Inductive-resonant theory of nonradiative transitions in lanthanide and transition metal ions (review)

Abstract

The review is devoted to the theory of nonradiative transitions in tricharged ions of lanthanides and transition metals in the condensed phase, which was proposed in 1971. The theory is based on the phenomenon of nonradiative energy transfer from an electronically excited ion to surrounding molecular groups with excitation of resonant vibrational states and makes it possible to calculate the nonradiative transition rate constant (k nr) by a formula that is similar to the Forster formula. The primary emphasis is placed on recent experimental works that directly confirm the proposed theory. It is shown that the theory satisfactorily quantitatively accounts for (i) the effect of deuteration of molecular groups surrounding ions on k nr, (ii) the energy gap law, and (iii) the dependence of k nr on the distance between the ion and deactivating groups. Furthermore, it is shown that (iv) the theory makes it possible to satisfactorily quantitatively calculate in the dipole-dipole approximation the constant k nr of the electronic transition based on the knowledge of the radiative rate constant and the vibrational absorption spectra of molecular groups in the range of overlap with the luminescence spectrum of the ion; (v) the temperature dependence of k nr; and (vi) the anomalously low k nr in the case where the corresponding radiative transition is caused by the magnetic rather than the electric dipole. Literature data are presented that directly experimentally support the proposed theory of nonradiative transitions. In addition, works where this approach is used to calculate k nr of transitions in laser media are described.