Color center formation in α-Al2O3 induced by high energy heavy ions

Single crystals of alpha-alumina were irradiated at room temperature with 1.157 GeV 56Fe, 1.755 GeV 136Xe and 2.636 GeV 238U ions to fluences range from 8.7 × 109 to 6 × 1012 ions/cm2. Virgin and irradiated samples were investigated by ultraviolet–visible absorption measurements. The investigation reveals the presence of various color centers (F,F+,F22+,F2+andF2centers) appearing in the irradiated samples. It is found that the ratio of peak absorbance of F2 to F centers increases with the increase of the atomic numbers of the incident ions from Fe, Xe to U ions, so do the absorbance ratio of F22+ to F+ centers and of large defect cluster to F centers, indicating that larger defect clusters are preferred to be produced under heavier ion irradiation. Largest color center production cross-section was found for the U ion irradiation. The number density of single anion vacancy scales better with the energy deposition through processes of nuclear stopping, indicating that the nuclear energy loss processes determines the production of F-type defects in heavy ion irradiated alpha-alumina.