These proceedings report the lectures and seminars presented at the NATO Advanced Study Institute on "Optical Properties of Ions in Solids," held at Erice, Italy, June 6-21, 1974. The Institute was the first activity of the International School of Atomic and Molecular Spectroscopy of the "Ettore Majorana" Centre for Scientific Culture. The Institute consisted of a series of lectures on optical properties of ions in solids that, starting at a fundamental level, finally reached the current level of research. The sequence of lectures and the organization of the material taught were in keeping with a didactical presentation. In essence the Institute had the two-fold purpose of organizing what was known on the subject, and updating the knowledge in the field. Fif'teen series of lectures for a total of 44 hours were given. Five one-hour seminars and five twenty-minute seminars were presented. A total of 57 participants came from 40 laboratories in the following countries: Belgium, Canada, France, Germany, Ireland, Israel, Italy, Netherlands; Polatid, Romania, Switzerland, the United Ki~gdom, and the United States. The secretaries of the Institute were: D. Pacheco for the scientific aspects and A. La Francesca for the administrative aspects of the meeting. These proceedings report the lectures, the one-hour seminars (abstracts only) and the twenty-minute- seminars (titles only). The proceedings report also the contributions sent by Prof. K. Rebane and Dr. L. A. Rebane who, unfortunately, were not able to come.

Inhalt
Historical Survey of Studies of the Optical Properties of Ions in solids.- Abstract.- I. Introduction.- II. Early Investigations of Optical Transitions.- III. Quantum Mechanical Considerations.- IV. Crystal and Ligand Field Theory.- V. Energy Transfer.- VI. Ion Pairs.- VII. Multiphoton Transitions.- VIII. Concluding Remarks.- References.- Magnetic Ions in Solids.- Abstract.- I. Introduction.- II. Symmetry Concepts.- III. Energy Levels of Atoms.- IV. Magnetic Ions in Crystals.- IV. F Kramers' Theorem.- V. Effect of Covalent Bonding.- References.- Fundamentals of Radiative Transitions of Ions and of Ion Pairs in Solids.- Abstract.- I. Introduction.- II. Transitions Induced by Perturbations Periodic in Time.- III. Transitions Induced by the Electromagnetic Radiation Field.- IV. Spontaneous Radiative Transitions.- V. Applications of the Theory to Radiative Transitions of Ions in Solids.- References.- Absorption and Emission Spectra.- Abstract.- I. The One-Dimensional Configurational Coordinate Model.- II. The Huang and Rhys Model.- III. A Deeper Insight into the Shape of the Spectra.- IV. A Study of Some Experimental Cases.- References.- Quantum Theory of Lattice Vibrations.- Abstract.- I. Lattice Vibrations.- II. Thermodynamic Properties of Lattice Vibrations.- References.- Theory of Vibronic Spectra.- Abstract.- I. Introduction.- II. Infrared Absorption.- III. Raman Scattering.- IV. Neutron Scattering.- V. Vibronic Spectra.- VI. Example: Analysis of 2Eg ? 4A2g Sideband of MgO:V2+.- References.- Luminescence and Spectroscopy of Small Molecular Ions in Crystals.- Abstract.- I. Introduction.- II. General Description of the Spectra of Molecular Centres in Crystals.- III. Rotation and Libration of the NO2- Ion in Potassium Halide Crystals.- IV. Reorientation of S2- in KI.-References.- Some Problems of the Vibrational Structure of Optical Spectra of Impurities in Solids.- Abstract.- I. No-Phonon Lines and Phonon Wings (Sidebands).- II. Inhomogeneous Broadening of Luminescence Spectra.- References.- Spectroscopy of Magnetic Insulators.- Abstract.- I. Introduction.- II. Interacting Ions.- III. Crystalline Systems.- IV. Electronic Structure of Magnetic Crystals.- V. Examples of Spectra of Magnetic Crystals.- References.- Energy Transfer Phenomena.- Abstract.- I. Introduction.- II. Ion-Ion Interactions.- III. Statistical Treatment.- IV. Inhomogeneous Broadening.- References.- Stepwise Upconversion and Cooperative Phenomena in Fluorescent Systems.- Abstract.- I. Introduction.- II. Stepwise Upconversion.- III. Cooperative Transfer.- IV. Energy Transfer with Photon Cooperation.- References.- Relaxation and Energy Transfer.- Abstract.- I. Introduction.- II. Non-Radiative Relaxation.- III. Energy Transfer.- IV. Summary and Future Prospects.- References.- Charge Transfer Spectra.- Abstract.- I. Introduction.- II. Elementary Aspects of Charge Transfer.- III. Relation between Optical and Chemical Charge Transfer.- IV. Theory of Charge Transfer Spectra.- V. Conclusions.- References.- The Role of the Jahn-Teller Effect in the Optical Spectra of Ions in Solids.- Abstract.- I. Introduction.- II. The Jahn-Teller Theorem.- III. A Model Illustrating the Jahn-Teller Effect.- IV. The Hamiltonian for a Magnetic Ion in a Crystal.- V. Configuration-Coordinate Diagrams.- VI. Broad Band Optical Spectra.- VII. Vibronic Structure in Energy Levels and Optical Spectra.- VIII. Concluding Remarks.- References.- Spectra of Associated Donor-Acceptor Pairs.- Abstract.- I. Introduction.- II. The Matrix Element for D-A Transition Probabilities.- III. Capture Cross-Sections.- IV. Shape of the Spectrum.- References.- Zero-Phonon and Phonon-Assisted Radiative Transitions of Donor-Acceptor Pairs in Luminescent Semiconductors.- Abstract.- I. Introduction.- II. Analysis of Experimental Spectra.- III. Application of the Theory.- References.- Present Trends in Luminescence Research.- Abstract.- I. Introduction.- II. Unusual Materials.- III. Recent Phenomena.- IV. Applied Research on Luminescence.- Long Seminars (Abstracts).- Application of Vibronic Spectroscopy Strontium Titanate as an Example.- Radiationless Decay of Impurity Ions in Solids.- Luminescence from Yag: Cr3+, MgO:V2+ and MgO:Cr3+.- Spectroscopy of 5f-Systems: Actinides Versus Lanthanides.- Electronic and Vibrational Transitions of Lead Azide and Effects Thereon of Photodecomposition.- Short Seminars (Titles Only).- Contributors.