Luminescence of excitons and Eu 2+ v c – centres in KI:Eu 2+ crystals

Luminescence characteristics of KI:Eu 2+ crystals are studied at 11.5–300 K under excitation in the 3.0–6.3 eV energy range. Besides the known 2.88 eV emission of Eu 2+ v c – centers, the new emission bands peaking at ∼3.75 eV, ∼3.3 eV, 3.06 eV, and 2.38 eV are found. The bands, located in the 3.1–4.3 eV energy range and strongly distorted due to their overlap with the Eu 2+ v c – absorption bands, are ascribed to the self‐trapped exciton emission. The 3.06 eV and 2.88 eV bands are ascribed to the electronic transitions from two close levels of the splitted T 2g excited state of an Eu 2+ ion. The 2.38 eV emission is ascribed to the radiative decay of an exciton localized near an Eu 2+ ion. It is assumed that the appearance of the self‐trapped exciton emission under excitation in the Eu 2+ ‐related absorption bands is connected with the radiative decay of excitons, which are formed at the recombination of electrons and holes, produced in the crystal as a result of the photostimulated charge transfer from the Eu 2+ ‐perturbed I – states. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)