The term ``sensitized luminescence'' in crystalline phosphors refers to the phenomenon whereby an impurity (activator, or emitter) is enabled to luminesce upon the absorption of light in a different type of center (sensitizer, or absorber) and upon the subsequent radiationless transfer of energy from the sensitizer to the activator The resonance theory of Forster, which involves only allowed transitions, is extended to include transfer by means of forbidden transitions which, it is concluded, are responsible for the transfer in all inorganic systems yet investigated The transfer mechanisms of importance are, in order of decreasing strength, the overlapping of the electric dipole fields of the sensitizer and the activator, the overlapping of the dipole field of the sensitizer with the quadrupole field of the activator, and exchange effects These mechanisms will give rise to ``sensitization'' of about 103−104, 102, and 30 lattice sites surrounding each sensitizer in typical systems The dependence of transfer efficiency upon sensitizer and activator concentrations and on temperature are discussed Application is made of the theory to experimental results on inorganic phosphors, and further experiments are suggested

A Theory of Sensitized Luminescence in Solids

Magnetic and electric dipole transitions between levels of the 4fx configuration perturbed by a static crystalline field are treated. The expression obtained for the pure‐electronic electric‐dipole transition probability involves matrix elements of an even‐order unit tensor between the two 4fx states involved in the transition. The contributions to the transition probability from interactions, via the crystalline field, with the nd 94fx−1, 4fx−1 nd, 4fx−1 ng configurations are shown to add linearly, in such a manner as to multiply each odd k crystal‐field parameter Ak q by a constant. If ``J mixing'' in the 4fx configuration is neglected ΔJ between the upper and lower 4fx levels is restricted to six units or less. If ``L mixing'' is neglected then ΔL is also restricted to six units or less. Application is made to the fluorescence spectra of PrCl3 and EuCl3. Many of the missing and weak transitions are explained.

Intensities of Crystal Spectra of Rare‐Earth Ions

It is pointed out that one of the main effects of correlation phenomena in d- and f-bands is to give rise to behaviour characteristic of the atomic or Heitler-London model. To investigate this situation a simple, approximate model for the interaction of electrons in narrow energy bands is introduced. The results of applying the Hartree-Fock approximation to this model are examined. Using a Green function technique an approximate solution of the correlation problem for this model is obtained. This solution has the property of reducing to the exact atomic solution in the appropriate limit and to the ordinary uncorrelated band picture in the opposite limit. The condition for ferromagnetism of this solution is discussed. To clarify the physical meaning of the solution a two-electron example is examined.

Electron correlations in narrow energy bands

Editorial Board: W. G. E. Caldwell, OC, FRSC (University of Western Ontario); K. G. Davey, OC, FRSC (York University); S. Gubins (Annual Reviews); B. K. Hall, FRSC (Dalhousie University); P. Jefferson (Agriculture & Agri-Food Canada); W. H. Lewis (Washington University); A. W. May, OC (Memorial University of Newfoundland); N. R. Morgenstern, CM, AOL, FRSC (University of Alberta); B. P. Dancik, Editor-in-Chief, NRC Research Press (University of Alberta)

Molecular symmetry and spectroscopy

Ranging from the physics of elementary particles to the structure of viruses, the subject matter of this book stresses the importance of optical activity and chirality in modern science and will be of interest to a wide range of scientists. Using classical and quantum methods with a strong emphasis on symmetry principles, the volume develops the theory of varied optical activity and related phenomena from the perspective of molecular scattering of polarized light. First Edition Hb (1983): 0-521-24602-4

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Molecular Light Scattering and Optical Activity

1. Introduction 2. The quantum mechanical method 3. Angular momentum 4. The theory of radiation 5. One-electron spectra 6. The central-field approximation 7. The Russell-Saunders case: energy levels 8. The Russell-Saunders case: eigenfunctions 9. The Russell-Saunders case: line strengths 10. Coupling 11. Intermediate coupling 12. Transformations in the theory of complex spectra 13. Configurations containing almost closed shells. X-rays 14. Central fields 15. Configuration interaction 16. The Zeeman effect 17. The Stark effect 18. The nucleus in atomic spectra Appendix. Universal constants and natural atomic units.

The Theory of Atomic Spectra

The theory of atomic spectra

A systematic comparison of the known data on the singlets and triplets arising from sp, sd, sf, and d 9 s configurations with the theory of Houston shows that the theory gives a good account of the deviations from the Lande interval rule which accompany departure from Russell-Saunders coupling. There are numerous significant discrepancies, however. Writing 1 L l and 3L l +1, 3 L l , 3 L l -1 with L = P, D, F, when l = 1, 2, 3 for the term values, we plot as abscissa (3 L l -1 - 3 L l +1)/|3 L l - 1L l | and (3 L l -1 - 3 L l )/(3 L l - 3 L l +1) as ordinate if (3 L l - 1 L l +1) is positive, otherwise the reciprocal of this quantity. Houston’s equations (12) give functional relations between these interval ratios which are compared with the experimental values.

G. H. Shortley

Papers

The Theory of Atomic Spectra

The Theory of Atomic Spectra

The theory of atomic spectra

Singlet-Triplet Interval Ratios for sp, sd, sf, p 5 s and d 9 s Configurations