Electronic band gap, excitonic binding energy, and electron-hole exchange energy of KI under high pressure

In this paper we investigate the electronic (excitonic) energy levels in KI under hydrostatic pressure using multiphoton excitation. The technique of three-photon absorption spectroscopy was used to find the pressure dependence of the n=2 exciton polariton and the nominally forbidden F=2 paraexciton. These data enable us to calculate the pressure dependence of the band gap, the excitonic binding energy, and of the electron-hole exchange energy for KI.