Association of the 6-eV Optical Band in Sapphire with Oxygen Vacancies

Abstract

Arnold and Compton⁽¹⁾ have demonstrated that the prominent 6-eV optical absorption band observed in reactor irradiated crystalline sapphire by Levy and Dienes^(2,3) and Mitchell et al.⁽⁴⁾ is due to atomic displacement events and not to ionizing radiation alone, as x-ray and γ-irradiation will not produce this band. The orientationally averaged displacement threshold energies associated with the product ion of the 6-eV band were determined to be 90±5 and 50± eV when the absorption is associated with respectively anion or cation vacancies by a series of low temperature 0.6-to-1.8 MeV electron irradiations. However, they were unable to determine which damaged sublattice, anion or cation, is responsible for the uv optical absorption. Arnold^(5,6) et al. and Evans⁽⁷⁾ have subsequently shown that energetic light ions such as 50-keV and 200-keV H⁺, 100-keV D⁺ (and 100-keV ³He⁺ to lesser degree) at fluences of 10¹⁶ cm^-2 also produce the intense 6-eV, whereas bombardment to the same fluence with heavier ions such as 220-keV 0⁺, 500-keV A⁺ and 200-keV Xe⁺ results in virtually none of these characteristic bands. Arnold⁽⁵⁾ has offered an explanation of these observations based on defect center charge decoration.