Influence of oxygen doping and hydration on photostimulated luminescence of CsBr and CsBr:Eu2+

Powdered samples of CsBr:O2− and CsBr:Eu2+,O2− with oxygen concentrations ranging from 0.01 to 5.00 mol% have been synthesized and are shown to have photostimulated luminescence (PSL) properties which are strongly influenced by the oxygen concentration. In europium free CsBr:O2−, it was found that weak PSL emission at 460 nm arises from oxygen impurities while with oxygen concentrations higher than 0.05 mol% the emission shifts to the 379 nm emission of the CsBr matrix, which is attributed to the nonexcitability of oxygen agglomerates. The F-center concentration in CsBr:O2− is observed to increase with oxygen concentration, due to an increase in Br-vacancies as charge compensation centers for the O2− ions. In all CsBr:Eu2+ samples studied, intense PSL emission arises only following room temperature hydration in an atmosphere of 99% relative humidity, and it is concluded that the presence of water molecules is essential for the PSL in CsBr:Eu2+. In CsBr:Eu2+,O2− this enhancement effect of PSL intensity is reduced as the oxygen concentration increases above 0.05 mol% due to competition between the Eu2+ and O2− luminescence centers. It was found that the effects of hydration can be partially reversed following exposure to a vacuum while the material is rendered completely PSL inactive following thermal annealing up to 600 °C which is caused by agglomeration of the highly mobile Eu2+ ions and subsequent loss of Eu2+ luminescence.