Thermoluminescence (TL) and radio-thermoluminescence spectral analysis techniques have been applied to doped calcium sulphate samples designed for radiation measurements at elevated temperatures. CaSO4:Dy, when co-doped with Ag, provides a TL dosimetric peak near 350 degrees C which is useful for radiation measurements at high temperatures. Dopants of Ce, Mn and Dy variously move the peak temperature from 400 degrees C to 200 degrees C. Each dopant ion gives a characteristic emission spectra, which for CaSO4:Ce, Mn samples indicate that there is a systematic temperature difference of similar to 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 near T = 200 degrees C and a decrease in the radioluminescence fluorescence in the same temperature region. In each case it is proposed that the dopants form part of large, complex defects, instead of isolated trapping and recombination centres. The data offer further evidence for a localized phase transition of the defect complex at 200 degrees C. Low-temperature data, from 20 K, show similar differences in the peak temperature from the various dopants and additionally indicate reproducible discontinuities in the wavelength positions and intensities, for all samples, at T = 230 K. This again suggests structural phase adjustments of the defect sites.