Linear and nonlinear optical properties, pyroelectricity and vibrational spectroscopy of polar guanidinium hydrogen phosphite, GuH2PO3 , and hydrogen selenite, GuHSeO3

For the non-centrosymmetric guanidinium compounds GuH(2)PO(3) and GuHSeO(3) with polar symmetry P2(1) a fundamental characterization as optical materials is given, including X-ray crystal structure analysis and a vibrational spectroscopy (Raman and IR) study. In addition, for both polar crystals the pyroelectric coefficients and their temperature dependence are evaluated. Using large single crystals grown from aqueous solution, refractive indices and their dispersion in the wavelength range 435-1083 nm are determined by the prism method. From the data phase matching conditions for collinear second harmonic generation (SHG) are analysed. Both crystals allow the realization of phase matching for SHG of both, type I and type II processes. Quantification of SHG properties was performed for both powdered salts and GuH(2)PO(3) single crystals. The measurements of the pyroelectric coefficients in the temperature range 100-340 K show pronounced pyroelectricity but no indication for ferroelectric behaviour of the two crystals.