A theory of hydrogen-like impurity centres in ionic crystals in the presence of an external magnetic or electric field is developed. The coupling t o longitudinal optical phonons is taken into account, and the results are valid for arbitrary interaction strength. Feynmans path-integral representation for the partition function of the phonon-impurity system and a variational principle connected with a quadratic trial Lagrangian are used. A simple
Absorption and luminescence of a concentration series of (Bi1−x Prx)4Ge3O12 single crystals are investigated. The intensity analysis of Pr3+ spectral lines in Bi4Ge3O12 crystals shows that the Judd‐Ofelt approach is inadequate. Therefore experimental methods are applied to obtain the main spectroscopic characteristics. The study of probabilities of non‐radiative transitions from different states of activator ions allowed to estimate the luminescence quantum yield from the metastable 3P0 state of Pr3+ ions in Bi4Ge3O12 crystals. 4Ge3O12Pr3+ crystals are promising active media for cryogenic and room temperature lasers in the visible spectral region.
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