Theory of Surface Frenkel Excitons in Cubic Systems: K_⁄⁄- and Polarization-Dependent Oscillator Strength

Abstract

Frenkel excitons localized at the surface of a cubic Bravais lattice are investigated theoretically in terms of a simple model. The dipole-dipole interaction is expressed in a planewise form and it is argued that the interaction between two planes consists of two components, short-range and long-range interactions, each of which is related to the Lorentz local field and the macroscopic electric field, respectively. Dyson’s equation for the Green’s function is solved in the wave number space. The surface excitons are shown to split into two levels and the criteria for their existence are clarified. In some cases the oscillator strength of the surface excitons depends strongly on the polarization of the excitation light.