Attenuated quantum confinement of the exciton in semiconductor nanoparticles

A new effect, called attenuated quantum confinement, is described using a theoretical approach, based on the effective mass approximation. It assumes that the exciton, generated in a semiconductor nanocrystal, can penetrate the medium outside the crystal boundary. An equation is derived for the energy of attenuated quantum confinement depending on the penetration depth and mass of exciton outside the crystalline core. It gives lower absorption energy, which is observed experimentally for very small nanocrystals, compared to that predicted by usual quantum confinement. The penetration depth calculated for compound semiconductors is found to be of the same magnitude as that of the thickness of organic capping layer for CdS, CdSe, PbS and InAs nanoparticles. Our finding can also explain other practical processes of charge generation and transportation in a matrix with embedded nanocrystals.