DYNAMICS OF COUPLED ELECTRON-PHONON MODES IN LIY1-XHOXF4

In single crystals of LiY1-xHoxF4, Ho3+ ions are found to be useful lu minescent detectors for phonons of frequencies in the range 6-72 cm(-1 ). Furthermore. by use of neutron diffraction, coupled electron-phonon modes associated with the lowest Stark levels of the I-5(8) ground mu ltiplet are observed in LiHoF4. The coupled modes account for anomalou s phonon diffusion and a strong magnetic-field dependence of the relax ation within the F-5(5) excited multiplet for crystals with x greater than or similar to 0.1.