We report an observation of the intrinsic fluorescence of Gd(OH${)}_3$ arising from exciton band-to-band transitions occurring primarily at the edge of the Brillouin zone. Using the ${}_{}{}^8{}_{}{}^{}\mathrm{S}_{7/2}^{}{}_{}{}^{}$, $M_J$=-(5/2, magnon dispersion, we found an exciton dispersion of 1.8 ${\mathrm{cm}}^{\mathrm{-}1}$ for the ${}_{}{}^6{}_{}{}^{}\mathrm{P}_{7/2}^{}{}_{}{}^{}$, $M_J$=-(7/2 crystal state at 2 K in an applied magnetic field of 35 kG. Transitions involving the second excited spin state of the ground manifold have also been observed in absorption and emission. In contrast to the magnon state, the $M_J$=-(3/2 state has little or no dispersion. By time resolving the emission, it is clear that the relaxation of the initially excited k=0 excitons to k values at the zone edge takes place faster than 10 nsec.

• Received 2 October 1989

DOI:https://doi.org/10.1103/PhysRevB.41.1735