Optical properties of Eu2+-ions immersed as substitutional impurities in a novel spatially-coherent composite host obtained from a melt of KCl,KBr and KI

The optical properties of doping Eu²⁺-ions in a novel composite host, consisting of a spatially-coherent aggregate of crystallites of KBr(0.097):KI(0.903) and KBr(0.459):KCl(0.511):KI(0.030), are investigated. The absorption spectrum consists of two broad absorption bands peaking at 353 and 279 nm while the fluorescence spectrum has a single emission band peaking at 422 nm. These spectra, formed by the spectral contributions from the phases in the composite, are similar in overall shape to the spectra of the Eu²⁺-doped alkali halides used as mother salts, indicating that they are similar in electronic origin. However, in relation to these alkali halides, the phases in the Eu²⁺-doped composite have low 10Dq-splittings (5684 and 8034 cm^?1), low 5d-level barycentre shifts (corresponding to decrements of about ?3351, ?2839, and ?1823 cm^?1, respectively, for one of the phases in the composite, and ?2411, ?1899 and ?916 cm^?1, respectively, for the other) and low Stokes shifts (4632 and 5496 cm^?1). Such low values are discussed to be due to the effect of the mixed ionic character of the impurity environment on the local crystal field as well as to an impurity preference for host cation lattice sites where an iodide ion is nearby to lie at.