Silicon Nanocrystals: Properties, Synthesis, Characterization, and Applications

Silicon nanocrystals (Si NCs) have attracted considerable interest over the last 30 years because of their distinctive size-dependent luminescence and their potential for incorporation into established silicon-based technologies. In contrast to bulk silicon, an indirect-bandgap material characterized by suboptimal light emission, Si NCs exhibit effective photoluminescence due to quantum confinement, surface state engineering, and exciton recombination processes. The emission characteristics may be adjusted across the visible and near-infrared spectra by manipulating nanocrystal dimensions, surface passivation, and the surrounding dielectric environment. Recent advancements in synthetic methodologies such as chemical vapor deposition (CVD), plasma-based procedures, and solution-phase-based processes have facilitated precise control of Si NC shape, crystallinity, and surface chemistry, thereby improving luminescence efficiency and stability. Furthermore, advances in theoretical modeling have enhanced our understanding of carrier dynamics, defect-mediated processes, and energy transfer mechanisms in Si NCs. These advancements have broadened the use of Si NCs, including in light-emitting devices, bioimaging, photovoltaics, photonics, and quantum technologies. This review summarizes the core mechanisms regulating luminescence in Si NCs, describes recent developments in Si NC synthesis and surface engineering, examines emerging applications, and identifies challenges and future research trajectories essential for converting laboratory advancements in Si NCs into practical technologies.