TEMPERATURE-DEPENDENCE OF OPTICAL LINEWIDTHS AND SPECIFIC-HEAT OF RARE-EARTH-DOPED SILICATE-GLASSES

Optical dephasing and specific heat measurements were performed on two rare-earth-doped silicate glasses. The effective homogeneous linewidt h of the optical transition, GAMMA(hom), was compared to the two-level -system (TLS) contribution to the specific heat, C(v)TLS, between 0.4 and 12 K. Both GAMMA(hom) and C(v)TLS vary as T(alpha) with the same v alue of alpha for a given rare-earth/glass sample, but with different alpha for the two samples (alpha = 1.3 for the Pr3+/glass, alpha = 1.0 for Eu3+/glass). From the ratio of GAMMA(hom) to C(v)TLS for each gla ss, it appears that the coupling strengths to the TLS for each rare-ea rth optical transition are similar, but that the density of TLS differ due to their different compositions.