OPTICAL-DAMAGE-RESISTANT IMPURITIES IN LITHIUM-NIOBATE

We analyzed the properties of damage-resistant LiNbO3 crystals doped with Mg, Zn, or In. Damage resistance is due to an essential increase in the photoconductivity sigma(p). In the first two compounds the increase in sigma(p) is most pronounced at concentrations exceeding certain threshold (5.5 mol.% MgO or 7 mol. % ZnO in the congruent melt), whereas in In-doped crystals it occurs at any In concentration. The increase in sigma(p) is directly related to the reduction of the intrinsic defects Nb(Li) because of their substitution by damage-resistant impurities. If an iron impurity is present, then an abrupt decrease in the capture cross section of Fe3+ acceptors at Mg or Zn concentrations higher than the threshold is responsible for the observed increase in sigma(p).