Observations on the luminescence of α-Al2O3 (synthetic sapphire) in a reactor environment

Optical components made of α-Al2O3 (synthetic sapphire) are used in optical systems (nuclear-pumped lasers, fission cells, etc.) to operate in a reactor in-core environment. Absorption and luminescence, which may take place in windows or lenses exposed to a reactor environment, will falsify results of optical measurements. For this reason, the knowledge of radiation-induced properties of optical materials is necessary. Measurements concerning optical absorption and luminescence of reactor-irradiated commercially available sapphire were made. The observed luminescence exhibits peaks around 3300 and 4100 A. The 3300-A peak increases as a function of irradiation time and saturates after 30 h of irradiation. The 4100-A peak decreases monotonically. The absorption coefficient after 69 h of irradiation was measured. It ranges from 7 cm-1 at 3000 A to 0.5 cm-1 at 6000 A