Raman scattering and photoluminescence inCu2O under hydrostatic pressure

Excitonic transitions and phonon frequencies in ${\mathrm{Cu}}_2$O were measured by luminescence and Raman spectroscopy at hydrostatic pressures up to 8.5 GPa and at a temperature of 6 K. The exciton Rydberg energy is found to decrease at a rate of -2.4 meV/GPa. The band gap increases at a rate of 12.5 meV/GPa, which corresponds to a band-gap deformation potential of -1.38 eV. The electron-hole exchange energy, i.e., the energy difference between orthoexciton and paraexciton, is independent of pressure. The mode Grüneisen parameters for the zone-center phonons vary between -3.4 and +1.7. A rigid-ion model for the pressure dependence of k=0 phonon frequencies yields mode Grüneisen parameters which are consistent with the experimental data.