Abstract
Introduction of modern technologies and methods and quality analysis for the gemstone industry are the main strategic initiatives of the Small and Medium Development Authority (SMEDA) of Pakistan. In this regard, four natural gemstones Quartz, Pyrope-Almandine Garnet, Black tourmaline, and Amethyst brought from Hunza valley Pakistan were analyzed by state-of-the-art spectroscopic techniques including EDX, UV-VIS, and FTIR spectroscopy. EDX revealed the traces of Fe, Mg, and Ca in Pyrope-Almandine garnet, Mg and Fe in Black tourmaline, Au and Ca in Amethyst. UV-VIS data revealed the values of Urbach energies 520, 210, 460, and 430 meV, and the values of direct bandgap energies 5.14, 6.12, 5.54, 5.74 eV, respectively. The higher structural disorder due to the presence of Fe and other impurities in stones except Quartz was attributed to the higher values of Urbach energies and decrease in band gaps: FTIR data Fe-O and Si-O stretching vibration in Pyrope-Almandine garnet, Si-O bending vibrations and O-H stretching vibration in Quartz, Si-O-Si bending and stretching vibrations and C=O stretching vibrations in Black tourmaline, Ca-O stretching vibrations and Si-OH weak-vibrations in Amethyst. Photoluminescence results also showed useful information in investigating the properties of gemstones.
Highlights
Mineral deposits play a vital role in the economic development of a country, and in this regard, Pakistan is well known for its abundance of natural resources and beauty
Chemical analysis of samples was carried out by SEM/EDX that revealed the concentration of each component element and impurity traces. e results of EDX are tabulated in Table 1 and it can be seen as follows: (i) Traces of Ca, Mg and Fe in Pyrope-Almandine Garnet (ii) Traces of Mg and Fe in Black tourmaline (iii) Traces of Au and Ca in Amethyst (iv) No trace elements or impurity contents were observed in Quartz
E absorbed energy of the electron must be equal to the energy gap between the two levels; as a result of the aforementioned electronic transition phenomena, an absorption spectrum is obtained, called ultraviolet visible (UV-VIS) absorption spectrum
Summary
Mineral deposits play a vital role in the economic development of a country, and in this regard, Pakistan is well known for its abundance of natural resources and beauty. In order to have fully explored the nature of scientific phenomena responsible for giving color to gemstones, various spectroscopic methodologies including UV-VIS, FTIR, XRD, XRF, EDX spectroscopy, are used [11,12,13]. In this regard, Kassem et al [14] have characterized the Quartz sample (milky color) belonging to a wadi of the eastern desert of Egypt, i.e., Araba, while using a number of techniques including SEM, XRD, UV-VIS, FTIR, XRF, and inductively coupled plasma-optical emission spectra (ICPOES) and electron spin resonance (ESR) technique to assess the radiation treatment effect on the color of Quartz. A Photoluminescence study was carried out to further investigate the trace elements and meaningful information about the identification of gemstones
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