Eu3+↔ Eu2+redox reactions in bulk and nano CaF2:Eu

Eu3+→Eu2+ conversion caused by thermal treatments and exposures to ionizing radiations was studied using photoluminescence in bulk and nano powders of CaF2:Eu. It was found that there is no radiation-induced Eu3+→Eu2+ conversion in the nano powders. Thermal Eu3+→Eu2+ conversion, on the other hand, takes place at much lower temperatures in the nano powders as compared to the bulk. The different behaviors are discussed in terms of the quantum confinement and the differences in the local environments.