Synthetic particles that range from 1 to 100 nanometers in diameter. Semiconductor nanoparticles around 1–20 nm in diameter are often called quantum dots, nanocrystals, or Q-particles. These particles possess short-range structures that are essentially the same as the bulk semiconductors, yet have optical or electronic properties that are dramatically different fromthe bulk properties. The confinement of electrons within a semiconductor nanocrystal results in a shift of the band gap to higher energy with smaller crystalline size. This effect is known as the quantum size effect. In the strong confinement regime, the actual size of the semiconductor particle determines the allowed energy levels and thus the optical and electronic properties of the material.
Due to their finite, small size and the high surfaceto-volume ratio, nanoparticles often exhibit novel properties. These properties can ultimately lead to new applications, ranging from catalysis, ceramics, microelectronics, sensors, pigments, and magnetic storage, to drug delivery and biomedical applications. Research in this area is motivated by the possibility of designing nanostructured materials that possess novel electronic, optical, magnetic, mechanical, photochemical, and catalytic properties. Such materials are essential for technological advances in photonics, quantum electronics, nonlinear optics, and information storage and processing.