Luminescence spectra of CaSO₄with Ce, Dy, Mn and Ag codopants

Abstract

Thermoluminescence (TL) and radio-thermoluminescence spectral analysis techniques have been applied to doped calcium sulphate samples designed for radiation measurements at elevated temperatures. CaSO 4 :Dy, when co-doped with Ag, provides a TL dosimetric peak near 350 • C which is useful for radiation measurements at high temperatures. Dopants of Ce, Mn and Dy variously move the peak temperature from 400 • C to 200 • C. Each dopant ion gives a characteristic emission spectra, which for CaSO 4 :Ce, Mn samples indicate that there is a systematic temperature difference of ∼7 • C between the glow peaks from the Ce and Mn sites. The CaSO 4 :Dy samples show a discontinuity in the emission wavelength from the Dy ions near T = 200 • 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 • 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.

Thermoluminescence characteristics of LiNaSO4 doped with rare earths Eu and Dy

“…), there have always been attempts to either prepare new phosphors with better TL characteristics or simply improve upon the already existing phosphors by varying the concentration of the dopants of the phosphor or by co-doping well known phosphors with other elements. In fact very interesting results have been found earlier on codoping well known phosphors such as CaSO 4 :Dy and K 2 Ca 2 (SO 4 ) 3 :Eu with other elements [1][2][3][4][5]. The mixed sulphate LiNaSO 4 doped with the rare earth element Eu (resulting in the compound LiNaSO 4 :Eu) has been reported earlier [6][7][8] to be more sensitive than the commercially available standard phosphor CaSO 4 :Dy.…”

Influence of Li dopants on thermoluminescence spectra of CaSO4 doped with Dy or Tm

“…6. Other low temperature TL has been reported for CaSO 4 co-doped with Ce and Mn [35]. There were signals, which could be spectrally separated and related to Ce and Mn sites.…”

Factors controlling the thermoluminescence spectra of rare earth doped calcium fluoride

“…The rare earth ions vary in size from the calcium ion site that they occupy, and they also exist in a different charge state. The many consequences of these variations include the fact that the lattice is distorted, there is a need for charge compensating defects in the vicinity of the site and, as seen in earlier data for other material [10,[25][26][27][28], there is a high probability that the impurities will not be accommodated as individual dopants, but instead are likely to cluster in some fashion. The inherent consequences are that the defect structures and their stability (hence also the TL signals) will vary with (a) ion size, (b) dopant concentration and (c) thermal treatments which allow dissolution or clustering and production of intrinsic lattice vacancies.…”