Excitonic Processes in Solids

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.- 1.4.1 Effective Mass Approximation.- 1.4.2 The Role of Spin.- 1.4.3 Interplay of Spin-Orbit and Exchange Interactions.- 1.4.4 Davydov Splitting.- 1.4.5 Charge Transfer Excitons.- 1.5 Optical Absorption Spectra.- 1.5.1 Allowed Edge Case.- 1.5.2 Forbidden Edge Case.- 1.5.3 Transition from Frenkel to Wannier-Mott Exciton.- 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.- 2.2.1 Binding Energy and Electronic Structure of Excitonic Molecule in a Simple System — CuX.- 2.2.2 The Metallic Droplet and Excitonic Molecule in Many-Valley Structures — Ge and Si.- 2.2.3 The Excitonic Molecule in Many-Valley Systems — TlX and AgX.- 2.2.4 Influence of the Polarizable Lattice and the Effect of Anisotropic Effective Mass — CdS and CdSe.- 2.2.5 The Direct Forbidden Exciton — Cu2O.- 2.3 Optical Response of an Excitonic Molecule.- 2.3.1 Luminescence Spectrum.- 2.3.2 Relaxation by Emission of Acoustic Phonons.- 2.3.3 Optical Conversion of Excitons into Excitonic Molecules.- 2.3.4 Giant Two-Photon Absorption.- 2.4 Coherent Optical Phenomena Due to the Excitonic Molecule.- 2.4.1 Hyper-Raman Scattering and Luminescence.- 2.4.2 Two-Polariton Scattering Due to the Excitonic Molecule.- 2.4.3 Dispersion of the Exciton Polariton and Excitonic Molecule.- 2.4.4 Four-Wave Mixing Due to the Excitonic Molecule.- 2.4.5 Phase-Conjugation by Four-Wave Mixing.- 2.5 The Excitonic Molecule at High Densities.- 2.5.1 Renormalization of the Exciton Polariton Due to the Excitonic Molecule Giant Two-Photon Absorption.- 2.5.2 Polarization Rotation Effects Due to Two-Photon Excitation of the Excitonic Molecule.- 2.5.3 Multi-Polariton Scattering Via Excitonic Molecules.- 2.5.4 Optical Bistability Due to the Excitonic Molecule.- 2.5.5 Relaxation and Bose Condensation of Excitonic Molecules.- 3. The Exciton and Excitonic Molecule in Cuprous Halides.- 3.1 Band Structure and Excitonic States.- 3.2 Exciton Absorption, Reflection, and Emission Spectra.- 3.2.1 Absorption and Reflection Spectra.- 3.2.2 Splitting of Exciton Bands by Perturbations.- 3.2.3 Emission Spectra.- 3.2.4 Phonon Structure in the Excitation Spectra of Free-Exciton Emission.- 3.2.5 Bound Excitons.- 3.2.6 CuCl-CuBr Solid Solutions.- 3.3 High-Density Excitation Effects.- 3.3.1 Exciton-Electron Interaction.- 3.3.2 Effect on Exciton Absorption Bands.- 3.3.3 Creation of the Excitonic Molecule by Exciton-Exciton Collision.- 3.4 Giant Two-Photon Excitation of the Excitonic Molecule.- 3.4.1 Evidence of Giant Two-Photon Creation.- 3.4.2 Giant Two-Photon Absorption.- 3.5 Two-Photon Resonant Raman Scattering Via the Excitonic Molecule.- 3.5.1 Backward Scattering.- 3.5.2 Forward Scattering.- 3.5.3 Scattering with Recoil of the Upper-Branch Polariton.- 3.5.4 Polarization Character — Geometrical Selection Rules.- 3.5.5 Nonlinear Change of Exciton-Polariton Dispersion Associated with the GTA.- 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.- 3.8.1 Calculation of Line-Shapes of the Excitonic Molcecule Luminescence.- 3.9 Relaxation of the Excitonic Molecule Due to Intermolecular Collisions: Influence on the GTA and Secondary Emissions.- 3.9.1 Effect on the GTA Spectra.- 3.9.2 Effect on Secondary Emissions.- 3.10 Spatial Dispersion of the Exciton and Excitonic Molecule.- 3.10.1 CuCl.- 3.10.2 CuBr.- 3.11 Higher Excited States of the Excitonic Molecule.- 4. Theory of Excitons in Phonon Fields.- 4.1 Electron-Phonon Interactions.- 4.1.1 Types and Ranges of Electron-Phonon Interactions.- 4.1.2 The Polaron.- 4.1.3 Exciton-Phonon Interactions and the Form Factor.- 4.1.4 Polaron Effects of an Exciton.- 4.2 The Exciton in Spatially Fluctuating Fields.- 4.2.1 Localization Versus Delocalization.- 4.2.2 Overall Line-Shape of the Absorption Spectra.- 4.2.3 Coherent Potential Approximation for an Exciton in a Mixed Crystal and in a Phonon Field.- 4.2.4 The Urbach Rule and Exciton Localization.- 4.3 Phonon Structures in Exciton Spectra.- 4.3.1 Motional Reduction of Phonon Sidebands.- 4.3.2 Multicomponent Line-Shape Formula.- 4.3.3 The Electron-Hole Relative Motion and the Phonon Sideband of an Exciton.- 4.4 Self-Trapping.- 4.4.1 Local Stabilities of Free and Self-Trapped States.- 4.4.2 Continuum Model for Self-Trapping.- 4.4.3 Adiabatic Potentials for Self-Trapping.- 4.4.4 Effective Mass Change in the F—S Transition.- 4.4.5 Extrinsic Self-Trapping and Shallow-Deep Instability.- 4.4.6 Instabilities in the Relative Motion of a Pair of Charged Particles.- 4.4.7 Survey of Experimental Studies of Self-Trapping and Related Instabilities.- 4.5 Electron-Hole Recombination.- 4.5.1 Polariton Bottleneck.- 4.5.2 Resonant Secondary Radiation.- 4.5.3 Capture, Recombination, and Enhanced Defect Reaction Via a Deep Impurity Level in a Semiconductor.- 4.5.4 Self-Trapping and Recombination of an Exciton as a Multiphonon Process.- 4.6 Excitonic Instability and Phase Changes.- 4.6.1 t-U-S Problem.- 4.6.2 Two-Site Two-Electron System.- 4.6.3 Hückel’s (4n + 2) Rule for Ring Systems.- 4.6.4 One-Dimensional Hubbard-Peierls System.- 4.6.5 Prospects.- 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.- 5.3.1 Exciton Absorption Spectra.- 5.3.2 Nature of Relaxed Excitons in Condensed Rare Gases.- 5.3.3 Formation of Self-Trapped Exciton Bubbles in Condensed Neon.- 5.3.4 Relaxation of Free Excitons in Photo-Excited Rare Gas Solids.- 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.- 6.2.1 Exciton Transitions in Pure Crystals.- 6.2.2 Exciton Transitions in Mixed Crystals.- 6.2.3 Bound-Exciton Transitions at an Isoelectronic Iodine Impurity.- 6.3 Relaxation Processes of Photo-Excited States in Silver and Alkali Halides.- 6.4 Localized Electrons and Holes in Silver Halides.- 6.4.1 Nature of Localized Centers in Silver Halides Compared to Color Centers in Alkali Halides.- 6.4.2 Bound Polarons in Silver and Alkali Halides.- 6.4.3 Photochemical Reactions in Silver Halides at Higher Temperatures.- 7. Excitons and Their Interactions with Phonons and External Fields in Thallous Halides.- 7.1 Band Structures and Exciton States of Thallous Halides.- 7.1.1 Thallous Halides.- 7.1.2 Band Structures.- 7.1.3 Exciton States.- 7.2 Optical Spectra of Thallous Halides.- 7.2.1 Absorption and Reflection Spectra in a Wide Energy Range.- 7.2.2 Spectra of X6+ × X6? Direct Excitons.- 7.2.3 Spectra of X6+ × R6? Indirect Excitons.- 7.2.4 Free-Exciton Emission.- 7.2.5 Excitonic Molecules of X6+ × R6? Excitons.- 7.3 Resonant Raman Scattering by Excitons in Thallous Halides.- 7.3.1 LO Phonon Scattering Resonant to a Direct Exciton.- 7.3.2 Intervalley Scattering of a Direct Exciton.- 7.4 Excitons and Induced Self-Trapping in Mixed Crystals of Thallous Halides.- 7.4.1 Exciton States in a Mixed Crystal.- 7.4.2 Self-Trapping Induced by Alloying.- 7.5 Excitons in Thallous Halides in External Fields.- 7.5.1 Magnetic Field.- 7.5.2 Electric Field.- 7.5.3 Uniaxial Stress Field.- 8. Photocarrier Motion in Ionic Crystals.- 8.1 Photocurrent and Measurement.- 8.1.1 Photocurrent.- 8.1.2 Blocking Electrode Method and Response.- 8.1.3 Spectral Dependence of Photoconductivity.- 8.2 Measurements of Carrier Mobility and Cyclotron Resonance in Insulating Photoconductors.- 8.2.1 Carrier Mobility.- 8.2.2 Drift Mobility Measurement.- 8.2.3 Hall and Magnetoresistance Mobility Measurements.- 8.2.4 Detection of Cyclotron Resonance.- 8.3 Polaron and Mobility.- 8.3.1 Polaron Masses and Coupling Constants.- 8.3.2 Polaron Mobilities.- 8.4 Magnetoconductivity.- 8.4.1 Spin-Dependent Magnetoconductivity.- 8.4.2 Photomagnetocurrent.- 8.5 Polarons with High Energy.- 8.5.1 Nonparabolicity of the Polaron Energy Spectrum.- 8.5.2 Hot-Polaron Transport Phenomena.- 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.