RARE-EARTH IONS AS SPECTROSCOPIC PROBES OF DYNAMIC PROPERTIES OF INSULATORS

Various ways in which the sharp line spectra of rare earth ions are used as probes of dynamic events occurring in their hosts are reviewed; recent developments including the emergence of real temporal, frequency and spatially resolved high frequency phonon spectroscopy based on rare earth ions are described. The laser heated pedestal growth (LHPG) method of material synthesis has made available a great variety of new samples and new materials and has proven to be a powerful new tool in the study of the dynamic properties of solids. We present a number of examples in which the crystalline fibers obtained through LHPG are employed in this fashion.