Non-Centrosymmetric Ammonium Rare Earth Nitrates (NH4)2Ln(NO3)5•4H2O - Crystal Structure, Crystal Growth and Optical Properties

For crystals of (NH4)(2)Ln(NO3)(5)center dot 4H(2)O (Ln = La, Ce, Pr, Nd), the piezoelectric and the pyroelectric effect was demonstrated unambiguously. X-ray structure determination shows that all four compounds are isomorphic, with monoclinic, non-centrosymmetric space group Cc, and are further isomorphic to the related rubidium compounds Rb(2)Ln(NO3)(5)center dot 4H(2)O. Large single crystals of the colourless compounds (NH4)(2)La(NO3)(5)center dot 4H(2)O and (NH4)(2)Ce(NO3)(5)center dot 4H(2)O were grown. On the basis of determined precise refractive indices and their dispersion in the wavelength region 0.365-1.083 mu m, phase-matching conditions for collinear second harmonic generation were analyzed. In both crystals, type I phase matching can be realized for wavelengths from 0.893 mu m (La) or 0.892 mu m (Ce) to the near IR, where first absorption bands appear.