Ultraviolet Absorption Spectra in Ruby

The optical properties of highly doped rubies have been investigated. Al₂{O}₃$ and ${Cr}₂O₃ form a complete solid-solution series; single crystals containing up to 5 mole% chromia were grown by the Verneuil technique. The optical absorption of a group of ultraviolet crystal-field bands near 3400 A was studied as a function of temperature, crystal orientation, and chemical composition. The intensity of these absorption bands varies with the square of the Cr concentration, perhaps indicating strong chromium-pair interactions.