Blue Thermoluminescence Research Articles

TL and ESR of quartz from the astrobleme of Aorounga (Sahara of Chad)

The present work was intended to evaluate the time that elapsed since the meteorite fall that produced the giant astrobleme of Aorounga (Sahara of Chad). For this purpose the TL and ESR dating techniques using the additive dose method were applied to quartz grains extracted from an impactite and from a sandstone shocked and baked during the impact. The ESR Al centre was measured and resulted in an age of about 800 ka. The red TL and the blue TL showed unusual TL features: the additive dose response curves were marked by an initial saturated part followed by a second rise at around +0.5 kGy; the peaks showed erratic temperature shifts with dose; fading was observed for high temperature peaks. By comparison with previous work using samples baked by lava flows more than 1 Ma ago and presenting some of those features, it was assumed that the minimum age of the astrobleme was of the same order of magnitude. This is in agreement with other observations. A preliminary explanation for those ageing features is proposed. It is suspected that radiation induced traps contribute to the TL of the studied quartz grains. Most probably the ‘malign-behaviour’ of the quartz grains is also connected with shock effects.

Changes in luminescence colour images from quartz slices with thermal annealing treatments

Changes in the thermoluminescence (TL) glow curves of quartz grains after thermal annealing have been investigated. For the grain samples from Madagascar crystal rocks, intrinsic blue-TL (BTL) sensitivity in the higher glow curve temperature regions is enhanced linearly with the annealing temperature beyond 700°C, while at the same time red-TL (RTL) was newly induced and increased steeply beyond 800°C. Both peaks from BTL and RTL glow curves tend to move towards higher temperatures with annealing temperatures. These results suggest correlations to β-quartz/tridymite phase inversion temperature at 870°C. For Z-cut quartz slices from the Madagascar rock crystal, two-dimensional luminescence images of TL and after glow (AG) have been semi-quantitatively analyzed using a colour image analyzer with particular concern for luminescence property changes accompanied by thermal annealing treatment at 1000°C. Every luminescence image showed interesting stripe or zonal patterns resulting from the crystal formation conditions. A prominent colour change from the originally weak BTL into RTL and RAG (red-AG) has unexpectedly occurred on the quartz slices, while the original BTL has transferred into more intense BTL after the annealing treatment. These changes in the TL colour image (TLCI) patterns were also correlated with the aluminium concentrations using images from an electron probe microanalyzer (EPMA). From these results, it was verified that the BTL on the original slice is inversely proportional to aluminium and sodium contents whereas both TLCI and AGCI patterns on the annealed slice offered positive correlation with aluminium concentrations along the crystal growth direction.

Test of thermoluminescence dating of loess from New Zealand and Alaska

The accuracy of thermoluminescence (TL) ages for loess (and sediments in general) greater than ∼100 ka is disputed. We tested the accuracy of three common TL sediment-dating techniques applied to 4–11 μm sized polymineral grains from known-age loess, using 16 samples from North Island and South Island, New Zealand, and 2 samples from central Alaska. Estimated sample ages range from 20–26 to ∼800 ka. We varied the optical bleaching spectrum, the selected window of the emission spectra (ultraviolet or uv, blue and green wavelengths), the pre-readout heat treatment, and the TL equivalent-dose measurement technique. Most of the 20–26 ka samples gave TL age underestimates of 3–6 ka that may be attributed to post-burial open system behavior. For the older samples, the partial-bleach TL method gave expected ages up to ∼300 ka, and the total-bleach TL method produced expected ages above ∼100 ka. The partial-bleach regeneration TL method gave significant age underestimates for samples older than ∼100 ka, with a maximum TL age of ∼250 ka for samples having expected ages up to ∼350 ka. Two 300–360 ka,samples which gave total-bleach age underestimates with use of uv TL and green TL, gave expected ages with use of blue TL. These results demonstrate that reliable TL ages for loess from New Zealand and Alaska up to ∼800 ka can be obtained if uv (and green?) emissions and the various regeneration methods are avoided. This age range is well above the former putative 80–100 ka upper age limit for TL dating of loess from other regions, which was thought to be a global limit. Application of our successful procedures to such loess is encouraged.

Dependence of red thermoluminescence on Eu-anomaly in natural quartzes

The causes of red colour thermoluminescence (RTL) from natural quartzes have been sought in some impurity elements. Some kinds of impurities in 31 varieties of natural quartz extracts, determined by a neutron activation analysis, have been examined with respect to a meaningful correlation of the RTL to the total detectable TL strength. Generally, the higher impurity contents were found in quartzes of volcanic origin, which always emit purely RTL colour, whereas the lower impurities were usually detected in the hydrothermal quartzes, which emit purely blue TL (BTL) in all absorbed doses. Among the impurities, the middle part of the REE (rare earth elements), involving Eu and Sm, particularly offered considerable correlation with RTL emission with the exception of the pegmatite quartzes. It was found from the chondrite-normalized REE patterns that the positive Eu anomaly or flattened Eu distribution brough relatively higher RTL proportions, while the negative Eu anomaly always showed extremely weak RTL intensity. Thus, it was concluded that the quantity of Eu 3+ state, formed from the oxidizable surrounding or high oxygen fugacity relative to Cl chondrite formation, should be remarkably related to the RTL intensity in natural quartzes.

Editorial

This paper presents TL age estimates of Pleistocene raised marine terraces from southern Calabria (southern Italy). It focuses on the dating of last interglacial shallow-marine sand deposits, including several Tyrrhenian key reference deposits whose stratigraphic assignment is based on biostratigraphic evidence (presence of a Strombus bubonius fauna) and geochronometric data (amino-acid data calibrated with UTh dates on coral). The TL age estimates are obtained on alkali feldspar coarse grains using their blue TL emission. They are in good agreement with the IR-OSL age estimates obtained on the same feldspar samples. Our feldspar TL method is tested on two Tyrrhenian key reference sites, Ravagnese and Bovetto, in the Reggio di Calabria area. Their measured TL age estimates (97 ± 11 ka and 100 ± 10 ka) are lower than their estimated geological age (i.e. Oxygen Isotope Substage 5e). The correction for long-term fading suggested by Mejdahl (1988), is tested on these two samples using a lifetime of 446 ka as estimated from both Calabrian and Miocene sand collected within the same area. This correction would yield preliminary TL ages (116 ± 13 ka and 116 ± 12 ka) that are in better agreement with the expected geological age. The application of our TL method to paleoshorelines lying below the Tyrrhenian reference shoreline of Ravagnese-Bovetto, yields stratigraphically consistent TL age estimates. The TL method is also applied to two supposedly pre-last interglacial paleoshorelines which are geomorphologically older than the Tyrrhenian reference shorelines. They remain however chronologically undifferentiated, both by the TL and the amino-acid methods. Finally, the preliminary feldspar TL results obtained on the Miocene and the Calabrian sand deposits (> 1 Ma), suggest that our feldspar TL method is limited, in the SW Calabrian area, to about 200 ka.

Emission properties of thermoluminescence from natural quartz-blue and red TL response to absorbed dose

The TL spectrometry of natural quartz exposed to 8.8 kGy proved that the red TL, mainly from volcanically originated quartz, has a broad emission band with a peak around 620 nm, while the blue TL from plutonically originated quartz also has a broad emission band giving a peak around 470 nm. These typical red or blue intrinsic colours were also confirmed on the thermoluminescence colour images (abbreviated to TLCI by the authors) to the lowest observable dose region in quartz grains of different origins. Exceptionally, a pegmatite quartz changed its TLCI colour from red to blue when the absorbed dose was increased. By using colour filter assemblies, all these quartz samples were ascertained to emit more or less blue and red TLs, which have distinctly different TL responses to the absorbed dose; the blue invariably showed a supralinearity relation between 1 and 10 kGy dose. For the purpose of dating, the use of red TL, passed through red-filter assemblies, is preferable if the specimens contain red TL quartz grains as attributed from their origin or from the TLCI observation. The red TL component was verified to be correlated with the impurity Eu content in quartz minerals.

Thermoluminescence color images from quartzs of beach sands.

Some quartzose beach sands, collected from the northern part of Niigata district, were examined by thermoluminescence color image (TLCI) analyses. Analyses were performed after purification of the quartz fraction by magnetic separation. Purified samples underwent chemical etching followed by gamma-ray irradiation. The proportion of red TL-emitting grains to blue ones seems to be related to the origin of the respective beach sands. Red TL grains are tentatively attributable to a volcanic dominated source, whereas the blue ones are mainly weathering products of plutonic rocks such as granite. TL-spectrophotometric analyses have been attempted to obtain more quantitative information on the TL-emission of the two different colors for these beach sands. The intensity ratios of red to blue TL were evaluated from analyses of respective glow-curves, corresponding to different wavelength regions. The ratios were concordant with the TLCI parterns. The applications of TLCI and TL-spectrophotometry to geological and archaeological samples are also suggested.

Excitation and pre-excitation of glow curves in natural semiconducting diamonds

The uv excited glow peaks at ∼150 K and ∼250 K were investigated. The mainly blue thermoluminescence (TL) peak appearing at 150 K in semiconducting diamonds was found to have also red and infrared components all appearing at the same temperature. Another red peak appearing at 260 K included an infrared component at a somewhat higher temperature. The intensity of this red peak behaved superlinearly with the dose of the 360 nm excitation. It was possible to pre-excite the 250 K blue peak using infrared light when the exciting light was 225 nm; however, this caused a partial bleaching of the 150 K blue peak. The investigation also included pre-excitation at various temperatures, intensity vs dose measurements of pre-excitation, and intensity vs dose measurements at various temperatures. It was found that the red TL peak produced by 500 nm could be excited more efficiently at 180 K than at liquid nitrogen temperature. The energy level model is reviewed in accordance with the new results.

Luminescence and Thermoluminescence Induced by Bombardment with Protons of 159 Million Electron Volts

We have observed a red luminescence, qualitatively similar to that of enstatite achondrites, in unsorted fines, their separated mineral phases, and rock chips. The energy efficiency of the plagioclase fraction is approximately 1 percent. At -196 degrees C the effect is enhanced by a factor between 1 and 2. All fractions except ilmenite exhibit blue thermoluminescence with a glow peak near -135 degrees C and an energy efficiency approximately 4 x 10(-6). Unlike the thermoluminescence of terrestrial and meteoritic material, it is nonrepeatable even after annealing at 200 degrees C. Similar thermoluminescence is seen in rock chips, but in unsorted fines it is masked by the opaque fractions.

A Study of the Effect of Deformation on the ESR, Luminescence, and Absorption of MgO Single Crystals

AbstractThe effect of plastic deformation on the optical absorption, ESR, and thermoluminescent properties of MgO has been investigated. Plastic deformation produces an optical absorption band at about 217 nm whose intensity is proportional to the percent of deformation. No new ESR signals were detected in the deformed crystals. When deformed crystals are irradiated with 60CO γ‐rays, however, the ESR signal from the F‐center is observed and several new optical absorption bands also appear. Impurity ion ESR signals in γ‐irradiated samples have been compared with thermoluminescence spectra. The results indicate that the blue thermoluminescence at 3.3 eV and 85°C is due to Fe2+ converting to Fe3+ and the red thermoluminescence at 1.7 eV and 85°C is due to the formation of Cr3+.

Thermoluminescent Formation of Cr2+ in Magnesium Oxide

In undoped crystals of MgO, x irradiation converts a large fraction of Cr3+ in octahedral symmetry to Cr2+. Heating such crystals until a blue thermoluminescence has been observed causes further reduction. Usually 95% or more of the Cr3+ is converted by the combined treatments. However, in Cr-doped MgO one is able to reduce only a small fraction of the octahedral chromium to Cr2+. The Cr2+ is reconverted to Cr3+ by heating. ESR measurements show that in the same temperature interval nearly all of the Fe1+ formed on x irradiation has disappeared. The source of electrons acquired by Cr3+ thus appears to be the Fe1+ ions. The thermoluminescence is ascribed to the Cr3+-electron interaction, as suggested by Hansler and Segelken.