Exciton spectra in thin crystals

A theory is presented of the observed dependence of exciton series spectra on crystal thickness [2,3]. When the latter is comparable to the Wannier exciton radius the effective confinement of the exciton bound states, by the uncertainty principle, raises the kinetic energy. This confinement is introduced by the boundary condition which requires the Wannier wave function to vanish outside the crystal. Allowance is made for thick crystal anisotropy, and its effects on the binding energy calculated for the low excited states.