Exciton Absorption in KI-RbI Mixture

Abstract

The fundamental absorption spectra of the mixture of KI and RbI are investigated. The first Peak of four prominent exciton absorption bands and the so called interband transition `step' absorption are displaced in parallel each other and almost linearly with the change of composition of the mixture. This means that the binding energy of the first exciton remains constant over the whole concentration range. The second and the third ones above the step reverse their relative intensities at about 20 atomic percent of RbI concentration. The separation between them becomes narrower as the concentration of the dopant is increased, and at about 40 percent of RbI, it amounts to less then 3/4 of those in pure materials. A hump on the low energy tail of the fourth peak becomes indistinguishable at concentration higher than 10 percent of dopants. No new absorption is observed below 7.5 eV. The possible interpretation of the absorption spectra is discussed.