STOKES SHIFTS IN TL-DOPED ALKALI-HALIDES

This article presents some electronic ab initio calculations of ion clusters simulating a piece of alkali halide crystal, both pure and doped with Tl+. In the case of pure crystals, we calculate the (direct) energy band gap from the cluster energy levels. For the case of doped crystals, we calculate the absorption and emission energies and the corresponding Stokes shifts. The cluster model consists of a central cation surrounded by three or four shells of ions, with and without point charges embedding the cluster. (C) 1995 John Wiley & Sons, Inc.