New features of self-trapped-exciton luminescence in rubidium iodide

Picosecond-resolution spectroscopy of the three intrinsic self-trapped-exciton luminescence bands in Rb, i.e., {σ}, Eₓ, and {π}, is reported. For T{≥}17 K, the Eₓ 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 Vₖ+e model.