nanocrystal

A nanocrystal is a crystalline particle whose dimensions lie in the nanometer range, typically from about 1 to 100 nanometers. At this scale, materials often show properties that differ from their bulk counterparts, including size-dependent optical, electronic, and catalytic behaviors.

Nanocrystals can be broadly categorized into inorganic semiconductor quantum dots, noble metal nanocrystals, magnetic nanocrystals, perovskite nanocrystals, and oxide nanocrystals. Semiconductor nanocrystals, such as CdSe or CsPbBr3, exhibit quantum confinement that tunes their optical absorption and emission with size. Noble metal nanocrystals, like gold or silver, display localized surface plasmon resonances. Magnetic nanocrystals, such as iron oxide, can show superparamagnetic behavior. Core–shell and alloy nanocrystals are common to improve stability, brightness, or functionality.

Synthesis is typically bottom-up, assembling atoms into nanocrystals from molecular precursors. Colloidal synthesis in solution, including hot-injection and solvothermal routes, enables control over size, shape, and composition through precursor choice, temperature, and reaction time. Surface ligands or surfactants cap the nanocrystal facets to passivate surface states and provide solubility; this surface chemistry is crucial for stability and processing. Core–shell architectures and surface modifications expand performance and compatibility with devices or biological systems.

Characterization methods include transmission electron microscopy and X-ray diffraction for structure, UV–visible absorption and photoluminescence for optical properties, and quantum yield measurements. Applications span light-emitting devices, lasers, solar cells, bioimaging, sensing, and catalysis, with ongoing work to improve stability, environmental safety, and scalable production.