Ultraviolet radiation dosimetry using CaF2 TL phosphors- state of the art

Photoluminescence (PL), optical absorption (OA) and thermoluminescence (TL) of undoped and Dy, Tb- and Eu activated CaF2 TL phosphors has been re-investigated after heat treatment (600-1100 degC) in air. The study confirmed the earlier observed increase in intrinsic UV response of CaF2: Dy3+ after 900 degC heat treatment. Enhancement in UV response was also observed in undoped CaF2 thus indicating the base matrix related phenomenon. However, the enhancement observed in UV sensitivity and the optimum treatment temperature for high UV sensitivity is different for different activators. It is activator specific and needs further probing. UV response of undoped CaF2 monotonically increases as the treatment temperature (in air) is increased from 600 degC to 1100 degC. Similar increase is observed in case of CaF2: Tb3+ also. However, CaF2: Dy3+ and CaF2:Eu2+ follow a different pattern. Heat treatment in air increases UV response of CaF2: Dy3+ up to 900 degC, and a decrease is observed at higher temperatures. UV response of CaF2: Eu2+ is maximum for 600 degC treatment in air and decreases thereafter. TL response of CaF2: Tb and CaF2: Eu2+ phosphors to UV is high, can be employed over the range 10-2 - 2 mJ.cm-2 and is rate independent for 250±10 nm UV. (author)