Large Difference in Nonlinear Optical Activity of Rare Earth Ion Substitution of Bi in ATeBO (A = Bi, La, Pr, Nd, Sm-Dy).

A series of oxides with high rare earth contents, RETeBO (RE = La, Pr, Nd, Sm-Dy), were synthesized, and they all crystallize in the noncentrosymmetric space group 6 resembling that of a previously reported BiTeBO ( , , 14190-14193), which showed a very strong second harmonic generation (SHG) signal believed to come from all three structural units [BO], [TeO], and [BiO]. Surprisingly, compared with the isostructural compound BiTeBO, both theoretical calculations and powder SHG tests show that RETeBO has an abnormally small SHG effect (0.2 × KDP). Based on the group theory analysis, the possible reasons are attributed to the misalignments and lack of distortions of the [BO], [TeO], and [REO] groups in the unit cell. The 2 symmetric operation (a subset operation of the 6-screw axis) of the [TeO], [BO], and [REO] groups leads to complete cancellation of their contributions to the directions, while the absence of lone pair electrons in RE and Te results in small distortion in the axis, hence small contributions to the SHG coefficients involving the axis. Diffuse reflectance spectra of RETeBO (RE = La, Pr, Nd, Sm-Dy) show typical absorption of different RE, and the similarity of their infrared spectra is due to the same crystal structure and same structural units of the [TeO] and [BO] groups. The strong fluorescence intensities of EuTeBO and TbTeBO show the characteristic emissions of Eu and Tb, which may serve as luminescence materials with proper doping.