A simple way of preparing fluorescent silicon nanoparticles (SiNPs) with a mean diameter of similar to 5 nm was demonstrated from used silicon wafers. Anodic etching of used wafers performed in a customized electrochemical cell produced H-terminated, nano- and micropores on the wafer surface, and SiNPs were attained by mechanically crumbling the nano-/microporous Si surface structures on the etched wafers in an ultrasonic bath. The obtained SiNPs were then re-etched in different ratios of HF/HNO3 acid mixture to produce different PL intensities, sizes, and yields. When the particle sizes were decreased by adjusting the experimental conditions (e.g., strength of the acid mixture, reaction time), the PL spectra from etched SiNPs were also shifted from red to blue, indicating the quantum confinement effect from the nanoparticles. Typically, blue-emitting SiNPs were observed with an average diameter of 2.7 nm and a yield of 0.3 mg/cm(2) of used wafers. Re-etched SiNPs were dialyzed by a 1K-dialysis membrane for purification and for potential use in bioapplications. The efficient method of preparing fluorescent nanoparticles from used monocrystalline Si wafers was demonstrated with a high production yield. The produced particles showed outstanding physical and chemical properties, indicating the applicability of these materials in semiconductor research and bioapplications.