Recent progress in understanding the origin of the lanthanide crystal field is summarized. The basic assumption of the crystal field parametrization is shown to be that the crystalline environment can be represented as a one-electron potential, and the consequences of removing this assumption are traced. It is further shown that overlap and covalency make the dominant contributions to the observed field, the electrostatic contributions only being inportant for the potential components with low angular dependence (i.e. the n=2 parameters). In some circumstances it is found that the observed parameters can usefully be analysed into superposed contributions from the neighbouring ions in the crystal. The importance of crystal field concepts in related problems is emphasized as well as the stimulus crystal field theory gives to the development of formalisms for dealing with non-orthogonal basis states.

Theory of lanthanide crystal fields

Publisher Summary There have been many reviews and books on electron spin resonance (ESR) and several on transition metal ions. Many of these publications have been written by physicists or theoreticians and are very comprehensive. This review is aimed at inorganic chemists, who have had no experience relating to electron spin resonance and who are becoming more and more likely either to use the technique or to need to appreciate the significance of the information available from the technique. The first part of the review gives an elementary account of the relevant theory. There are many good books for further reading for the inorganic chemist, who wishes to go deeper into the subject. The second part of the review is a comprehensive survey of the results of ESR studies on compounds of transition elements. Inevitably, there has had to be some selection of material, and the criteria for inclusion or rejection has been based upon the likely interest of an inorganic chemist might have in the species. This is particularly in the areas, where there is a lot of related work, e.g., the Mn2+ host-lattice data. In the case of copper dg complexes, there has been much duplication of work and papers devoted to the spectra of complexes where a minor substitutive change has been made to a bulky organic ligand.

Electron Spin Resonance of Transition Metal Complexes

The dynamical complexity of optically injected semiconductor lasers

Publisher Summary This chapter describes the application of electron spin resonance techniques to a particular group of crystalline semiconductors, including Si and related group IV elements and compounds, InSb and related 111-V compounds, and ZnS and related 11-VI compounds. The semiconductors discussed in the chapter have a number of characteristics that make them particularly interesting subjects for resonance study. One characteristic is that the semiconductors are intrinsically diamagnetic and show no cooperative magnetic phenomena, such as ferromagnetism and antiferromagnetism. Crystals that are examined in the chapter are typically dilute in magnetically active impurities and have narrow resonance lines. Another characteristic is the tetrahedral symmetry about each lattice site. However, semiconductors are an ideal group of materials for investigating the effects of covalency. There are several features of the resonance technique that make it a particularly useful tool for the study of semiconductors. Electrical, optical, and other properties of semiconductors are extremely sensitive to small concentrations of impurities. Spin resonance is one of the most sensitive and powerful tools for investigating the detailed nature of impurity sites. Moreover, it is often possible to study one impurity in the presence of much larger concentrations of other impurities.

Electron Spin Resonance in Semiconductors

Oxovanadium(IV) complexes

The electron spin resonance spectrum of the vanadyl ion (VO2+) in single crystals of Zn (NH4)2(SO4)2·6H2O is studied and the properties of x‐ray produced V2+ are compared to those of the V2+ grown directly into the same host lattice. In the unirradiated samples the V–O axis is found to have three possible orientations with populations in the ratio 20:5:1. For the most populous position the spin Hamiltonian parameters at X band are S=½, gx=1.9813, gy=1.9801, gz=1.9331, Ax=0.007120/cm, Ay=0.007244/cm, Az=0.018281/cm, and Q′=7×10—5/cm with the x, y principal axes of the g and A tensor being displaced from each other by 23°20′. Furthermore, the vanadyl hyperfine lines show an additional anisotropic structure of five lines, absent in deuterated samples. The parameters for V2+ at K band in both the as‐grown and irradiated crystals are S=3/2, gz=1.9717, gy=1.9733, D=—0.15613/cm, E=—0.02280/cm, and A=—0.00825/cm. A study of the effect of x‐ray dose upon the line intensity is made. An impurity model of a vanadyl p...

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VO2+ and X‐Ray Produced V2+ in Tutton Salt

Paramagnetic Resonance of CdTe: Mn and CdS: Mn

Maser Action in Ruby

The theory of the paramagnetic‐resonance absorption of ions with S=52 in crystalline fields of trigonal symmetry is presented. The case of manganous ions in calcite (CaCO3) is taken as an example. It is shown that the splitting of the fine‐structure satellites into doublets first reported by Hurd, Sachs, and Hershberger [Phys. Rev. 93, 373 (1954)] can be accounted for by assuming that the manganous ions can occupy the two nonequivalent Ca++ sites at random. The maximum splitting was measured at X band and K band and found to be 19.3±0.5 gauss. The value computed from the theory, assuming an ionic model, is 23.8 gauss. In addition, five pairs of weak lines were found, each pair occurring midway between adjacent hyperfine groups. The origin of these lines is uncertain. The applicability of the present theory to Al2O3:Fe, a zero‐field maser material, and to the photosensitive Fe+++ center in CdS is pointed out.

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Chihiro Kikuchi

Papers

VO2+ and X‐Ray Produced V2+ in Tutton Salt

Paramagnetic Resonance of CdTe: Mn and CdS: Mn

Maser Action in Ruby

Paramagnetic‐Resonance Absorption of Ions with Spin 5/2: Mn++ in Calcite

Coherence and Two-Photon Absorption