Spin—Lattice Relaxation in Some Rare-Earth Trichlorides

Studies of spin—lattice relaxation of the ions Ce3+, Nd3+, Sm3+, Ho3+, and Er3+ present in low concentrations (0.2% to 2%) in the host lattice of LaCl3 have been made in the liquid-helium region by the pulsed-microwave method. The variation of the relaxation time τ with temperature permits separation of the contributions to the relaxation from the two-phonon (resonant and nonresonant) and single-phonon processes. The substances studied are not ``well behaved''; features such as nonexponential decays and variability of the derived values for the splitting between the ground and first excited levels are discussed. Some of the ions exhibit a significant variation of τ with concentration and Nd3+ shows an interestingly large anisotropy of τ in the Raman process.