Intensity and optical resetting of Infrared Photoluminescence (IRPL) and Infrared Stimulated Luminescence (IRSL) signals in feldspars

J. A. Winzar*, G. A.T. Duller, H. M. Roberts, M. Gunn, A. M.T. Bell

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Feldspars vary in major and minor element chemistry and mineral structure. For luminescence dating, separating feldspar types in sediments using density separation techniques is challenging, and when using rock slices and fine-grain samples it is not possible. For 19 chemically and structurally diverse feldspars, the intensity and optical resetting behaviour of different Infrared Photoluminescence (IRPL) and Infrared Stimulated Luminescence (IRSL) signals is investigated. After a 140 Gy beta dose IRPL was observed from each feldspar, and IRSL signals were seen in all except the most Ca-rich sample. The intensity of IRPL was more strongly related to feldspar major element chemistry than appeared to be the case for IRSL signals, where some K-rich and K-poor feldspars have similar IRSL intensities. Correlations between Fe and Mn concentrations with IRSL and IRPL signal intensity were found. The influence of mineral structure, particularly the state of Al,Si order also appeared to affect IRSL intensity. Bleaching experiments showed that IRPL signals are more difficult to bleach in comparison to IRSL. In some K-rich and K-poor feldspars resetting of IRPL was limited, and an IRPL component with lower optical sensitivity was observed in each IRPL signal. The IRPL signal remaining after subtracting this component, and also delta IRPL (ΔIRPL) signals, bleach in a similar manner to IRSL signals measured at elevated temperatures (225 and 290 °C). IRSL bleached reproducibly across the samples, with most IRSL50 and pIR50 IRSL225 signals decreasing to below 5% of the initial signal intensity after ∼1000 s and ∼10,000 s, respectively. A relationship was seen between IRPL bleaching and Ca-content, but no clear trends were observed between bleaching and Na and K contents, or minor element chemistry and mineral structure. This study shows that the suitability of IRPL signals for dating in terms of their potential to be effectively bleached in nature can be enhanced by subtracting the less optically sensitive component from the signals used.

Original languageEnglish
Article number121018
JournalJournal of Luminescence
Volume278
Early online date08 Dec 2024
DOIs
Publication statusE-pub ahead of print - 08 Dec 2024

Keywords

  • Feldspar
  • Intensity
  • IRPL
  • IRSL
  • Luminescence
  • Optical resetting
  • ΔIRPL

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