Silicon nanoparticles synthesized by two different methods were surface modified with 3-mercaptopropyltrimethoxysilane. The particles of ~2 nm size exhibit photoluminescence (PL) in the UV-Vis range of the spectrum. The most intense PL band at 430 nm with an emission lifetime of 1-2 ns is attributed to the presence of the surface defects Si-O-Si, generated after anchoring the organic molecule onto the interface. The excitation-emission matrix of this band is essentially independent of the technique of synthesis, crystalline structure, and size of the silicon nanoparticles.