F-center fluorescence in neutron-bombarded sapphire

The efficiency of the 3.0‐eV photoluminescence band which results from optical excitation into the 6.1‐eV F band in single‐crystal sapphire is much weaker for F centers introduced by fast neutron bombardment than for those produced thermochemically (i.e., by either deliberate additive coloration or by coloration during growth). The luminescent efficiency has been monitored at room temperature following successive isochronal annealing stages up to 580 °C for samples exposed to ∼1017 neutrons cm−2. The relative emission intensity per F center increased rapidly as the F centers were thermally destroyed and reached a value at the upper end of the annealing range which was 40 times the preanneal value. It is suggested that the initial relatively weak emission is due to concentration quenching which results from the highly inhomogeneous distribution of lattice defects, i.e., displacement cascades, produced by fast neutron bombardment.