Morphology and polarization-dependent second harmonic generation in single hexagonal sodium niobate micro/nano-crystals

We synthesized NaNbO₃ micro/nano-crystals with six morphologies and three different crystal structures using the hydrothermal method. Each single hexagonal NaNbO₃ micro/nano-crystal (samples No. 1-3) exhibited a strong second-order nonlinear response. By calculating the average intensity and measuring the polarization response of each of these hexagonal crystals (samples No. 1-3), it was demonstrated that the same crystal structure displays a similar optical second harmonic generation (SHG) response. Furthermore, SHG was shown to be independent of the morphology and identical for similar crystals, which is expected for a volume effect with a second-order susceptibility tensor depending on the properties of the material. The optical SHG properties of these NaNbO₃ micro/nano-crystals together with the previous related research suggest that these non-toxic crystals may find promising applications in biological imaging and related fields.