Theory of Vibronic Spectra
Prominent sidebands often appear in the absorption and fluorescence spectra of systems consisting of a small quantity of magnetic ions in an ionic host lattice. The sidebands are called vibronic, and result from a dynamic coupling of the magnetic ion to the motion of other lattice constituents. These sidebands may reflect a frequency distribution for the perfect or perturbed lattice modes. An interpretation of the vibronic structure for the perfect lattice case, as first presented by R. A. Satten, is discussed.
A vibronic analysis requires a correlation of available information on lattice modes with optical data, and so the first portion of the discussion reviews infrared absorption, Raman scattering, and neutron scattering theory. A simple model for vibronic processes is then presented. Selection rules for vibronic transitions are formulated from group-theoretical considerations regarding the uncoupled electronic and vibrational systems. The role of critical points and their effect upon the frequency distribution of lattice modes is also taken into account. Finally, the system MgO:V2+ is treated in some detail.
KeywordsWave Vector Selection Rule Raman Scattering Lattice Mode Coherent Scattering
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