Optical properties of -ions immersed as substitutional impurities in a mixed KBr–RbBr host

This work was undertaken to know the optical properties of the ion Eu2+ immersed as a substitutional impurity in freshly-quenched Eu2+-doped mixed KBr–RbBr crystals and, also, to know how these properties change during annealing at 200 °C. X-ray diffraction was used to characterize the mixed matrix. It consists of a conglomerate of crystallites, about 1380 Å in mean size and 7.1×10−4 in mean non-uniform strain, of the F-type-cubic solid solution K0.51Rb0.49Br ( a 0 = 6.743 ± 0.001 Å ). The absorption spectrum of freshly-quenched specimens shows two broad absorption bands peaking at about 328 and 250 nm while the fluorescence spectrum of these specimens shows a single emission band peaking at about 418 nm. A 10Dq-splitting value of 10540±480 cm−1 characterizes the local crystal field at the impurity site in freshly-quenched samples. These spectra, which are similar in overall shape to the corresponding spectra of single crystals of KBr:Eu2+ and RbBr:Eu2+, change drastically during the annealing treatment. The absorption spectrum of long annealed specimens consists of two absorption bands peaking at about 332 and 280 nm while the fluorescence spectrum of these specimens consists of four emission bands peaking at 419, 427, 454 and 520 nm. A10Dq-splitting value of about 7500 cm−1 was estimated for long annealed samples. During annealing, the evolution of the optical spectra is similar to the evolution of the corresponding optical spectra of KBr:Eu2+ and RbBr:Eu2+ under annealing at the same temperature. Different aggregation–precipitation states adopted, as a result of the annealing treatment, by the Eu2+-ion impurities within the mixed matrix are discussed to be responsible for the changes suffered, during this treatment, by the optical properties under study.