In gemology, which term refers to a defect that can influence absorption of visible light?

• A. Band Gap
• B. Color Center
• C. Colored Lamellae
• D. Selective Absorption

Answer: (B)

Color centers are lattice defects that can alter how a crystal absorbs light, creating color in gemstones. These defects introduce localized energy levels within the crystal’s band gap, so when visible-light photons match transitions to or from those levels, specific wavelengths are absorbed. That selective absorption gives the gem its color. In diamonds, nitrogen-related centers are a common source of yellow to brown hues, while other defect combinations can produce blue or green colors depending on the exact defect structure and its electronic states.

Band gap describes the overall energy separation between the valence and conduction bands of the material and influences what wavelengths can be absorbed, but it isn’t a defect itself. Colored lamellae are growth-related features that can affect appearance without being the defect type that creates absorption bands. Selective absorption describes the phenomenon of absorbing certain wavelengths, not a defect term.