Undoped, Cr doped and Mg, Cr codoped LiNbO 3 crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV-Visible spectroscopy. Infrared optical absorption for OH⎯ ion has been used to study the effect of dopants on the crystals. The peak position of OH⎯ shift to 3535 cm -1 for Mg, Cr codoped crystals compared to 3484 cm -1 for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm -1 ) and 653 nm (15313 cm -1 ) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm -1 ) and 678 nm (14749 cm -1 ). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO 3 crystals.
Para-nitroaniline(p-NA)-dimethyl formamide (DMF) adduct has been synthesized chemically. The formation of adduct is confirmed via UV, FTIR, CHN analyses and other techniques. The adduct formation takes place due to dipolar interaction and hydrogen bonding. The parent polar molecules, viz. p-NA and DMF, crystallize in symmetric forms and do not exhibit optical second harmonic generation (SHG). The adduct has been found to exhibit a considerable SHG efficiency and hence this confirms that the adduct crystallizes in a noncentrosymmetric form. These observations suggest a Λ-shaped structure of the molecule, which is further established theoretically via geometry optimization.
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