology of the etched structures. Depending on the experimental conditions, the implanted area can be (i) converted into a porous structure, (ii) completely etched out, or (iii) show a nearly intact surface layer covering a buried porous structure. The occurrence of such a top layer can he explained by the implant depth profile and the presence or absence of such a top layer can determine whether PL is observed or not.