Topics in Applied Physics Volume 49 Topics in Applied Physics Founded by Helmut K. V. Lotsch Dye Lasers 2nd Ed. Editor: F. P. Schafer 27 Photoemission in Solids II. Case Studies 2 Laser Spectroscopy of Atoms Editors: L. Ley and M. Cardona and Molecules. Editor: H. Walther 28 Hydrogen in Metals I. Basic Properties 3 Numerical and Asymptotic Techniques Editors: G. Alefeld and 1. Viilkl in Electromagnetics Editor: R. Mittra 29 Hydrogen in Metals II Application-Oriented Properties 4 Interactions on Metal Surfaces Editors: G. Alefeld and 1. Viilkl Editor: R. Gomer 30 Excimer Lasers Editor: Ch. K. Rhodes 5 Miissbauer Spectroscopy Editor: U. Gonser 31 Solar Energy Conversion. Solid-State 6 Picture Processing and Digital Filtering Physics Aspects. Editor: B. O. Seraphin 2nd Edition. Editor: T. S. Huang 32 Image Reconstruction from Projections 7 Integrated Optics 2nd Ed. Editor: T. Tamir Implementation and Applications 8 Light Scattering in Solids Editor: G. T. Herman Editor: M. Cardona 33 Electrets Editor: G. M. Sessler 9 Laser Speckle and Related Phenomena 34 Nonlinear Methods of Spectral Analysis Editor: J. C. Dainty Editor: S. Haykin 10 Transient Electromagnetic Fields 35 Uranium Enrichment Editor: S. Villani Editor: L. B. Felsen 36 Amorphous Semiconductors 11 Digital Picture Analysis Editor: A. Rosenfeld Editor: M. H. Brodsky 12 Turbulence 2nd Ed. Editor: P. Bradshaw 37 ThermaUy Stimulated Relaxation in Solids 13 High-Resolution Laser Spectroscopy Editor: P. Braunlich Editor: K. Shimoda 38 Charge-Coupled Devices Editor: D. F. Barbe 14 Laser Monitoring of the Atmosphere 39 Semiconductor Devices Editor: E. D. Hinkley for Optical Communication 15 Radiationless Processes in Molecules Editor: H. Kressel and Condensed Phases. Editor: F. K. Fong 40 Display Devices Editor: J. I. Pankove 41 Computer Application in Optical Research 16 Nonlinear Infrared Generation Editor: B. R. Frieden Editor: Y.-R. Shen 17 Electroluminescence Editor: 1. I. Pankove 42 Two-Dimensional Digital Signal Processing I. Linear Filters 18 Ultrashort Light Pulses Editor: T. S. Huang Picosecond Techniques and Applications Editor: S. L. Shapiro 43 Two-Dimensional Digital Signal Processing II. Transforms 19 Optical and Infrared Detectors 2nd Ed. and Median Filters. Editor: T. S. Huang Editor: R. J. Keyes 44 Turbulent Reacting Flows 20 Holographic Recording Materials Editors: P. A. Libby and F. A. Williams Editor: H. M. Smith 45 Hydrodynamic Instabilities and the Transition 21 Solid Electrolytes Editor: S. Gener to Turbulence 22 X-Ray Optics. Applications to Solids Editors: H. L. Swinney and 1. P. Gollub Editor: H.-J. Queisser 46 Glassy Metals I 23 Optical Data Processing. Applications Editors: H.-1. Giintherodt and H. Beck Editor: D. Casasent 47 Sputtering by Particle Bombardment I 24 Acoustic Surface Waves Editor: A. A.OIiner Editor: R. Behrisch 25 Laser Beam Propagation in the Atmosphere 48 Optical Information Processing Editor: 1. W. Strohbehn Fundamentals. Editor: S. H. Lee 26 Photoemission in Solids I. General Principles 49 Laser Spectroscopy of Solids Editors: M. Cardona and L. Ley Editors: W. M. Yen and P. M. Selzer Laser Spectroscopy of Solids Edited by W. M. Yen and P. M. Selzer With Contributions by A.H.Francis T.Holstein D.L.Huber G.F.Imbusch R.Kopelman S.K.Lyo R.Orbach P.M. Selzer M.J.Weber W.M. Yen With 117 Figures Springer-Verlag Berlin Heidelberg GmbH 1981 Professor William M. Yen Department of Physics, University of Wisconsin Madison, WI 53706, USA Peter M. Se/zer, Ph.D. Scientific Research Laboratory, Ford Motor Company Dearborn, MI 48121, USA ISBN 978-3-662-12215-0 ISBN 978-3-662-12213-6 (eBook) DOI 10.1007/978-3-662-12213-6 This work is subject to copyright. AII rights are reserved. whether the whole Of part of the material is concerned. specifically those of translation, reprinting, reuse of illustrations, broadcasting, reproduction by photocopying machi ne or similar means, and storage in data banks. Under § 54 of the German Copyright Law, where copies are made for other than private use, a fee is payable to "Yerwertungsgesellschaft Wort", Munich. © by Springer-Yerlag Berlin Heidelberg 1981 Originally published by Springer-Yerlag Berlin Heidelberg New York in 1981 Softcover reprint ofthe hardcover Ist edition 1981 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. 2153/3130-543210 Preface In this volume we have attempted to present a concise survey of the spectroscopic properties of insulators as derived from the application of tunable laser spectro scopic techniques. As has been the case in gaseous atomic spectroscopy, the use of tunable lasers has allowed the extension and the refmement of optical measure ments in the condensed phases to unprecedented resolutions in the frequency and temporal domains. In turn, this firmer base of empirical fmdings has led to a more sophisticated theoretical understanding of the spectroscopy of optically excited states with major modifications being apparent in the area of their dynamic be havior. Yet the revivalistic nature of these advances implies that additional advan ces are to be expected as the techniques and developments outlined in this volume are put to widespread use. Regardless, it is our hope and that of our distinguished colleagues in this venture that the reviews presented here will be useful to neo phytes and veterans to this field alike - to the former as a laissez-passer into solid-state spectroscopy, to the latter as a useful synopsis and reference of recent developments. We have also attempted to expose the reader to the concept that optically active materials, be they organic or inorganic, as universality would require, be have in a like manner and, though terminology may vary in detail, the outline and general features of all insulators remain constant. The book is organized as follows: Chapter 1 surveys in general terms the field of spectroscopy of insulators and establishes the basic features the other chapters refer to. Chapters 2 and 3, respectively, deal with the microscopic and macroscopic aspects of the theory of dynamics of optically excited states with emphasis on ion-ion interactions which are responsible for optical energy transfer and diffusion in condensed phases. Chapter 4 details experimental techniques which are used in laser spectroscopy in solids. Finally, the last three chapters pre sent surveys of the empirical status of these studies in ionic or crystalline, glassine or amorphous, and organic solids, respectively. The other areas in the study of optical properties of condensed matter where lasers have played crucial roles and where considerable advances have been made, such as semiconductors and the various types of light scattering experimonts, are not the principal focus ofthis volume and, hence, will not be reviewed here. Finally, we wish to acknowledge the many people who have encouraged us and collaborated with us in various phases of compilation. We specially wish to thank Dr. H.K.V. Lotsch and the editorial staff of Springer for their help and VI Preface patient guidance, and Dr. E. Strauss and Dr. S.T. Lai for their assistance during the preparation of this volume. A special note of thanks is due Ms. Karen M. Wick who did the majority of the type composition of this volume; her ability was only surpassed by her patience and understanding. One of us (W.M.Y.) has bene fitted from support from the John Simon Guggenheim Memorial Foundation during the 1979-80 academic year. We also acknowledge support from the Na tional Science Foundation and the Army Research Office for the preparation of the manuscripts. January 1981 W. M Yen· P. M Selzer Contents 1. Optical Spectroscopy of Electronic Centers in Solids By G. F. Imbusch and R. Kopelman (With 20 Figures) . . . . . . . . . . . . . . 1 1.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Interaction of Electronic Center with Optical Radiation. . . . . . . . . . 1 1.3 Eigenstates for the Electronic Center in a Solid ............... 3 1.4 Energy Levels and Radiative Transitions in Ionic Centers . . . . . . . . . 5 1.4.1 Rare Earth Ions in Static Environment . . . . . . . . . . . . . . . . . 5 1.4.2 Transition Metal Ions in a Static Environment .. . . . . . . . . . . 9 1.4.3 Interaction of the Optically Active Ion with Lattice Modes. . .. 12 1.5 Energy Levels and Radiative Transitions in Isolated Molecular Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15 1.6 Broadening of the No-Phonon Line ....................... 18 1.7 Nonradiative Relaxation .............................. 22 1.8 Increased Concentration and Excitation Transfer ...... . . . . . . .. 25 1.8.1 Increased Concentration - Ionic Solids ................ , 25 1.8.2 Increased Concentration - Molecular Solids ............. 28 1.9 Fully Concentrated Materials ........................... 30 1.9.1 Fully Concentrated Material - Ionic Solids ............. , 31 1.9.2 Fully Concentrated Materials - Molecular Solids ........ " 35 References .......................................... 36 2. Excitation Transfer in Disordered Systems By T. Holstein, S. K. Lyo, and R. Orbach (With 7 Figures) .......... , 39 2.1 Excitation Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 39 2.2 Phonon-Assisted Excitation Transfer ...................... 40 2.3 Nonresonant Excitation Transfer. . . . . . . . . . . . . . . . . . . . . . . .. 42 2.3.1 Formulation of the Problem ....................... , 43 2.3.2 One-Phonon-Assisted Process ....................... 45 2.3.3 Two-Phonon-Assisted Processes .................... " 49 2.4 Phonon-Assisted Radiative Transfer ..................... " 63 2.4.1 One-Phonon-Assisted Process ....................... 64 2.4.2 Two-Phonon-Assisted Processes. . . . . . . . . . . . . . . . . . . . .. 71 2.5 Phonon Trapping ........... . . . . . . . . . . . . . . . . . . . . . . .. 75 2.5.1 Relationship to Radiative Trapping ................... 76 2.5.2 Frequency Shifting Mechanism by Energy Transfer. . . . . . . .. 77 VIII Contents 2.6 Conclusion ....................................... 79 Note Added in Proof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 80 References .......................................... 80 3. Dynarnicsoflncoherent Transfer. By D. L. Huber (With 12 Figures) . . . . .. 83 3.1 Rate Equations .................................... 83 3.2 Fluorescence Line Narrowing .. . . . . . . . . . . . . . . . . . . . . . . . .. 85 3.2.1 General Theory and Exact Results. . . . . . . . . . . . . . . . . . .. 85 3.2.2 Approximations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 87 3.2.3 Further Approximations .......................... 90 3.2.4 Development of the Background Fluorescence. . . . . . . . . . .. 91 3.2.5 Experimental Studies ............................ 94 3.3 Fluorescence in the Presence of Traps, Exact Results. . . . . . . . . . .. 96 3.3.1 Early Models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 97 3.3.2 Average T-Matrix Approximation .................... 99 3.3.3 Experimental Studies ............................ 102 3.4 Summary and Outlook ............................... 106 Appendix 3.A ........................................ 107 Appendix 3.B ........................................ 109 References .......................................... 110 Additional References with Titles ........................... 111 4. General Techniques and Experimental Methods in Laser Spectroscopy of Solids. By P. M. Selzer (With 7 Figures) . . . . . . . . . . . . . . . . . . . . .. 113 4.1 Fluorescence Line Narrowing in Solids. . . . . . . . . . . . . . . . . . . .. 115 4.1.1 Phenomenological Model. . . . . . . . . . . . . . . . . . . . . . . . .. 115 4.1.2 Sources of Residual Broadening. . . . . . . . . . . . . . . . . . . . .. 117 4.1.3 Spectral Dynamics .............................. 120 4.1.4 Experimental Details. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 122 4.2 Saturation Spectroscopy in Solids .. . . . . . . . . . . . . . . . . . . . . .. 126 4.2.1 Hole Burning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 127 4.2.2 Polarization Spectroscopy ......................... 130 4.3 Coherent Transient Spectroscopy ........................ 131 4.4 Light Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 135 4.5 Photoacoustic (or Optoacoustic) Spectroscopy. . . . . . . . . . . . . . .. 135 4.6 Degenerate Four-Wave Mixing (Transient Grating Spectroscopy) . . .. 136 4.7 Conclusion ....................................... 137 References .......................................... 137 5. High Resolution Laser Spectroscopy of Ions in Crystals By W. M. Yen and P. M. Selzer (With 25 Figures) ................. 141 5.1 Homogeneous Linewidth Studies. . . . . . . . . . . . . . . . . . . . . . . .. 141 Contents IX 5.1.1 Ruby [AlZ03: Cr3+] ............................. 142 5.1.2 TrivalentPraseodynium in LanthinumFluoride [LaF3 :P~+] ... 149 5.1.3 Actinides and Other Centers. . . . . . . . . . . . . . . . . . . . . . .. 152 5.2 Static Spectral Features ............................... 154 5.2.1 Hyperfine and Other Structures ..................... , 154 5.2.2 Site and Impurity Selectivity ....................... 158 5.2.3 Assisted Transitions ............................. 160 5.3 Single-Ion and Interion Dynamics ........................ 162 5.3.1 Single-Ion Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 162 5.3.2 Energy Transfer .............................. " 165 5.4 Concentrated Materials and Excitonic Effects ................ 175 5.4.1PrF3 andPrCI3 .........•...................... 175 5.4.2 Tb(OHh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 177 5.4.3 Magnetic Excitons .............................. 178 5.4.4 Other Concentrated Materials ..................... " 182 5.5 Conclusion ....................................... 183 References .......................................... 184 Additional References with Titles .......................•... 188 6. Laser Excited Fluorescence Spectroscopy in Glass By M. J. Weber (With 22 Figures) ........................... 189 6.1 Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 189 6.2 Glass Properties ........ . . . . . . . . . . . . . . . . . . . . . . . . . . .. 191 6.2.1 Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 191 6.2.2 Activator Ions and Molecules ....................... 192 6.3 Experimental Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 196 6.3.1 Fluorescence Line Narrowing ...................... , 196 6.3.2 Temporal Dependence. . . . . . . . . . . . . . . . . . . . . . . . . . .. 198 6.3.3 Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 199 6.3.4 Excitation-Fluorescence Schemes .................... 200 6.3.5 Accidential Coincidence. . . . . . . . . . . . . • . . . . . . . . . . . .. 201 6.4 Experimental Apparatus .............................. 202 6.5 Experimental Results ................................ 203 6.5.1 Energy Levels ................................. 203 6.5.2 Transition Probabilities ......................... " 214 6.5.3 Homogeneous Linewidth . . . . . . . . . . . . . . . . . . . . . . . . .. 219 6.5.4 Energy Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 223 6.6 Applications of Fluorescence Line Narrowing ................ 227 6.6.1 Glass Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 227 6.6.2 Structural Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 231 6.6.3 Laser Glass ................................... 233 6.7 Concluding Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 234 References .......................................... 236 Recent References (added in proof) . . . . . . . . . . . . . . . . . . . . . . . . .. 239 X Contents 7. Excitation Dynamics in Molecular Solids By A. H. Francis and R. Kopelman (With 24 Figures) .............. 241 7.1 Lineshape Studies of Excitation Dynamics .................. 241 7.1.1 Pure Crystal Lineshape Theory ...................... 243 7.1.2 Lineshape Studies in Pure Crystals . . . . . . . . . . . . . . . . . . .. 251 7.1.3 Chemically Mixed Crystal Lineshape Theory . . . . . . . . . . . .. 257 7.1.4 Lineshape Studies in Chemically Mixed Crystals. . . . . . . . . .. 261 7.2 Excitation Migration in Ordered Crystals ("Neat" and Lightly Doped) . . . . . . . . . . . . . . . . . . . . . . . . . . .. 265 7.2.1 Exciton Fusion Experiments. . . . . . . . . . . . . . . . . . . . . . .. 266 7.2.2 Exciton Trapping Experiments . . . . . . . . . . . . . . . . . . . . .. 269 7.3 Excitation Migration in Substitutionally Disordered Crystals. . . . . .. 271 7.3.1 Trap-to-Trap Transfer ............................ 271 7.3.2 Cluster-to-Cluster Migration ... . . . . . . . . . . . . . . . . . . . .. 272 7.3.3 Critical Concentrations ............................ 273 7.3.4 Cluster Percolation. . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. 276 7.3.5 Exciton Percolation Formalism . . . . . . . . . . . . . . . . . . . . .. 280 7.3.6 Dynamic Percolation. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 282 7.3.7 Anderson-Mott Transition ......................... 286 7.3.8 Universality and Exciton Percolation ...... . . . . . . . . . . .. 290 7.3.9 Ordered vs Disordered Crystals ...................... 293 Epilogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 299 References .......................................... 299 Subject Index .......................................... 303