We have studied the photoluminescence (PL) process in amorphous silicon (a-Si) and crystalline silicon (c-Si) nanoparticles in order to understand the quantum confinement and localization of electron wave functions in nanometer and molecular scale materials. The a-Si and c-Si nanoparticles were prepared by electrochemical etching of hydrogenated a-Si films and c-Si wafers. The PL spectra of a-Si and c-Si nanoparticles are blueshifted from those of bulk a-Si and c-Si. The global PL spectrum of a-Si nanoparticles is similar to that of c-Si nanoparticles. However, the characteristics of resonantly excited PL spectra and PL decay dynamics of a-Si nanoparticles are different from those of c-Si nanoparticles. Luminescence properties of a-Si and c-Si nanoparticles are discussed in terms of the quantum confinement and the Anderson localization of electron wave functions in nanoscale materials.