Which two elements are primarily responsible for blue coloration in sapphire?

• A. Copper and nickel
• B. Iron and Titanium
• C. Chromium and vanadium
• D. Cobalt and manganese

Answer: (B)

Blue sapphire color comes from trace impurities in the crystal lattice of corundum, specifically iron and titanium. When these elements are present, they interact electronically in a way that allows light to be absorbed at certain wavelengths. The Fe2+/Ti4+ interaction (often described as an intervalence charge transfer) removes some yellow-green light from the spectrum, so the light that remains appears blue. The saturation and shade of blue depend on how much of these dopants are present and how they couple with the lattice. Other elements would produce different hues—chromium and vanadium are linked to red colors in rubies, manganese tends toward pinks, and cobalt can give blue in some specimens but is far less common. Because iron and titanium are the established culprits driving blue sapphire coloration, they are the best explanation for the blue color observed.