Structure and properties of oxygen centers in CaF2crystals fromab initioembedded cluster calculations

Abstract

We present the results of ab initio calculations of several intrinsic and oxygen-containing defects in CaF${}_{2}$ including an $F$ center, a substitutional O${}^{\ensuremath{-}}$ ion, an O${}^{2\ensuremath{-}}$-vacancy dipole, and ${F}_{A}$(O${}^{2\ensuremath{-}}$) and ${F}_{2A}^{+}$(O${}^{2\ensuremath{-}}$) centers. The calculations have been performed using a hybrid density functional and an embedded cluster method. The calculated optical absorption (OA) spectra and magnetic properties are in a very good agreement with available experimental data. It is suggested that isolated substitutional O${}^{\ensuremath{-}}$ ions induce an OA band in the vacuum ultraviolet region at about 7 eV. The nature of the OA bands associated with O${}^{2\ensuremath{-}}$-vacancy dipoles and other, more complex, defects is clarified and corresponding luminescence mechanisms are discussed.