High pressure effects on self-trapped excitons in RbI

Abstract

Pressure dependence of three intrinsic luminescence bands ascribed to the radiative decay of self-trapped excitons in RbI is investigated. The intensity of the π 2 (2.3 eV) band decreases rapidly below 0.2 GPa. The E x (3.1 eV) band first increases with pressure up to 0.2 GPa and then decreases to disappear near 1 GPa. The intensity of the α (3.9 eV) band is almost unchanged and remains after both the π 2 and E x bands have disappeared. Pressure coefficients of the peak energies for the E x and α bands are 0.28 and 0.33 eV/GPa, respectively, both of which are larger than that for a free exciton of the 1 s type. These features are explained by a model that the α exciton involves on-center distortion, while the π 2 and E x excitons involve large and small off-center distortions, respectively. The pressure-induced instability of self-trapped excitons with off-center distortions is well explained by the decrease of the Rabin-Klick ratio with increasing pressure.