Study on Fluorescence Spectrometry of Natural and Organic Filling Treated Turquoise
XU Feng-shun1, CHEN Quan-li1*, DING Wei1, WANG Hai-tao2
1. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
2. College of Creative Design, Shenzhen Technology University, Shenzhen 518118, China
Abstract：Turquoise is mainly presented as colors like blue, green and variegated, among which blue and green possessing the highest value due to their vividness are preferred as optimization products. Organic matter injection is the most commonly used treatment to optimize turquoise, usually divided into organic matter soaking treatment and filling treatment. By means of test methods like the conventional gemological characteristic test, FTIR, 3D fluorescence spectrometer and X-ray fluorescence, this paper has conducted a thoroughly comparative study, among natural turquoise and those treatments with organic matter glue injection, upon their mineralogical and spectroscopic characteristics such as exterior features, density, ultraviolet fluorescence, infrared absorption spectrum, fluorescence spectrum and chemical composition. The test results revel that the LW fluorescent of natural turquoise is correlated with the hue and density exhibiting medium to the inert degree of fluorescence. The soaking treated turquoise under LW ultraviolet displays a higher degree of fluorescence than that of natural turquoise in the same color. And filling treated turquoise has a medium degree of fluorescence under the LW and SW. In addition to the characteristic peaks of turquoise itself, the infrared absorption spectra of the soaking treated turquoise can also be seen the absorption peaks ofν(C═O) 1 739，2 926 and 2 851 cm-1 methylene peaks, and the filling treated turquoise characteristic absorption peaks of benzene ring skeleton at 1 508 cm-1 were observed. 3D fluorescence spectra show that natural blue turquoise has a medium intensity fluorescence peak with Ex of 370 nm, and its FWHM is about 100 nm, while green, mixed color and low-density turquoise have very weak fluorescence, blue soaking treatment turquoise has a strong symmetrical fluorescence peak in Ex 380~400 nm, and green soaking treatment turquoise has a strong fluorescence characteristic peak with FWHM about 80 nm. Blue filling treatment turquoise has two weak fluorescence characteristic peaks near 278 and 390 nm, respectively. Green filling treatment turquoise has a medium-intensity fluorescence peak with a half-width of about 150 nm. The increase of the fluorescence peak region may be due to the presence of more organic matter. The XRF reveals that the Fe content holds a degree of inhibitory effect on the fluorescence in the turquoise. The turquoise testing of fluorescence characteristics and three-dimensional fluorescence spectrum as non-destructive testing techniques have advantages like simplicity, convenience, fastness and effectiveness, which are vital to accurate identification of nature turquoise and its organically filled product.
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