What does FTIR spectroscopy measure in diamonds?

• A. Fourier-transform infrared (FTIR) spectroscopy measures a diamond's absorption of infrared energy.
• B. FTIR spectroscopy measures visible light absorption.
• C. FTIR determines carat.
• D. FTIR is used to photograph diamonds.

Answer: (A)

FTIR spectroscopy in diamonds measures how the crystal absorbs infrared energy, which tells us about the vibrations of the lattice and any impurities present. This infrared absorption reveals specific features associated with nitrogen or hydrogen impurities and other defects, enabling identification of diamond type (for example, Type I vs Type IIa) and the nitrogen-aggregation state. From these absorption patterns, gemologists can assess natural versus treated stones and gain insights into the diamond’s composition and structure.

It doesn’t measure visible light absorption, which would require a different range of spectroscopy. It doesn’t determine carat, since carat is a weight measurement obtained separately with a scale. And it isn’t used to photograph diamonds, since that’s an imaging technique.