  The mechanism of Stokes shift in semiconductor quantum dots is investigated
by calculating the energy of the excitonic states. We have taken into account
all possible contributions to the total electronic energy in the dot, i.e,
dielectric mismatch between dot and surrounding medium, the effects of finite
barrier height and electron-hole exchange interaction. The Stokes shift is
calculated as a function of radius of dot and compared with experimental data
on two different semiconductor based quantum dots. These results provide
evidence for exchange splitting of excitonic states, as the mechanism of Stokes
shift in quantum dot
