**2. Brief history of quantum dots**

Since the early days of 1960s colloidal semiconductor crystallites or quantum dots concept has been suggested as a new structure of semiconductor materials. In 1981 Ekimove [1] reported the existence of semiconductor crystallitesin a glass matrix. In 1985 Louis Brus developed a quantum model of spherical quantum dots based on effective mass model [2]. Quantum dot term was coined in 1988 by Reed's group [3]. Smith and his coworkers [4] successfully reported the growth of quantum film by depositing 3D silver Ag islands on gallium arsenide GaAs substrate in a two-step process. By the end of the 1990s, commercial productions of colloidal quantum dots becomefeasible. In 2004 a research group at Los Alamos [5] reported that a quantum dotis capable of emitting up to three electrons per photon, as opposed to onlyone for standard single crystalline layer semiconductors. It is now well established that absorption of high energy photon ( 8×Eg) quantum dot is capable of generation seven photo-generated charge carriers due to inverse Auger recombination [6]. Now a days quantum dots are promising nanostructure materials in photonics and biomedical applications.
