Energy transfer assisted by localized excitations in amorphous solids

The contribution of low-energy localized harmonic excitations, which are ch aracteristic of the disordered state, to the non-radiative optical excitati on transfer between rare earth ions in a glass matrix is investigated. We f ind that the transition probability per unit lime of an optical excitation transfer between two sites has a cubic temperature dependence for character istic values of the impurity - soft mode coupling constant. This behavior h ad been previously observed in our laboratory in various Nd3+-doped fluorid e glasses. The implications of this result are briefly discussed. (C) 1999 Elsevier Science B.V. All rights reserved.