2pand 2sexciton polariton energies versus pressure in KI

We measured the 2p and 2s exciton polariton energies in KI versus pressure and temperature using two- and three-photon excitation spectroscopy. The results give reliable values for the 2s and 2p energies of the excitons in the same crystal at the same time under substantially identical conditions to reduce systematic errors in small energy differences. The hydrostatic pressure shift of the 2p excitons in KI was measured. From our results we obtain improved values for the excitonic binding energy R₀ of KI, the phonon-induced Lamb shift between the 2s and 2p exciton states and the spherical parameter {μ} and cubic parameter {δ} characterizing the splitting of the 2p exciton. We also report a value for the excitonic phonon self-energy of the 2s exciton. The data also enable us to extract values for the Kohn-Luttinger parameters γ₁, γ₂, and γ₃ and the light- and heavy-hole masses of the highest valence band.