Publications
First-principles study of intrinsic and Fe3+-related luminescence mechanisms in feldspar
Physical Review B, Vol 113, Issue 13, 134107
Abstract
Feldspar is the most abundant mineral group in the Earth’s continental crust and almost invariably contains Fe3+impurities in natural samples. These impurities dominate the characteristic deep-red luminescence of feldspar, while the host lattice itself also exhibits intrinsic luminescence associated with self-trapped excitons (STEs). Despite the central role of feldspar in luminescence dosimetry and geochronology, the microscopic mechanisms underlying both intrinsic and Fe3+–related luminescence remain incompletely understood. Here, we present a comprehensive first-principles investigation of disorder, intrinsic defects, and impurity-related charge trapping in K-feldspar. Using a cluster expansion trained on density functional theory calculations, we determine the ground-state Al–Si ordering and quantify the formation of Al–O–Al linkages at high temperatures. Based on this structure, we identify energetically favorable intrinsic defects and demonstrate that hole polarons localize preferentially on oxygen atoms bridging AlO4 and SiO4 tetrahedra, while Si–O–Si bridges do not stabilize holes. Rare Al–O–Al bridges formed at melting temperatures are shown to be particularly efficient hole traps. We compute STE configurations and vertical emission energies using a hybrid functional approach, obtaining emission energies in excellent agreement with experimental measurements. Furthermore, we show that Fe3+impurities strongly modify local charge trapping: Fe3+ preferentially captures electrons to form Fe2+, while also stabilizing hole polarons on neighboring oxygen sites, forming metal-oxyl complexes. Based on these results, we propose a microscopic mechanism for Fe3+–related luminescence in which electron capture by Fe3+ is followed by spin-selective recombination that populates the Fe3+ excited state 4𝑇1. Our results provide a unified atomistic picture of intrinsic and impurity-driven luminescence in feldspar and establish a quantitative foundation for modelling charge trapping and recombination processes relevant to luminescence dating.
Further investigations into the accuracy of infrared radiofluorescence (IR-RF) and its inter-comparison with infrared photoluminescence (IRPL) dating
Geochronology, Vol 7, Issue 3, 289–308
Abstract
Infrared radiofluorescence (IR-RF) is an alternative dating technique for potassium feldspar grains, offering a higher signal stability and based on a simpler underlying mechanism than more common luminescence dating approaches. However, its accuracy when tested on known-age samples has so far shown inconsistent results. In this study, we present a refined accuracy assessment using samples that have previously produced unreliable IR-RF ages. Our approach incorporates two major methodological advancements developed over the past decade: elevated temperature measurements using the IR-RF70 protocol and sensitivity change correction by vertical sliding. To expand the dose range comparison, we included two additional samples: one expected to be in saturation and another of modern age. Additionally, we evaluated the effect of using a narrower bandpass filter to exclude any signal contributions from potentially contaminating shorter wavelength emissions. Our results following the IR-RF70 protocol with sensitivity corrections show an improvement over the original room-temperature results. For four out of the seven tested known-age samples spanning ca. 100–300 Gy (20–130 ka), we obtained results in keeping with the expected doses. Two additional modern samples, however, yielded slight dose underestimations. Introduction of a multiple-aliquot regenerative dose (MAR) protocol improved the accuracy of two out of three samples with large sensitivity changes. Finally, we also compared the new IR-RF equivalent doses (De) to those obtained with the newer dating method, infrared photoluminescence (IRPL), for the same samples, including previously published values and new measurements. Like IR-RF, IRPL is also expected to be trap-specific. We observe that, with the new improvements, the success rate of IR-RF is comparable to that of IRPL.
Multi-method luminescence dating of late Cenozoic northern Upper Rhine Graben fluvial sediments
Quaternary Geochronology, Vol 90, 101689
Abstract
The Upper Rhine Graben (URG) contains one of the most continuous sequences of unconsolidated Plio-Pleistocene sediments in central Europe. In order to understand the driving factors behind the sedimentation and erosion processes of the river Rhine fluvial system as well as the geological evolution of the rift system during the Quaternary and beyond, numerical dating of the sediments is indispensable. In 2020 and 2021, the Hessian State Agency for Nature Conservation, Environment and Geology (HLNUG) carried out a new continental drilling project near Riedstadt-Erfelden in Hesse, Germany, to obtain further information on the development of the northern part of the URG. Here, we present geochronological information derived from a multi-method luminescence dating approach of samples from the upper section of the core. Preliminary results from optically stimulated luminescence (OSL) of quartz and infrared-radiofluorescence (IR-RF) of K-feldspar are complemented by new measurements using infrared-stimulated luminescence (IRSL), post-infrared-IRSL (pIRIR) and infrared photoluminescence (IRPL). The latter is a relatively novel approach with the usage of a potentially non-fading and non-destructive signal from K-feldspar. For the first time, we apply a multiple elevated temperature (MET)-pIRIR-IRPL single aliquot regenerated dose (SAR) protocol on fluvial samples and present fading rates for the IRSL and IRPL signals derived from the protocol. We find that IRPL ages agree generally well with Middle Pleistocene luminescence ages of previous studies and biostratigraphic data while showing negligible fading and less sensitivity to a varying test dose. OSL ages up to ∼65 ka match phases of aggradationreported in earlier studies. Although IRPL and IR-RF ages are thought to arise from the same dosimetric trap, discrepancies in ages observed from both signals could be due to the required difference in sensitivity correction methods, though we note that as the signals approach saturation, the ages from both methods converge (>200 ka). The pIRIR225 and pIRIR290 ages generally overestimate OSL and IRPL ages. Fading correction of IRSL50 ages was not successful as they still underestimate quartz ages. Our results indicate an Elsterian-Holsteinian (MIS 12-11) to late Weichselian (MIS 2) age of the Mannheim formation and a Cromerian (MIS 13–21) deposition of the Ludwigshafen formation.
Unravelling Earth’s story: how crystals reveal the secrets of landscape evolution
Project Repository Journal, Vol 20, 78-81
Abstract
Our planet’s surface is constantly evolving. To understand these changes, scientists seek ways to measure the rates of Earth’s surface processes like erosion and sediment transport on different spatial and temporal scales. The LUMIN project focuses on illuminating how charge moves within feldspar, a common mineral on Earth’s surface. This knowledge will help create new tools to measure such rates so that the history of Earth’s landscapes may be deciphered, thereby helping us predict their future.
Excited state lifetime of electron trapping centres in alkali feldspars
Radiation Measurements, Vol 172, 107081