Abstract
We present results of calibration-free laser-induced breakdown spectroscopy (CF-LIBS) and energy-dispersive X-ray (EDX) analysis of natural colorless topaz crystal of local Pakistani origin. Topaz plasma was produced in the ambient air using a nanosecond laser pulse of width 5 ns and wavelength 532 nm. For the purpose of detection of maximum possible constituent elements within the Topaz sample, the laser fluences were varied, ranging 19.6–37.6 J·cm−2 and optical emission from the plasma was recorded within the spectral range of 250–870 nm. The spectrum obtained has shown the presence of seven elements viz. Al, Si, F, O, H, Na and N. Results shows that the fluorine was detected at laser fluence higher than 35 J·cm−2 and plasma temperature of >1 eV. Al and Si were found as the major compositional elements in topaz crystals. The ratios of concentrations of Al and Si were found as 1.55 and 1.59 estimated by CF-LIBS and EDX, respectively. Furthermore, no impurity was found in the investigated colorless topaz samples.
Highlights
Topaz is a popular silicate mineral (Al2 SiO4 (F,OH)2 ) and is naturally found in a wide range of colors and colorless forms
This work aims to investigate the existence of impurities, if any, in the colorless topaz crystal that may help in the future to establish the role of impurities in the TL character of topaz
The absence of N and Na in the energy-dispersive X-ray (EDX) spectrum has confirmed that the presence of N lines in the Laser-induced breakdown spectroscopy (LIBS) spectrum was due to air, and the Na line could possibly be due to surface contamination
Summary
Topaz is a popular silicate mineral (Al2 SiO4 (F,OH)2 ) and is naturally found in a wide range of colors and colorless forms. Natural colorless topaz is largely utilized in jewelry, and the irradiation process is commonly employed to artificially induce colors in it [2]. Artificial methods are employed to induce colors in topaz, which include (i) irradiation with neutron, electrons and gamma rays followed by low-temperature annealing, (ii) colored metal oxide coating and (iii) heat treatment in different chemical atmospheres [3,4]. The thermoluminescent property makes topaz potentially an important candidate for its use as a thermoluminescent dosimeter (TLD) [5]. This property is exhibited by the insulators or semiconductors in which ionizing radiations are absorbed and remain trapped within the localized defects for a sufficiently long time. High-energy TLD based on topaz crystals has been developed previously [7,8,9,10,11]
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