Diamond glow

Diamonds are expensive because they’re beautiful and rare. But fake diamonds often sell for a lot of money, too. And that’s because they can look very real. Now, scientists have discovered a way to tell apart certain genuine diamonds from fakes. The new technique works with a rare form of blue diamond that glows in the dark.

The famous Hope Diamond looks blue under normal light (above), but it glows bright red (below) after being exposed to ultraviolet light. Together, the color of its glow and how quickly the glow fades act as a sort of fingerprint for the gem.

C. Clark/Smithsonian Institution

J. Hatleberg

Diamonds that belong to a group called type IIb usually look blue. After they absorb high-energy light, though, type IIb diamonds glow in the dark, for a little while. This glow ranges in color from blue to pink and fiery red, depending on the diamond.

Type IIb diamonds can be stunning, and some of them are quite famous. The large Hope Diamond, for one, glows orange-red for up to one minute after the lights go out. (The Hope Diamond is on display at the Smithsonian Institution’s National Museum of Natural History in Washington, D.C.)

Despite these diamonds’ rarity and fame, however, scientists hadn’t paid much attention to them until recently.

To learn more about the gems, chemical engineer Sally Eaton-Magaña of the Gemological Institute of America in Carlsbad, Calif., and her colleagues studied the Aurora Heart Collection. This set contains 239 colored diamonds, including many blue, type IIb gems.

They also studied the Smithsonian’s Hope Diamond and its Blue Heart Diamond. In all, the researchers did experiments with 67 natural blue diamonds, three manmade gems and a gray diamond that scientists had turned blue with a combination of temperature and pressure treatments.

In one test, the scientists shone ultraviolet light — a type of high-energy light — on each gemstone for 20 seconds. Afterward, all the natural type IIb diamonds glowed for several seconds. This glow contained two wavelengths of visible light: greenish-blue and reddish. The relative strength of each wavelength determined the color of the final glow. And because each diamond is different, the scientists could use the color of the glow and how quickly the glow fades as a sort of fingerprint to identify individual gems.

The technique also proved to be a good way to separate real gems from fakes. Neither manmade diamonds nor the falsely colored gray diamond glowed in the reddish wavelength.

The new strategy might help solve one of the diamond market’s biggest problems: hard-to-spot fakes.

Further Readings

S. Perkins. “Hued afterglow: Fingerprinting diamonds via phosphorescence.” Science News. Vol. 173, January 12, 2008, p.19. Available at http://www.sciencenews.org/articles/20080112/fob2.asp .

E. Sohn. “Unscrambling a gem of a mystery.” Science News for Students. Dec. 17, 2003. Available at http://www.sciencenewsforkids.org/articles/20031217/Note2.asp .