Two-photon absorption in CuCl and CuBr under hydrostatic pressure

Two-photon absorption is used to measure the shift of the longitudinal ${\mathit{Z}}_3$ and ${\mathit{Z}}_{1,2}$ excitons and the 2p exciton in CuCl under hydrostatic pressure. Hydrostatic deformation potentials for excitons and band states are determined with high accuracy. In CuBr the shift of the longitudinal ${\mathit{Z}}_{1,2}$ exciton is measured, showing a pronounced superlinear pressure dependence. In the high-pressure phase (above 4 GPa) the pressure dependence of luminescence is observed up to 9 GPa in both compounds.