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Title: The dynamic Pseudo-Jahn-Teller problem in cubic symmetry and a vibronic model for the relaxed excited state of the F centre in some alkali halides
Author: Greusmühl, Hans Ulrich
ISNI:       0000 0001 3518 9825
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1976
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The results of recent experiments on Stark effects in F-band luminescence of various alkali halides have suggested a model for the relaxed excited state of the F centre in which non-degenerate 2s and 2p electronic states interact in cubic symmetry via a triply degenerate odd-parity (Tlu)vibrational mode. A general exact solution of this vibronic problem has been given by Ham (1973a). We extend the work by a numerical investigation of this ideal pseudo-Jahn-Teller problem. Vibronic energy levels and wave functions, emission spectra at various temperatures, absorption lines and spectra at T=0, and reduction factors are calculated for various values of the vibronic coupling strength and of the electronic 2s-2p spacing. The results are compared with explicit expressions of the weak and strong coupling limit. In addition, the absorption line shape is calculated in semi-classical approximation. The relaxed excited state of the F centre is investigated within this model by a perturbation analysis for the case of weak electron-phonon coupling. The resulting predictions are compared with available data on radiative lifetimes, Stark effects, magnetic circular polarization, and stress-induced polarization of F-band luminescence. It is shown that a consistent quantitative interpretation of most of these data is possible on this basis if the 2s electronic state lies below the 2p state in the relaxed cubic configuration.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available