Effect of thermal preannealing on fluorescence, thermostimulated luminescence and cathodoluminescence of CaSO4 doped with europium

This study addresses the important influence of air thermal preannealings ( 500-1150 degreesC) on the emissions of Eu2+ and Ed(3+) ions in CaSO4 sample s doped with various Eu concentrations (10-2000 ppm) and synthesized under oxidizing conditions. The characteristics of optical excitation, optical ab sorption, fluorescence and cathodoluminescence spectra are given before and after the annealings. The role of UV, X-ray or electron irradiation is dis cussed. An irreversible conversion Eu3+ --> Eu2+ is obtained beyond 600-900 degreesC, even for low Eu concentrations (<50 ppm). There exists an intens e change in the ratio of Eu2+/Eu3+ emissions at about 125-100 ppm. Moreover , the present paper shows again how careful one must be with the interpreta tion of the presence of Eu2+ in CaSO4:Eu when considering cathodoluminescen ce results only. Two types of Eu2+ centres seem to be obtained in CaSO4:Eu2 + by thermal preannealings and/or under ionizing (X-ray, cathode-ray) irrad iations.