Understanding defect dynamics under irradiation in quartz: case study of a 1.4 Ga granite sample investigated by multispectroscopic methods

Point defects in quartz and their response to irradiation hold geological significance but are not well understood. They can be analyzed using methods like optically stimulated luminescence (OSL), electron spin resonance (ESR), and scanning electron microscopy with cathodoluminescence (SEM-CL). This study examines point defects in a granite sample (~1.4 Ga crystallization age, ~20–23 Ma cooling age) from the Catalina Metamorphic Core Complex, southwestern USA, part of a Proterozoic anorogenic granitic province.

Defects analyzed include intrinsic ones (e.g., O-vacancies, Si vacancies, and nonbridging oxygen centers) and impurity-related defects (e.g., [AlO₄]⁰ and [TiO₄/M⁺]⁰). ESR identified E', peroxy, Al-, and Ti-related defects, with Al and Ti defects showing higher intensities. The Al-hole center increased exponentially with dose up to 40,000 Gy, while the Ti-electron center showed a nonmonotonic trend, peaking at 10,000 Gy and then decreasing, consistent with Benzid and Timar-Gabor (2020) and Woda and Wagner (2007). Oxygen-related defects were weak and generally dose-independent. OSL decay was dominated by a fast component, and SEM-CL showed strong blue emissions (~450 nm) and weak red emissions (~650 nm, related to NBOHC), confirming Ti-related defect dominance.

One can explain the features of luminescence and ESR signal in quartz, especially their dependence on the irradiation dose, by modelling the charge transport processes during its exposure to high-energy radiation or light. So far, models based on the band theory used in simulations of the luminescence in quartz (e. g. Bailey, 2001) have not considered that, next to electrons, ions also carry the charge in this material. Ionic conduction in quartz is primarily related to interstitial light metal cations M⁺. These ions provide a charge balance in the lattice disturbed by substituting a silicon atom with an aluminium atom at the crystallization stage. Radiation generates free electrons and holes, causing local potential changes that induce cation transport in the crystal. Ionic conduction in quartz requires, therefore, considering, in the modelling, both electronic transitions and changes in the state of ions from bound to free and vice versa.

A kinetic model was developed with differential equations describing M⁺-binding centers (Al and Ti), electronic states, and free electron and ion concentrations. The results, which provide insights into point defect dynamics in granitic quartz, will be discussed at the conference, offering new perspectives.

References:

Benzid, K., Timar-Gabor, A., 2020. Phenomenological model of aluminium-hole ([AlO₄/h⁺]⁰) defect formation in sedimentary quartz upon room temperature irradiation: electron spin resonance (ESR) study, Radiation Measurements, 130,106187.

Woda, C., Wagner, G. A., 2007. Non-monotonic dose dependence of the Ge-and Ti-centres in quartz. Radiation measurements, 42(9), 1441-1452.

Bailey, R. M., 2001. Towards a General Kinetic Model for Optically and Thermally Stimulated Luminescence of Quartz. Radiation Measurements 33: 17-45.

Acknowledgement: This research is funded by European Research Council ERC grant PROGRESS-CoG “Reading provenance from ubiquitous quartz: understanding the changes occurring in its lattice defects in its journey in time and space by physical methods”