Effect of pressure on the luminescence properties of gypsum, anhydrite, calcite and Dy doped CaSO4

Pressure-induced changes in the luminescent properties of gypsum (CaSO4.2H2O), calcite (CaCO3), CaSO4:Dy and anhydrite (CaSO4) are reported. A systematic reduction in the thermostimulated luminescence (TSL) [as well as photoluminescence (PL) in the case of CaSO4:Dy] sensitivity with the pressure applied is seen with the former three materials. However, an exactly reverse trend, i.e., a systematic increase in the TSL sensitivity with the pressure was witnessed in the case of anhydrite. While the application of pressure (7 MPa) reduced the TSL sensitivity of CaSO4:Dy to 43% of its initial value, a 700 °C, 1 h anneal could restore its value to only 51%. This shows that the pressure-induced changes are more or less permanent, unlike the case reported with LiF TLD. No change in the XRD data was seen in all these samples on the application of pressure (7 MPa) which shows that the changes observed in TSL and PL should be attributed to the damage (in the cases of calcite, gypsum and CaSO4:Dy)/creation (in the case of anhydrite) of traps/luminescent centres rather than to the damage to their crystal structure. Pressure applied before or after the irradiation produced no difference in CaSO4:Dy. However, in γ-ray exposed anhydrite and gypsum, pressure-induced changes in the TSL sensitivity were quite complex though no change in its glow curve structure was seen. Results showed that in anhydrite, there is a competition between two opposing pressure-induced phenomena-one is radiation damage to the filled traps and the other is the increased luminescence efficiency.