Exciton-Exciton Interaction in KMnF3

Exciton dynamics in KMn${\mathrm{F}}_3$ at exciton densities up to ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are examined with time-resolved emission spectroscopy. The exciton emission line shifts and broadens with increasing exciton density. A nonlinear exciton decay channel is observed. These effects are found to be consistent with an exciton-exciton process. The shift scales with the exciton density and suggests that the effect is dominated by pairwise interactions up to the densities reached in these experiments.