Radiative recombination and self-trapping of excitons via biexciton states in RbI

We have observed a luminescence band at 5.675 eV in RbI under dense excitation with a uv laser. The band is located 50 meV lower than the main peak of the free-exciton luminescence (FEL). The intensity of the band increases with an increase in the excitation intensity depending quadratically on the FEL intensity. The 5.675-eV band is assigned to luminescence of a biexciton leaving an exciton behind. The luminescence spectrum of self-napped excitons changes with the appearance of the biexciton luminescence. The spectral change is explained by a model including formation and decomposition processes of biexcitons.