An exciton is an electronic excitation wave consisting of an electron-hole pair which propagates in a nonmetallic solid. Since the pioneering research of Fren kel, Wannier and the Pohl group in the 1930s, a large number of experimental and theoretical studies have been made. Due to these investigations the exciton is now a well-established concept and the electronic structure has been clarified in great detail. The next subjects for investigation are, naturally, dynamical processes of excitons such as excitation, relaxation, annihilation and molecule formation and, in fact, many interesting phenomena have been disclosed by recent works. These excitonic processes have been recognized to be quite important in solid-state physics because they involve a number of basic interactions between excitons and other elementary excitations. It is the aim of this quasi monograph to describe these excitonic processes from both theoretical and experimental points of view. we take a few To discuss and illustrate the excitonic processes in solids, important and well-investigated insulating crystals as playgrounds for excitons on which they play in a manner characteristic of each material. The selection of the materials is made in such a way that they possess some unique properties of excitonic processes and are adequate to cover important interactions in which excitons are involved. In each material, excitonic processes are described in detail from the experimental side in order to show the whole story of excitons in a particular material.

Inhalt

1. Introduction.- 1.1 The Ground State of Many-Body Systems and the Modes of Excitation.- 1.2 Electronic Excitation in Insulators and the Wannier-Mott Exciton.- 1.3 The Frenkel Exciton.- 1.4 The General Case.- 1.5 Optical Absorption Spectra.- 1.6 The Polariton and Spatial Dispersion.- 1.7 Scope of the Present Book.- 2. Theoretical Aspects of Excitonic Molecules.- 2.1 Fission and Fusion of Excitons vs. Chemical Reaction into Excitonic Molecules.- 2.2 The Excitonic Molecule and Electron-Hole Liquid.- 2.3 Optical Response of an Excitonic Molecule.- 2.4 Coherent Optical Phenomena Due to the Excitonic Molecule.- 2.5 The Excitonic Molecule at High Densities.- 3. The Exciton and Excitonic Molecule in Cuprous Halides.- 3.1 Band Structure and Excitonic States.- 3.2 Exciton Absorption, Reflection, and Emission Spectra.- 3.3 High-Density Excitation Effects.- 3.4 Giant Two-Photon Excitation of the Excitonic Molecule.- 3.5 Two-Photon Resonant Raman Scattering Via the Excitonic Molecule.- 3.6 Acoustic-Phonon Interaction of the Excitonic Molecule.- 3.7 Coexistence of Luminescence and Raman Components in the Resonant Excitation.- 3.8 Redistribution of Excitonic Molecules Resonantly Generated by Two-Photon Excitation.- 3.9 Relaxation of the Excitonic Molecule Due to Intermolecular Collisions: Influence on the GTA and Secondary Emissions.- 3.10 Spatial Dispersion of the Exciton and Excitonic Molecule.- 3.11 Higher Excited States of the Excitonic Molecule.- 4. Theory of Excitons in Phonon Fields.- 4.1 Electron-Phonon Interactions.- 4.2 The Exciton in Spatially Fluctuating Fields.- 4.3 Phonon Structures in Exciton Spectra.- 4.4 Self-Trapping.- 4.5 Electron-Hole Recombination.- 4.6 Excitonic Instability and Phase Changes.- 5. Excitons in Condensed Rare Gases.- 5.1 Electronic Structure of Condensed Rare Gases.- 5.2 Charge Carriers in Condensed Rare Gases.- 5.3 Excitons and Exciton-Phonon Interactions in Condensed Rare Gases.- 6. Exciton-Phonon Processes in Silver Halides.- 6.1 Electronic and Lattice Properties of Silver Halides.- 6.2 Excitons and Exciton-Phonon Interactions in Silver Halides.- 6.3 Relaxation Processes of Photo-Excited States in Silver and Alkali Halides.- 6.4 Localized Electrons and Holes in Silver Halides.- 7. Excitons and Their Interactions with Phonons and External Fields in Thallous Halides.- 7.1 Band Structures and Exciton States of Thallous Halides.- 7.2 Optical Spectra of Thallous Halides.- 7.3 Resonant Raman Scattering by Excitons in Thallous Halides.- 7.4 Excitons and Induced Self-Trapping in Mixed Crystals of Thallous Halides.- 7.5 Excitons in Thallous Halides in External Fields.- 8. Photocarrier Motion in Ionic Crystals.- 8.1 Photocurrent and Measurement.- 8.2 Measurements of Carrier Mobility and Cyclotron Resonance in Insulating Photoconductors.- 8.3 Polaron and Mobility.- 8.4 Magnetoconductivity.- 8.5 Polarons with High Energy.- 9. Excitons and Phonon Couplings in Quasi-One-Dimensional Crystals.- 9.1 Halogen-Bridged Mixed-Valence Chain Compounds.- 9.2 Polyacetylene.- 9.3 Mixed Stacked Donor-Acceptor Charge Transfer Complexes.- 9.4 Segregated Stacked Donor-Acceptor Charge Transfer Complexes.- References.