Optical properties of the F+ center in crystalline Al2O3

Abstract

Ultraviolet optical absorption, emission, and excitation spectra are presented for 14-MeV neutron-irradiated high-purity crystalline ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$. Low-temperature polarized excitation spectra for the 3.8-eV luminescence correlated well with polarized absorption at 4.8 eV (both polarizations) and 5.4 eV ($\overrightarrow{\mathrm{E}}\perp \overrightarrow{\mathrm{c}}$). These optical properties compare favorably with those predicted using wave functions from an earlier pointion calculation for the ${\mathrm{F}}^{+}$ center by La, Bartram, and Cox. The 4.8- and 5.4-eV absorption bands are assigned to the $1A\to 1B$ and $1A\to 2A$ transitions, respectively, of the $F^{+}$ center and the 3.8-eV luminescence is assigned to the $1B\to 1A$ transition. The $1A\to 2B$ transition could not be conclusively identified, but preliminary evidence suggests it occurs near 6.3 eV. Similar absorption and emission bands are observed following energetic-proton and ${\mathrm{Al}}^{+}$ bombardment. Other uv optical properties are presented, including the quantum efficiency, lifetime, and temperature dependence of the emission.