Lattice relaxation of outermost core holes in Auger-free luminescence of CsCl

The effect of lattice relaxation of the outermost core hole in the Auger-free luminescence (AFL) in CsCl is studied by an extended deformable cluster model. It is proposed that the initial state of the AFL is a weakly self-trapped state of the core hole. A simple tight-binding calculation of the electronic states is carried out, and the AFL spectra at finite temperatures are calculated. The high energy band at 5.2eV is assigned as originating from the transition of the self-trapped hole to the localized state in the valence band due to the attractive potential of the lattice deformation created in the initial state. The final state of the emission band at 4.5 eV is, on the other hand, the extended state in the valence band. The difference in the thermal broadening characteristic of these two bands is well simulated by the calculation.