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).