Relaxed exciton luminescence of KCl crystals heavily doped with KI

Localized relaxed exciton luminescence in heavily doped KCl crystals containing iodine impurities has been investigated at 6 K. The excitation spectra of the I- dimer emission at 4.64 eV exhibit that the excitation peak shifts to the lower energy for the lowest excitation band with increase of the concentration of I- ions, which is ascribed to the formation of trimer and clusters of I- ions for heavily doped KCl crystals. Considering the iodine concentration dependence of luminescence and excitation spectra, it is concluded that the luminescence of heavily doped KCl: I originates from the localized relaxed excitons in a complex of three iodine ions (I- trimer) and lager sizes of iodine ions (KI cluster) in addition to usual monomer and dimer I- impurities. The effect of UV-light irradiation on the relaxed exciton luminescence of heavily doped KCl: I crystal has been also examined. The UV-light irradiated crystals exhibit an enhancement of the luminescence due to the dimer and the composite clusters. The lowest excitation band of the emission was found to become broad and to shift on the lower energy side. This suggests the formation of KI clusters under the UV-light irradiation. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim