Modification of the electronic and optical properties of YVO4:Eu induced by different charge states of the Eu ion

Abstract

By employing first-principles calculations within the frame of density functional theory, we investigated the modifications of the electronic and optical properties of isolated Eu impurities within YVO4:Eu3+ compound in the presence of additional electron charges. This scenario arises when YVO4:Eu3+ is exposed to gamma radiation that ejects electrons from certain ions and makes them available for capture by others. Our findings reveal that a significant portion of the additional charge is captured by the Eu3+ ion (0.32 e), but this portion is insufficient to confirm a change in the Eu oxidation state from 3+ to 2+. Nevertheless, this capture significantly modifies the Eu electronic configuration, elevating the energy of its occupied 4f-states and bringing them closer to the conduction band bottom. This fact causes the optical absorption of Eu to be generated by 4f → 5d electron transitions, instead of 4f → 4f as in the case of the non-irradiated compound. The presented results qualitatively explain drastic changes in the Eu emission spectrum induced by gamma irradiation of the YVO4:Eu3+, perceived experimentally.