Spin dynamics of rare-earth ions in phosphate laser glasses

The spin dynamics of rare-earth ions (Er, Nd, Sm, and Gd) in heavily doped phosphate glasses have been investigated using ${}^{31}\mathrm{P}$ NMR. A model involving inhomogeneous broadening of the NMR resonance lines, with distinct sample regions corresponding to the presence or absence of nuclear spin diffusion, has been used in extracting the electron-spin-correlation times from the NMR measurements. Correlation times in the range ${10}^{\ensuremath{-}2}\char21{}{10}^{\ensuremath{-}12} \mathrm{s}$ have been obtained for temperatures between 4 and 100 K. No evidence of spin-spin coupling between the ions has been found and spin relaxation occurs via phonon processes, including the Orbach process. The importance of such processes in doped glasses is firmly established in this work. The rare-earth ions experience crystal-field effects produced by the close-to-octahedral symmetry of the local environment.