Colour centre in YAG: Cr3+ crystals

YAG crystals doped with 0.01 wt% Cr were grown by Czochralski method using 98% Ar + 2% H₂ protective atmosphere. Four colour varieties of the crystals were prepared in the dependence of the Al₂O₃ :Y₂O₃ ratio in the melt and the sign of electrical potential above the melt level. New absorption bands were attributed to the O⁻ centre (400 to 480 nm), F centre (357, 500, and 833 nm) or Cr³⁺ at another site than octahedral (455, and 612 nm).