EFFECT OF CRYSTAL-POTENTIAL ON DYNAMIC POLARIZABILITY OF NEGATIVE-IONS

We combine a time-dependent approach with a crystal potential model to study environment-specific optical linear response of closed-shell io ns within crystals under the influence of an external time-varying fie ld. It is shown how the dynamic dipole polarizability of free halogen anions within the normal dispersion region is altered due to the cryst al potentials felt by the anions in environments appropriate for diffe rent binary cubic ionic lattices. The pole-positions of the in-crystal anion polarizability are found to be consistent with the vacuum ultra violet absorption edges of the corresponding alkali halides and to var y linearly with the lattice potentials at the anion sites in these sal ts. It is observed that the crystal potential induces quite a large en hancement in the anionic absorption oscillator strengths of these dipo le transitions, thereby making these values conform well with those of the first excitonic absorptions in such crystals.