In a semiconductor quantum dot, the confinement of the electron or hole orbit (Bohr diameter) influences the excitonic energy levels significantly. In small nanocrystals, the electronic energy levels are not continuous as in the bulk but are discrete because of the confinement of the electronic wave function to the physical dimensions of the particles. This phenomenon is called quantum confinement and therefore nanocrystals are also referred to as quantum dots (QDs). Properties such as the band gap and characteristic emission of isolated semiconductor nanocrystals are greatly influenced by the size in the 2 to10nm range. In any material, substantial variation of fundamental electrical and optical properties with reduced size will be observed when the energy spacing between the electronic levels exceeds the thermal energy (kT). Moreover, nanocrystals possess a high surface are and a large fraction of the atoms in a nanocrystal are on its surface. Since this fraction depends largely on the size of the particle (30% for a 1-nm crystal, 15% for a 10 nm crystal), it will be reflected as size effects in chemical and physical properties of the nanocrystal. A quantum confinement atomic-system has numerous possibilities for the next generation devices in the field of lighting, displays, sensors, bio-tags and lasers. quantum dots find applications in bio-tags for gene identification and medical imaging, protein analysis, flat-slim displays, lasers and optical components, magneto-optical memories, self-organized smart materials.