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Determination of the chemical states of impurities in natural kyanite by the ionoluminescence technique

Ionoluminescence (IL) of natural kyanite crystals was studied during 120 MeV Au9+ ion irradiation in the fluence range 1.50−12 × 1011 ions/cm2. The IL spectrum exhibits sharp peaks at ∼689, 694, 705, 713 and 716 nm, along with a broad emission peak at 530 nm recorded for all samples investigated. The sharp emission peaks at 689 and 694 nm are attributed to R2 and R1 lines of Cr3+ impurities, and they are related to the transition 2Eg → 4A2g. The peaks at 705–716 nm are attributed to Fe3+ impurities and are related to the transition 4T1g → 6A1g. It was observed that up to a given fluence, the IL peak intensity grows, reaches a maximum and gradually decreases with increase of Au9+ ion fluence. The decrease in IL intensity might be attributed to disorder produced by dense electronic excitation under swift heavy ion irradiation. The stability of the chemical species was studied both with and without irradiation by means of FTIR spectroscopy. The results confirm that the Si−O−Al, Al−O and Si−O (2ν3) type species are destroyed due to amorphization.