X-ray absorption spectroscopy and X-ray photoelectron spectroscopy studies of CaSO4:Dy thermoluminescent phosphors

Extended X-ray absorption fine structure (EXAFS) measurements have been carried out on CaSO₄:Dy phosphor samples at the Dy L₃ edge with synchrotron radiation. Measurements were carried out on a set of samples which were subjected to post-preparation annealing at different temperatures and for different cycles. The EXAFS data have been analysed to find the Dy-S and Dy-O bond lengths in the neighbourhood of the Dy atoms in a CaSO₄ matrix. The observations from EXAFS measurements were verified with XANES and XPS techniques. On the basis of these measurements, efforts were made to explain the loss of thermoluminescence sensitivity of CaSO₄:Dy phosphors after repeated cycles of annealing at 400 °C in air for 1 h.