Silicon nanoparticles of 1–5 nm size (SiNPs) were synthesized by a bottom-up (BU) approach involving a chemical wet method. The contribution of different emitters to the overall excitation–emission matrix was analyzed on the assumption that pure substances existing in a unique form show an excitation wavelength-invariant emission spectrum. The occurrence of emitters differing in size and aggregation was supported by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), time-resolved single photon counting, and time-resolved anisotropy experiments. The effect on photoluminescence (PL) of the particle surface oxidation as a result of aging is studied and compared to that of surface oxidized particles obtained by a top-down (TD) approach following an electrochemical method with HF etching. Surface oxidation to SiO x seems to introduce two different effects on the SiNP PL. An emission originated in surface states associated to SiO x was identified and observed for SiNPs synthesized by both BU and TD approaches. Blue-shifted excitation–emission spectra associated to a silicon core in embedded SiO x nanostructures were also identified. Theoretical studies were carried out to help understand the observed results.