Low-energy optical transitions in intercalated graphite

Abstract
Interband transitions characteristic of pure graphite persist from (at least) stage 9 to stage 4 in acceptor-intercalated samples, and to stage 3 in donor samples. The absence of a Burstein-Moss shift is interpreted to mean that the partially ionized intercalant layers are screened by the compensating free carriers within one layer spacing, in agreement with a recent calculation. This in turn means that the Madelung energy has a negligible effect in stabilizing the ordered c-axis superlattice observed in dilute compounds.