MULTIPHONON RELAXATION OF THE H- LOCAL MODE IN CAF2

We have investigated the non-radiative relaxation of the substitutiona l H(-)local mode (v = 965 cm(-1)) in CaF2. This system is attractive d ue to its simplicity, the only possible decay mechanism, aside from ra diative relaxation, is non-radiative multiphonon decay into host phono ns. Saturation experiments were performed at the Stanford Picosecond F ree Electron Laser Center, using a pump-probe technique. We find an en ergy relaxation time T-1 of 45 ps at low temperature. We compare this result with the relaxation of the local mode of an interstitial H(-)io n next to a Lanthanum impurity ion, and find a much more rapid relaxat ion time T-1 of 6 ps. (C) 1998 Elsevier Science B.V. All rights reserv ed.