Electron-phonon coupling for heavy RE3+ ions in crystals

The near resonant effects of electron-phonon coupling in the optical spectr a of rare earth (RE) ions are analysed. A theoretical treatment that could describe effects such as splittings or temperature shifts and broadening of zero-phonon lines is presented. The main factors that determine the magnit udes of the near resonant effects are the strength of electron-phonon coupl ing and the peaks in the phonon density in the resonance region. Experiment al data refer to heavy RE3+ ions, i.e. Tm3+ and Yb3+ in Y3Al5O12 (YAG), kno wn as important laser systems. The fitting of experimental data with theory allows the identification of the electronic levels with a good approximati on. The obtained data concerning the strength of the electron-phonon coupli ng show the tendency of increasing from Tm3+ to Yb3+. (C) 1999 Elsevier Sci ence B.V. All rights reserved.