Luminescence fromFCenters in Calcium Oxide

This paper reports data on the luminescence spectra associated with $F$ and $F^{+}$ centers in calcium oxide. Irradiation in the $F$ band excites emission bands at 500 and 627 nm, which we identify with the transitions ${}_{}{}^1{}_{}{}^{}P\to {}_{}{}^1{}_{}{}^{}S$ and ${}_{}{}^3{}_{}{}^{}P\to {}_{}{}^1{}_{}{}^{}S$, respectively, of the $F$ center. Radiative-lifetime measurements are consistent with this assignment. It is suggested that the weakness of the 500-nm band relative to the 627-nm band is due to competition between the ${}_{}{}^1{}_{}{}^{}P\to {}_{}{}^1{}_{}{}^{}S$ transition and a radiationless decay from the ${}_{}{}^1{}_{}{}^{}P$ to the ${}_{}{}^3{}_{}{}^{}P$ level. At 4.2 K, well-resolved fine structure is observed on the high-energy side of both the 627-nm band and the 369.7-nm ($F^{+}$) band. For both bands, the phonon-assisted structure can be reconstructed using only three vibrational modes.