X-RAY AND SPECTRAL CHARACTERIZATION OF DEFECTS IN GARNETS

New information on the defects in high temperature (HT) grown YAG (Y3A l5O12) and GGG(Gd3Ga5O12) obtained from X-ray and optical spectroscopy of various rare earth dopants are presented. Low intensity {222} X-ra y reflections, forbidden in the cubic garnet Ia3d space group, with eq uivalent intensities for the four [111] directions are observed in bot h crystals. Structural arguments in connection with optical spectrosco py data on Various ions (Nd3+, Tm3+, Pr3+) allow us to assign these re flections (absent in flux grown crystals) to local reduction of symmet ry introduced by nonstoichiometric random occupancy of octahedral site s by Y3+ or Gd3+ ions in HT garnets.