Using SIMS to diagnose color changes in heat treated gem sapphires

In early 2002, a large number of orange colored sapphires began to appear in the gem market and showed clear evidence of being treated by bulk/lattice diffusion of a surface impurity element. Initial analyses of these stones using EPMA and LA-ICP did not indicate any difference between the center of the stone and the colored rim. However, mass spectral analysis of the cores and rims of these stones using SIMS detected a higher Be content in the colored rims. Subsequent experimental work has shown that diffusion of Be into the sapphires within a controlled oxygen atmosphere is the cause of the color change. We have now calibrated 14 elements by using ion-implanted semiconductor-grade sapphire standards. All measurements have been done using a PHI 6600 quadrupole SIMS instrument. Repeat analyses of the implanted reference material show a relative standard deviation of 8.5% for Be and 12% for Fe. By using a low beam current and small raster, the analysis crater is practically invisible on faceted stones, in contrast to laser ablation shots in the LA-ICP. Use of the quadrupole instrument makes charge compensation easy and the ability to tilt the stage makes alignment of small facets possible. A background of about 0.6 ppm wt. is caused by interference from Al3þ for Be. # 2004 Elsevier B.V. All rights reserved