Optical Absorption and Nonradiative Decay Mechanism ofE′Center in Silica

Abstract

We report ab initio configuration interaction calculations on the optical transitions of the ${E}^{\ensuremath{'}}$ center, a hole trapped at an oxygen vacancy, $(---\mathrm{O}{)}_{3}{\mathrm{Si}}^{\ifmmode\bullet\else\textbullet\fi{}}$ ${}^{+}\mathrm{Si}(\mathrm{O}---{)}_{3}$, in silica. We found two competing excitation mechanisms: (1) promotion of one electron from an $\mathrm{O}(2p)$ valence band orbital to the singly occupied Si dangling bond; (2) charge transfer (CT) transition from $(---\mathrm{O}{)}_{3}{\mathrm{Si}}^{\ifmmode\bullet\else\textbullet\fi{}}$ to ${}^{+}\mathrm{Si}(\mathrm{O}---{)}_{3}$. The two excitations occur at similar energies, $\ensuremath{\approx}5.8--6\mathrm{eV}$ (5.85 eV in the experiment), but only the CT has a strong intensity. The excitation is followed by a complex nonradiative decay process which may explain the absence of luminescence for this center.