Ionoluminescence of zircon: rare earth emissions and radiation damage

Abstract

The luminescence of synthetic rare earth (RE)-doped zircons and three natural zircons has been studied by ion beam excitation (ion beam luminescence or ionoluminescence (IL)). Luminescence results from electronic transitions between energy levels of the RE ions, giving emissions with characteristic energies. Studies of co-doped Ho : Dy zircon show that electronic cascades from Ho3+ to Dy3+ ions result in intense Dy3+ luminescence even when Ho is far more abundant. Dy3+ ions have the greatest luminescence cross-section of common RE3+ ions. Implantation of heavier N+ ions into zircon, chosen to mimic accelerated radiation-induced structural modification, causes significant sample degradation. Frenkel-type defects and groups in the zircon are associated with a broad luminescence band of ∼600 nm, and these defects modify energy cascades between RE3+ ions, thereby reducing the efficiency of energy deposition via the Dy3+ luminescence decay pathway. The broad band of ∼600 nm created by implantation is common in natural zircons and is attributed primarily to intrinsic Frenkel defects caused by natural radiation. Dy3+ luminescence is apparent from natural zircons even though Dy is one of the least abundant RE ions in zircon, and this behaviour is explained by the high luminescence cross-section of Dy3+ in zircon. Radiation-induced structural damage reduces the efficiency of energy transport between different RE3+ ions. IL provides key insights into both the interactions between defects and the nature of luminescence centres in zircon.