gems, gemology, gem research, gem testing, advanced instruments, spectroscopy

Optical spectroscopy, also known as ultraviolet/visible/near-infrared spectroscopy, measures how electromagnetic radiation around the visible range is preferentially absorbed by a gemstone. A transparent gemstone can absorb certain wavelengths of light that pass through it, creating color in the transmitted light, whereas an opaque gemstone absorbs light on its surface and creates color in the reflected light. The physics of how electromagnetic radiation of different wavelengths interacts with materials is summarized to provide a basic understanding of how electronic transitions in gemstones can cause different colors. The different instruments and configurations suitable for various gemstone types are also explained. Specific routine applications of ultraviolet/visible/near-infrared spectroscopy to colored gemstones, fancy-color diamonds, and saltwater pearls are summarized, showcasing how identifying the chromophores in gemstones can facilitate varietal calls, origin determination, and treatment detection in a gemological laboratory.