The first experimental evidence for distinct spectral and spatial energy transfer in ruby via nonradiative coupling is presented. Monochromatic laser excitation of the $R_1$ line results in a rise of the inhomogeneous background on a millisecond time scale, consistent with a one-phonon—assisted process and contrary to recent theory. However, time-resolved studies of trap fluorescence suggest a rapid, coherent, spatial transfer within the $R_1$ line which does not shift frequency.

• Received 29 November 1976

DOI:https://doi.org/10.1103/PhysRevLett.38.858