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 Γ₁₂ level lies below the Γ₁ (Onodera's assignment).