Laser-induced time-resolved luminescence of natural sillimanite Al2SiO5 and synthetic Al2SiO5 activated by chromium

Luminescence of natural sillimanite Al₂SiO₅ was studied by a laser-induced time-resolved technique combined with absorption spectroscopy. It was found that two red broad emission bands are connected to Fe³⁺ and Cr³⁺ luminescence centers. Chromium participation in luminescence was proved by the study of synthetic sillimanite activated by Cr. Several narrow emission lines have been found which were preliminary ascribed to Mn⁴⁺ and V²⁺ luminescence centers.     

Rehydroxyiation of clay minerals and hydration in ancient pottery from the ‘Land of Geshur’

Rehydroxylation of clay minerals and hydration in Bronze and Iron Age pottery from the Land of Geshur (east of the Sea of Galilee), were investigated by IR thermospectrometry. A weak OH band, which resembles those in smectite or illite, exists in most samples, but it is masked by the water bands at lower temperature. Two types of transformation of clay minerals occur during firing of raw materials, reversible and nonreversible dehydroxylation, taking place at a relatively low and high firing temperatures, respectively.Clay minerals rehydroxylate and reconstruct after relatively higher firing temperatures in noncalcareous raw materials than in calcareous ones. These processes take place after higher temperatures in cooking pots made from the former type of raw material as compared with storage and table-ware vessels made from the latter.The absorbed water in the pottery is mainly connected with the dominant X-ray amorphous matter formed by the firing process.

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Zusammenfassung Mittels IR-Thermospektrometrie wurde die Rehydroxylierung von Tonerdemineralien und die Hydratierung in Geschirr aus dem Bronze- und Eisenzeitalter, aus dem Land der Geshur (Osten des Galiläischen Meeres) untersucht. Eine schwache OH-Bande, die denen in Smektit oder Illit ähnelt, existiert in den meisten Proben, es wird aber bei niedrigeren Temperaturen durch Wasserbanden verdeckt. Während des Brennens von Rohmaterial finden zweierlei Umwandlungen der Tonerdemineralien statt, bei relativ niedrigen Temperaturen reversible und bei relativ hohen Temperaturen nichtreversible Dehydroxylierung.Tonerdemineralien werden in kalkfreiem Rohmaterial nach relativ höheren Brenntemperaturen rehydroxyliert und wiederaufgebaut als in kalkhaltigen. Diese Prozesse verlaufen nach höheren Temperaturen in Kochtöpfen aus ersterem Rohmaterial im Vergleich zu Vorrats- und Eßgeschirr aus letzterem Material.Das in der Töpferware adsorbierte Wasser ist in erster Linie an dem beim Brennprozeß gebildeten, röntgenmäßig amorphen Material gebunden.

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Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60^th birthday

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This research was supported by the Basic Research Foundation administered by the Israel Academy of Sciences and Humanities. This support is gratefully acknowledged.

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The pottery was excavated by the Land of Geshur Archaeological Project, the Institute of Archaeology, Tel-Aviv University, M. Kochavi, director.

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The work was carried out while the first author was a visiting scientist at the Geological Survey in Jerusalem. The author expresses his appreciation to Dr. Yaacov Nathan and Mr. Yoetz Deutsch of the Geological Survey, for the hospitality and helpful discussions.

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The authors express their appreciation to L. Vinitzky from the Institute of Archaeology, Tel-Aviv University for supplying the Intermediate Bronze pottery and useful discussions.     

Application of thermal treatment for the interpretation of photoluminescent centres in minerals

The influence of thermal treatments on photoluminescence spectra of several minerals has been investigated. By applying step-wise heating, new luminescence centres were detected which had been not previously recognized in the corresponding minerals. Luminsecence centres appearing as result of valence changing during oxidizing heating include:

1. (UO₂)²⁺ as a result of nonluminescent U⁶⁺ transformation in zircon, barite, francolite and chert;
2. Eu²⁺ as a result of nonluminescent Eu⁺ transformation in barite.

Luminescence centres which were most stable under thermal treatment were Fe³⁺ in zircon and Mn²⁺ in barite. Luminescence centres with similar spectral-kinetic properties but with different thermal stability which allowed them to be separated and properly identified were different metaloxygen complexes (MeO_n)^m? in zircon.     

Europium probe for estimation of site symmetry in glass films,glasses and crystals

The paper is devoted to the memory of Brian Wybourne the pioneer in theory of symmetry and spectra of trivalent rare earths. We evaluate here the influence of site symmetry of the surrounding molecules in glass matrices on europium ion used as a probe. A method by which systematic classification can be performed on descending site symmetry in a large number of solid hosts is based on the ratios of intensities of electric to magnetic dipole transition. Experimental work involves preparation of a number of glass matrices prepared by a sol–gel method, and incorporating trivalent europium. The fluorescence arising from the quintet D state is used to evaluate the site symmetry of the probe europium ion in the prepared matrices, crystals, conventionally prepared glasses, solutions, and complexes incorporated in sol–gel matrices. From the large amount of tabulated data one can see that for totally symmetric sites the factor I(D₀–F₂)/I(D₀–F₁) is lower than one, and increases to 10 for systems with very low symmetry sites. The absolute intensities of the transitions depend also on the amount of covalency of Eu with the surrounding ligands.     

Doubly ionized ion emission in laser-induced breakdown spectroscopy in air

The emission from doubly ionized species in laser-induced plasmas has not been properly investigated before since most analytical measurements were made at relatively long delays. This work proves that doubly ionized species, such as boron (B) III and iron (Fe) III, can exist during the first 150–200 ns of the plasma lifetime in plasmas produced in air by typical lasers with irradiances of 10⁹–10¹¹ W/cm². The emission from these ions was detected using both the double- and single-pulse excitations. The sum of the second ionization potential and the energy of corresponding excited states is approximately 30 eV. The presence of doubly charged ions in the early plasma was additionally confirmed by computer simulations using a collision-dominated plasma model. The emission from doubly ionized species may be used for analytical purpose. For example, in the spectrum from a B–Fe ore, the B III analytical line at 206.6 nm is free from Fe spectral interference thus enabling the online laser-induced breakdown spectroscopy sorting of ores into three products with high, medium, and low B₂O₃ contents.     

Laser induced breakdown spectroscopy for bulk minerals online analyses

The purpose of the work was to prove the ability of LIBS to provide on-line analyses for raw ores in field conditions. An industrial LIBS machine was developed and successfully tested for on-belt evaluation of phosphate measuring Mg, Fe, Al, Bone Phosphate Lime (BPL), Insoluble phase and Metal Impurity Ratio (MER) and of coal measuring its ash content. The comparison of LIBS on-line data with control analyses revealed good correlation, which corresponds to the required detection limits and accuracy. With frequent elemental data from a LIBS system, process engineers have the tools to best optimize the process. These processes could be minerals blending and separation to meet customer specifications, monitoring and controlling the efficiency of a minerals process, or a minerals accounting function.     

Application of thermal treatment of zircon for the interpretation of luminescence centers

The photoluminescence (PL) of zircon is characterized by a broad structureless spectral band down to 4.6 K, which does not enable correct interpretation of the nature of the luminescence centres (LC). By applying step-like thermal treatment, a radiation treatment and timeresolved spectroscopy, seven pure bands were separated and their individual spectral-kinetic properties were determined.The yellow PL is connected with three LC: