Color-causing defects create absorption by forming energy steps within the band gap. Which statement describes this process?

• A. They widen the band gap to stop absorption
• B. They cause broad, uniform absorption across all wavelengths
• C. They provide discrete energy steps within the band gap enabling visible light absorption
• D. They only affect infrared absorption

Answer: (C)

Color-causing defects introduce energy levels inside the band gap. These mid-gap states create specific energy spacings, so electrons can absorb photons whose energy matches those spacings. That selective absorption occurs at particular wavelengths, often in the visible range, which is what gives the material its color. If the band gap were simply widened, absorption would be reduced or shifted; if absorption were broad and uniform, the material would appear more neutral or gray rather than colored; and these defect levels can enable visible rather than being limited only to infrared.