Electron spin resonance characterisation of sedimentary quartz of different grain sizes

Different optically stimulated luminescence (OSL) single aliquot regenerative (SAR) saturation characteristics have been previously reported for quartz of diverse grain sizes. This preliminary electron spin resonance (ESR) study documents on paramagnetic signals in natural sedimentary quartz extracts of different grain sizes (4–11 μm, 63–90 μm, 90–125 μm, 125–180 μm, 180–250 μm) extracted from loess and sand samples that are amendable to OSL and ESR dating. Spectra recorded at room temperature and low power (< 1mW) are dominated by the E1’ centre, whose intensity in natural samples was found to decreases with increasing grain size. The signature of titanium centre could not be detected in fine (4–11 μm) quartz. For coarse fractions (> 63 μm) titanium-lithium [TiO4/Li+]0 signals increase with increasing grain size. Aluminium-hole ([AlO4]0) signals are observed in all natural and laboratory irradiated investigated samples when spectra are recorded at low temperature (90 K). The intensity of these signals appears to decrease with increasing grain size, however, room temperature measurements show that these signals are highly interfered by a variety of signals tentatively attributed to peroxy (g≈2.007 and g≈2.004) with significantly higher intensities in fine grains (4–11 μm). A decrease of their intensity is reported when grain size increases and partial evidence that these defects are preferentially located in damaged regions of the grains is presented. A dose dependent paramagnetic signal at g≈2.011 was detected only in 4–11 μm quartz. The stronger signature of the [TiO4/Li+]0 signals in larger grains coupledwith the weaker signals of peroxy signals interfering with [AlO4]0 signal measurement is suggesting that coarser fractions should be preferred for conventional ESR dating using aluminium-hole and titanium signals. The understanding of the implication of these defects in OSL dating alongside with their concentration dependency on grain size requires further investigations