This book focuses on methods for producing nanosilicon, its electronic and optical properties, research methods to characterize its spectral and structural properties, and its possible applications. The book covers the basic properties of semiconductors, gives special attention to the photoluminescence of silicon nanoparticles, and describes methods used for studying and controlling the structure and properties of nanocrystalline silicon. It also explores the practical applications of nanocrystalline silicon, including the use of nanoparticles in sunscreens.