GemResearch Swisslab (GRS) Specializing in Origin Determination of Fine Rubies and Sapphires

Origin of Color Analysis of Natural Fancy Sapphires from Madagascar and Tanzania (Songea) Enhanced by the New E(IM1)-Method


Fig. 26 Polarized UV-VIS-NIR absorption spectra of natural pastel orangy-pink (Origin: Madagascar) to vivid orange-red sapphires (origin: Songea, Tanzania) enhanced with the new E(IM)-method. Absorption spectra can be interpreted as absorption bands and lines caused by trace elements iron (Fe³⁺ line at 388nm, Fe³⁺ -pairs, line at 450nm) and chromium (Cr³⁺, dominated by band centered at 405-410nm and band centered at 550-560nm) and magnesium (Mg²⁺ -Trapped Hole Color Centers, general absorption in the blue region of the spectrum). Chemical analyses by ED-XRF and LA-ICP-MS (See Fig. 20, 33 and Tables 6 and 4). Increase in intensity of the 450 absorption line can be correlated with increasing Fe-concentrations (Fe³⁺ -pairs) in the gemstones (Images on top right).

Fig. 27 UV-VIS-NIR absorption spectra of natural sapphires from Madagascar enhanced with the new E(IM1) method. Sapphire Colors: White (black line), yellow (yellow line), pinkish-orange - "Padparadscha" - (pink line), vivid orange (brown line) and blue sapphire (blue line). The chemical compositions are dominated by Mg, Fe, Cr and Ti (Beryllium subordinate). ED-XRF and LA-ICP-MS data on chemical compositions See Tab.4 and 5. Effect of unstable color centers to the absorption spectra See a Fig. 5 and Fig. 29. Interpretation of color centers based on measured Mg-concentrations and the absorption characteristics in the blue region of the spectrum (See also Lit. 04).

Table 4: Averaged chemical compositions (LA-ICP-MS data in ppm) of samples investigated by UV-VIS-NIR absorption spectroscopy (Fig. 27). Detection limits See page 24.