Infrared radiofluorescence (IR-RF) dating: A review

Abstract

Luminescence dating methods on natural minerals such as quartz and feldspars are indispensable for establishing chronologies in Quaternary Science. Commonly applied sediment dating methods are optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL). In 1999, Trautmann et al. (1999a, b) proposed a new related technique called infrared radiofluorescence (IR-RF). IR-RF denotes the infrared luminescence signal of feldspar resulting from exposure to ionizing radiation and potentially offers a significant methodological advance compared to OSL and IRSL regarding luminescence signal stability, dating range and required measurement time. The method has rarely been applied due to a lack of commercially available measurement equipment but experienced a revival during the last years. The present article provides a state-of-the-art overview of the physical background of IR-RF, its challenges, applications and the potential as a dating method. The paper particularly addresses practical considerations for applying IR-RF dating, including signal bleachability and saturation behaviour, and summarizes proposed solutions.

Introduction

In the late 1990s, Trautmann et al. (1998) characterized radioluminescence signals, the emission stimulated by ionizing radiation, from various feldspar specimens to investigate their potential for dating applications. Focusing first on radiation-induced emissions in the UV and yellow wavelength ranges, where luminescence signal increases with radiation dose, they incidentally observed the opposite for potassium bearing (K-) feldspar specimen such as microcline and orthoclase: a dose-dependent signal decrease of the emission centred at 854 nm (1.45 eV; based on peak tail fitting only). Later, Trautmann et al. (1999a, b), Schilles (2002) and Erfurt and Krbetschek (2003a) determined that the emission peak was centred at 865 nm (1.43 eV). Trautmann et al. (1998) recognized that this emission energy is similar to the excitation energy used for infrared stimulated luminescence (IRSL; Hütt et al., 1988) and consequently interpreted this process as a luminescent transition (trapping) of electrons. Their pioneer work paved the way to what is known today as infrared radiofluorescence (IR-RF) dating, the method first proposed by Trautmann et al. (1999a, b) and termed by Erfurt and Krbetschek (2003a, b). The IR-RF signal is believed to be a direct measure of the fraction of empty electron traps, unlike conventional luminescence dating methods such as those based on thermoluminescence (TL; cf. Aitken, 1985a), optically stimulated luminescence (OSL, Huntley et al., 1985; Aitken, 1998) and infrared stimulated luminescence (IRSL, Hütt et al., 1988), for which the signals are associated with more complex recombination pathways. Since the IR-RF signal intensity decreases with increasing dose, it can be used for dosimetry and dating purposes. IR-RF may provide advantages over conventional single aliquot regenerative (SAR; Murray and Wintle, 2000) dose, IRSL dating methods (e.g. SAR IRSL; Wallinga et al., 2000) or its derivatives deploying higher reading temperatures (post-IR IRSL, Thomsen et al., 2008; MET-pIRIR, Li and Li, 2011a) in terms of required measurement time (relatively short protocol, cf. Erfurt and Krbetschek, 2003b), resolution of the dose-response curve (continuous recording of data points) and dating range (Sec. 7). Nevertheless, IR-RF as a dating method is still subject to ongoing research, with its general applicability being questioned (Buylaert et al., 2012). On the contrary, recent technological and methodological work, e.g. on the optical resetting of the IR-RF signal, and improved routines for dose estimation have yielded promising results (Frouin, 2014; Frouin et al., 2015, 2017; Huot et al., 2015; Kreutzer et al., 2017; Murari et al., 2018).

This contribution provides an overview of past and recent developments of IR-RF from K-feldspar as a dating method. We summarize current knowledge on existing models on the origin of IR-RF, outline commonly applied measurement procedures and equipment, and highlight shortfalls, challenges and open questions. Understanding what remains unknown may stimulate discussions and lead to improved experimental designs towards a full establishment of IR-RF as a valuable chronological tool.