Effect of Charge Compensator/Co-dopant Ions on the TL Characteristics of CaSO4:Dy and CaSO4:Tm Phosphors

Abstract

The effect of charge compensating ions (Na + or P 5+ ) has been studied in CaSO 4 :Dy/Tm phosphors. For CaSO 4 :Dy, Na, the thermoluminescence emission between 380 and 404 K seems to be well correlated with Na co-dopant which increases the formation and stabilisation of the SO 4 - centre. ESR as well as fluorescence measurements also showed an enhanced signal for the SO - 4 radical in CaSO 4 :Dy,Na samples. Co-doping of phosphorus in CaSO 4 :Dy/Tm resulted in increasing the TL sensitivity by about 40% when compared with that in the conventional CaSO 4 :Dy/Tm TL phosphors. In CaSO 4 :Dy,P and CaSO 4 :Dy, while ESR measurements showed no change in ESR signal intensity, TL measurements showed higher intensity for CaSO 4 :Dy,P samples. On the other hand, addition of Zr 4+ to CaSO 4 :Dy did not result in any enhancement in TL intensity of the dosimetric peak; however, ESR measurements showed enhanced intensity for the SO 3 - radical (stable up to 300°C) in CaSO 4 :Dy,Zr. These results tend to show that charge compensator ions such as Na + and P 5+ when present in CaSO 4 :Dy/Tm, result in higher luminescence efficiency either due to better incorporation of activator ions or due to improvement in energy transfer processes. On the other hand incorporation of co-dopant ions with higher effective charge such as Zr 4+ would increase the concentration of cation vacancies but did not result in an increase in the luminescence efficiency.