Browsing by Author "Dharmaratne, T.S."

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    Investigation of Geuda Gemstones, before and after the Heat Treatment using FTIR Spectroscopy
    (Uva Wellassa University of Sri Lanka, 2020) Ramesh, T.G.; Jaliya, R.G.C.; Illangasinghe, I.K.M.S.C.K.; Diyabalanage, S.; Jayasinghe, N.; Dharmaratne, T.S.
    Geuda is a low-quality form of corundum and abundant in the most gem enriched regions in Sri Lanka and can transfer into premium blue sapphires, similar to the natural in appearance through heat treatments. The study intended to identify characteristic features to distinguish heated geuda from natural sapphire using FTIR Spectroscopy. 53 geuda samples were collected from five gem bearing localities Ratnapura, Ridiyagama, Okkampitiya, Bakamuna, and Katharagama and heat treated up to 1800°C for the onehour soaking period under reducing environmental condition. Study samples were subjected to FTIR analysis before and after the heat treatment and could identify the development of a distinctive peak at 3310 cm-1 after treatment. This is due to the diffusion of atmospheric Hydrogen back into the crystal and appears in the absorption spectrum as an interstitial O-H bond in the corundum crystal structure. Further, two absorption bands at 2342 or 2362 cm-1 which corresponds to atmospheric CO2 and CO2 gas in negative crystals were observant in almost of the samples and as a direct response to CO2 gas in negative crystals, the intensity of this particular peak is found to be significantly less for Ridiyagama samples with respect to other localities. This reveals that the Ridiyagama samples are with less CO2 trapped inclusions. Nevertheless, certain 2853 and 2924 cm-1 peaks were observed before and after heat treated stones due to the C-H bond resulted in contamination. Furthermore, 3620 and 3697 cm-1 absorption bands related to Kaolinite hydrous mineral inclusions have been disappeared with heat treatment. This concludes to identify heat treated sapphires with 3310 cm-1 peaks and remaining of 3620 and 3697 cm-1 peaks verify it as a non-heat-treated sapphire. Hence, the FTIR technique could be clarified as one of the best methods to identify heat treated blue sapphires. Keywords: Heat treatment, FTIR analysis, Negative crystals, Absorption spectrum, Inclusions
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    Preliminary Investigation on the Occurrence of Reddish Brown Colour in Zircon from Kolonna, Sri Lanka
    (Uva Wellassa University of Sri Lanka, 2020) Rifkhan, M.N.M.; Wewegedara, W.G.C.N.; Jayasinghe, R.M.N.P.K.; Dharmaratne, T.S.; Malaviarachchi, M.A.S.P.K.; Rohana, C.
    Sri Lanka is famous for various types of gem minerals. From among these minerals, gemquality zircon is found in both primary and secondary deposits. Kolonna is a location where zircon is found in primary deposits with a reddish-brown colour. The main objective of this study was to investigate the occurrence of reddish-brown colour in zircon from Kolonna area. Although many factors could cause the colour of gem minerals, the colour of zircons is known to be produced by trace elements (transition metals, lanthanides, actinides, and REEs), radiation damage (radiation-induced color centers) and charge transfer. Five randomly selected reddish-brown zircon samples were selected for this study. All samples were translucent, highly fractured, sub-adamantine, and with euhedral to subhedral crystal form. Samples were analyzed with EDXRF, UV-Vis Spectrophotometer, and FTIR methods. The UV-Vis spectrum of these samples showed an increase in absorption towards the UV region and declines towards the NIR region with a shoulder at around 500 nm. This can be identified as a structurally defected colour center that may occur due to the radiation damage caused by radioactive elements such as U and Th. This was further confirmed by the U4+ peak at 654 and 690 nm. The U5+ peak at 6663 cm-1 in the FTIR spectrum further confirmed the presence of U in samples. This was confirmed by the EDXRF analyses that showed a trace amount of radioactive elements. The average weight percentage of U and Th were 0.06 and 0.02, respectively. It was also noted an occurrence of an OH- group indicated at 3196 cm-1 on FTIR spectra. This may be probably due to slight radiation damage caused by radioactive elements in zircon samples. This study revealed the presence of U which accounts for structural defects that form colour centers in reddish-brown zircon from the Kolonna region. Keywords: Absorption, Colour center, Cause of color, Zircon, Radiation