Analysis of Impurity Effects on the Coloration of Corundum by Laser-Induced Breakdown Spectroscopy (LIBS)

Abstract

Corundum was analyzed using laser-induced breakdown spectroscopy (LIBS) for impurity effects in their multiple colorings. Qualitative measurements were attained for impurities of chromium, magnesium, iron, and titanium in red, yellow, and blue samples. Moreover, treatment with a beryllium diffusion, which can modify corundum to obtain an attractive color, was tested in the yellow sample. In this work, most of the measurements were acquired using a laser pulse energy of 5 mJ and impurity emissions were appreciable. The signal-to-noise ratios were 11, 6.5, 10, and 4 for the Cr 425.44 nm, Fe 404.58 nm, Be 313.04 nm, and Mg 285.21 nm lines, respectively, for five laser shots. The amount of damage to the corundum samples was also monitored by measuring the craters after laser analysis. It was found that the crater size was about 30 μm after 10 laser shots. As such, the damage to corundum sample is almost imperceptible after the LIBS analysis.

Mechanism of Be-Thermodiffusion in Rutile Inclusions of Fancy Sapphires

“…The chemical data on the corundum matrix indicate the presence of small amounts of Fe 2 O 3 (see Table for the average amounts) as follows: between 0.59 and 0.79 wt % in the A1 sample, between 1.02 and 1.30 wt % in F1, between 0.77 and 1.11 wt % in FR01, and between 0.31 and 1.03 wt % in the A3 sample. These values are in agreement with the literature . Concerning the blue halos, small amounts of TiO 2 and Fe 2 O 3 phases were detected (see Table ) in the following respective quantities: 0.47 and 0.94 wt % in the A1 sample, 0.24 and 0.57 wt % in F1, 0.33 and 0.60 wt % in A3, and 0.331 and 0.838 wt % in the FR01 sample.…”

“…These values are in agreement with the literature. 4 Concerning the blue halos, small amounts of TiO 2 and Fe 2 O 3 phases were detected (see Table 1) in the following respective quantities: 0.47 and 0.94 wt % in the A1 sample, 0.24 and 0.57 wt % in F1, 0.33 and 0.60 wt % in A3, and 0.331 and 0.838 wt % in the FR01 sample. The collected data on the inclusions indicate the presence of tialite (Al 2 TiO 5 ), rutile (TiO 2 ), tistarite (Ti 2 O 3 ), and tistarite− hematite (Ti 2 O 3 −FeTiO 3 ) solid solution (Table 2).…”

“…It does not have any color of its own and has no absorption from 160 to 5,000 nm. , Different colors and tonalities of the gemstones derive from the presence of transition metal impurities placed in the octahedral sites in simple or coupled substitution. This happens for well-known crimson rubies (α-Al 2 O 3 : Cr 3+ ), blue sapphires (α-Al 2 O 3 : Fe 2+ –Ti 4+ ), “padparadscha” (pink-orange sapphire), yellow and orange corundum (α-Al 2 O 3 : Fe 3+ , Mg 2+ ), or purple corundum (α-Al 2 O 3 : Cr 3+ , Fe 2+ –Ti 4+ ). − Point defects can also be the origin of coloration. The most typical ones are F-centers, involving the absence of O 2– ions, which may or may not be replaced by one or two electrons.…”

Characterization of Coloured Gemstones by X-ray Micro Computed Tomography

“…These include infrared and ultraviolet-visible spectrometers, energy-dispersive X-ray fluorescence, X-ray diffraction and Raman microscopy instrumentation. In addition, the use of techniques providing chemical analysis with low detection limits, such as secondary ion mass spectrometry, laser ablation-inductively coupled plasma-mass spectrometry and laser induced breakdown spectroscopy became essential [3,12]. It remains essential however, that alternative, but complementary methods to all the above are developed that are preferably non-destructive and provide accurate results at reasonable cost.…”