Identification of Be-diffusion treated corundum

Subsequent research developed theoretical investigation such as mechanism of colour alteration of Be (beryllium) -diffusion treatment to some extent. However, it turned out that advanced analytical techniques which are beyond the gem identification field such as SIMS or LA-ICP-MS were required to detect Be and this fact created a controversy about a whole concept of identification technique and gem industry was urged to revise its ruling. In this study we report on current progress of laboratory techniques such as LA-ICP-MS, LIBS or FT-IR analysis for identification of Be-diffusion treatment.<BR> ♦LA-ICP-MS Analysis<BR> Present researches reported that some of blue sapphire contain Be with natural origin. Be in the material is assumedly related to minute inclusions and not to replace elements in the crystal lattice. In this study trace elements such as Ta (tantalum), Nb (niobium) or Th (Thorium) are often detected together with natural-origin Be in a stone, and it is confirmed that this can be applied for distinction from Be originates from diffusion treatment.<BR> ♦LIBS Analysis<BR> Our laboratory recently replaced the infrared laser (1064 nm) by UV laser (266 nm) with freshly adopting optical crystal. By this alteration the trail can be reduced in its size from about 100 μm (0.1 mm) to 30 μm (0.03 mm) while keeping the sensitivity the same. In addition, by changing infrared to ultraviolet light the energy efficiency per unit area on the irradiated face improved and detecting ability for Be concentration was raised as sensible as 1 ppm.<BR> ♦FT-IR Analysis<BR> Corundum generally contains hydrogen atoms, which combine with oxygen in the crystal lattice to exist as OH or H₂O. Non-heated blue sapphires with non-basalt related origin generally show very low concentration of OH band absorption in infrared region.<BR> When pale coloured rough stone (such as geuda) from Sri Lanka or Madagascar is heated in reducing atmosphere with hydrogen gas aiming at colour improvement, absorptions originate from OH come appear at 3310, 3233 and 3185 cm^-1. Be-diffusion treatment has been undergone in reducing condition, such OH band may not be detected. Also, some certain localities corundum containing a solid phase of diaspore as minute inclusions show a series of characteristic absorptions around 3020, 2885, 2120 and 1980 cm^-1. They disappear the form by high temperature heating, and such characteristic absorption does not exist in Be-diffused corundum generally. From our routine identification work, data of infrared absorption on Be-diffused corundum have been accumulated and it is now known that some stones do show absorption about at 3068 cm^-1. The cause of this peak is not understood yet but it is not seen in Non-heated stones and it may give a clue to prove engagement of Be-diffusion treatment.