Optical-phonon relaxation by electronic excitations in CoF2

We propose a new phonon relaxation mechanism, in which the phonon couples to two electronic excitations, nearly resonant in energy. As a striking illustration of this effect we explain the anomalous temperature dependence of the linewidth of the k→, Eg phonon in CoF2 by its coupling to physically renormalized exciton-magnon states which detune with increasing temperature. © 1971 The American Physical Society.