Semiconductor nanocrystallites having radii smaller than the bulk exciton Bohr radius constitute a class of materials intermediate between molecular and bulk forms of matter. Quantum confinement of both the electron and hole in all three dimensions leads to an increase in the effective band gap of the material with decreasing crystallite size. Consequently, both the optical absorption and emission of nanocrystallites shift to the blue (i.e., to higher energies) as the size of the crystallite gets smaller.
Bawendi and co-workers have described a method of preparing monodisperse semiconductor nanocrystallites by pyrolysis of organometallic reagents injected into a hot coordinating solvent (J. Am. Chem. Soc., 115:8706 (1993)). This permits temporally discrete nucleation and results in the controlled growth of macroscopic quantities of nanocrystallites. The particle size distribution can be refined by size selective precipitation. The narrow size distribution of nanocrystallites can allow the particles to have narrow spectral width emissions. These techniques can yield excellent results in the production of selenium-containing II-VI semiconductor nanocrystallites.