Lanthanide-based luminescent hybrid materials.

Interpretation of europium(III) spectra

The optical spectra of the lanthanides doped into single crystal LaF3 have been interpreted in terms of transitions within 4f N configurations. Energy matrices combining free‐ion terms with a crystal field for an approximate model which assumes C2v instead of the actual C2 site symmetry were diagonalized. Excellent correlations were obtained between experimental transition energies and the computed level structures. We also report the results of previously unpublished experimental spectroscopic investigations of Nd3+ and Sm3+:LaF3, as well as predicted energy levels for Pm3+:LaF3. The spectroscopic data for each ion were independently interpreted using an effective‐operator model, then the model parameters were intercompared. Systematic trends have been identified, and a comprehensive energy level diagram is presented.

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A systematic analysis of the spectra of the lanthanides doped into single crystal LaF3

The superposition model was originally developed to separate the geometrical and physical information in crystal field parameters. Its success in the analysis of lanthanide spectra has been paralleled by the success of the related angular overlap model in the analysis of d-electron spectra. The basic ideas, method of application and reliability of the superposition model are discussed and its relationship with the angular overlap model is clarified. Developments described are the application of the superposition model to the ground (L=0) multiplet splittings of d5 and f7 ions, orbit-lattice interactions, transition intensities and correlation crystal fields. Special attention is paid to work which has been claimed to support or disprove the postulates of the model.

https://iopscience.iop.org/article/10.1088/0034-4885/52/6/002/pdf

The superposition model of crystal fields

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure–property relationships in these systems.

Lanthanides in molecular magnetism: old tools in a new field

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

Although a considerable body of data exists on the parametrization of the ground-state splittings of S-state ions in crystals, relatively little progress has been made in obtaining a quantitative understanding of the mechanisms which determine these parameters. In the course of summarizing our present understanding, we emphasize the need for making planned experiments explicitly aimed at testing theoretical models, such as those proposed in this article. The variable frequency E.P.R. technique is described in some detail, as it has proved to be particularly useful in this respect.

Interpretation of S-state ion E.P.R. spectra

List of contributors Preface Introduction 1 Crystal field splitting mechanisms D J Newman and Betty Ng 2 Empirical crystal fields D J Newman and Betty Ng 3 Fitting crystal field parameters D J Newman and Betty Ng 4 Lanthanide and actinide optical spectra G K Liu 5 Superposition model D J Newman and Betty Ng 6 Effects of electron correlation on crystal field splitting M F Reid and D J Newman 7 Ground state splittings in S-state ions D J Newman and Betty Ng 8 Invariants and moments Y Y Yeung 9 Semiclassical model K S Chan 10 Transition intensities M F Reid Appendix 1 Point symmetry D J Newman and Betty Ng Appendix 2 QBASIC programs D J Newman and Betty Ng Appendix 3 Accessible program packages Y Y Yeung, M F Reid and D J Newman Appendix 4 Computer package CST Cz Rudowicz Bibliography Index

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D.J. Newman

Papers

The superposition model of crystal fields

Theory of lanthanide crystal fields

Interpretation of S-state ion E.P.R. spectra

Crystal Field Handbook

Superposition-model analyses for the Cr3+ 4A2 ground state.