The role of segregations and oxygen doping in the photostimulation mechanism of CsBr:Eu2+

The influence of the formation of segregations as well as the role of oxygen during annealing are investigated concerning their relevance for an increased photostimulated luminescence (PSL) yield. It will be shown that the segregations are composed of at least two degraded phases of CsEuBr3 and contain solely trivalent europium ions excluding them from playing an active role in the PSL process. Therefore, oxygen also being present during annealing seems to be more likely the cause of the increased yield. In order to prove such a hypothesis the annealing has been performed in an oxygen-analogue sulphur atmosphere which yielded an even larger gain in PSL yield. PSL lifetime measurements indicate a reduced lifetime for the sulphur treated samples compared to the oxygen treated ones indicating a correlation between the sulphur ion and the Eu2+ ion. From such results it has been concluded that during annealing Eu2+-S2- and accordingly Eu2+-O2- dumbbells are created as PSL active emission centres. Thereby the increased number of such dumbbells explains the observed increase in the PSL yield and the difference in the gain for oxygen and sulphur treatment is explained by the accompanying strengths of the dipole fields of such dumbbells assumed to be responsible for the separation of the X-ray generated electron and hole pairs.