Exciton-Phonon Coupling in KI and RbI under Two-Photon Excitation

Excitation spectra for the intrinsic luminescence induced by two-photon absorption in KI and RbI single crystals have been studied at LHeT, and a weak coupling between the 2p exciton and LO phonon has been suggested. A sharp peak appears at 6.197±0.003eV or 6.127±0.003eV in the excitation spectra of KI or RbI. respectively, and is assigned to the 2p exciton band. This peak is followed by small peaks separated by 17.3±0.6meV or 12 meV, which almost coincides with the LO phonon energy, 17.94meV or 13.34meV, at the Γ point in each crystal. The coupling between excitons and phonons in KI and RbI is discussed.