Influence of the interband transitions on the absorption spectrum of CsBr crystals containing colloids

The contribution of interband transitions to the optical absorption of Cs colloids in a CsBr crystal has been calculated by introducing the expression of Wilson and Butcher for the imaginary part of the dielectric constant of cesium into the standard Mie theory. The resulting absorption bands are smaller and much broader than those corresponding to the free-electron model. The dependence of the calculated band half-width on colloid radius is compared with experimental data. The agreement obtained is considerably better than that corresponding to the sole Drude contribution