Energy transfer and migration in highly forbidden transitions of lanthanide ion doped crystals

Forster-Dexter theory for resonant energy transfer is extended to higher or der and applied to explain the rates of energy transfer and migration proce sses in highly forbidden transitions for some solid-state lanthanide (Ln) i on systems for which experimental results are available. The second-order t wo-body energy transfer mechanism involves two inter-ion correlated dipole electrostatic interactions, i.e. dipole dipole-dipole dipole (dd-dd) energy transfer, also termed Axe-Axe energy transfer in view of the similarity of the theoretical formalism with that for two-photon transitions. Each of th e dipolar transitions consists of a transition from the 4f(n) configuration to an opposite-parity configuration, taken to be 4f(n-1)5d. dd-dd energy t ransfer is a short-range (R-12) interaction so that it is most important in systems with short donor Ln-acceptor Ln separations. The energy transfer f ormalism is extended to include spin-forbidden transitions at one or two si tes, the so-called Axe-Judd-Pooler (Axe-JP) and JP-JP energy transfer. In s ome cases the dd-dd mechanism is the dominant energy transfer process, as e xemplified herein for energy migration in the D-5(0) State of Sm2+ in SrF2, and also in the D-5(0) State of Eu3+ in Cs2NaEuCl6. (C) 1999 Elsevier Scie nce B.V. All rights reserved.