Picosecond-resolution spectroscopy of the three intrinsic self-trapped-exciton luminescence bands in Rb, i.e., σ, ${\mathit{E}}_{\mathit{x}}$, and π, is reported. For T≥17 K, the ${\mathit{E}}_{\mathit{x}}$ and π bands each display a rapid rise coincident with the 15-ps rise time of the σ band, followed by a second-stage growth matching the 3.4-ns decay of the σ luminescence. The results provide confirmation of recent theoretical models attributing all three luminescence bands to progressive degrees of ‘‘off-center’’ relaxation of the self-trapped exciton, in contrast to the well-known ${\mathit{V}}_{\mathit{k}}$+e model.

• Received 5 September 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.2140