Two Slowly Decaying Luminescence Bands in Alkali Iodides

Effects of optical excitation of the self-trapped excitons on the intensities of the two slowly-decaying luminescence bands in RbI and KI have been measured. The excitation-induced fractional decreases in the intensity of the two luminescence bands in RbI are found to be almost the same, irrespective of the excitation photon energy. The degree of polarization of the decrements of the two luminescene bands in RbI induced by the hole-excitation was found to be identical. The decay times of the two slowly-decaying luminescence bands in Na-doped KI and K-doped RbI are also measured and it is found that impurity-associated two slowly-decaying luminescence bands are induced in each of these doped crystals. We conclude that both of the two slowly-decaying luminescence bands in RbI are intrinsic. It is suggested that the exciton in RbI is relaxed either into the three-center-type self-trapped exciton as well as into the two-center-type self-trapped exciton.