Comparison of thermoluminescence (TL) and cathodoluminescence (ESEM-CL) properties between hydrothermal and metamorphic quartzes

Accurate-parametric SAR-TL dating protocols for older sediments using quartz

Thermoluminescence (TL) dating is one of the most significant chronological tools used in Quaternary research. However, for changes in the characteristics of quartz, the larger deviation is still a problem in TL dating, especially with the single-aliquot regeneration-does (SAR) procedure. In the SAR-TL protocol, changes in the characteristics of quartz inevitably cause a shift in the TL peak position and a reduction in the sensitivity of the TL peak during repetitive thermal treatment. In this paper, we studied the optimal TL parameters to minimize the effect of the above problems for TL dating. Based on the optimization experiment combining OSL and TL measurements, the optimal preheat temperature was found to be 300 °C for both silt-sized grains and sand-sized grains, which eliminates the remainder of the 325 °C TL signals and inhibits the 375 °C TL peak position shift. Referring to the test does in SAR-OSL dating protocol, the optimal test doses, 200 Gy and 250 Gy for the silt-sized grains and sand-sized grains respectively, were determined to correct the reduction in TL sensitivity, and they were added to improve the SAR-TL protocol. The improved SAR-TL protocol with the optimal measurement parameters, which we called the accurate-parametric SAR-TL protocol, improves the accuracy of quartz TL dating and expands the range of accurate TL dating. For the experimental doses of 400 Gy and 700 Gy, the relative error of D_e obtained by the accurate-parametric SAR-TL protocol was less than ±5.5% for both silt-sized grains and sand-sized grains. In addition, we discussed the application conditions of the accurate-parametric SAR-TL protocol and the method that obtains the same level of thermal lag for different luminescence measurement equipment.

Unusual Luminescence of Quartz from La Sassa, Tuscany: Insights on the Crystal and Defect Nanostructure of Quartz

Quartz from La Sassa (Tuscany, Italy) presents a unique luminescence related to intrinsic and extrinsic defects in the crystal lattice due to the growth mechanisms in hydrothermal conditions. The bright fluorescence under the UV lamp was apparent to collectors since the early 1970s, and it entered the literature as a reference case of yellow-luminescent quartz. Early reports present the history of the discovery, the geological context, and preliminary luminescence measurements of the quartz nodules, suggesting various activators as potentially responsible of the peculiar luminescence effects: uranyl groups (UO22+), rare earths (Tb3+, Eu3+, Dy3+, Sm3+, Ce3+) and polycyclic aromatic compounds (PAH). Here, we report a full investigation of the La Sassa material, by a multi-analytical approach encompassing cathodoluminescence optical microscopy (OM-CL), laser-induced fluorescence (LIF), wavelength resolved thermally stimulated luminescence (WR-TSL), trace elements analysis by mass spectrometry (ICP-MS) and Raman spectroscopy (RS). The results provide a significant step forward in the interpretation of the luminescence mechanisms: the main luminescent centres are identified as alkali-compensated (mainly Li+ and Na+, K+ and H+) aluminum [AlO4/M+]0 centres substituting for Si, where the recombination of a self-trapped exciton (STE) or an electron at a nonbridging oxygen hole centre (NBOHC) are active.

Gamma radiation-induced thermoluminescence, trace element and paramagnetic defect of quartz from the Sambagawa metamorphic belt, Central Shikoku, Japan

This study analyzes the Thermoluminescence (TL) emissions for five emission bands, trace element concentrations and defects in quartz grains extracted from metamorphic rocks and quartz veins in the Sambagawa metamorphic belt, central Shikoku. An emission of 500nm with 195, 245, and 320-325°C glow peaks are observed through the lowest to highest grade samples. A 450nm emission band with intense 195 and 245°C glow peaks and a 320-325°C shoulder peak is found in the higher grade samples. A 570nm emission band with a 170°C glow peak is observed in the samples derived from the lower grade zones. These characteristics of TL emissions of quartz suggest that they can be an indicator for the identification of rock derived from different metamorphic grades. The higher metamorphic grade samples with 450nm emission bands in particular show higher intensities of the E₁' center. This relation indicates that the activation of the E₁' center in higher metamorphic conditions possibly contributed to the 450nm emission band. Also, the 500nm emission band is generally observed in the samples with the signal intensities of the Aluminum hole center, suggesting that the center is the source of this emission band. We also observed that the lower metamorphic grade samples contain lower signal intensities of the Aluminum hole center, despite higher aluminum concentrations. This inconsistency indicates that the formation of interstitial aluminum ions cause local lattice distortion regions, where self-trapped excitons can be formed and presumably provide the 570nm emissions.