Optical properties of the Eu2+-ion immersed as a doping impurity into a KCl:KBr:RbBr solid solution: Influence of the different aggregation-precipitation states of the doping ions

Abstract

The optical properties of the Eu2+-ion immersed as a doping impurity in mixed KCl–KBr–RbBr crystals were investigated together with the changes that these properties suffer by thermal quenching at liquid-N2 temperature and, also, during thermal annealing at 523 K. The crystal matrix, as characterised by X-ray diffraction, consists of a strongly-textured F-type cubic ternary KCl:KBr:RbBr solid solution (a0 = 6.59 ± 0.02 Å). The absorption spectrum of freshly-quenched samples shows two broad absorption bands peaking at about 328 and 247 nm (10Dq = 9998 ± 143 cm−1) whereas the fluorescence spectrum of these samples shows a single nearly-symmetric emission band peaking at about 420 nm. These spectra, being similar in general to the corresponding ones of freshly-quenched single crystals of KCl:Eu2+, KBr:Eu2+ and RbBr:Eu2+, change during the annealing treatment so that, for well-annealed samples, the absorption bands peak at 277 and 333 nm (10Dq = 6689 ± 91 cm−1) whereas the fluorescence spectrum consists of four emission bands peaking at about 420, 427, 449 and 480 nm. These changes, indicating that the doping ion environment evolves during annealing, are discussed to be due to the occurrence of different precipitation states of the doping ions. The structural nature of these states, and, also, an aggregation-precipitation kinetics, is proposed.