RESUMO
The thermoluminescence (TL) spectra and dose responses of strontium sulphate doped with rare earth ions show that the SrSO4:Eu2+ phosphor might reasonably be assumed a isoelectronic trap sample which has unique TL characteristics: there is only one obvious glow peak at 385 nm, 489 K in the TL 3D emission spectra and its TL dose response is linear-sublinear. However, there are several elementary glow peaks in the TL 3D emission spectra and their TL dose responses are linear-supralinear for SrSO4:RE3+ (RE = Dy, Tm). These TL peaks occurred from low to high temperature indicate that the traps are distributed in different energy levels. When a suitable amount of other impurities co-doped into these SrSO4:RE3+, such as phosphorus, the relative intensities of these elementary glow peaks are changed significantly, especially the TL peak ~500 K is enhanced while the peaks at lower temperature are suppressed. The enhanced peak of SrSO4:RE3+,P is attributed to the deep traps. Their dose responses remain in nonlinearity when co-doped phosphorus. The above results and the luminescence properties of other sulphate doped rare earths impurities illustrate that the TL characteristics depend on the structure of defect complexes which can be assumed the basic elements in the TL multi-stage processes.
