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Volume 18 Issue 3
Sep.  2021
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REN Qianqian, CHEN Meihua, WANG Chengsi, WU Gai. Analysis of UV-Vis Spectrum on Pink-Purple Spinel from Burma before and after Heat Treatment[J]. Journal of Gems & Gemmology, 2016, 18(3): 24-30.
Citation: REN Qianqian, CHEN Meihua, WANG Chengsi, WU Gai. Analysis of UV-Vis Spectrum on Pink-Purple Spinel from Burma before and after Heat Treatment[J]. Journal of Gems & Gemmology, 2016, 18(3): 24-30.
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Analysis of UV-Vis Spectrum on Pink-Purple Spinel from Burma before and after Heat Treatment

  • 1. Gemmological Institute, China University of Geosciences, Wuhan 430074, China;

  • 2. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China

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  • Received Date: January 24, 2016
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    • Abstract
  • In this paper, 5 pieces of pink-purple spinels from Burma were selected as experimental samples and heated at 1 200℃ and 1 600℃ for 10 hours respectively.Through laser induced breakdown spectroscopy (LIBS) analysis for the chemical compositions and UV-Vis spectroscopy, it was found that all samples were MgAl2O4 with trace amount of element Fe and the UV-Vis absorption bands were basically the same in the range 350-600 nm.The causes for their colours may be related to spin-forbidden transition of Fe3+ in octahedral site and Fe2+ in tetrahedral site and charge transfer between these pairs.Comparing UV-Vis spectra before and after heat treatment, it was found that the absorption intensity of all samples were enhaced dramatically in 350-430 nm and 500-600 nm areas.The absorption band at 350-430 nm is believed to be caused by increasing intervalence charge transfer between O2-→Fe2+、Fe3+ after the disorder structural transition.The absorption band at 500-600 nm is believed to be caused by Fe3+ in tetrahedral site effected by Fe2+ in adjacent site.After the heat treatment at temperature of 1 600℃, the absorption intensity in near ultraviolet region increased again and led to a clear change in UV-Vis spectrum, which making the apparent colour of samples become redder, however, some samples fail to follow this result due to internal fissures and lower transparency.
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