Quantification of radiation damage in zircon and other accessory minerals using rare-earth element µ-photoluminescence spectroscopy

Many accessory minerals, i.e., zircon, incorporate variable amounts of actinides, whose radioactive decay creates structural defects in their crystal structures. The increased susceptibility of radiation-damaged zircon to chemical alteration or aqueous leaching is of enormous importance as these processes may bias results of chemical and isotopic age determinations. Here, we present a new concept based on the luminescence emission of REE3+ that provides an estimate of the amorphous fraction from laser-induced PL measurements using state-of-the-art confocal spectrometers with spatial resolution in the µm-range. A careful investigation of PL spectra from self-irradiated zircon samples from Sri Lanka and Mt. Malosa (Malawi) reveal that the Dy3+-luminescence emission in zircon is basically a superposition of emissions from Dy ions in various, structurally different sites. The relative integrated area of a fitted model spectra from an amorphous reference sample in relation to the full integrated area of the obtained emission gives a good estimate of the amorphous fraction present in the probed sample volume. This opens up the possibility to investigate the accumulation of radiation damage in single crystals of zircon in great detail and give rise to direct comparison with damage accumulation in heavy ion irradiation experiments.

Acknowledgments

C.L. gratefully acknowledges the use of instrumentation within an honorary associate agreement with the ARC CFSS at Macquarie University. Financial support of C.L. by Austrian Science Fund (FWF) project J3662-N19 is kindly acknowledged.

References

Lenz et al. (2020) The in-situ quantification of structural radiation damage in zircon using laser-induced confocal photoluminescence spectroscopy. Minerals. 2020; 10(1):83