Role of Cr and V in Colour Change Effect of Gemstones

Modern testing techniques have been applied to various gemstones that show colour change effect. Based on crystal field theory, the mechanism of colour change effect and the role of Cr and V are discussed. Colour change effect is the result of combination of light source with selective absorption of colouring ion to visible light. The spectral characteristic of a colour-change gemstone should show balanced absorption in red region and green region.