Second-harmonic generating properties of polar noncentrosymmetric aluminoborate solid solutions, Al5-xGaxBO9 (0.0 <= x <= 0.5)

Abstract

A series of solid solutions of polar aluminoborate materials, Al5-xGaxBO9 (0.0 <= x <= 0.5) have been synthesized by standard solid-state reactions using Al2O3, Ga2O5, and B(OH)(3) as reagents. The phase purities, crystal structures, and solid solution behavior of the reported materials have been investigated by powder X-ray diffraction. Solid solutions of Al5-xGaxBO9 crystallize in the polar noncentrosymmetric space group, Cmc2(1), with a three-dimensional structure consisting of distorted MO4, MO5, MO6, and BO3 polyhedra (M = Al or Ga). Powder second-harmonic generating (SHG) measurements on the Al5BO9 using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 2 times that of alpha-SiO2 and is not phase-matchable (type 1). Further nonlinear optical (NLO) measurements on the Al5-xGaxBO9 solid solutions indicate a sharp increase in SHG efficiency up to 10 times that of alpha-SiO2 for x >= 0.4. Close structural examination suggests that the alignment of the asymmetric p-delocalization of BO3 groups is responsible for the abrupt increase of SHG efficiency.