Growth and Characterization of DL-Methionine Doped KDP Crystals

Potassium Dihydrogen Phosphate (KDP) crystals are one of the most popular crystals used for Non-linear Optical (NLO) applications. Most of the amino acids also exhibit NLO properties; therefore, the effect of doping of one of the amino acids, DL-methionine, in KDP crystals has been investigated. Pure and DL-methionine doped KDP crystals were grown by slow solvent evaporation solution growth technique. For growing the doped crystal, 0.3 and 0.4 weight percent DL-methionine was added to aqueous solution of KDP. Good quality transparent crystals were obtained within 8 to 10 days. Doping of amino acid DL-methionine in grown crystals was confirmed by the CHN analysis and FT-IR spectroscopy studies. The powder XRD indicated the single phase nature of samples and the unit cell parameters were not altered much due to doping. The value of second harmonic generation (SHG) efficiency and optical transmission in UV-Vis spectra increased as the doping of DL- methionine increased in KDP crystals. The variation of dielectric constant, dielectric loss (tanδ), with frequency of applied field in the range from 100 Hz to 100 kHz is reported. The dielectric constant and dielectric loss decreased with increase the value of frequency of applied field. The dielectric constant and the dielectric loss of DL- methionine doped KDP crystals were lower than the pure KDP crystals. Thermal stability of the grown crystals was studied by employing thermo-gravimetry analysis (TGA). It was found that the doping of DL-methionine decreased thermal stability of KDP marginally, but enhanced optical properties.