Effects of neutron irradiation and subsequent annealing on the optical characteristics of sapphire

In this paper, the effect of neutron irradiation on sapphire single crystal with fast neutron of 1.0×1018 and 1.0×1019 neutrons/cm2 has been investigated along with the effect of annealing temperature. It is found that the colorless transparent sapphire single crystals were turned yellow after 10 MeV fast neutron irradiation at room temperature. There are peaks at 206, 230, 258, 305, 358 and 452 nm after neutron irradiation. And the intensity of optical absorption bands decrease with wavelength and annealing temperature. A new absorption peak at 452 nm was found after isothermal annealing at 400 °C for 10 min, which was ascribed to F2+ color center. Because of the recombination of interstitial ions and vacancies, color centers were almost removed after annealing at 1000 °C. The TL peaks were found to shift to higher temperature after neutron irradiation. And a higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks at 176 and 227 °C.

Research Highlights
► Sapphire single crystal is irradiated by fast neutron.
► Neutron irradiation results in surface lattice disorder in sapphire crystal.
► F, F2+ and F2 color centers are produced after neutron irradiation.
► With the increase is annealing temperature, the aggregate color center first increased and then decomposed.
► A higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks.