Excitons: Frenkel vs. Wannier conduction band valence band Frenkel (Xe, Organics, …) Wannier (Si, Ge, Cu 2 O, …) J. Frenkel, Phys. Rev., 37, 17 (1931) G. H. Wannier, Phys. Rev., 52 191 (1937)
Alkali halides – an intermediate case “Excitation” model Dexter, D. L., Exciton models in alkali halides, Phys. Rev. 108, 707-712 (1957) It’s all just Wannier Hopfield, J. J., & Worlock, J. M., Two-quantum absorption spectrum in KI and CsI, Phys. Rev. 137, A1455-A1464 (1965) GW correction / Solve Bethe-Saltpeter eqn. Rohlfing, M., & Louie, S. G., Electron-hole excitations in semiconductors and insulators, Phys. Rev. Lett. 81, 2312-2315 (1998) Discovery of excitons in alkali halides Hilsch, R., & Pohl, R. W., Über die ersten ultravioletten Eigenfrequenzen einiger einfacher kristalle, Z. Physik 48, 384-396 (1928) Marginal case btwn. Frenkel and Wannier Mott, N. F., Conduction in polar crystals. II. The conduction band and ultra-violet absorption of alkali halide crystals, Trans. Faraday Soc. 34, 500-506 (1938) Electron transfer model Overhauser, A. W., Multiplet structure of excitons in ionic crystals, Phys. Rev. 101, 1702-1712 (1956)