Ultraviolet-induced charge transfer in CaSO₄:Eu

Abstract

The ultraviolet-induced reduction of Eu3+ to Eu2+ in CaSO4:Eu has been found to proceed via a charge transfer (CT) transition of the Eu3+-O8 complex followed by the liberation, migration and trapping of the hole generated by the CT. A kinetic model of this process based on the thermally stimulated transfer of the electronic population between Eu3+ upper 4f6 states and the Eu3+-O charge transfer state is proposed and some of its implications for the production of thermoluminescence (TL) in CaSO4:Eu discussed. The UV-induced TL response of CaSO4:Eu was found to be correlated with the production rate of Eu2+ for wavelengths greater than 230 nm, however the same correlation was not apparent for shorter wavelengths.