Theory of nonradiative multiphonon transitions in impurity centers with extremely weak electron‐phonon coupling

Abstract The nonradiative multiphonon (NMP) electron transition rate in impurity centers in ionic crystals is calculated taking into account high‐order anharmonicity terms in expansion of the electronphonon (EP) interaction in atomic displacements. In the extremely weak coupling limit the traditional potential energy surface displacement relaxational mechanism is shown to be inefficient and NMP relaxation is caused mainly by high anharmonicity of the EP interaction. For this limit a new formula is obtained, which may be applied, e.g., in analysing the NMP relaxation of RE ions in ionic crystals.

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