Optical properties, defects, and composition of La 3 Ga 5.5 Ta 0.5 O 14 crystals

La 3 Ga 5.5 Ta 0.5 O 14 crystals were grown in pure argon and in an argon + 2% oxygen atmosphere. The growth atmosphere significantly effects the elemental composition of the crystals, their color, and the genesis and intensity of absorption bands in the ultraviolet, visible, and infrared spectral regions. Two types of defects were identified in the crystals: planar interstitial defects and nearly spherical vacancy-type defects.