Deformation Potentials for Excitons in CsI

The shifts of the first two exciton peaks with hydrostatic pressure have been measured in CsI films at 78°K and found to be linear. The deformation potentials deduced are -2.10 eV and +2.10 eV, respectively. These results confirm Onodera's assignment of the two peaks to excitons derived from bands of different symmetry. The data indicate that above 7 kbar the conduction bands cross and the ${\Gamma }_{12}$ level lies below the ${\Gamma }_1$ (Onodera's assignment).