We have studied the effect of ion‐irradiation on porous Si formation, microstructure, and optical properties. Porous Si was first self‐implanted and then fabricated by anodization. With increasing implantation dose, the photoluminescence (PL) intensity decreased, and the PL spectra were also red shifted. Porous Si formed from crystal Si emitted light, while that from preamorphized Si did not. Porous Si luminescent patterns with a resolution of 2 &mgr;m features were formed by selective ion implantation. ©1996 American Institute of Physics.