R. Mohan Kumar

Influence of pH on the growth and characteristics of nonlinear optical zinc thiourea chloride (ZTC) single crystals

Abstract Growth of bulk zinc thiourea chloride (ZTC) single crystals from aqueous solution by low temperature solution growth technique has been reported. In this report we bring out the influence of pH on the structural, optical, electrical and mechanical properties of the grown crystals. At pH 5.3, the crystals are elongated along a -axis. Bulk crystals have been grown from the optimized pH value of 3.0. The single crystal XRD analysis confirms the change in lattice parameters for the crystals grown at these different solution pH values. The change in the crystal morphology at pH 5.3, and at 3.0 and 4.0 is accounted based on the difference in the nature of the species transported to the crystal. At pH 5.3, it appears that Zn 2+ is preferentially transported from solution to the crystal surface, and this is followed by 2Cl − ions and two thiourea molecules to give enhanced growth rate along the a -axis. Previously reported unit cell structure is used to support this view. At pH 3.0 and 4.0, protonated thiourea is preferentially transported to the crystal surface leading to increase in growth rate along b -axis. Cl − ions already bounded to Zn 2+ in the crystal are expected to offer the necessary driving force and this is followed by the transport of other species. This idea is based on the fact that free Zn 2+ is expected to be less at low pH due to formation of ZnCl 4 2− FTIR and laser Raman spectra confirm the presence of all functional groups. The dielectric loss of ZTC grown from the optimized pH value is low indicating that the crystals have fewer defects. Crystals grown at an optimized pH value possess higher transmittance. The second harmonic generation conversion efficiency measured using Nd:YAG laser was found to be comparable with KDP crystals. Hardness property increases for crystals grown from lower pH values.

Growth and characterization of non-linear optical l-hystidine tetrafluoroborate (l-HFB) single crystals

Abstract Single crystals of l -hystidine tetrafluoroborate ( l -HFB) have been grown by low temperature solution growth technique. Solubility studies have been carried out for three different solvents (water, water+acetone and water+ethanol). Among the three solvents, the l -HFB has the highest solubility in water and hence, crystals have been grown from aqueous solution. The grown crystals have been subjected to single crystal and powder X-ray diffraction studies to identify the morphology and structure. FTIR and optical transmission spectra reveal the optical properties of the grown crystals. The NLO property of the crystal has been confirmed by Kurtz SHG test. Comparing the output power, it has been confirmed that l -HFB crystals possess higher SHG efficiency than KDP. Microhardness studies carried out on different planes show an anisotropy in the hardness behavior.

Investigation on the nucleation kinetics of zinc thiourea chloride (ZTC) single crystals

Nucleation parameters such as radius of critical nucleus, critical free energy change and interfacial tension have been investigated for the aqueous solution growth of zinc thiourea chloride (ZTC) single crystals. The formation of ZTC compounds was confirmed by single crystal X-ray diffraction and the functional groups are confirmed by FTIR analysis. Solubility of ZTC has been determined for various temperatures. Metastable zonewidth and induction period values have been determined in order to optimize the growth parameters. The interfacial tension values estimated using the experimentally determined induction period are found to be comparable with theoretical values. Bulk crystals of ZTC have been grown from the optimized growth parameters.

Habit modification of potassium acid phthalate (KAP) single crystals by impurities

Abstract Nonlinear optical materials potassium dihydrogen phosphate (KDP), urea and l -arginine phosphate (LAP)-doped KAP crystals were grown by the slow cooling method. The LAP-doped crystals show pronounced habit modification compared to KDP and urea doping. The effect of these impurities on growth kinetics, surface morphology, habit modification, structure, optical and mechanical properties have been studied. Among the three impurities, urea doping yields high mechanical stability and optical transmission and for KDP and LAP doping there is a decrease in optical transmission.

Growth and characterization of L-lysine doped TGS and TGSP single crystals

Abstract Growth aspects of l -lysine doped TGS and TGSP single crystals from aqueous solution by a temperature reduction method have been investigated. The effect of dopant on morphology and crystal properties has been studied. Ferroelectric domain patterns have been observed on the b-cut plates of doped crystals. Powder X-ray diffraction analysis confirms the structure and change in lattice parameter values for the doped crystals. The presence of dopant in the crystal lattice has been qualitatively confirmed by FTIR analysis. The dielectric permittivity and spontaneous polarization values have been estimated and the Curie temperature is found to increase upon doping. Hardness measurements were carried out on the grown crystals.

Comparison between pure and deuterated potassium acid phthalate (DKAP) single crystals

Single crystals of pure and deuterated potassium acid phthalate (DKAP) have been grown from aqueous solution by slow cooling method. The effect of deuterium on morphology and crystal properties has been studied. Powder X-ray diffraction analysis confirms the structure and changes in lattice parameter values for the deuterated crystals. The presence of deuterium in the crystal lattice has been confirmed by FTIR analysis. The DKAP crystals possess relatively lower hardness values than the pure crystals. The transmittance of DKAP is found to be higher than KAP crystals.

Growth aspects of semi-organic nonlinear optical l-arginine tetrafluoroborate single crystals

Abstract Single crystals of l -arginine tetrafluoroborate ( l -AFB), a semi-organic NLO material, have been grown from aqueous solution. Since l -AFB is known to form highly viscous solution in water, growth by slow cooling has been difficult for optical quality crystals. In this study, highly transparent l -AFB crystals have been successfully grown by slow evaporation by keeping the saturated solution under special condition. The grown crystals were subjected to structural, optical and mechanical property studies. XRD studies reveal that l -AFB crystals possess orthorhombic structure. Fourier transform infrared absorption studies confirm the chemical constituents and presence of functional groups in the grown crystals. l -AFB crystals possess a higher hardness values compared to other semi-organic crystals. The linear and nonlinear optical properties of the grown crystals have also been studied.