Influence of γ-Irradiation on Some Properties of NaCl:Eu++ Crystals (II). Colourability

The room temperature colouration process of NaCl:Eu++ crystals strongly depends on both the dopant concentration, represented by the absorption coefficient α(eg), and the dopant dispersion state as well. It has been found that within the UV spectral range either some V-type absorption bands appear or only the background absorption increases. For heavily irradiated crystals the clustering of halogen-interstitial results in the formation of dislocation loops. In dependence of the dopant concentration the colourability of as received crystals is either larger (α(eg) ⪅, or smaller (α(eg) ⪆ ⁻¹) of that characteristic of the solution treated ones. The difference in the effectiveness of the halogen-interstitials trapping-process has been explained in terms of the various structure and/or composition of the europium-related aggregates and/or precipitates.