Phosphorescent diamonds help identify fakes and frauds
Beautiful and rare, natural diamonds are extremely valuable, which makes them a widespread and obvious target for thieves, and fake diamonds that look real (most of which do, even to the expert eye) often sell at a high price too. But after observing the afterglow of the world’s largest deep-blue diamond, experts discovered a unique method to pick out synthetic diamonds from natural gems and help identify stolen diamonds.
Diamonds that belong to a group called type IIB usually look blue. After they absorb high-energy light like UV light however, type IIB diamonds glow in the dark for a short time. This afterglow refers to the phosphorescence of a diamond which ranges in colour from blue to pink and fiery red, depending on the diamond.
Type IIB diamonds can be stunning, and some of them are incredibly famous. The world renowned Hope Diamond for example glows a beautiful orange-red for up to one minute after the lights go out. The glow is believed to be an interaction between ultraviolet light, boron that is found in blue diamonds and nitrogen in the stones. While most blue diamonds appear to glow bluish-green after ultraviolet exposure, the study showed that blue often covers up a red phosphorescence and that the Hope Diamond simply has a stronger red glow than most.
To learn more about these phosphorescent glowing gems, chemical engineers from the Gemological Institute of America studied the Aurora Heart Collection which contains 239 coloured diamonds and an array of blue, type IIB stones in additional to the Smithsonian’s Hope Diamond and its Blue Heart Diamond. In total, the researchers did experiments with 67 natural blue diamonds, three man-made gems and a gray diamond that scientists had turned blue with a combination of temperature and pressure treatments.
In one test, the scientists shone an ultraviolet light — a type of high-energy light — on each gemstone for 20 seconds. After being exposed to this light, each one of the natural type IIB diamonds glowed for several seconds. Once studied, it was revealed that the glow contained two wavelengths of visible light: greenish-blue and reddish. The relative strength of each wavelength determined the colour of the final glow.
Because each and every diamond is different, the scientists realised they could use the colour of the glow and how quickly the glow fades as a type of fingerprint to identify individual gems. As neither manmade diamonds nor the falsely coloured gray diamond glowed in the reddish wavelength, this characteristic of natural diamonds can also help to solve one of the diamond market’s biggest problems – identifying authentic-looking fake gems.
Is phosphorescence glow different from fluorescence that is found in many diamonds?
Yes. Fluorescence defines the emission of light by a mineral such as a diamond while exposed under certain types of light, such as ultraviolet (UV) light. Phosphorescence on the other hand defines the emission of light by a material after exposure to light- like the “glow in the dark” stars that you may have glued to your ceiling as a child.