  We show how to calculate the optical functions of a nanoplatelet, taking into
account the effect of a dielectric confinement on excitonic states. Real
density matrix approach is employed to obtain analytical and semi-analytical
relations for the absorption coefficient, the exciton resonance energy and
binding energy of nanoplatelets and nanodisks. The impact of plate geometry
(thickness, area) on the spectrum is discussed and the results are compared
with the available experimental data.
