Piezoreflectivity Studies on Excitons and Band to Band Transitions in Alkali Bromides and Iodides under Uniaxial Stress

Piezoreflectivity spectra of KI and RbBr in the fundamental absorption region were measured at liquid N 2 temperature and splitting energies due to trigonal deformations were obtained on the first and second excitons and the steps which are the onset of band to band transitions. The splitting energies were calculated with a single splitting parameter in the p -levels of the valence band, together with the exchange energy and the spin-orbit coupling constant introduced by Onodera and Toyozawa. A good agreement was obtained with the experimental results. Reported values of the splitting energies in RbI and KBr were also shown to be consistent with the calculation. It is concluded that the first and second excitons are mixtures of the states which manifest themselves as the first and second steps.