Professional Jeweler Archive: Checking Sapphires for Beryllium Diffusion

November 2003

Gemstones & Pearls/Gemology

Checking Sapphires for Beryllium Diffusion

European scientists detail a simple test to check parcels of yellow-to-orange corundum

Experts have advised gemologists that identifying whether yellow-to-orange sapphires have been lattice-diffused with beryllium is a real challenge. Most recent publications tackling the two-year-old issue explain the necessity of using chemical analysis such as SIMS, ICPMS-LA. But these instruments are sophisticated, not easily available and expensive (Professional Jeweler, May 2003, p. 36).

However, it appears classical gemology may have been forgotten a little too soon. Jeweler-gemologists can use a few simple tests to identify most beryllium-diffused yellow-to-orange sapphires.

UV Fluorescence is Key

In most cases, the diffusion of beryllium in corundum induces a bright yellow orange fluorescence under longwave ultraviolet light. [Note: The scientists tested hundreds of yellow-to-orange sapphires in making their observations of fluorescence clues]. This fluorescence is seen easily in pictures of a slice of sapphire in which the doping element (beryllium) did not penetrate to the core (top). The same reaction is apparent in sapphires that haven’t been sliced, but you have to examine the stones carefully.

However, pinpointing luminescence alone is not enough for an identification of beryllium diffusion because the same color of fluorescence (approximately) can be seen in a few natural sapphires, even colorless ones. To make a more definitive identification, you also need to check for a difference in fluorescence between diffused and non-diffused stones.

If you observe strong orange emission in a yellow or orange sapphire, you must take another step to pinpoint the location of the fluorescence:

u In non-diffused yellow-to-orange sapphires, emission of fluorescence is almost always in near-colorless zones. If only colorless zones of a sapphire luminesce, it’s not beryllium-diffused.

u In beryllium-diffused yellow-to-orange sapphire, the orange fluorescence is located only in the yellow-to-orange areas. If you see this, there’s a very high probability the stone has been diffused with beryllium.

These characteristics should be noted in a darkened room using a longwave UV lamp. It’s also helpful to make the observations using some form of magnification – such as a loupe or a binocular microscope – so you can more easily see distinctions in color zoning.

Luminescence spectroscopy demonstrates the scientific foundation for the above observations. The nature of the strong orange luminescence in beryllium-diffused sapphires is different from that in orange-luminescing, non-diffused sapphires: There are extra emission peaks after beryllium diffusion.

This slab of pink sapphire shows an orange color zone caused by partial penetration of beryllium (left). The same area fluoresces orange (right). Photos by Gemtech Lab.
Most yellow-to-orange sapphires on the market result from heat treatment and often show marked color zoning, with dark yellow zones in a near-colorless matrix. Orange luminescence is limited to these colorless areas in non-beryllium-diffused stones. Photos by Gemtech Lab.
These spectra describe the emission of orange light by different sapphires, showing extra emission peaks in a beryllium-diffused stone. Chart by Gemtech Lab/Fritsch.
This macro photograph shows a small Songea, Tanzania, sapphire with bright orange coloration resulting from beryllium-lattice-diffusion treatment.

– by Emmanuel Fritsch, IMN-CNRS and the University of Nantes, Nantes, France and Franck Notari and Candice Grobon of GemTech Lab 2, Geneva, Switzerland

Copyright © 2003 by Bond Communications