Inner-shell excitations and secondary excitons in rare-gas solids

Luminescence of the rare gas solids Xenon, Krypton, and Argon was investigated following excitation of the inner-shell levels using time-resolved photoluminescence techniques. As a probe for luminescence, emission from the free and self-trapped exciton states was used. The measurements were performed in the energy range of 35-750 eV, covering excitations from the 4d, 4p, and 3d shells of Xe, the 3d shells in Kr, and the 2p shells in Ar. For fast emissions, the time structure on the nanosecond scale shows two distinct regions, the region of prompt luminescence from excitons created simultaneously with the excitation, and the delayed luminescence, which stems from slow recombinational excitons. For the prompt luminescence, a resonance is observed for photon energies above a threshold which equals the ionization energy of the respective core state plus the energy of the valence exciton. This threshold is explained in two independent models, the multiple parabolic branch band model, and the electronic polaron complex model. A comparison with related measurements from the literature demonstrates that the occurrence of the resonance in prompt exciton creation is a fundamental property of the rare gas solids. The structure of the delayed luminescence shows a marked dependency on the excitation density. The shift of the decay structure to shorter times with increasing density is explained in a recombinational model for electrons and holes. Numerical simulations within the frame of this model are presented, which reproduce the measured date within good accuracy. (orig.)