Radiation resistance of synthetic sapphire crystal irradiated by low-energy neutron flux

In this paper, high-quality sapphire crystal grown by an improved Kyropoulos-like method, was irradiated by low-energy neutron (i.e. high proportion of thermal neutron) with various flux (low: 7.5×10¹⁵ n/cm², medium: 7.0×10¹⁶ n/cm² and high: 3.8×10¹⁷ n/cm²). The characteristic features of neutron fluence dependence of radiation-defect formation process, mainly including its change of the structural and optical properties prior to and after irradiation, were investigated by optical absorption (OA), photoluminescence (PL), electron paramagnetic resonance (EPR) and positron annihilation spectroscopy (PAS). It is found that sapphire crystal exhibits high radiation resistance to low-energy neutron with low fluence. But with the increase of irradiation fluence, it is still sensitive to neutron irradiation mostly in the UV-visible spectral range, as irradiationinduced color centers appear, including F-type and their aggregate centers. Finally, t e formation mechanism of the irradiation defects is also discussed.