Luminescence spectra of CaSO4 with Ce, Dy, Mn and Ag codopants

Thermoluminescence (TL) and radio-thermoluminescence spectral analysis tech niques have been applied to doped calcium sulphate samples designed for rad iation measurements at elevated temperatures. CaSO4:Dy, when co-doped with Ag, provides a TL dosimetric peak near 350 degrees C which is useful for ra diation measurements at high temperatures. Dopants of Ce, Mn and Dy various ly move the peak temperature from 400 degrees C to 200 degrees C. Each dopa nt ion gives a characteristic emission spectra, which for CaSO4:Ce, Mn samp les indicate that there is a systematic temperature difference of similar t o 7 degrees C between the glow peaks from the Ce and Mn sites. The CaSO4:Dy samples show a discontinuity in the emission wavelength from the Dy ions n ear T = 200 degrees C and a decrease in the radioluminescence fluorescence in the same temperature region. In each case it is proposed that the dopant s form part of large, complex defects, instead of isolated trapping and rec ombination centres. The data offer further evidence for a localized phase t ransition of the defect complex at 200 degrees C. Low-temperature data, fro m 20 K, show similar differences in the peak temperature from the various d opants and additionally indicate reproducible discontinuities in the wavele ngth positions and intensities, for all samples, at T = 230 K. This again s uggests structural phase adjustments of the defect sites.